Year-round records of thermal stratification in the Great Lakes are rare, and there are few observations of thermal stratification during winter. In this paper we analyze temperature data from 13 temperature logger chains and from over 130 benthic acoustic receivers that were deployed across Lake Ontario for two years. The timing and duration of the fall overturn correlates with the local average water depth, and shallow sites (<50 m depth) overturn up to a month before deep sites (> 100 m depths). Likewise, in spring the shallow sites warm faster. Lake Ontario has partial ice cover, so wind driven mixing stirs the water column throughout winter and inverse thermal stratification is largely absent. The depth-averaged winter water temperatures vary between 0 – 4oC, with the coldest temperatures (near 0.1oC) found in the shallow Kingston basin, and warmest temperatures (near 4oC) at sites near the 244 m deep Rochester Basin. Lake Ontario appears to be a warm monomictic lake, rather than having a dimictic mixing pattern – there is no sustained ice cover or inverse stratification that inhibits vertical mixing in winter. Winter is a poorly understood season for many aquatic processes, including fish bioenergetics, fish distribution, biochemical processes, invertebrate distribution and production. Moreover, lack of knowledge of winter has hampered the use of correct initial conditions for running large lake hydrodynamic models. We discuss the implications of these 2-year observations of thermal stratification in Lake Ontario for interpreting fish habitat usage and fish reproductive phenology and for fisheries management.
How to cite: Wells, M., Johnson, T., Robinson, R., Midwood, J., Larouque, S., Eddie, A., O'Malley, B., Morton, K., and Gorsky, D.: Thermal mixing patterns in Lake Ontario as revealed by novel year-round observations of thermal stratification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4555, https://doi.org/10.5194/egusphere-egu25-4555, 2025.
Topographic constraints, such as sills or constrictions, play a critical role in regulating water exchange between different basins, often creating complex circulation patterns that influence the transport and distribution of sediments, nutrients, and oxygen. Although extensively studied in oceanography, these topographic features are also present in multi-basin Swiss lakes (e.g., Lake Lucerne, Lake Zug, Lake Lugano) but have received less attention. This study examines the inter- basin exchange in Lake Zug, where two basins, a shallow northern basin (100 m deep) and a deeper southern basin (180 m deep), are connected by a lateral constriction. Lake Zug is meromictic, remaining stratified throughout the year, with anoxic conditions prevailing below approximately 120 m. Consequently, the shallow northern basin remains well-oxygenated, while the bottom 60 m of the southern basin is characterised by anoxic water. Past fine-scale measurements have revealed the presence of oxygen intrusions at depth, suggesting episodic oxygen supply to the anoxic zones of the southern basin.
We hypothesise that the constriction between the basins influences lateral inter-basin exchange, thereby controlling the oxygen supply from the oxic northern basin to the deep anoxic zones of the southern basin. The primary aim of this study is to identify the dynamics within each basin and determine the nature of the hydraulic control exerted by the constriction. By identifying the physical mechanisms that drive inter-basin exchange, this study seeks to clarify the factors influencing oxygen supply in the southern basin and its impact on the vertical zonation of redox processes. A combination of field measurements, including temperature, oxygen, turbidity, and velocity, and a 3D numerical model are employed to investigate both lateral and vertical transport in the lake. Preliminary findings on the dynamics of Lake Zug, with a focus on the physical processes at the constriction, will be presented. An understanding of the hydraulic control in Lake Zug could enhance our knowledge of exchange flows and their impact on oxygen distribution in multi-basin lakes.
How to cite: Rama, J., Doda, T., Sepúlveda Steiner, O., N. Ulloa, H., Janssen, D., and Bouffard, D.: The role of a lateral constriction in controling water exchange and oxygen distribution in a two-basin lake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14922, https://doi.org/10.5194/egusphere-egu25-14922, 2025.
Lakes are an important part of the environment, being influenced by their inflows and influencing their outflows. The physical properties of lake water, such as temperature and dissolved oxygen concentration, affect downstream habitats and ecosystems. Limnological processes, such as upwelling, can rapidly change downstream river properties. Upwelling introduces a sudden influx of cold water downstream, potentially disrupting the riverine ecosystem, including salmon migration, which is closely tied to water temperature.
Upwelling occurs in thermally stratified lakes when wind forces cause cold water from the hypolimnion to rise to the warm lake surface. For this to happen, wind must have sufficient amplitude and fetch (Wedderburn number close to one) and persist for sufficient duration (exceeding one-quarter of the lake's fundamental seiche period). Upwelling typically occurs during periods of weak stratification, mainly at the beginning or end of the stratification season, and is more pronounced near lake boundaries, where outflows originate.
One example of such a lake-river system is Quesnel Lake, a fjord-type lake in British Columbia, Canada. It is the source of the Quesnel River, which feeds into the Fraser River and one of the world's most productive salmon-bearing systems. Quesnel Lake is a three-armed, Y-shaped lake with West, North, and East Arms. The West Arm is divided by a shallow sill (maximum depth of 35 m) and contraction into the West Basin and the Main Basin, which includes the North and East Arms. The Main Basin reaches a maximum depth of 511 m and includes 97.7% of the lake volume. The Quesnel River originates from the western end of the West Basin and is thus affected by upwelling in the West Basin. The lake’s complex geometry (i.e. multiple arms and basins), combined with complex surrounding topography that creates local wind patterns, complicates the upwelling process
This study uses nine years (2016-2024) of mooring and meteorological data to investigate upwelling in the West Basin of Quesnel Lake and how it affects temperature in the Quesnel River. Data were collected using moorings and meteorological stations in all three Arms to capture the spatial variability of wind and temperature. Temperature loggers, ADCPs, wind speed and direction were used to identify upwelling in the West Basin, as well as the wind patterns that generate upwelling and the river’s response.
During each year of observation, upwelling in the West Basin occurs multiple times during summer stratification, despite the strong thermal stratification. Upwelling is correlated with winds aligned with the lake’s thalweg, exceeding the 80th percentile of wind speed, and lasts 3-6 days, causing temperature drops of over 5°C in the Quesnel River. The most pronounced lake surface temperature drops occur at the Quesnel River mouth and moorings in the West Basin. Within the West Basin, the narrowing and shallowing of the lake toward the river mouth further contributes to the temperature decrease in the river. Therefore, the lake’s geometry not only complicates the occurrence of upwelling but also amplifies its downstream impacts.
How to cite: Sadeghpour, A., E Laval, B., and Vagle, S.: Investigating Upwelling Events in Multi-Arm Fjord-Type Lakes: A Case Study of Quesnel Lake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7455, https://doi.org/10.5194/egusphere-egu25-7455, 2025.
Deep lakes in temperate climates represent around 50% of the world’s surface, liquid freshwater storage, yet the mechanisms governing their seasonal deepwater renewal—and, in turn, their ability to support ecosystems—remain somewhat elusive. These lakes have depths of hundreds of meters thus experience extreme hydrostatic pressures, causing compressibility to significantly affect circulation. Combined with windstorms and inverse thermal stratification, this compressibility is hypothesized to trigger thermobaric instability which ultimately results in hypolimnetic ventilation. In this study, we investigate deep ventilation in Quesnel Lake, with a maximum depth of 511 m. The lake has a Y-shaped morphology formed by three arms and a horizontal extent of approximately 100 km. Our focus is on the East Arm, where the maximum depth occurs, which is surrounded by mountainous terrain which channels and amplifies wind forces.
To assess long-term trends in deep ventilation, we analyzed data from two moorings within the East Arm (M9 and M14, respectively in 500 and 400m water depth), including years when they were deployed independently or when meteorological stations were inactive. To better understand deep water renewal mechanisms that occur during individual events, we focused on two winters with the most comprehensive coverage of water temperature and meteorological data. In 2007, M9 and M14 were operational simultaneously, complemented by a third mooring (M11 in 175m of water) and a meteorological station both near the eastern end of the East Arm. In 2023, M14 and M9, as well as a weather station at Hurricane Point (the narrowest section of the East Arm) were all simultaneously operational.
For M9 (2003–2012, 2024) and M14 (2007, 2016–2024), a significant series of events during inverse-thermal stratification occurred in each observational year in mid-January. These events were observed to consistently reset the bottom temperature, evident as a rapid cooling as expected from thermobaric instability. We observed two distinct cooling modes. The first is characterized by the sequential vertical descent of cool water plumes through each mooring from top to bottom, which is typically associated with thermobaric instability theory. The second mode involves a sudden horizontal intrusion of colder water at depths of 400 m and 500 m, while the shallower thermistors are less affected. In January 2007, these series of events led to a net cooling of around 0.25°C at the deepest point of the lake (M9) and 0.4°C at M14. In both 2007 and 2024, meteorological data showed that windstorms, necessary to trigger thermobaric instability, accompanied by severe sub-zero air temperatures (reaching -23°C) preceded the bottom water-cooling events. Whether the mechanism of deep-water renewal occurs vertically or horizontally, over two decades of records consistently reveal an interaction between the lake’s deepest regions and surface waters.
How to cite: Alaa Ibrahim, S., E Laval, B., and Vagle, S.: Observations of Mixing and Deep Convection in a deep Fjord-Type Lake, Quesnel Lake, Canada, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13090, https://doi.org/10.5194/egusphere-egu25-13090, 2025.
Reservoirs lose significant amounts of water through evaporation, particularly for large canyon-shaped reservoirs with dams on major rivers. The canyon-shaped reservoirs, characterized by their long, narrow, and deep water bodies within steep V-shaped or U-shaped valleys, differ significantly from lakes but are often mistakenly studied as ‘artificial lakes’, leading to substantial biases in evaporation estimates. Canyon-shaped reservoirs boast the largest storage capacities among reservoir types in China and globally. This study, utilizing eight years observations from a floating pan on the Three Gorges Reservoir (TGR)—China’s largest reservoir, explores the evaporation processes unique to canyon-shaped reservoirs from both the mass transfer and energy balance perspectives.
Regarding the energy balance, the results reveal that evaporation from the floating pan exhibits a bimodal pattern in August and December, contrasting sharply with the unimodal pattern observed in lakes or lake-type reservoirs. The December peak lags the net radiation by four months. The water body’s energy balance follows a seasonal trajectory, with a heat storage period from March to August and a heat release period from September to February. An energy budget analysis of seven cross-sections based on water temperature along the TGR’s main stream highlights the critical roles of heat storage and advected energy, which are influenced by varying water depth and flowing water.
In terms of mass transfer, we discovered that the evaporation rate over the TGR is intensified by temperature inversions within the boundary layer (negative water-to-air temperature differences), a characteristic hydrothermal feature of canyon-shaped reservoirs. Unlike lakes, the evaporation rate per unit water-to-air vapor pressure difference does not depend on horizontal wind speed but significantly increases during temperature inversions, primarily occurring from March to August. This phenomenon is attributed to river-valley breezes, which generate significant vertical air movements that drive evaporation. The enhancement in evaporation rate is roughly estimated to be 117 mm annually.
These findings underscore that canyon-shaped reservoirs should not be treated as artificial lakes when studying evaporation. The impacts of varying water depth and horizontal flow should be seriously considered when investigating the energy balance for evaporation, and the role of river-valley breezes must be carefully examined when studying the turbulent transfer for water evaporation over the water surface.
How to cite: Han, S., Zhang, B., and Wang, L.: Should canyon-shaped Three Gorges Reservoir be treated as an artificial lake in evaporation studies? Results from eight years floating pan observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7720, https://doi.org/10.5194/egusphere-egu25-7720, 2025.
Lake Stechlin (A = 4.3 km2, mean depth = 23.3 m, max depth = 69.5 m, V = 96.9 × 106 m3) is a deep clearwater lake situated in northern Germany. Formerly known for its excellent water quality, the lake experienced severe increases in total phosphorus (P) concentrations between 2014 and 2020, most likely related to shifts in the macrophyte communities in the shallow sediments and associated P mobilisation. After 2020, P levels began to decrease again. Dissolved oxygen (DO) concentrations followed these changes: the DO depletion rate increased from 0.4-0.6 g/m2/d in the pre-eutrophication period to more than 1 g/m2/d during 2019-2021, before starting to decrease again afterwards. Consequently, large areas of the deep hypolimnion became anoxic.
Here we present long-term monitoring data combined with results from two high-resolution measurement campaigns of temperature, dissolved oxygen (DO), and current velocities near the lake sediment at three different depths (45 m, 50 m, and 55 m). During the beginning of the measurements in summer, DO concentrations were comparable or even slightly higher in 2024 compared to 2023. In the fall, anoxic conditions occurred 1 meter above the sediment at all three depths in 2023 but not in 2024, when phosphorus concentrations were considerably lower. We attribute the higher DO concentrations during summer 2024 compared to 2023 to an earlier onset of summer stratification and the lower concentrations during fall 2023 to lower depletion rates in response to decreasing nutrient concentrations. In both years, oxygen fluctuations with amplitudes of up to 4 mg/L were observed and caused by internal waves with periods of approximately 24 h and 6-8 h. Especially in 2023, the sediments experienced periodically changing redox conditions during fall at all three measurement depths. The impact of these fluctuations is still unknown although large fractions of the lake sediments are situated in areas that can potentially become periodically anoxic in Lake Stechlin and other lakes worldwide.
The results illustrate extensive areas of Lake Stechlin experience periodic anoxia, which cannot be detected by monthly routine measurements. The also indicate that oxygen depletion rates respond quickly to changes in the nutrient concentrations. Oxygen concentrations are influenced by multiple factors such as varying nutrient concentrations and differences in the stratification phenology due to meteorological conditions. For reliable future prediction of oxygen budgets, a good mechanistic understanding of their influence is desirable.
How to cite: Schwefel, R., Jordan, S., and Hupfer, M.: Oxygen dynamics in a stratified clearwater lake: hourly to decadal timescales, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4038, https://doi.org/10.5194/egusphere-egu25-4038, 2025.
Lake Zmajevo Oko (ZO) is a small marine lake (A = 9904 m2; V = 90692 m3) near Rogoznica (Croatia). The ZO is strongly stratified: An upper oxic layer with rich planktonic and benthic populations, a thin middle layer with high microbial activity and a deeper, anoxic layer. In the last thirty years, however, five sudden anoxic overturns have been observed in autumn, accompanied by progressive deoxygenation and mass mortality in the lake. The ZO is connected to the nearby Adriatic Sea through the fissures in the karst rocks. However, the possible contribution of this connection to the above-mentioned processes is still unclear. From 2020 to 2023, we conducted a series of opportunistic measurements of temperature, salinity, dissolved oxygen, nutrients and sea level at sites in and around ZO, particularly in caves where optically distinct water layers had been detected. We found that attenuated tides enter the lake and influence the lateral boundary temperature of the upper layer by entering ZO as either warmer (winter season) or colder (summer season) water. As the salinity of the infiltrating water is between the salinity of the lake and the sea, it can be concluded that there is considerable mixing with groundwater. Due to the observed differences in salinity and temperature, this water could also influence the stability of the water column in ZO. We have also found that dissolved oxygen and nutrients in the upper layer fluctuate during the tidal cycle at sites with higher rates of subsurface water exchange. We plan to continue this research by conducting more detailed, targeted analyses to determine the role of karst water exchange in anoxia events and long-term deoxygenation and to incorporate this exchange into the numerical model of the ZO currently being developed. The physical processes forcing deoxygenation in small coastal systems (such as the ZO) need to be distinguished and quantified, especially considering recent climate change. This would also allow the definition of sustainable future maintenance practises, as the ZO ecosystem may currently be jeopardised by anticipated construction projects in Rogoznica.
How to cite: Dominović Novković, I., Marguš, M., Bakran-Petricioli, T., Petricioli, D., Ciglenečki, I., and Vilibić, I.: Tide-controlled water exchange in the strongly stratified marine lakeZmajevo oko (Rogoznica, Croatia), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-403, https://doi.org/10.5194/egusphere-egu25-403, 2025.
Rogoznica Lake–Dragon Eye (RL) is a unique, highly eutrophic, stratified euxinic marine system on the Adriatic coast, sensitive to dynamic environmental shifts. Key physico-chemical transformations in the lake, directly driven by environmental changes, include water column warming, deoxygenation, accumulation of reduced compounds such as toxic sulfides and ammonia, and a increased frequency of anoxic holomictic events, contributing to the pronounced eutrophication [1-2]. All these changes highly impacts organic matter (OM) dynamics and properties. Long-term studies of OM dynamics reveal the accumulation of particulate (POC) and dissolved (DOC) organic carbon, especially in the anoxic hypolimnion, with DOC concentrations ranging from 0.809 to 7.16 mgL-1 and POC from 0.572 to 10.5 mgL-1 [2]. Qualitative changes in OM are evaluated using normalized surface activity (NSA = SAS/DOC) achieved by monitoring of DOC and its surface activity, i.e. surface active substances (SAS) [2-4]. Further characterization of organic matter (OM) is achieved through the analysis of stable isotopes of light elements (13C/12C, 15N/14N, 34S/32S) and the C:N ratio in the POC fraction providing insights into the structure of phytoplankton communities, the sources and origins of OM, and its role in biogeochemical cycles, utilizing the isotope-ratio mass spectrometry (IRMS) method.
Preliminary results (δ¹³C, δ¹⁵N, δ³⁴S) from seasonal RL water column samples revealed isotope values ranging from -20.89 to -32.30 ‰ for δ¹³C, -8.07 to 7.24 ‰ for δ¹⁵N, and -10.83 to 21.74 ‰ for δ³⁴S, with noticeable seasonal shifts along the water column related to variable physico-chemical parameters, including salinity fluctuations, oxygen saturation, and atmospheric deposition. The position of the chemocline, which separates the surface oxic and bottom anoxic water layers, is distinctly observable from the δ³⁴S values, also showing pronounced seasonality. These findings suggest that the OM in the RL water column is predominantly autochthonous, largely derived from phytoplankton activity, with occasional allochthonous inputs, as indicated by the C:N ratio (ranging from 1.09 to 6.51), contributing to eutrophication. During holomictic events, when the otherwise stratified water column becomes mixed and anoxic throughout, isotope ratios point to the presence of bacterially-produced OM. The isotopic data, in conjunction with other organic matter parameters (DOC, POC, SAS, NSA), reveal qualitative and quantitative changes in the composition of OM, offering deeper insight into the influence of environmental shifts on OM dynamics within RL.
This work was result of research activities within the MARRES (IP-2018-01-1717) and the ISO-ZOKO (IP-2024-05-2377) projects.
[1] I. Ciglenečki, Z. Ljubešić, I. Janeković, M. Batistić, in R.D. Gulati, E.S. Zadereev, A.G. Degermendzhi (eds) “Ecology of meromictic lakes”. Springer 2017, Cham, p 125−154.
[2] Simonović, N., Dominović, I., Marguš, M., Matek, A., Ljubešić, Z., Ciglenečki, I. Sci. Total Environ. 863 (2023) 161076.
[3] I. Ciglenečki, I. Vilibić, J. Dautović, V. Vojvodić, B. Ćosović, P. Zemunik, N. Dunić, H. Mihajlović, Sci. Total Environ. 730 (2020) 139104.
[4] Simonović; N., Marguš, M., Paliaga, P., Budiša, A., Ciglenečki, I. Mediterr. Mar. Sci. 25(1) (2024) 160-178.
How to cite: Simonović, N., Marguš, M., Potočnik, D., Ogrinc, N., and Ciglenečki, I.: Isotopic Analysis of Organic Matter Components in Stratified Marine Lake: Assessing Environmental Shifts and Eutrophication Drivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9295, https://doi.org/10.5194/egusphere-egu25-9295, 2025.
Laboratory experiments were conducted in a walk-in freezer containing an open tank filled with brackish water (S=0.4 g/L). We describe the circulation starting with convection and cooling in the ‘fall’ when the air temperature was below freezing (-20 °C). As the water cooled toward the temperature of maximum density, we observed the decay of the convective currents. Then we observed the formation of reverse stratification and the onset of ice cover. The salt excluded at the base of the growing ice generated salt-fingers that transported salt downward (Olsthoorn et al., 2022).
Five hours after ice-on, the freezer was set to 10 °C, and air temperature began to rise. As the air temperature approached 0 °C, the salt-fingering decayed. After the air temperature rose above freezing, the circulation was dominated by warming through the side-walls of the tank; this warming generated relatively fresh water flowing downward along the side walls to the bottom of the tank. This freshened the bottom of the water column and initiated inverse salt-fingers or ‘fresh-fingers’. After the ice melted, warming convection was observed. As the water warmed toward the temperature of maximum density, the convective currents decayed. These experiments simulated the expected circulation in a brackish lake subject to ice cover.
How to cite: Tedford, E. W., Lawrence, G., Watt, J., and Olsthoorn, J.: Laboratory investigation of seasonal circulation in a brackish lake subject to ice cover, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2009, https://doi.org/10.5194/egusphere-egu25-2009, 2025.
The Dead Sea has warmed up by more than 2°C since the overturn of 1979. This unusually fast warming rate has attracted little attention in comparison with the man-induced rapid lake level fall that has gone unabated since the 1950s. Here we develop a thermal model of the Dead Sea to investigate the causes of the lake temperature increase. The monthly-resolved model quantifies all major heat fluxes at the air-water interface with generic physical equations, uses an empirically-based scheme to simulate lake stratification, and incorporates for the first time the heat flux related to the precipitation of halite (sodium chloride, NaCl). This results in a very good agreement with monitoring data for the net air-water heat flux and for the temperatures of the upper and deep lake layers. The various contributions to the energy budget can be disentangled by turning them on or off in the simulations. We thus explore the role of heat released by halite precipitation and of seasonal air temperature in controlling the temperature of the lake. We find a major role of the heat released by halite precipitation, which was previously ignored and has major implications on the understanding of the water budget of the lake. This study paves the way for a better understanding of the hydrological crisis faced by hypersaline lakes around the world, and opens new perspectives in the study of the past climates that led to the accumulation of evaporite deposits.
How to cite: Guillerm, E., Gardien, V., Bärenbold, F., Lowenstein, T. K., Brauer, A., Bouffard, D., and Caupin, F.: The unexpectedly large impact of salt precipitation on water temperature: A revised energy and mass budget of the Dead Sea during 1979 - 2019, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11330, https://doi.org/10.5194/egusphere-egu25-11330, 2025.
Observations and model data showed a gradual increase in desert dust intrusions into the Eastern Mediterranean region. The role of dust intrusions in the formation of lake heatwaves has not been investigated in previous studies. In our study we focused on this point. In-situ buoy measurements showed that, in the two lakes located in the Eastern Mediterranean: freshwater Lake Kinneret and the hypersaline Dead Sea, - a severe dust intrusion (AOD of over 2.5 and surface dust concentration of over 4000 µg/m3) caused the formation of lake heatwaves (LHWs), as appeared in September 2015. This was because desert dust absorbed both shortwave solar radiation and longwave terrestrial radiation contributing to air heating in the near-ground atmospheric layer and water heating at the lake surface.
At the water surface, for 10 days in a row (7 – 17 September), the LHWs were represented by abnormally high daily maximal and minimal surface water temperature (SWT) in comparison with their seasonally varied 90th percentile thresholds. The intensity of surface LHWs was as high as 3 oC. We compared satellite (METEOSAT and MODIS-Terra) SWT data with actual SWT based on buoy measurements. First, spatial distribution of METEOSAT and MODIS-Terra SWT showed that, over any part of the Dead Sea, SWT on dusty days was lower than SWT on clear-sky September 6. This contradicted the increase in actual SWT in the presence of the dust intrusion. Next, we conducted quantitative comparison between satellite SWT data and actual SWT. Our quantitative comparison showed that, in the presence of the dust intrusion, both orbital (MODIS-Terra) and geostationary (METEOSAT) satellites were incapable of representing the surface LHWs. Unexpectedly, in the two lakes, the satellite SWT retrievals underestimated actual SWT by more than 10 °C. This indicates the satellites’ inability to represent the observed LHW phenomenon. The obtained significant difference between the satellite-derived SWT and actual SWT can be explained by the impact of the dust-caused infrared (IR) perturbations on satellite IR measurements. This should be considered when using satellite data to analyze heatwaves in the presence of dust pollution.
As for the subsurface LHWs in the two lakes, our findings imply the following significant point: the physical nature of subsurface LHWs in the hypersaline Dead Sea is essentially different from that of subsurface LHWs in fresh-water lakes. This is because double-diffusive processes are thought to be essential to the formation of abnormal vertical temperature distribution at a depth from 5 m to 20 m causing the development of subsurface LHWs.
Reference: Kishcha et al., Remote Sensing 2024, https://doi.org/10.3390/rs16132314
How to cite: Kishcha, P., Lechinsky, Y., Gertman, I., and Starobinets, B.: Dust-related heatwaves in the hypersaline Dead Sea and freshwater Lake Kinneret which were missed by satellite observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3316, https://doi.org/10.5194/egusphere-egu25-3316, 2025.
In May 2022, a unique dry easterly windstorm generated extreme surface waves on Lake Kinneret, leading to the destruction of the eastern coastal promenade. Wind speeds exceeded 90 km/h in the northern part of the lake and 60 km/h in its eastern part, resulting in significant mixing captured by an in-situ sensor network. Since the lake was already thermally stratified, the atmospheric storm generated a steep-fronted internal surge that propagated along the thermocline. This surge caused intensified mixing, deepened the thermocline, and triggered sediment resuspension as it shoaled over the lake’s slope.
To assess the storm's impact on lake mixing and the role of air-sea interactions, we applied a 3D coupled lake-atmosphere model. The study examines the storm-driven internal surge within the context of a pre-existing internal wave field generated by the daily Mediterranean breeze. Our findings suggest that this internal wave field plays a role in modulating the excitation of the internal surge. Furthermore, we analyze the spatiotemporal variability of lake mixing regimes and the interactions between the lake and atmosphere during the May 2022 storm. The results are supported by observations from multiple locations within the lake and simulations conducted with both coupled and uncoupled 3D simulations.
How to cite: Amitai, Y. and Ehud Strobach, E.: Lake’s Response to an Extreme Synoptic Storm: Internal Waves and Air-Lake Coupling , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12040, https://doi.org/10.5194/egusphere-egu25-12040, 2025.
Lentic Small Water Bodies (LSWBs), including ponds, lakes, and reservoirs, are crucial for ecological balance,
biodiversity, and ecosystem services. However, their seasonal dynamics, nutrient cycling, and the influence
of surrounding land use and landscape patterns are often under-studied. Using integrated machine
learning and remote sensing tools, this study mapped LSWBs across India and analyzed their socioeconomic and environmental impacts in four states. Land use changes, especially urban expansion, caused
LWB degradation nationwide. Socioeconomic factors revealed disparities in development and LWBs across
states, emphasizing the need for tailored regional management strategies. Strategies proposed include
targeted pollution control in urban areas and incentives for sustainable agricultural practices to reduce
detrimental agricultural runoff.
Further, to understand the physio-chemical dynamics of LSWBs, this study examined seasonal patterns,
vertical stratification, and the trophic level index (TLI) in Haridwar district, northern India. Analysis indicated
that nutrient concentrations rose at inlets during the monsoon, and Chl-a levels increased near LSWB
edges, showing significant seasonal variations. Pre-monsoon, vertical stratification of pH, temperature, and
TN was observed but decreased during monsoon mixing. The TLI revealed a shift from oligotrophic (0 to 30)
to hypereutrophic (70 to 100) states, mainly due to agricultural runoff. The TN: TP ratio (< 10) suggests
nitrogen limitation drives algal blooms during monsoons, worsening water quality.
In conclusion, effective management strategies must address nutrient dynamics, stratification, and
eutrophication while considering environmental and socioeconomic factors. Additionally, long-term
monitoring and adaptive management strategies are essential to mitigate ongoing and future challenges.
How to cite: Singh, P. and Yadav, B.: Understanding Lentic water Bodies: Multiscale perspective and Socioeconomic Implications , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-308, https://doi.org/10.5194/egusphere-egu25-308, 2025.
Eutrophication, usually caused by excessive nutrients from human activities, may cause dire environmental consequences such as harmful algal blooms and fish kills. Turnover in eutrophic and stratified lakes is dangerous for aquatic life. Solutions such as reducing stormwater run-off and lake restoration are costly and take years to develop. Therefore, real-time modelling and intervention of lake turnovers are important for improving water quality and aquatic life. Mechanistic models that solve the equations governing the lake processes require significant computational time and are not suitable for real-time modelling. A priori knowledge of the processes is required. This research develops Artificial Intelligence (AI) models for turnovers in Eymir Lake, Turkey with an aim to develop autonomous pre-emptive water quality measurement and intervention systems as well as to understand the factors causing lake turnovers. Because there is no consensus as to the best indicating parameters for lake turnovers, AI models with three separate turnover related target variables, namely (i) difference in dissolved oxygen; (ii) difference in temperature; and (iii) the average of (i) and (ii) were trained and compared. To test the effect of time-lagging on prediction accuracy, predictor variables with time lags of 3 hours, 6 hours, 12 hours, 18 hours, 24 hours, 48 hours, 72 hours, 5 days and 7 days were used as AI model inputs. AI models for different timescales are developed because the controlling parameters for short- and long-term turnovers are different. Fourier transform and high-pass filters were applied to separate the data into short-term (within 2 days) and long-term time series. The effects of temperature, wind speed, dissolved oxygen, and surface water temperature on turnover dynamics were investigated, concentrating on spring turnover in Eymir Lake. The findings from the Artificial Neural Network (ANN) model for short-term data show that: i) Adding time-lagged input factors greatly increased the accuracy of turnover forecasts contributed to the prediction, except for surface water temperature without time lags; and ii) "Temperature Difference" is the best variable to be considered as the target. These results can help develop better forecasting models and offer insightful information on the intricate interactions between variables causing lake turnover events. As a threshold temperature difference indicating lake turnover is not available, such a threshold was determined with an unsupervised K-Means cluster algorithm. The algorithm differentiates the data into two different phases, namely 1) Mixing phase, and 2) Stratification phase. In future, the data analysis results will be connected to the physical lake processes with the help of e.g. Schmidt stability coefficient. Wavelet analysis will be conducted on the data to further determine underlying seasonal trends of the input-target relationship.
How to cite: Amini, H., Lam, M. Y., and Ahmadian, R.: Artificial Intelligence predictive models for diurnal and seasonal shallow lake turnovers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20975, https://doi.org/10.5194/egusphere-egu25-20975, 2025.
Paucity in long-term measurements and monitoring of accurate water quality parameter profiles is evident for small and deep tropical lakes in Southeast Asia. This leads to poor understanding of stratification and mixing dynamics of the lakes in this region. The water quality dynamics of Sampaloc Lake, a tropical crater lake (104 ha, 27 m deep) in the Philippines, was investigated to understand how monsoon-driven conditions impact water quality and ecological health. Located in an urban area with approximately 10% of its surface area allocated to aquaculture, the lake is subject to distinct seasonal changes associated with the Northeast (NE) and Southwest (SW) monsoons. NE Monsoon typically occurs from October to April while SW monsoon, from May to September. These monsoons influence the lake’s water temperature, dissolved oxygen (DO), chlorophyll-α (chl-α), phycocyanin (PC), and turbidity, leading to significant seasonal variability. Monthly field observations of water quality parameters were made from October 2022 to September 2023 using a multi-parameter probe, YSI ProDSS, together with the collection of meteorological data during the same period. During the NE monsoon, cooler air temperatures and winds with sustained speeds caused surface water temperatures to drop from 30.9 ºC in October to 25.5 ºC in January, resulting in the weakening of stratification and eventually in lake turnover. This turnover redistributed nutrients from hypolimnetic layers to surface layers, increasing chl-α and PC levels (14-41 and 0-2 µg/L) throughout the water column. Fish kill was also observed during the lake’s turnover event as a result of the mixing of hypoxic hypolimnetic waters. Turbidity levels (0-3 NTU) were generally low but showed mid-column peaks in October, which was linked to thermocline-related effects, while low values in November followed heavy rainfall dilution and mixing effects. Conversely, the SW monsoon showed increased surface temperatures (28-30 ºC), shallow thermocline formations (3-11 m), and lower surface chl-α and PC levels (2-8 and 0-0.5 µg/L, respectively), likely due to limited nutrient mixing and more stable stratification. Turbidity was notably higher also in July (11-15 NTU) due to intense rainfall and reduced light penetration, which minimized photosynthetic activity. The SW monsoon also coincided with the typhoon season in the study area, resulting in partial upwelling of nutrients during strong storm events. These findings emphasize the need for continued monitoring of Sampaloc Lake’s seasonal water quality patterns, as monsoon-driven changes are crucial to maintaining its ecological balance and sustainability.
How to cite: Duka, M., Tamayo, L. V., and Casim, N. C.: Effects of Two Distinct Monsoon Seasons on the Water Quality of a Tropical Crater Lake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1301, https://doi.org/10.5194/egusphere-egu25-1301, 2025.
Large Eurasian lakes are an integrator of climate processes at the regional scale and a good indicator of climate changes. Variability of ice and snow regime is important for their physical, chemical and biological properties, and for human activity.
We address drivers and patterns of eddy generation during ice-free season before and after vertical overturning in lake Baikal (Russia). We use satellite remote sensing, historical observations and in situ data to follow the different stages of warm and cold anticyclonic eddy generation before and after vertical overturning. Thermal satellite images (Landsat-5-7-8) for 1998-2022 indicate a stable repeating seasonal pattern which is classified into stage of eddy generation and development. Field observations complement satellite imagery to characterise the vertical structure of the eddies. The main source of eddy generation of eddies is the outflow from Barguzin Bay which interacts with the coastline. Subsequent eddy generation is driven by density gradients and geostrophic adjustment. In summer this outflow is dominated by river inflow and lead to the formation of warm anticyclonic eddies. After autumnal vertical overturn, the outflow is forced by the wind bringing cold water from the bay to Middle Baikal and creating cold anticyclonic eddies. We suggest that in the autumn, when the surrounding water cools to a temperature below about 4°C, these cold eddies sink and transform into intrathermocline lens-like eddies that persist under ice and can later create giant ice rings on the Baikal ice cover.
Better understanding of eddy dynamics and continued monitoring help to improve safety for people travelling or working on the ice. There is a need for timely communication of results for non-scientific audience - fishermen, tourism agencies, tourists, journalists and local administration.
This research was supported by the CNES TOSCA Lakeddies, TRISHNA and SWIRL projects, P.P. Shirshov Institute of Oceanology Project N FMWE-2024-0016) and Institute of Water Problems Project N FMWZ-2022-0001.
How to cite: Kouraev, A. V., Zakharova, E. A., Kostianoy, A. G., Hall, N. M. J., Ginzburg, A. I., and Suknev, A. Ya.: Eddy generation in Lake Baikal during ice-free season from satellite remote sensing and field observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8300, https://doi.org/10.5194/egusphere-egu25-8300, 2025.
Global warming is impacting lakes and reservoirs through change in the water temperature and thermal stratification which are affecting ecosystem processes like nutrient recycling that can fuel re-eutrophication or increase methane emission. To quantify these impacts and plan mitigation strategies, process-based projections of water temperature and stratification are needed. For projections on individual lakes, these models are usually calibrated using historic water temperature observations. However, sufficient observations are generally not available, so for global simulations it is common to apply the models without a lake or region specific calibration, which adds additional uncertainty to the projections. As part of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) we calibrated four 1D lake temperature models (FLake, GLM, GOTM, Simstrat) using a standardized methodology to a global set of 73 lakes for which in-situ water temperature observations are available. We evaluated the performance of the lake models, estimated the sensitivity of the calibrated model parameters, and related the results to the different model structures and lake characteristics. We highlight how each model differed in their ability to replicate the water temperature dynamics of specific lake types, but also acknowledge that each of the models performed best for a particular subset of lakes. Even though we did not find general relationships between model parameters and lake characteristics, we underscore modeling takeaways to improve global simulations without the need for model-specific calibration. For most models, the most sensitive parameter was the scaling factor for wind speed. Further, our results indicate that accounting for internal seiches in the model can likely increase model performance. From our findings we want to discuss possible paths forward to further improve the quality of global simulations, i.e. improvements in forcing data, model process description, and using (multi-model) ensemble techniques.
How to cite: Feldbauer, J., Mesman, J. P., Andersen, T. K., Ladwig, R., and Petzoldt, T.: How to improve global lake water temperature projections: findings from calibrating 4 lake temperature models to 73 lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6179, https://doi.org/10.5194/egusphere-egu25-6179, 2025.
Hydrodynamic lake models simulate water temperature at various depths using physics-based equations. These models rely on parameters representing system properties that are not directly measurable, and are generally adjusted through deterministic calibration (DC) methods to find a single parameter set that aligns simulated temperatures with observed data. However, DC overlooks the inherent prediction uncertainties arising from (1) inadequate process representation in the model, (2) measurement errors in hydrometeorological inputs, and (3) errors in water temperature observations used for calibration. Additionally, temperature observations in many lakes and reservoirs are often restricted to a single depth with frequent gaps, necessitating synthetic gap-filling techniques like interpolation, which increase uncertainty and compromise predictive accuracy.
This study explores the potential of probabilistic parameter estimation (PE), which evaluates the uncertainty around likely parameter values, to address these limitations and improve prediction performance in a lake hydrodynamic model. Using the Generalized Likelihood Uncertainty Estimation (GLUE) method, we quantify uncertainty in model predictions by identifying and aggregating acceptable parameter sets that meet predefined performance criteria conditioned on observed data. Unlike DC, GLUE emphasizes the range of plausible outcomes rather than a single optimal solution. We also propose a method to eliminate the subjectivity in selecting the performance criteria.
We apply this approach to the General Lake Model (GLM), a state-of-the-art 1D vertical hydrodynamic model, using Lake Mendota (WI, USA) as a case study. We use 8 years of hourly seasonal observations, including water temperature measurements at 1-meter intervals from the surface to a depth of 20 meters. Our analysis investigates the impact of data gaps and synthetic gap-filling on prediction accuracy and uncertainty. We systematically compare PE and DC to determine which method better handles data scarcity and improves predictive accuracy. Furthermore, we assess whether PE with multi-depth profile observations provide better predictions than single-depth observations and identify the optimal location for single-depth calibration, focusing on the surface mixed layer (SML), metalimnion, and hypolimnion.
Our results reveal that non-calibrated GLM tends to predict better in the SML than in the hypolimnion and PE becomes increasingly necessary as prediction depth increases. Strikingly, single-depth hypolimnion observations yield more accurate prediction uncertainty bounds across the water column and reduce overfitting compared to profile observations. In contrast, including observations from the SML and metalimnion weakens prediction performance at greater depths. Additionally, synthetic gap-filling in observational data degrades prediction accuracy and amplifies uncertainty. Furthermore, PE consistently outperforms DC in predictive accuracy, especially in deeper waters, and proves more robust under conditions of limited data availability.
These results offer practical insights into instrumentation, data collection and calibration strategies for lake hydrodynamic modeling. They underscore the value of probabilistic approaches like GLUE for robust model development and provide guidance for addressing similar challenges in other aquatic systems.
How to cite: Onen, M. O., Rougé, C., Ladwig, R., Douterelo Soler, I., and Darch, G.: Leveraging Probabilistic Parameter Estimation to Address Data Scarcity in Lake Hydrodynamic Modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9017, https://doi.org/10.5194/egusphere-egu25-9017, 2025.
The deoxygenation of deep-water during summer stratification presents a significant challenge for lake ecosystems, further exacerbated by climate change. To better understand future oxygen dynamics and evaluate mitigation strategies, we developed a simple 1-D model that incorporates water-column and sediment oxygen consumption, as well as vertical mixing. This model estimates deep-water oxygen profiles during summer stratification based on temperature profiles, bathymetry and oxygen depletion parameters. We apply the model to Lake Erken in Sweden, achieving an RMSE of less than 1 mg L-1 and an average oxygen demand of 0.55 mg L-1 d-1. Projected water temperature and diffusivity from a hydrodynamic model were used to drive the oxygen model under different Representative Concentration Pathways (RCPs). Climate projections indicate from 2020 to 2099, the deep-water annual anoxic (<0.5 mg L-1) period will increase by 21 days under RCP 6.0 and 32 days under RCP 8.5. Extended stratification periods, ranging from 1 to 5 days per decade, emerge as the key driver of future deoxygenation. To maintain current oxygen levels by the end of this century, oxygen consumption rates would need to be reduced by approximately 20% under RCP 6.0 and 30% under RCP 8.5. Ensuring oxygen stability is crucial for preventing further water quality degradation and protecting fish habitats. Our approach offers a transferable, data-efficient framework for climate-adaptive eutrophication management.
How to cite: Yaghouti, M., Ayala, A. I., Mesman, J., Pierson, D., Shatwell, T., Gutani T Nkwalale, L., Rinke, K., Jennings, E., Hunter, P., Woolway, R. I., and D. Jones, I.: A framework for stabilizing deep-water oxygen under future climate change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3778, https://doi.org/10.5194/egusphere-egu25-3778, 2025.
In the absence of O2, anaerobic biogeochemical cycling is driven by a host of electron acceptors (Mn(IV), NO3-, Fe(III), SO42-), with decreasing energy yield for equivalent reactions. The anoxic environments in which these chemical species drive biogeochemical cycling have a disproportionately high impact on global processes through their roles in climate-active gas fluxes, regulating nutrient availability, and sequestration of trace elements. In modern surface waters, such environments can be found year-round in marine basins with limited deep-water renewal (e.g., the Black and Baltic Seas) and in lakes where vertical mixing is restricted, for example, by strong salinity-driven density gradients (e.g., Lake Cadagno). Despite a range of potential electron acceptors, in most systems these are quickly exhausted, resulting in more strongly reducing anoxic environments, characterized by either high dissolved Fe (ferruginous) or sulfide (euxinic) concentrations, reflecting respiration driven by reduction of Fe(III) and SO42-, respectively.
Lake Zug (Switzerland) is an exception to this, with the maintenance of an intermediate anoxic redox state. The south basin of Lake Zug (198 m deep) is anoxic for approximately the lower 60-70 m, with some seasonal and interannual variation. Deep waters have been regularly anoxic since monitoring began in the 1950s; however, despite the stability of anoxia, the typical strongly reducing ferruginous or euxinic conditions found in other such basins are not reached. Instead, NO3- concentrations remain moderate in anoxic waters, with minimal NO2- and with NH4+ accumulating only well below the oxic-anoxic interface. Similarly, Mn is reactive across the oxic-anoxic interface, with the reduction of manganese oxides and the accumulation of dissolved Mn(II). However, both Fe and SO42- show low reactivity across the oxic-anoxic interface, with minimal net Fe(III) and SO42- reduction apparent throughout almost the entire anoxic zone. This strongly contrasts other seasonally (or permanently anoxic systems (e.g., the Black & Baltic Seas, Saanich Inlet, Lake Pavin, Lake Matano). This high abundance of electron acceptors in anoxic Lake Zug water, in contrast to other anoxic basins, has implications for the biogeochemical cycling of nutrients and climate active gasses. Potential mechanisms for maintaining this state, as well as influences on redox-sensitive major and minor elements, will be discussed.
How to cite: Janssen, D., Rama, J., Vonlanthen DiNenna, P., Kirichenko, Y., Sepúlveda Steiner, O., Doda, T., and Bouffard, D.: The maintenance of intermediate redox states in deep waters of Lake Zug, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21771, https://doi.org/10.5194/egusphere-egu25-21771, 2025.
Oxygen depletion constitutes a major threat to lake ecosystems and the services they provide. Most of the world’s lakes are located >45° N, where accelerated climate warming and elevated carbon loads might severely increase the risk of hypoxia, but this has not been systematically examined. Here analysis of 2.6 million water chemistry observations from 8,288 lakes shows that between 1960 and 2022, most northern lakes experienced rapid deoxygenation. This oxygen loss was linked primarily to prolongation of summer stratification associated with climate warming. Oxygen levels deteriorated most in small lakes (<10 ha) owing to their greater volumetric oxygen demand and surface warming rates, while the largest lakes gained oxygen under minimal stratification changes and improved aeration at spring overturns. Seasonal oxygen consumption rates declined, despite widespread browning. Proliferating anoxia enhanced seasonal internal loading of C, P and N but depleted P long-term, indicating that deoxygenation can exhaust redox-sensitive fractions of sediment nutrient reservoirs. In this presentation I will discuss the use of supervised machine learning tools and hierarchical models to analyse ‘big’ ecological datasets, in this case to examine the physical and biological causes of long-term oxygen loss in northern lakes.
How to cite: Jansen, J., Simpson, G. L., Weyhenmeyer, G. A., Härkönen, L. H., Paterson, A. M., del Giorgio, P. A., and Prairie, Y. T.: Causes and consequences of long-term oxygen depletion in northern lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9413, https://doi.org/10.5194/egusphere-egu25-9413, 2025.
The subarctic region of northern Canada, including the Mackenzie River basin is deeply impacted by the changing climate. Unprecedented rates of warming in Canada’s North, up to four times the global average, have been observed in the region over the past few decades. This brings significant implications for regional hydrology, ecosystems, and human activities. A major controlling feature in the Mackenzie River Basin is Great Slave Lake, which is the second largest lake in the Northwest Territories of Canada and the deepest lake in North America. With over 60% of the population of Northwest Territories living along its shores, Great Slave Lake is a vital ecological and societal asset in the region. This study aims to further our understanding of water circulation and stratification patterns in Great Slave Lake through numerical simulation. Despite the status of Great Slave Lake as one of the largest and deepest lakes in North America, comprehensive numerical modelling has proven difficult due to lack of accurate bathymetric data. To address this gap, we collaborated with the Department of Fisheries and Oceans to develop the first complete bathymetric map of Great Slave Lake. Historical naval charts and field sheets were integrated with additional sounding data to produce a simulation domain tailored to the Nucleus for European Modelling of the Ocean (NEMO) at a horizontal resolution of 1km with 30 vertical layers. The NEMO model was chosen for application in this large lake for consistency with the existing model setup being used by Environment and Climate Change Canada (ECCC) for its operational forecasting system in the Laurentian Great Lakes. Atmospheric reanalysis is provided by ECCC’S Regional Deterministic Reanalysis System (RDRS), while surface runoff entering the lake is driven by the Community Environmental Modelling System – Surface & Hydrology (MESH) outputs from the Global Water Futures reanalysis efforts. The resulting NEMO model shows good capability of simulating lake processes with preliminary results indicating that the lake exhibits seasonal thermal stratification, consistent with dimictic behaviour, where full vertical mixing occurs twice annually. Our results also show that wind-induced mixing appears to also play a significant role in lake circulation, and a counterclockwise circulation pattern is observed, with prominent gyres in the main basin of the lake. Ongoing work focuses on further validation of the temperature profiles at select locations and sensitivity analysis to improve the overall simulation capabilities of the model for future water resource management needs.
How to cite: Stankevicius, J., Pietroniro, A., and Zhou, Q.: Hydrodynamic Modelling of Great Slave Lake Using NEMO, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12669, https://doi.org/10.5194/egusphere-egu25-12669, 2025.
Lentic waters integrate atmosphere and catchment processes, and thus ultimately capture climate signals. However, studies of climate warming effects on lentic waters usually do not sufficiently account for a change in heat flux from the catchment through altered inflow temperature and discharge under climate change. This is particularly relevant for reservoirs, which are highly impacted by catchment hydrology and may be affected by upstream reservoirs or pre‐dams. This study explicitly quantified how the catchment and pre‐dams modify the thermal response of Rappbode Reservoir, Germany's largest drinking water reservoir system, to climate change. We established a catchment‐lake modeling chain in the main reservoir and its two pre‐dams utilizing the lake model GOTM, the catchment model mHM, and the stream temperature model Air2stream, forced by an ensemble of climate projections under RCP2.6 and 8.5 warming scenarios. Results exhibited a warming of 0.27/0.15°C decade−1 for the surface/bottom temperatures of the main reservoir, with approximately 8%/24% of this warming attributed to the catchment warming, respectively. The catchment warming amplified the deep water warming more than at the surface, contrary to the atmospheric warming effect, and advanced stratification by about 1 week, while having a minor impact on stratification intensity. On the other hand, pre‐dams reduced the inflow temperature into the main reservoir in spring, and consequently lowered the hypolimnetic temperature and postponed stratification onset. This shielded the main reservoir from climate warming, although overall the contribution of pre‐dams was minimal. Altogether, our study highlights the importance of catchment alterations and seasonality when projecting reservoir warming, and provides insights into catchment‐reservoir coupling under climate change.
How to cite: Gai, B., Kumar, R., Hüesker, F., Mi, C., Kong, X., Boehrer, B., Rinke, K., and Shatwell, T.: Catchments Amplify Reservoir Thermal Response to Climate Warming, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13713, https://doi.org/10.5194/egusphere-egu25-13713, 2025.
Lake Titicaca, located in the tropical Andes of South America and shared by Peru and Bolivia, has experienced extreme variations in water levels, leading to droughts and floods over the last 50 years. In the early 1990s, a master plan was developed, proposing the construction of a gate to regulate the lake's outflows and mitigate hydrological risks. While the gate was completed in the early 2000s, regulation was never implemented due to a lack of management agreement between the two countries. The effectiveness of the operating rules for managing hydrological risks under ongoing climate change remains unknown. To address this issue, we used an integrated water balance model to evaluate both natural and regulated release options under observed climate conditions (1982–2016) and future scenarios of precipitation and air temperature. Future climates were generated using the perturbation method based on changes projected by 21 GCMs from CMIP6 for the period 2036–2070. Drought was defined as a drop in water levels (and associated released flows) below a threshold linked to downstream irrigation requirements. Flooding was defined as the condition when water levels (and associated released flows) exceed the flooding threshold in the shore zone of the lake. The risks were evaluated in terms of their intensity, duration, and frequency using appropriate indicators. Under a projected warming of 3.4 °C (as suggested by an ensemble of GCMs by 2050) and no changes in precipitation, the lake's water levels could drop below the outlet level, disconnecting it from the Desaguadero River. Regulation under observed climate conditions reduces risks in the shore zone and downstream areas. However, under future climate scenarios, regulation is likely to be less effective. In the Warm–Dry, Hot–Dry, ensemble mean scenarios, more intense and prolonged droughts are expected, while in the Warm–Wet and Hot–Wet scenarios, the risk of flooding could increase significantly. The differences in the effectiveness of natural and regulated release options are minimal. This suggests that managing releases alone will be insufficient to mitigate hydrological risks under future climate conditions. These findings provide valuable insights for improving management and guiding the identification of additional intervention measures, such as land-use planning, to ensure Lake Titicaca's resilience to future droughts and floods.
How to cite: Lima-Quispe, N., Ruelland, D., and Condom, T.: Future droughts and floods in Lake Titicaca cannot be prevented by release management alone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4270, https://doi.org/10.5194/egusphere-egu25-4270, 2025.
Lakes account for 3% of the Earth's surface and they constitute important habitats for manifold biota [1]. In the 19th century at Walden pond (Massachusetts, USA) the research field of limnology developed, which is nowadays dealing with physical, chemical and biotic aspects in all kind of freshwaters [2,3]. While in the past pollution was a main driver in lake ecosystems [4], nowadays rising water temperatures negatively affect Alpine lakes throughout the world [5]. Thus, we selected two mountainous lakes in the Alps as well in the Altai Mountains - two distant, but ecologically similar regions - to compare their characteristics, research history, pressures as well as management strategies.
Lake Achensee is the largest lake (6,8 km²) of the Austrian federal state Tyrol at an altitude of 928.78 m. It`s length is 8.6 km and the maximal depth amounts to 133.02 m. Investigations of the lake started in the beginning of the 20th century, focusing on zooplankton [6] and bathymetry. Since 1927 this natural lake is used as a reservoir for hydropower production, with water level fluctuations of up to 5 m. In the 1970ties intensified tourism, resulted in an eutrophication of the lake and blooms of Planktothrix rubescens. Since the construction of a sewer around the lake, the situation improved, and it is again considered as an oligotrophic lake since the end of the 20th century. Commercial fisheries were stopped in 2000, due to reduced stocks (reduction of nutrients) as well as the occurrence of Triaenophorus crassus [7]. Nowadays only recreational fishing takes place. In Europe lakes > 50 hectares are assessed regularly under the WFD, including the biological quality elements phytoplankton, macrophytes and fish – revealing a good ecological potential of the lake.
The 78 km long Lake Teletskoye (Altyn-Kol) is the largest (223 km²) and deepest (up to 325 m) lake of the Russian Altai at an altitude of 434 m. It has been known since the 17th century, but the first large-scale studies, including bathymetric measurements and hydrobiological collections, started only in 1901 [9]. This cold oligotrophic lake is characterized by very low fish productivity. Attempts to organize industrial fishing were made in the 1930ties, but the fishery was considered impractical. At the same time, Lake Teletskoye is one of the largest tourist and recreational centers in Russia, and in conditions of outbound tourism restrictions, the tourist flow increases annually. The state environmental monitoring of the lake includes hydrological and hydrochemical measurements only. Since 1987, a scientific floating station of the Russian Academy of Sciences is operating on the lake, whose tasks include analyzing long-term changes in the composition and structure of aquatic communities [e.g. 10, 11]. The available data indicate the high ecological status of Lake Teletskoye.
Our synthesis highlights, that long-term data is crucial in order to understand changes related to human activities as well as climate change. We exemplify dynamics and catchment interactions of mountain lakes, using two lakes and discuss similarities and differences.
How to cite: Schletterer, M. and Yanygina, L. V.: Achensee and Lk. Teletskoye - 5000 km apart: similarities and differences of two mountain lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20247, https://doi.org/10.5194/egusphere-egu25-20247, 2025.
Lake Vomb is a 12 km2 large lake located in southern Sweden which has served as a vital drinking water source for approximately 500,000 inhabitants since the 40s. The lake is highly productive due to its location in a highly dense agricultural region and, therefore, has high phosphorous concentrations that periodically cause extensive and occasionally toxic algal blooms. This poses challenges not only for the drinking water production but also for the local communities in the area. Various measures, such as artificial wetlands and natural flooding areas, have been implemented in the catchment to decrease nutrient loading. However, these measures have shown limited effects on improving water quality in the lake.
Monitoring data has been collected since the 50s, but much of this historical data has remained unused due to a lack of digitalisation. In this study these archived records was recovered and digitalised to create a comprehensive long-term dataset with the aim of analysing trends in nutrient fluxes, the effectiveness of mitigation measures, changes in land-use and agricultural activities and the impact of climate change. Preliminary results show a decrease in nutrient concentrations in the inflowing waterbodies which is not seen in the lake itself, posing the question of in-lake processes continuing driving the eutrophication of the lake, such as internal phosphorus loading. By evaluating these long-term trends insight in lake dynamics could be gained as well as help to identify relevant and cost-effective measures for improving the lake water quality.
How to cite: Söderman, A.: Long-Term Water Quality Trends in Lake Vomb, Sweden, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9683, https://doi.org/10.5194/egusphere-egu25-9683, 2025.
Satellite remote sensing can potentially provide objective, broad scope, high frequency, and continuous measurements of inland water quality by capturing water colour information. However, challenges brought about by the optical complexity of inland waters and overlying atmosphere, and interference due to adjacency effects have hindered the development of valid Earth observation (EO) approaches for water quality monitoring in inland waters compared with the ocean applications. Water colour has been recognized as one of the most important Essential Climate Variables of the lake ecosystem, as it is directly related to changes in water constituents and almost all of the lake's ecological changes could alter water colour. Given the high retrieval accuracy from existing Earth observation satellite data, water colour, in terms of Forel Ule Index (FUI) and hue angle, can be a realistic indicator to track the long-term changes in the lake ecosystem and further explore the lake response to environmental changes. Through developing a global algorithm of FUI and hue angle for diverse types of inland waters and multiple source satellite datasets, datasets of FUI and hue angle for local and global lakes were constructed using satellite datasets. Lake colour have therefore emerged as a means to addressing scientific issues, such as the spatial patterns and long-term change trends of lake ecosystem, how water colour associated with climate change and local anthropogenic activities, spanning from local to global scales. Opportunities of leveraging water colour information observed from multisource satellite datasets in limnological research will be concluded and discussed in this report. We will also discuss in depth the challenges and possible countermeasures in estimating and reducing observation uncertainties associated with optical water types and multi-source satellite datasets.
How to cite: Wang, S. and Zhang, B.: Earth observation of lake colour dynamics across local to global scales: opportunities and challenges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20, https://doi.org/10.5194/egusphere-egu25-20, 2025.
Aquatic ecosystems are essential for human well-being, yet they are increasingly threatened by climate change and anthropogenic pressures. Effective management of lakes and lagoons depends on understanding the interactions between their drainage basins and water bodies. This study addresses these dynamics in the Mar Menor, one of Europe’s largest saltwater lagoons, located in southeastern Spain. Intensive agricultural activities in its catchment have driven a eutrophication crisis, marked by recurrent algal blooms and anoxic events. To assess the impact of climate change and agricultural practices, we developed an integrated modeling framework by coupling the SWAT+ model for the watershed with the GOTM-WET model for the lagoon. Using bias-corrected climate projections from five global models, we simulated future runoff, sediment transport, and nutrient loading under various management scenarios, along with key lagoon conditions such as oxygen levels and chlorophyll-a concentrations to evaluate the frequency of hypoxia and algal blooms. Results indicate that more intense precipitation events will increase runoff, leading to an 11% rise in sediment transport and a significant increase in phosphorus input to the lagoon, more than doubling current levels. Consequently, the frequency and duration of algal blooms and anoxic conditions are expected to worsen. Among the evaluated management strategies, crop rotation was the most effective for reducing sediment transport (by approximately 50%), while contour farming yielded the greatest reductions in algal bloom days (from 93 to 29) and anoxia days (from 45 to 9). Moreover, combining all proposed practices produced a synergistic effect, enhancing resilience against climate change impacts. These findings underscore the importance of holistic management approaches to safeguard the ecological health of the Mar Menor and similar vulnerable aquatic systems. This study forms part of the AGROALNEXT programme and was supported by MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1).
How to cite: Jiménez-Navarro, I. C., López-Ballestero, A., Mesman, J. P., Trolle, D., Pierson, D., and Senent-Aparicio, J.: Mitigating Climate Change Impacts with Agricultural Practices in a Coastal Lagoon, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16167, https://doi.org/10.5194/egusphere-egu25-16167, 2025.
Urban water bodies, such as lakes in the rapidly growing cities of the Global South, are being severely impacted by unsustainable urbanisation. This has resulted in tremendous stress on the interconnected system of lakes in Bengaluru, India. Existing studies related to degradation of lakes considers individual lakes as the unit of analysis, thus failing to address the issues due to the interconnected or cascaded nature of lakes in the city. To address these gaps, this study adopts lake series scale as the unit of analysis, to analyse the cascading impacts of urbanisation, focusing on the severely degraded Yele Mallappa Shetty Lake Series (YMSLS) in Bengaluru.
The study uses SRTM DEM(30m) for delineation of individual lake catchment areas and identify stream orders for spatial analysis. Further, extent of urbanisation in the catchment is quantified by the Land use land cover (LULC) change analysis(1993-2023) using supervised classification techniques with Landsat 5 (TM, 30m) and Landsat 8 (OLI+TIRS, 30m) satellite images. Spatio-temporal variation of surface water quality of lakes in the catchment is analysed using the Weighted Arithmetic Water Quality Index (WAWQI) and the Overall Index of Pollution (OIP) derived from monthly water quality data (2023-2024).
LULC change analysis revealed that in 1993, the YMSLS catchment area comprised open spaces (53.4%) and agricultural land with vegetation (35%), while built-up areas were limited to 7.2%. However, by 2023, the built-up area expanded to 34.6% of the 285 sq. km catchment, becoming the dominant land use. Rapid urbanisation has led to improper disposal of wastewater and caused water quality degradation and increase in aquatic vegetation growth in the lakes. Temporal analysis of surface water quality showed seasonal variations, wherein the WAWQI and OIP values were lowest during the post-monsoon season (Mean ± SD; 107.9 ± 43.5, 4.4 ± 1.3), followed by the monsoon season (109.3 ± 44; 4.6 ± 1.87), and peaked in the summer season (193.5 ± 62.1; 4.8 ± 1.3). Spatial analysis showed that lakes receiving inflows from higher-order streams located at downstream areas exhibited higher WQI values, indicating greater pollution levels compared to lakes associated with first order streams located in upstream areas. Additionally, the individual catchment area of lakes demonstrated a strong positive correlation with WAWQI (r = 0.71, p < 0.05) and a moderate positive correlation with OIP (r = 0.6, p < 0.05). The spatio-temporal analysis demonstrates the flushing of pollution loads, including aquatic vegetation, from upstream to downstream lakes, with the reduction in pollution levels in upstream lakes facilitated by interconnectivity of lakes.
The study highlights the urgent need for an integrated approach following hydrological units, rather than the currently adopted administrative or lake-centric units, to effectively manage interconnected lakes and their catchments. A lake series approach addresses spatial interdependencies and cascading impacts, essential for sustainable lake management and water security in urban, water-stressed regions like Bengaluru.
How to cite: Mampilamthoda, P. and Chinnasamy, P.: Spatio-Temporal Dynamics of Surface Water Quality in Cascaded Lake Systems Due to Urbanisation: An Integrated Lake Series Approach for Bengaluru, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18725, https://doi.org/10.5194/egusphere-egu25-18725, 2025.
Posters on site: Fri, 2 May, 14:00–15:45 | Hall A
Africa is considered to be extremely vulnerable to climate change despite contributing little, and yet this vulnerability does not resonate with the breath or depth of research on the region, particularly regarding its inland freshwater systems. While lakes support million of livelihoods through several water uses supply, limnological studies in Sub-Sahelian Africa have largely focused on a few well-studied lakes, leaving vast regions underexplored.
Existing global studies on climate-change impacts on lake water quality and freshwater availability often operate at broad scales. However, such efforts rarely address sub-continental heterogeneity or provide the foundational climatological baselines. The first step of any global-scale study is the definition of the average seasonal behavior of any geophysical or geochemical variable considered. This being just an intermediate step towards more advanced analysis (e.g. detection of trends and anomalies, extremes detection), the climatology itself has generally received little attention. In ungauged regions where local in-situ data are scarce, identifying the drivers of ecological shifts is more challenging as a knowledge base on the average or past conditions of the lake is unavailable.
In this study, we present the first atlas of lake functioning across sub-Sahelian Africa, identifying regional clusters of climate and ecological analogs. We analyze the interplay between lakes and their surrounding environment -encompassing both climatic and anthropogenic drivers. Our results reveal three main regions of analogous lake functioning, where key climatic drivers interact with lake response in terms of water availability and water quality. These interactions are shaped by overarching processes (such as large-scale atmospheric circulation) as well as lake-specific conditions, such as morphological characteristics, climatic zones, human pressures like land use and population density.
By exploring the potential role of remote sensing to overcome data scarcity in sub-Sahelian African lakes, our study provides the first multivariate assessment of average lake-climate interactions and provides a baseline for future research in this region, in support of an informed monitoring of the lakes, a more sustainable management of water resources, and climate risk mitigation actions.
How to cite: Amadori, M., Greife, A. J., Carrea, L., Calamita, E., Woolway, I., and Pinardi, M.: A sub-continental scale assessment of lake-climate interactions in sub-Sahelian Africa, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4218, https://doi.org/10.5194/egusphere-egu25-4218, 2025.
Arctic ice-covered lakes are often considered to be quiescent systems as they are insulated from direct effects of sunlight and wind over extended periods of time. However, water circulation is driven by gravity currents resulting from sediment heat fluxes and wind-driven oscillations of the ice-cover cause considerable internal waves. Depending on the thickness of the snow cover, penetrative convection in fall can occur as long as sunlight is present. All these drivers of lake hydrodynamics are most influential in early winter when heat stored during summer is remaining in the sediments and the ice and snow cover remains thin.
Here we present multi-year measurements of under-ice temperatures and oxygen concentrations in five Arctic lakes with maximal depths ranging from 3 to 27 m and surface areas from 1 to 150 ha. The focus is on the period of early winter from the beginning of the ice-covered period to approximately 30 days after ice-on. During early winter, temperatures varied between 1 and 3.7°C and depended on summer temperatures and meteorological conditions preceding ice-on. Sediment heat fluxes of several W/m2 drove gravity currents with velocities in the order of several mm/s. Oxygen depletion was higher in early winter compared to late winter periods but lowered in early winter periods with penetrative convection occurring.
In summary, the results show a high interannual variability and variability between lakes in early winter temperatures, gravity currents and oxygen depletion rates all of which depending on meteorological conditions and lake morphometry.
How to cite: Schwefel, R. and MacIntyre, S.: Temperatures and hydrodynamics during early winter in ice-covered lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4281, https://doi.org/10.5194/egusphere-egu25-4281, 2025.
Unhealthy nitrogen (N) and phosphorus (P) flows are key drivers of watershed eutrophication and ecosystem degradation, posing significant risks to water quality and environmental sustainability. Existing analytical methods fail to capture the complex interactions of nutrient flows between sources, pathways, and sinks, particularly the interplay between environmental and socio-economic factors. To address these challenges, we developed a novel Source-Transfer-Sink (STS) analytical framework that integrates Substance Flow Analysis (SFA), the SWAT model (Soil and Water Assessment Tool), and high-resolution geospatial technologies. This framework enables comprehensive and dynamic tracking of N and P sources, transfer pathways, and sinks within watersheds, providing critical support for enhanced nutrient management and policy formulation. The STS framework was applied to the Erhai Lake watershed in China, an ecologically sensitive region increasingly threatened by agricultural intensification, urbanization, and eutrophication. The results reveal that over the past 23 years, nutrient dynamics in the watershed have undergone a significant transformation, shifting from a high-input, low-cycling, high-emission model (2000-2013) to a low-input, high-cycling, low-emission model (2014-2022). In 2000-2013, excessive use of chemical fertilizers and improper management of livestock manure resulted in severe environmental losses. By 2022, the implementation of green development policies and strengthened environmental protection efforts increased nitrogen recycling by 64.47% and phosphorus recycling by 63.89%, while overall losses decreased sharply, with nitrogen and phosphorus emissions reduced by 68% and 77%, respectively. Spatial analysis identified nutrient hotspots, primarily concentrated in rural and farmland areas in the northern and western regions (especially Niujie Township and Yinqiao Town), where these areas experience the highest nutrient loss through runoff. By 2022, the nutrient loss intensity in these hotspot areas had significantly decreased and become more homogeneous. Urban areas benefited from advanced wastewater treatment technologies, which reduced nitrogen and phosphorus discharges into surface waters. This study provides a broader and more applicable Source-Transfer-Sink (STS) analytical framework for characterizing nitrogen and phosphorus cycling across watershed systems. It offers methodological support and policy insights for large lakes in rapidly developing regions or countries, enabling a clear presentation of nutrient flow structures and the sustainable management of nitrogen and phosphorus resources.
How to cite: Cheng, X., Dong, Y., Li, Y., and Wang, S.: New Source-Transfer-Sink Analytical Framework for Dynamic Tracking of Nitrogen and Phosphorus Flows and Changes in Watersheds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5073, https://doi.org/10.5194/egusphere-egu25-5073, 2025.
Alplakes is an interactive web application providing open access to operational simulations and remote sensing data for lakes in the European alpine region. The platform combines outputs from various research projects to create a digital twin of each lake. Designed with user-friendliness in mind, Alplakes enables a wide range of users to access operational lake models and remote sensing products developed by researchers. Here we focus on the three-dimensional hydrodynamic operational models featured in Alplakes. The project builds on the previous work of Meteolakes, which pioneered the integration of satellite Earth observation and three-dimensional hydrodynamic modeling. Since 2016, the Meteolakes web platform has attracted over 600,000 users. Alplakes expands on this foundation, now covering twelve Alpine lakes at elevations ranging from 60 to 1800 meters above sea level. This broader scope aims to provide comprehensive data for a diverse set of alpine water bodies. The goal is finally to discuss the possible interest to upscale such kind of initiative.
Website: https://www.alplakes.eawag.ch
How to cite: Bouffard, D., Amadori, M., Brescani, M., Giardino, C., Odermatt, D., Rahaghi, A. I., Runnalls, J., Schmid, M., Toffolon, M., and Werther, M.: ALPLAKES: advancing lake research and management through open integration ofremote sensing and hydrodynamic products, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8001, https://doi.org/10.5194/egusphere-egu25-8001, 2025.
Mine pit lakes, formed in abandoned open-pit mines, undergo complex hydrological processes that affect their water balance and environmental behaviour. Accurate evaporation estimates can be crucial for predicting a pit lake’s long-term behaviour. However, the lack of in situ measurements means that evaporation estimates often rely on models that have not been validated for pit lakes. In this study, three evaporation models were evaluated: an aerodynamic model, incorporating an equilibrium temperature approach, and the General Lake Model, a one-dimensional hydrodynamic model and traditional pan coefficient approach. The aerodynamic and GLM models were calibrated and validated using in situ daily measurements of evaporation and surface water temperature taken in a pit lake in central Queensland, Australia over a 21-month period. Based on minimising the RMSE, the aerodynamic model had a calibration period RMSE of 1.2 mm/day while the GLM model had 1.3 mm/day, with corresponding surface water temperature RMSEs of 0.9 °C and 1.2 °C. Validation period performances were similar for both evaporation and temperature. A pan coefficient model using a commonly assumed coefficient of 0.7 produced a calibration period RMSE of 2.8 mm/day. The aerodynamic model estimate exceeded that of the GLM on average by 34 mm/month in summer and 37 mm/month in autumn, with lower differences of 5.4 mm/month in spring and winter. This is because the aerodynamic model excludes rainfall-induced cooling and mixing of the lake in the summer wet season, leading to higher evaporation estimates. In spring and winter, with less rainfall and mixing, the models align more closely. These differences remained consistent under future climate scenarios due to low projected changes in summer rainfall. Sensitivity analysis of the GLM identified surface heat exchange parameters, wind speed, and radiation are key factors influencing evaporation and temperature simulations. It is concluded that the aerodynamic model is an accurate and easily applied model for estimating current and future evaporation in the case study region. There may be accuracy benefits of using the GLM model where long-term changes in lake inflows, such as increases in rainfall, can change the lake's energy balance.
How to cite: Kemanga, B., McIntyre, N., Bulovic, N., and McJannet, D.: Modelling evaporation from mine pit lakes: comparing three models under current and future climate., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9274, https://doi.org/10.5194/egusphere-egu25-9274, 2025.
Vertical one-dimensional aquatic ecosystem models (AEMs) are commonly used to project water quality changes in lakes, ponds and reservoirs. AEMs integrate a physical model, for water temperature dynamics and mixing, and a water quality model, which simulates biogeochemical cycles and ecological processes. Although powerful, assessing the performance of these models is challenging as observational data are often scarce and most models are overparameterized, making them mathematically ill-posed. A promising approach is the use of ensemble modeling to quantify the uncertainties of the underlying mathematical model parameters and the boundary data. In this study, we apply three AEMs (GLM-AED, GOTM-WET, GOTM-Selmaprotbas) to replicate observed long-term water quality dynamics of Lake Mendota, USA. Each model was configured conceptually similar, and parameters were calibrated to the same data, but optimization procedures differed. We assessed model performance through a hierarchical framework to evaluate fits on the state, process and system level. Although all AEMs sufficiently replicated most of the observed data - the states - they differed in their projected reaction pathways - the processes. As an example, modeled nitrate concentrations were close to observed data, but modeled nitrification and denitrification rates differed across models. This highlights the importance of considering the equifinality thesis, meaning that alternative modeling pathways exist simulating the same output data, for aquatic ecosystem modeling as an additional, and crucial, contributor to uncertainty. We recommend that future modeling studies should employ ensemble setups to further explore the role of equifinality.
How to cite: Ladwig, R., Mesman, J. P., Andersen, T. K., and Bucak, T.: A lurking uncertainty in lake ecosystem modeling: can equifinality arise from conceptually similar models?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9360, https://doi.org/10.5194/egusphere-egu25-9360, 2025.
The restoration of the North Aral was an unprecedented effort to save a large water basin by construction of a dam that separates it from the rest of the desiccating Aral Sea area. As a result, the lake volume has stabilized at 27.5 km3, the area has increased from 2800 km2 in 2006 to 3400 km2 in 2020, and the salinity has dropped from 18 to 10 g kg-1. The consequences of this unique experiment include highly dynamic changes of the thermal conditions, seasonal stratification, ice regime, and dissolved oxygen content and remain not fully quantified to date. We analyze the current state of the North Aral Sea with regard to stabilization of its long term dynamics, as well as consider the possible future projections in view of the global change effects on the regional hydrological regime and potential water management measures. Using data from two year-long observations, we analyze the current seasonal mixing regime and sub-seasonal oscillations due to lake-scale internal waves in the North Aral. We found that the seasonal stratification pattern is intermediate between dimictic and polymictic, with relatively weak summer thermal stratification occupying only a small deep part of the lake. Salinity does not contribute to the summer density stratification. On the background of weak thermal stratification, highly energetic internal waves with periods of 4.5 days dominate the near-bottom dynamics and facilitate mixing at the lake bottom. As a result, the bulk of the water column remains well saturated with oxygen throughout the year. However, low-oxygen conditions may develop in the deepest part of the lake in mid-summer. In summary, the mixing regime of the restarted lake favors vertical transport of dissolved matter and water-sediment mass exchange ensuring oxygenation of deep waters and supply of nutrients to the upper water column. While the North Aral Sea is restored to the well-mixed state similar to that before its desiccation started, its seasonal mixing regime is currently in unstable equilibrium, wobbling between polymictic and dimictic conditions. The fragility of this seasonal pattern is demonstrated by modeling results: slight changes of the water level or transparency may turn the Aral Sea to steadily dimictic or polymictic state.
How to cite: Kirillin, G., Shatwell, T., and Izhitsky, A.: Seasonal stratification and basin-scale internal waves in the North Aral Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9570, https://doi.org/10.5194/egusphere-egu25-9570, 2025.
Small lakes and ponds are hotspots of biodiversity, biogeochemical reactions, and hydrological interactions in the landscape. While providing the same functions as larger lakes, they often do so at higher rates per unit area. Despite their ecological importance and vulnerability to climate and land use changes, they are excluded from monitoring programs at the European and German national scales. This limits our ability to assess their responses to a changing climate and the cascading effects on surrounding ecosystems. The ecosystem functions of small lakes are closely tied to the permanent or seasonally consistent presence of water, making the understanding of their water budgets a crucial research priority.
In this study, we utilized Sentinel-2 satellite imagery to reconstruct water area time series for approximately 700 German small lakes and ponds (0.005–0.5 km²) from 2017 to 2024. These time series were used to calibrate simple water balance models and investigate the susceptibility of these lakes to temporary or permanent lack of water under current and projected climate conditions. Sensitivity analyses and climate projections, combined with lake characteristics from the German Small Lake and Pond Inventory (GSLPI), allowed us to identify key attributes—such as morphology, geographic location, and connectivity to river networks—that best explain the risk of falling dry.
Our findings indicate that many small lakes and ponds are at risk of transitioning from permanent to seasonal water presence in the coming decades. Importantly, individual lake characteristics, rather than regional hydro-climate conditions, are the strongest predictors of these changes. This work underscores the urgent need to include small lakes and ponds in monitoring frameworks to better understand their ecological functions and vulnerabilities in a rapidly changing climate.
How to cite: Wachholz, A. and Jawitz, J.: Vulnerable Hotspots: Understanding the hydrology of small German lakes and ponds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10614, https://doi.org/10.5194/egusphere-egu25-10614, 2025.
Fluvial lakes, due to their short renewal time, are particularly affected by upstream processes. This study focuses on the morphological evolution of the Lake Superiore (Mantua, Northern Italy) and of the upstream wetland. The lake is a shallow fluvial reservoir, regulated by a dam on the Mincio River, which is the main outlet of Lake Garda. The case study is located in the central part of the Po River Valley, one of the most productive agricultural areas in Italy. The farmland is irrigated by a huge ditch network with a total length of approximately 2000 km, almost 30 times the length of the Mincio River itself (75 km). Many of the river’s main tributaries are agricultural canals, resulting in a considerable amount of nutrients and fine sediment inputs due to surface runoff. During high rainfall events, the sediment plume released from these channels is clearly visible also from satellite images and can often reach the lake. As a result, Lake Superiore is hypertrophic due to nutrient loads and water stagnation, with a Secchi depth lower than 1 m and dissolved oxygen saturations that may exceed 400% during summers.
Using the previously tested “Deeper CHIRP+” low-cost SONAR, between 2023 and 2024 we acquired a detailed bathymetric map of the lake and of the wetland’s main channel network. We compared these maps with formerly acquired bathymetries of the two areas dating back to 2006 and 2016 respectively. Both areas showed a clear trend of deposition, with maximum differences in bed elevation of the order of 1 m, approximately 1/3 of the mean depth of the lake. The wetland, which has high naturalistic value (included in Nature 2000 sites), resulted particularly threatened by landfilling, with a risk of channels closure and loss of aquatic wildlife habitat.
Since February 2024, we have been acquiring monthly measurements of discharge, water quality, and suspended solids concentration in the Mincio River and in two of its main tributaries: the Goldone and Osone canals. Osone showed the highest values of suspended sediments, with a TSS concentration of 140 mg/L at a discharge of 12 m3/s, resulting in a load of 145 tons/day entering the wetland, while the incoming discharge in the Mincio River was comparable. Regarding nutrients, it reached a maximum concentration of 16 mg/L of total nitrogen, further worsening the ecological state of the system.
Due to either water scarcity or flood protection issues, management authorities of the Mincio River are skeptical about lake flushing activities. However, it could be possible to plan effective flushing operations within an integrated management framework. Increasing the discharge from the dam immediately after heavy rainfall events may reduce sedimentation at the time of maximum inputs. To achieve this objective, a good knowledge of the water and sediment distribution in the channel network is needed. For this reason, we are developing a numerical model to predict sedimentation rates in the wetland for different through-flowing discharges.
How to cite: De Vincenzi, M., Adami, L., and Tubino, M.: Impact of agricultural runoff on a shallow fluvial lake and wetland in the Mincio River basin (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11084, https://doi.org/10.5194/egusphere-egu25-11084, 2025.
In urban areas, small lakes provide many ecosystem services including biodiversity, landscape composition, cooling islands, recreation, etc. Many have been created during the recent decades as sand-pit lakes. Their origin comes from urbanisation which requires large quantities of sand and gravel for the construction of buildings and infrastructure. Gravel is often extracted from riverbeds, beach deposits or alluvial fans. When gravel extraction stops, the quarries fill up with groundwater and become artificial lakes.
The thermal regime and hydrodynamics of these lakes have a strong influence on their ecological functioning and on the fate of contaminants in the water column. In order to better understand their physical behaviour and to which extent it may be affected by climate change, numerical modelling can be very effective.
Calibration of the model parameters is a crucial step to obtain reliable modelling results. However, the available field data are generally too scarce to obtain a single set of parameter values. Performing a sensitivity analysis allows to identify the most sensitive parameters that need to be calibrated.
The results of the parameter sensitivity analysis and the calibration of a one-dimensional model (GLM, General Lake Model) (Hipsey et al., 2019) are presented. The sensitivity analysis was performed according to a global sensitivity analysis technique, the Morris method (Herman et al., 2013). For the parameter calibration, the CMA-ES method (Covariance Matrix Adaptation - Evolution Strategy), which has been previously used for GLM lake modelling (Ladwig et al., 2021), was applied. The study site is a sand-pit lake located in the Great Paris region. High-frequency water temperature records are available at 4 depths in the water column for the last two years (2023 and 2024).
The sensitivity analysis showed that the thermal regime of the lake is particularly sensitive to the values of 4 parameters that are related to the meteorological forcing (sw, a scaling factor to adjust the shortwave radiation data), the light attenuation in the water column (Kw), the latent heat flux transfer coefficient (Ce) and the mean sediment temperature (sed_temp_mean). Calibration of these 4 parameters was then conducted. The simulation obtained with the calibrated parameters was then compared with a reference simulation performed using default values for all parameters.
The results highlight the importance of including the sediment temperature to correctly simulate the temperature of the lake bottom layers. The high-frequency monitoring (time step = 15mn) allows to accurately check the efficiency of the calibration method. After the calibration of the 4 parameters identified in the sensitivity analysis, the simulation of the lake temperature is significantly improved, according to different metrics (e.g. RMSE decreasing from 1.8°C to 0.8°C).
How to cite: Paz, C., Marquet, A., Cartier, Y., Casenave, C., Santoro, P., Le Moguédec, G., and Vinçon-Leite, B.: Assessment of groundwater impact on the water temperature of small sand-pit lakes through one-dimensional modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11327, https://doi.org/10.5194/egusphere-egu25-11327, 2025.
The work aims at developing a multidisciplinary strategy for the monitoring, assessment, valorization and possible use of small reservoirs in the framework of resilient water resources management. Specifically, we focus on water quality and quantity analysis using an integrated approach between remote sensing data and in situ observations.
The topic is part of the SIGHTING- Small reservoIrs restoration: Green blu-infrastructures to enHance rural area resilience To clImate change-project, that is devoted to the study of lakes in the upper Umbria Region (Central Italy).
First, available satellite data, coupled also with the Google Earth Engine (GEE) platform, are used to investigate in the last decade, the spatial distribution, the seasonal variations and the inter-annual variations of target water quality parameters such as the chlorophyll Chl-a concentration and turbidity. Different products with increasing spatial resolution. e.g. Sentinel -2 and Planet-Scope (from 20m to 3.7m), freely available for research use, are tested. These data, acquired with a regular revisit time of few days, allows a continuous monitoring of the water resource.
The procedure is validated for a pilot cases study, calibrating derived results on the base of in situ monitoring data. In July 2024, the water quality survey has been conducted on a small shallow pilot study lake, of about 33200 m2, collecting 20 samples for chemical and physical analysis.
The procedure, even if limited to a pilot case study, allows to establish the potentialities and weakness of the free satellite data used, also in the context of a possible extension to a largest spatial scale (regional/national).
How to cite: Di Francesco, S., Giannone, F., Biondi, F., Casadei, S., Tosi, G., Todisco, F., Vergni, L., Fazi, S., D'Eugenio, M., and Casentini, B.: A multidisciplinary approach for Small reservoirs monitoring, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12013, https://doi.org/10.5194/egusphere-egu25-12013, 2025.
Lakes with multiple basins exhibit spatially variable biogeochemical and physical properties. In these systems, wind- and convection-driven inter-basin exchange facilitates the transport of heat and solutes between basins, contributing to both surface and deepwater renewal. Such exchanges may supply oxygen to the deep, anoxic waters of oligomictic lakes, in addition to winter vertical mixing. As a result, oxygen mass budgets require estimates of the horizontal and vertical turbulent fluxes generated by exchange flows. Yet, the spatial variability of turbulent mixing across lake basins and the turbulent signature of inter-basin exchange remain poorly understood. This study investigates these processes in Lake Zug, Switzerland (surface area of 38 km², mean depth of 83 m, maximal depth of 197 m), a two-basin oligomictic lake. The lake is divided into a shallow, well-ventilated North basin and a deep, redox-stratified South basin, separated by a one-kilometer-wide constriction. The zonation of redox processes in Lake Zug is governed by the sources and sinks of oxygen, necessitating the quantification of turbulent transport by exchange flows. We deployed three moorings equipped with a vertical array of thermistors, oxygen loggers and acoustic Doppler current profilers (ADCPs) for one year along the constriction, allowing us to characterize the nature and dynamics of exchange flows. Additionally, conductivity-temperature-depth (CTD) and microstructure profiles were collected along North-South transects with a VMP-500 free-falling profiler (Rockland Scientific International Inc.). We quantified the spatial variability of turbulent mixing by estimating Thorpe displacements (LT), turbulent kinetic energy dissipation rate (ε), and vertical turbulent diffusivity (Kz) from the microstructure data. These observations provide new insight into the effects of inter-basin exchange flows on the spatial heterogeneity of turbulence, improving our understanding of multi-basin lake physics and biogeochemistry.
How to cite: Doda, T., Rama, J., Sepúlveda Steiner, O., N. Ulloa, H., Janssen, D., and Bouffard, D.: Spatial variability of turbulent mixing across the constriction of a two-basin lake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12590, https://doi.org/10.5194/egusphere-egu25-12590, 2025.
Connected reservoirs along cascade systems have been constructed along large rivers worldwide, establishing a network of aquatic environments. To date, modeling studies largely ignore the ecological feedback on water quality in connected reservoirs, thus limiting the ecosystem representation and missing the mechanisms acting between them. Here, we applied a novel modelling framework that fully links reservoir processes along the cascade system, considering the input from each water body to the next in the system. The one-dimensional GLM-AED model was applied to simulate hydrodynamics and biogeochemical processes in six reservoirs along the Tietê River (Brazil) situated in the most populous Brazilian state (24 million inhabitants), playing a relevant role for the energy generation and water supply in the region. The model was run for the 2008-2016 period, calibrated and validated against measured field data. Eighteen scenarios of reducing nutrient loads were simulated to assess how restoration strategies modify the ecological state downstream. All six reservoirs were sensitive to nutrient load reductions, which changed the nutrient retention capacity, and triggered a domino effect along the cascade system, improving the ecological conditions further downstream. It reveals that local restoration strategies devoted to the uppermost reservoir in a cascade system are propagated and amplified along the system. This finding is of primary interest to water managers since the improvements from local strategies into the uppermost reservoir, rather than site-specific, act at catchment scale.
How to cite: M. V. Soares, L., Fernandes, T., F. G. Silva, T., and Calijuri, M. D. C.: Connected reservoirs: modelling aquatic ecosystems along a cascade system in Brazil, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14268, https://doi.org/10.5194/egusphere-egu25-14268, 2025.
In regions with freezing lakes, the stability and bearing capacity of lake ice cover are crucial to the safety of communities whose activities revolve around lake ice, and animals crossing the lake’s surface. In hydropower (HP) reservoirs, the development and integrity of the ice cover are influenced by the artificial movement of water, which alters the lake’s flow and thermal structure, and generates rapid and intense changes in water level. Knowledge of ice conditions and of safe limits for water level variations is therefore particularly important in these systems. However, monitoring the ice cover is often logistically challenging and there is still a limited understanding of the extent to which HP strategies for water level regulation can improve or disrupt the stability of the ice sheet, especially in reservoirs with complex bathymetry.
In this study, we investigate the state of the ice cover of two Norwegian HP reservoirs with complex bathymetry and large and frequent variations in water level, where ice monitoring is minimal to absent. We inspected multi-sensor remote sensing data (SAR and optical) over nine winters (2014-2023) to detect the presence of cracks and discontinuities in the ice sheet. We then analyzed water level and meteorological data to identify the primary driver and mechanism of cracking and used simple mechanical and thermal expansion models to interpret the results and isolate the effects of water level variations from those of temperature fluctuations. The satellite data revealed the presence of large cracks in the ice cover of the two reservoirs in each of the nine winters. The cracks consistently appeared in early winter (December/January), propagating from bathymetric obstacles such as sharp-edged coastal protrusions, rocks and islands, and persisted throughout the winter. The results of the mechanical model are consistent with this observation, showing that even a moderate decrease in water level can lead to cracking when an intermediate support (given by the bathymetric obstacle) is present. The analysis of water level and air temperature also supports this crack-formation mechanism, as a predominance of drops in water level is measured prior to the appearance of cracks, while no preferential dynamics in terms of warming or cooling are registered before cracking. These results suggest that the primary mechanism of crack formation in the ice cover of our study sites is the intense stress concentration above bathymetric obstacles encountered by the ice sheet during water level descent. This underlines the importance of investigating the role that modulation strategies of HP operations can play in maintaining or compromising the stability of the ice cover during the critical period for crack formation. We believe that further studies should extend this research to other systems with complex bathymetry and test the effects of environmental constraints on the rate of water level descent in monitored reservoirs.
How to cite: Hinegk, F., Adeva Bustos, A., and Toffolon, M.: Hydropower water level regulation: effects on the ice cover of two Norwegian reservoirs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16785, https://doi.org/10.5194/egusphere-egu25-16785, 2025.
Water quality and ecology in lakes depend on mixing and transport processes, hence on hydrodynamics. Understanding these processes requires a conceptual model, usually supported by measurements and numerical simulations. In situ measurements are carried out using various devices, such as thermistor chains and ADCPs, which have high temporal resolution but are very local. Conversely, remote sensing can provide large-scale spatial information, but only in the surface layers and often at low frequency, as in the case of satellite imagery. As the main driver of lake motions is typically wind, knowledge of the meteorological forcing and its spatial distribution is also crucial and is often a major source of uncertainty in lake models. Numerical models can be used to integrate this information, which in turn allows them to be calibrated and validated.
In recent years, Earth observation products have become increasingly more used. Satellite imagery is often used in inland water quality studies (multispectral imagery), while radar products, such as those derived from Synthetic Aperture Radar (SAR), are mostly used in open waters such as oceans, seas, and very large lakes. In this contribution, we focus on the use of SAR imagery to reconstruct the wind field, surface currents, and wind waves, in a medium-sized lake (Lake Garda, Italy). For this purpose, we have developed a modeling chain consisting of three numerical models: Weather Research and Forecasting (WRF), providing the spatio-temporal distribution of meteorological variables; Delft3D, forced by WRF, simulating the three-dimensional flow field and heat and mass transport; SWAN (Simulating Waves Nearshore), modeling the surface wind waves with a two-way coupling with Delft3D. Following a common approach, Delft3D was calibrated against pointwise in-situ measurements (vertical profiles of velocity and temperature, floating drifters’ trajectories) and validated considering spatial patterns of temperature and turbidity obtained from multispectral imagery.
As a novel element of the analysis, we used SAR backscatter amplitude and Doppler anomaly obtained by COSMO-SkyMed (CSK) to reconstruct wind speed and Surface Radial Velocity (SRV), respectively, by applying a Geophysical Model Function (GMF). The wind field reconstructed for Lake Garda with this approach shows consistent spatial distribution and magnitude when compared to the WRF results. The SRV obtained from CSK, on the other hand, shows a qualitative agreement with the results obtained from Delft3D+SWAN, but an overestimation of the magnitude of the flow current.
We are now planning an intensive field campaign in winter 2025, with in-situ measurements in parallel with satellite SAR and ground radar observations, to revise the GMF and further improve the understanding of how wind waves and bulk currents contribute to the SAR signal. The final goal is to derive detailed information of wind speed, wave amplitude and surface currents directly from Earth observation even in medium-sized lakes.
How to cite: Farrokhi, A., Amadori, M., and Toffolon, M.: Combining SAR and numerical modeling to reconstruct wind, waves and surface currents in Lake Garda, Italy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17024, https://doi.org/10.5194/egusphere-egu25-17024, 2025.
This study focuses on a three-dimensional (3D) thermo-hydrodynamic model aimed to simulate the full dynamics of stratified freshwaters. Based on the Navier-Stokes and energy balance equations (Grieffies, 2018), the mathematical model here considered is well suited for resolving convection and heat transfer within inland waterbodies. The solutions of the governing equations here considered are approximated numerically using a finite element scheme implemented within the Telemac3D framework (https://opentelemac.org), a well documented open-source hydrodynamic modeling software chosen for its efficiency and ability to handle complex geometries. While Telemac3D has been extensively applied to river and coastal simulations, its use in stratified saterbodies modeling is less common, highlighting the need for further validation studies regarding thermal stratification.
To evaluate the performance of Telemac3D and assess its capability of capturing convection and thermal stratification, numerical simulations of Lake Créteil (Greater Paris region, France) are conducted and compared against observational data as well as previous numerical simulations performed using Delft3D (Soulignac et al., 2017), a widely used open-source hydrodynamic modeling software (https://oss.deltares.nl/web/delft3d). Note that, given its limited size, Lake Créteil provides an ideal test case for model validation due to its comprehensive monitoring program and the thorough understanding of its hydrodynamic and thermal processes.
The presented results offer valuable insights for refining and improving thermo-hydrodynamic simulations of freshwaters in particular when using Telemac3D. Accurate modeling of thermo-hydrodynamic processes is indeed crucial for ensuring a reliable coupling with available water quality models, such as the AED2 library (https://aed.see.uwa.edu.au/research/models/AED/), already coupled with Telemac3D, which allows for the simulation of biogeochemical processes like phytoplankton dynamics and element cycling (carbon, nitrogen, and phosphorus).
GRIFFIES, Stephen. Fundamentals of ocean climate models. Princeton university press, 2018.
SOULIGNAC, Frédéric, et al. Performance assessment of a 3D hydrodynamic model using high temporal resolution measurements in a shallow urban lake. Environmental Modeling \& Assessment, 2017, 22: 309-322.
How to cite: Geddo, Z., Marquet, A., Guillot Legoff, A., Vinçon Leite, B., Boyaval, S., and Hong Le, M.: Three-dimensional thermo-hydrodynamic modeling of stratified inland waterbodies using Telemac3D, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18885, https://doi.org/10.5194/egusphere-egu25-18885, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot A
EGU25-2730 | Posters virtual | VPS10
Seasonal Changes in Water Columns of Historical Reservoir Lakes in the Upper Harz Mountains (Germany)Thu, 01 May, 14:00–15:45 (CEST) | vPA.13
Concerning water supply in mountainous regions where surface water plays an important role, the understanding of lake stratification or even hypolimnia can be important for water treatment actions.
The historical dam reservoirs were used for the continuous water supply to the ore mines in the Upper Harz Mountains. The first reservoirs were built in the 16th century. The dam heights reach up to 15 m and the stored water volumes are between 10,000 and 600,000 m3. There are about 70 of such lakes around Clausthal-Zellerfeld. Today only few of them are directly used for drinking water supply in the surrounding communities.
Hydrogeochemical data of the lakes have been investigated for about ten years. The specific electrical conductivity (SEC) of the lakes’ surface water ranges between 30 and 280 µS/cm (Bozau et al., 2015, Schäfer et al. 2024). Three lakes (Kiefhölzer, Langer and Oberer Grumbacher Teich) differing in chemical composition and morphometry (area, mean depth and maximum depth) were selected for the investigation of seasonal changes in the water columns. Samples were taken by boat with a Ruttner sampler. SEC and pH were measured on the boat. The titration for HCO3 was done directly after sampling. The main ions were analyzed by ion chromatography and the trace elements by ICP-MS.
Stratification during summer could be clearly observed in all of the three lakes. The degradation of organic material and accompanying redox reactions are seen in the measured pH, SEC, HCO3-, Fe(II), NO3-, NH4+ and SO42- concentrations. Each lake showed a characteristic temporal and chemical behaviour. The development of an anoxic hypolimnion above the lake sediments was obvious in the two shallower lakes Langer Teich (max. depth ~ 5 m) and Kiefhölzer Teich (max. depth ~ 7 m) as being accompanied by H2S-odor in the water column starting ~ 1 m above sediment. This feature was absent in the deepest lake Oberer Grumbacher Teich (max. depth ~ 9 m), which also showed weaker increase of SEC and HCO3- in the profile. The aeration of the hypolimnion started in autumn leading to a well mixed, chemically uniform water column.
Bozau, E., Licha, T., Stärk, H.-J., Strauch, G., Voss, I., Wiegand, B. (2015): Hydrogeochemische Studien im Harzer Einzugsgebiet der Innerste. Clausthaler Geowissenschaften, 10, 35-46.
Schäfer, T., Bozau, E., and Hutwalker, A.: Reservoir lakes in the Upper Harz Mountains (Germany): GIS Implementation and hydrochemical development, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5085, https://doi.org/10.5194/egusphere-egu24-5085, 2024.
How to cite: Schäfer, T., Bozau, E., and Hutwalker, A.: Seasonal Changes in Water Columns of Historical Reservoir Lakes in the Upper Harz Mountains (Germany), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2730, https://doi.org/10.5194/egusphere-egu25-2730, 2025.
EGU25-18985 | ECS | Posters virtual | VPS10
Long-term water temperature modeling in semi-arid alpine basinsThu, 01 May, 14:00–15:45 (CEST) | vPA.14
Temperature plays a critical role in the functioning of river ecosystems. Hence, understanding the processes that control water temperature in river networks across daily to multi-year scales is important when trying to manage river thermal regimes. This is particularly urgent in alpine semi-arid basins with substantial human impact, and, especially within the context of global change, where river ecosystem integrity is at risk. A process-based model has been developed to simulate water temperature in lakes and rivers at a regional (watershed) scale. The physically based and fully distributed hydrological model provides comprehensive hydrological and hydraulic simulations of river flow, including contributions from snowmelt, groundwater, and direct runoff at each node of the network. Additionally, the model accounts for the discharge of urban wastewater at its respective nodes. To overcome the computational cost and numerical problems associated with Eulerian methods in long-term simulations, the model uses a semi-Lagrangian approach to discretize the one-dimensional heat conservation equations in river reaches. Reservoir stratification and withdrawal temperatures are simulated with a 1D Lagrangian model (General Lake Model). This methodology ensures the accurate and detailed simulation of water temperature dynamics in rivers by integrating meteorological, hydrological, and hydraulic data, along with the impact of urban wastewater discharges and reservoir outflows. The model is applied to simulate water temperature in a small semi-alpine watershed upstream of the city of Granada that includes two water-supply reservoirs (Canales and Quéntar). Autonomous temperature sensors deployed at different sites are used for model validation. The model is forced with climate databases (reanalysis, regional climate simulation conducted with WRF, and measured data bases) and used in hindcast/forecast exercises to assess the impact of climate change on the thermal regime of inland waters.
Acknowledgments: This research has been supported by the project: STAGES-IPCC (TED2021-130744B-C22) from the Spanish Ministry of Science, Innovation and Universities
How to cite: Gulliver, Z., López-Padilla, S., Herrero, J., Huertas-Fernández, F., Collados-Lara, A. J., García-Valdecasas Ojeda, M., Ramón, C. L., Esteban-Parra, M. J., Pulido-Velázquez, D., and Rueda, F. J.: Long-term water temperature modeling in semi-arid alpine basins , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18985, https://doi.org/10.5194/egusphere-egu25-18985, 2025.
