HS10.9 | Lakes and inland seas in a changing environment
EDI
Lakes and inland seas in a changing environment
Convener: Georgiy Kirillin | Co-conveners: Giulia Valerio, Damien Bouffard, Tom Shatwell
Orals
| Fri, 28 Apr, 14:00–15:45 (CEST), 16:15–17:50 (CEST)
 
Room 2.31
Posters on site
| Attendance Fri, 28 Apr, 10:45–12:30 (CEST)
 
Hall A
Orals |
Fri, 14:00
Fri, 10:45
As confined water bodies with limited exchanges, lakes and inland seas are particularly vulnerable to climatic and human impacts accumulated over broad catchment areas. Hence, they mirror both the global change effects and
anthropogenic pressures, perhaps, stronger than any other aquatic objects. Lakes and inland seas
also play an important role in ecosystem services such as fisheries, aquaculture, tourism, and others. These multifunctional roles require careful governance measures to avoid hydrological and environmental deterioration.
Research of lakes and inland seas admits many common approaches and techniques. Oceanographic methodology and instrumentation are often applicable to limnological studies. Reciprocally, insights obtained from lakes can also be instructive with respect to marine systems. This interdisciplinary session provides a joint forum for oceanographers, limnologists, and hydrologists interested in processes governing physical, chemical, and biological regimes of various lakes and inland seas of the world, as well as their responses to climate change and anthropogenic impacts.

Orals: Fri, 28 Apr | Room 2.31

Chairpersons: Georgiy Kirillin, Giulia Valerio
14:00–14:05
14:05–14:15
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EGU23-1577
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On-site presentation
Pavel Kishcha, Yury Lechinsky, and Boris Starobinets

Cyprus lows are the main reason for precipitation over Lake Kinneret during the rainy season (December–May): these lows are centered over the Mediterranean Island of Cyprus. Cyprus lows are responsible for cold weather conditions when westerly winds transport cold moist air from the eastern Mediterranean into north Israel (including Lake Kinneret). Such cold weather conditions, accompanied by rainfall and a decrease in solar radiation (due to an increase in cloudiness over the lake), could cause cooling of Kinneret and eastern Mediterranean water temperature (WT) in rainy seasons.

However, in the Eastern Mediterranean and in Lake Kinneret, surface water temperature is increasing by ~1.5 oC over the last 40 years. Moreover, climate model predictions showed a reduction by one third in the appearance of Cyprus lows by the end of the 21st century. This suggests a reduction in cooling by Cyprus lows of water in the Eastern Mediterranean and in Lake Kinneret. Therefore, a comprehensive investigation of the influence of Cyprus lows on water temperature in subtropical Lake Kinneret and the Eastern Mediterranean is environmentally important.

Comparisons, conducted on a monthly basis, between high-precipitation (HP) years and low-precipitation (LP) years led to our main findings, which are as follows: Cyprus lows are instrumental in the cooling of surface and epilimnion water in subtropical Lake Kinneret and in the cooling of eastern Mediterranean surface water (Kishcha et al., 2022). In particular, comparison between HP and LP years of Kinneret surface water temperature (SWT) and epilimnion water temperature (WT) have shown water cooling of up to 2 °C in HP years, in the daytime. This study was carried out using the 21-year period of satellite and in-situ data: (1) MODIS 1 km × 1 km resolution records of SWT, and (2) shipboard measurements of WT vertical profiles down to a depth of 40 m (2000–2020). We found that the decrease in solar radiation (caused by Cyprus lows due to an increase in cloudiness) was the main factor contributing to Kinneret water cooling. In spring (March–April), SWT and epilimnion WT, averaged over the HP years, was lower by ~2 °C and ~1.4 °C, respectively, than SWT and epilimnion WT averaged over the LP years. This was when SR increased and became the main factor contributing to water heating. In situ shipboard measurements of WT at a depth of 1 m and 5 m, at five monitoring sites within Lake Kinneret, showed similar patterns of the WT difference between HP and LP years. This is evidence that cooling by Cyprus lows of Kinneret water was evenly distributed within the lake. Water cooling by Cyprus lows was also observed in eastern Mediterranean surface water. In particular, in the spring months (March–April), Mediterranean SST averaged over the same HP years was lower by ~1.2 oC than that averaged over LP years. This is evidence of the regional character of the water-cooling phenomenon caused by Cyprus lows.

Reference:

Kishcha et al. (2022).  Remote Sensing 2022, 14, 4709. https://doi.org/10.3390/rs14194709

How to cite: Kishcha, P., Lechinsky, Y., and Starobinets, B.: Cooling by Cyprus Lows of Surface and Epilimnion Water in Subtropical Lake Kinneret in Rainy Seasons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1577, https://doi.org/10.5194/egusphere-egu23-1577, 2023.

14:15–14:25
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EGU23-5873
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ECS
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Highlight
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On-site presentation
Ehud Strobach, Yael Amitai, Shmuel Assouline, David Hamilton, Aminadav Nishri, and Tamar Zohary

On May 31, 2012, thousands of dead fish were found along the north-western shore of the Sea of Galilee. Analysis of fish gill tissue revealed no evidence of poisoning, and the fish looked healthy. This event adds to reports of similar fish kills at the same location, from the early 1990s, from May 2007, and a subsequent event on June 27, 2012, a month after the May 31 event. The common hypothesis for the massive kill suggests that a seiche induced by strong winds caused the upwelling of colder and anoxic hypolimnetic water along the western shores of the lake. Still, this hypothesis has not yet been tested.

The WRF (The Weather Research and Forecasting) atmospheric model was recently coupled with the ocean model MITgcm (MIT general circulation model). The coupled model was named SKRIPS (Scripps–KAUST Regional Integrated Prediction System). The two SKRIPS model components (WRF and MITgcm) are well-tested at high resolution, allowing us to investigate the physical mechanism of the fish-kill event in an interactive system. To test the hypolimnetic water upwelling hypothesis for the massive fish-kill, we have set up and integrated the SKRIPS model for the May 31, 2012, event at a horizontal grid resolution of 400 m2, both for the atmospheric and lake component of the model.

In this talk, I will present results from a high-resolution coupled atmosphere-lake regional simulation indicating an upwelling of cold anoxic hypolimnetic water into the surface during the event. The upwelling of cold water is increased close to the shore. The discussion will be supplemented by field data of temperature and oxygen concentrations, collected before, during, and after the fish-kill event. Our simulation results agree with the field observations, adding confidence to the anoxic hypolimnetic water upwelling hypothesis. Such fish-kill events may explain the biblical ‘miraculous catch of fish’ and the ‘miracle of the loaves and fish’. Also, it may provide a possible seasonal time frame (spring) for their occurrence in the past.

How to cite: Strobach, E., Amitai, Y., Assouline, S., Hamilton, D., Nishri, A., and Zohary, T.: Seiche-induced fish-kills in the Sea of Galilee may explain the biblical miraculous catch of fish, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5873, https://doi.org/10.5194/egusphere-egu23-5873, 2023.

14:25–14:35
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EGU23-10658
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ECS
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On-site presentation
Khosro Morovati, Lidi Shi, Keer Zhang, Fuqiang Tian, Mahmut Tudaji, and Pouria Nakhaei

The flow regime of the largest lake in Southeast Asia, Tonle Sap Lake, is driven by the reverse flow phenomenon caused by its link with the Mekong River. This reverse flow makes the lake one of the most productive aquatic ecosystems globally and thus provides important economic opportunities for local communities. The recent human activities in the upstream, as well as climate variations, have resulted in unforeseen alterations in the flow regime of the Mekong River and Tonle Sap Lake. However, little is known about the explicit attribution of different parts of the upstream basin to these variations, which would be essential for transboundary water management. To unveil these attributions, we developed a novel modeling setup consisting of hydrodynamic, hydrological, and machine learning models. This modeling setup allowed us to separate the impacts of a) climate variation, b) human activities in the Chinese part of the basin, and b) the lower part of the basin (i.e., Laos, Thailand, and Vietnam). During the 2001–2009 baseline, when human modifications to the flow were still minimal, we found that Tonle Sap Lake received, on average, 42.4 km3/yr water from the Mekong, 48.2 % of the total inflow to the lake. During the period of increased human activities, 2010–2020, this decreased due to climate variation to 40.1 km3/yr (a 5.7 % drop), which was further exacerbated by the increased human activities in the upstream parts of the basin (China ~ 7.3%, Laos, Thailand, and Vietnam ~ 9 %). Additionally, during the flow period when water flows from the lake towards the Mekong, on average, 31 % of the total inflow into the Mekong Delta originated from the lake during the baseline period. Climate variation decreased this by 4 percentage points (pp), i.e., to 27 %, while the human activities in China and lower parts of the basin decreased this by 1.6 pp (25.4 %) and 1.9 pp (25.1 %), respectively. Our findings unveiled the attributions of different drivers on Tonle Sap Lake’s hydrology and will facilitate transboundary water management in the basin. The impacts of future plans on different parts of the basin should be carefully evaluated together with existing anthropogenic impacts, as well as climate change, to minimize the further impacts on the lake and Mekong River.

How to cite: Morovati, K., Shi, L., Zhang, K., Tian, F., Tudaji, M., and Nakhaei, P.: Contributions from climate variation and human activities to flow regime change of Tonle Sap Lake and Mekong River from 2001 to 2020, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10658, https://doi.org/10.5194/egusphere-egu23-10658, 2023.

14:35–14:45
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EGU23-2406
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On-site presentation
Wenqin Huang, Tengfei Hu, Jingqiao Mao, Carsten Montzka, Roland Bol, Songxian Wan, Jianxin Li, Jin Yue, and Huichao Dai

Hydrological processes are known as major driving forces in structuring wetland plant communities, but the specific relationships are not always well understood. The recent dry conditions of Poyang Lake (i.e., the largest freshwater lake in China) are having a profound impact on its wetland vegetation, leading to the degradation of the entire wetland ecosystem. We developed an integrated framework to quantitatively investigate the relationship between the spatial distribution of major wetland herbaceous communities and the hydrological regimes of Poyang Lake. First, the wetland herbaceous community classification was built using a support-vector machine and simultaneous parameter optimization, achieving an overall accuracy of over 98%. Secondly, based on the inundation conditions since 2000, four hydrological drivers of the spatial distribution of these communities were evaluated by canonical correspondence analysis. Finally, the hydrological niches of the communities were quantified by Gaussian regression and quantile methods. The results show that there were significant interspecific differences in terms of the hydrological niche. For example, Carex cinerascens Ass was the most adaptable to inundation, while Triarrhena lutarioriparia + Phragmites australis Ass was the least. Our integrated analytical framework can contribute to hydrological management to better maintain the wetland plant community structure in the Poyang Lake area.

How to cite: Huang, W., Hu, T., Mao, J., Montzka, C., Bol, R., Wan, S., Li, J., Yue, J., and Dai, H.: Hydrological Drivers for the Spatial Distribution of Wetland Herbaceous Communities in Poyang Lake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2406, https://doi.org/10.5194/egusphere-egu23-2406, 2023.

14:45–14:55
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EGU23-16642
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ECS
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On-site presentation
Subtropical lake under projected climate change: 3D model assessment and insights
(withdrawn)
Yael Amitai, Yoav Levi, and Edoardo Bucchignani Bucchignani
14:55–15:05
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EGU23-6490
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Highlight
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On-site presentation
Brigitte Vinçon-Leite, Guilherme Calabro-Souza, Felipe Breton, Céline Casenave, Mohamed Saad, Philippe Dubois, Bruno J. Lemaire, and Francesco Piccioni

Urban lakes provide essential ecosystem services (hotspot of biodiversity, stormwater management, reduction of pollutant loadings…).
During late summer and early autumn 2021, two whole-lake anoxia events occurred in Lake Champs-sur-Marne (Great Paris, France).  This sandpit lake, principally fed by groundwater from the nearby Marne River, is continuously monitored by an autonomous station equipped with underwater sensors (water temperature, oxygen, Chlorophyll-a, CDOM, Nitrate). At the same point, a meteorological station is installed on a buoy, above the lake surface.
During the two anoxia events (end of August and mid-September), oxygen concentration dropped from supersaturation level corresponding to a high peak of phytoplankton biomass, to 0% within a few days. During this summer period, successive heavy rainfall events occurred, causing a flood of the Marne River and rising the watertable level to unusual values in Summer. This resulted in high water and nutrient fluxes from the river towards the lake. 
The observed whole-lake anoxia can be explained according to the following assumptions: (1) the groundwater nutrient loading, favored by the high level of the Marne River, caused a huge phytoplankton production; (2) then, the phytoplankton decline was associated to an intense mineralization of the biomass organic carbon; (3) the lake oxygen was completely exhausted, leading to a massive fish kill. 
These results highlight the severe impact of a non-extreme but high and long hydro-meteorological event on a lake ecosystem. In Lake Champs-sur-Marne, the nutrient limitation of phytoplankton production generally occurs during late summer. In 2021, the limitation was removed by the Summer exceptional nutrient loading. In temperate regions, summer algal blooms are not limited by water temperature but by nutrient availability. Climate change is expected to increase the frequency of extreme hydro-meteorological events.  Higher frequency of summer heavy rainfall may trigger repeated phytoplankton blooms, deteriorating the ecological status of lake ecosystems.

How to cite: Vinçon-Leite, B., Calabro-Souza, G., Breton, F., Casenave, C., Saad, M., Dubois, P., Lemaire, B. J., and Piccioni, F.: Impact of extreme hydro-meteorological events on the anoxia dynamics in a small urban lake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6490, https://doi.org/10.5194/egusphere-egu23-6490, 2023.

15:05–15:25
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EGU23-16150
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solicited
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On-site presentation
Erich Draganits, Michael Weißl, András Zámolyi, and Michael Doneus

Lake Neusiedl and adjacent lakes at the Austrian/Hungarian boundary represent a unique wetland, situated at the geodynamical and geomorphological boundary between the Alps, Carpathians and the Pannonian Basin, and therefore represents an important transition zone concerning terrain, climate, vegetation and fauna. The more than 700 km2 large area is one of the flattest regions of Austria with less than 17 m relief variation. Today, Lake Neusiedl measures some 320 km2 with less than 1.8 m depth and a tectonic origin is widely accepted. East of the lake, about 30 shallow lakes still exist, of which the largest measures less than 2 km length and less than 1 m depth. At present, the water level of Lake Neusiedl shows the lowest values since 1965 and all the shallow lakes were dry during the summer 2022. We use high-resolution topographical, sedimentological, geomorphological as well as historical maps and historical charters to investigate the formation end evolution of Lake Neusiedl and adjacent lakes. Our data show that the present-day conditions and processes of Lake Neusiedl strongly diverge from conditions in the past. The earliest preserved record of modification of the lake´s hydrological conditions is from 1568, followed by increasing drainage efforts and the building of a dam road in the southeast, finished in 1780, which subsequently cut off the lake from its most important tributaries from the south. This palaeohydrological reconstruction of Lake Neusiedl and Hanság also implies an episodic lower salt content of the water compared to modern values, especially during flood periods. Therefore, it is not useful to compare the hydrological situation of Lake Neusiedl before 1780 (or even 1568) and after. The documented variation of the water level of Lake Neusiedl between desiccation and highest flood level is around 4.2 m. These variations affected enormous areas in this low-relief region, with a huge impact on the landscape, fauna, vegetation, human settlement patterns, land use, communication routes and even possible occurrence of malaria – which should be considered in regional archaeological, historical and biological interpretations. The numerous shallow lakes and presently dry basins, detected in the high-resolution airborne laser scanning data in the Seewinkel originally formed as thermokarst lakes during permafrost degradation after the end of the Last Glacial Maximum. In total, more than 370 enclosed depressions are visible. The depressions of eastern Austria represent one of the first Latest Pleistocene thermokarst lakes documented in central Europe. Although man-made climate change has a clear impact on the water balance of the lakes, they reinforce past hydrological modifications.

How to cite: Draganits, E., Weißl, M., Zámolyi, A., and Doneus, M.: Lake Neusiedl wetland (Austria/Hungary) in a changing environment: anthropogenic versus anthropogenic effects, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16150, https://doi.org/10.5194/egusphere-egu23-16150, 2023.

15:25–15:35
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EGU23-7630
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ECS
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Highlight
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On-site presentation
Katharina Enigl, Hanna Pritsch, and Rainer Kurmayer

Lake Surface Temperature (LST) is a key characteristic that reflects meteorological and climatological influences on lakes. In general, there is limited LST data from high elevation lakes available as these areas are remote and not part of regular monitoring programs. Nonetheless, for the development of effective management strategies for high-altitude lakes, it is important to understand their response to climate warming. This study aims at both the reconstruction of LST back to 1998 and the projection of LSTs for 21 alpine lakes (1500-2300 m a.s.l.) in the Niedere Tauern region in Austria until the year 2100. For the determination of the relationship between atmospheric variables (temperature and precipitation), near-lake snow depth and observed LST, general additive models were trained with a daily temporal resolution for the years 1998-2003, and 2019-2020. We subsequently employed the model with the highest fit to reconstruct LSTs for the whole period 1998 to 2003. Furthermore, we estimate LST until 2100 using an ensemble of regional climate projections for the RCP2.6 (in-line with the COP 21 Paris Agreement), RCP4.5 and RCP8.5 (“worst-case”) scenario. Under the RCP8.5 scenario, the average rise for August lake surface temperatures in the far future (2071-2100) is predicted to increase by 2.3 °C compared to temperatures in the near future (2020-2049).  Consequently, the ice-free period is expected to rise on average 1-1.2—fold in the near future (2031-2060) and 1-1.5-fold in the distant future. These alterations in the lakes’ temperature regime probably affect multiple limnological parameters related to ecological quality such as primary productivity and trophic state.

How to cite: Enigl, K., Pritsch, H., and Kurmayer, R.: Development of surface temperatures of alpine lakes in Austria under climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7630, https://doi.org/10.5194/egusphere-egu23-7630, 2023.

15:35–15:45
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EGU23-7710
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ECS
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On-site presentation
Pamela Alessandra Baur, Andreas Maier, Thomas Zechmeister, and Stephan Glatzel

Lake Neusiedl, a shallow brackish lake of Austria and Hungary, is the westernmost steppe lake of Europe with an area of ca. 320 km² and the second largest coherent reed population in Europe. Half of Lake Neusiedl consists of a wetland ecosystem dominated by Phragmites australis, which forms a seasonally varying mosaic of water, reed and sediment patches, is highly sensitive to climate variations and which we investigated here.

Little is known about the effects of climate change on reed dominated wetlands and the contribution of central European reed belts as a source of greenhouse gases (GHG). The current ongoing drought periods at Lake Neusiedl affect especially the water balance but also the carbon fluxes in the reed belt. Therefore, we investigated the drought influenced carbon and water fluxes and their drivers of the reed ecosystem of a brackish lake over the last three years.

We used the eddy covariance (EC) technique to continuously quantify the vertical turbulent GHG exchange between the reed belt and atmosphere. The EC observations have been conducted near Illmitz in the natural zone of National Park Lake Neusiedl from summer 2018 to now. For taking the reed development of the studied ecosystem into account, vegetation indices data were used.

The annual CO2 emissions decreased by 95 % from 200.5 g C m-2 in 2019 to 9.2 g C m-2 in 2021. Gross primary production and ecosystem respiration both increased from 2019 to 2021. The annual emissions of CH4 decreased by 59 % from 9.0±1.0 g C m-2 in 2019 to 3.7±1.9 g C m-2 in 2021. The reed belt tended from a strong to a low carbon source if only the vertical flows are taken into account. One explanation is the decreasing water level in the lake between 2019 to 2021, which was followed by a drying out of the reed belt (≙ no water above surface) in the late summer of 2020 and a longer period in 2021. The second explanation is the increasing reed growth (in area and biomass) inside the reed belt which increased the photosynthetic rate. The vegetation indices like NDVI, EVI and LAI from the reed belt support this by an increasing tendency from 2019 to 2021. The third explanation is that due to the low water levels less (or almost no) lateral exchange occurred via channels between the reed belt and the open water areas of the lake in 2021 compared to 2019.

The apparent disconnection between the open water area of Lake Neusiedl and the reed belt re-directs carbon cycles and ecosystem functioning.

How to cite: Baur, P. A., Maier, A., Zechmeister, T., and Glatzel, S.: Consequences of drying-out of Lake Neusiedl on the GHG budget of the reed belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7710, https://doi.org/10.5194/egusphere-egu23-7710, 2023.

Coffee break
Chairpersons: Damien Bouffard, Tom Shatwell
16:15–16:20
16:20–16:30
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EGU23-11079
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ECS
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On-site presentation
Turbidity variations in the epilimnion of a glacier-fed reservoir
(withdrawn)
Daniel Robb, Roger Pieters, and Gregory Lawrence
16:30–16:40
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EGU23-1430
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ECS
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On-site presentation
Amali Dahanayake, Angus Webb, Joe Greet, and Justin Brookes

Soil erosion on lakeshores due to the fluctuating water levels, waves, and other factors, remain a world-wide problem. Lakeshore vegetation can be helpful in preventing erosion. We investigated the effects of drawdown rate and depth on the growth and reproduction of a keystone lakeshore plant. We hypothesised that plants with access to water for longer would grow better and have higher reproductive output.

We subjected 108 Spiny Sedge (Cyperus gymnocaulos) plants to six treatments comprising three drawdown rates (static, slow, fast) and two water depths (shallow and deep). We measured plant stem heights and numbers of flowers and bulbils weekly, and the initial and final biomass of the above ground and below ground components.

Plants in treatments without access to water for long periods had the lowest growth and reproductive output. However, if the final water level was deep but drawdown was done slowly, plants were able to maintain similar growth and reproduction rates to plants with continuous access to water.

Fluctuating water levels in lakes cause lakeshore plants at lower elevations to be inundated for longer and plants at higher elevations to be deprived of water for longer. Plants located at mid-elevations will thrive if their roots have access to water and their above ground parts are not fully submerged.

Our findings are useful to water managers and ecologists concerned about preserving lakeshores from erosion by promoting vegetation. Both the rate and depth of drawdown should be considered in managing lake water levels. Where water levels fluctuate over large depths slower rates of drawdown will enable most plants to have access to water for longer, promoting their growth and reproduction, hence, reducing the lakeshore erosion.

 

 

Keywords: lakes, vegetation, drawdown, erosion, sustainability

How to cite: Dahanayake, A., Webb, A., Greet, J., and Brookes, J.: Slower drawdown rates in lakes promote the growth and reproduction of lakeshore vegetation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1430, https://doi.org/10.5194/egusphere-egu23-1430, 2023.

16:40–16:50
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EGU23-6928
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On-site presentation
Zheng Duan and Anna Schultze

Lake surface water temperature (LSWT) is a physical property of lakes. LSWT is a critical parameter for evaluating lakes' water quality and biodiversity. The change in LSWT can also be an indicator of climate change. Therefore, it is crucial to monitor LSWT to improve our understanding of the spatiotemporal dynamics of LSWT for many applications. Conventionally and ideally, we can install in-situ gauge stations or monitoring sites to measure surface water temperature in lakes, and these in-situ measurements are generally the most accurate. However, in-situ measurements in lakes are often sparse and limited in terms of spatial coverage and temporal length, which leaves many lakes with no measurements or lacking long-term continuous measurements. For example, Lake Vänern (surface area of about 5,655 km2, the largest lake in the European Union) has only two operational stations for measuring LSWT. The existing in-situ measurements are at irregular intervals (approximately bi-weekly) and have many data gaps. Many lakes globally have the same data situation as Lake Vänern. As a result, in-situ measurements cannot sufficiently capture the spatiotemporal dynamics of LSWT in large lakes.

Satellite remote sensing has emerged as an essential method to monitor LSWT. Thermal infrared satellite data have been widely used to estimate the surface temperature at relatively high spatial resolution (higher and up to 1 km resolution). One of the most used satellite products for surface temperature is the MODIS (Moderate Resolution Imaging Spectroradiometer) global land surface temperature product, which is available from 2000 at 1 km-daily spatial-temporal resolutions. However, many studies stressed that cloud influence could significantly degrade the quality and availability of satellite-derived surface temperature for certain lakes, calling for a dedicated investigation to address this issue. Besides MODIS data, there are many other satellite-derived LSWT products at different spatial-temporal resolutions and spatial coverage, e.g., the ones available at http://www.laketemp.net. In addition, the recent ERA5-Land, a state-of-the-art reanalysis dataset, can also provide spatially complete and temporally continuous land surface variables, including the lake temperature at 0.1 degree-hourly spatial-temporal resolutions from 1950 to present. Each of the aforementioned products has its own advantages and limitations.

Our initial analysis showed a significant data gap in LSWT from MODIS product for Lake Vänern due to cloud influence, which motivates us to conduct this study. This study aims to evaluate multiple existing LSWT products and, more importantly, to combine them with the advanced data fusion and bias correction method to develop a new spatially complete and temporally continuous LSWT dataset for Lake Vänern, Sweden. New in-situ measurements of LSWT will be collected from boats and drones at many locations of Lake Vänern; such measurements, together with existing data from the two stations, will be used to evaluate multiple LSWT products, the developed method, and the merged dataset. The newly developed LSWT dataset for Lake Vänern will benefit many applications, such as lake evaporation estimation, water balance analysis, air-lake interactions, and local climate forecasting.

How to cite: Duan, Z. and Schultze, A.: Development of a new spatially complete and daily continuous lake surface water temperature dataset for Lake Vänern, Sweden, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6928, https://doi.org/10.5194/egusphere-egu23-6928, 2023.

16:50–17:00
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EGU23-14467
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ECS
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Highlight
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On-site presentation
Iva Dominović, Marija Marguš, Mathieu Dutour Sikirić, and Irena Ciglenečki

Numerous limnological studies have been investigating lake overturning regimes in the frame of possible future climate scenarios, mainly regarding the predicted surface air temperature change. Overturning regime shifts are expected to manifest in the stratification onset and offset timing, as well as in stratification duration. In addition, the lakes' vertical water column is expected to become more stable, and thus less inclined to overturn. Since aquatic life in the lake depends thoroughly on its phenology, the predicted regime shifts are going to influence the whole lake ecosystem, along with the microclimate of its surrounding area.

An interesting example of regime shifting can be found in the central part of the Adriatic coast (43° 32' N, 15° 58' E). Lake Rogoznica (also known as "Dragon's Eye" lake) is a marine lake that is connected to the nearby Adriatic Sea through the porous karstic landscape. Although this connection is confirmed by high salinity values that reach those found in the surrounding sea (~38 PSU) and the visible tides, the newest research suggests that the complete overturning of the lake is governed by the delicate balance between the freshwater input (precipitation and runoff) and seawater input (Adriatic Sea), together with substantial surface air temperature fluctuations. Namely, Rogoznica Lake seems to exhibit complete overturns with irregular periodicity: sudden and abrupt holomixis occurred in the Autumn of 1997, 2011, 2016, 2020, and 2021. Another peculiarity of the lake is the complete anoxia with high levels of free sulfides that accompanies every such event, and the consequent mass mortality of the lake's aerobic life - the complete opposite of the oxygenation effect that seasonal overturning usually has in lakes.

It is still unclear whether sudden anoxic holomixis and their frequency are a consequence of local tourist activities, regional climate variability, or climate change affecting the Mediterranean, as the effects of all mentioned could have an intertwined effect on the small, complex system of Rogoznica Lake. In this work, we present the latest findings regarding the Rogoznica Lake water column stratification with a two-sided approach: a comprehensive sea-atmosphere measurements analysis and numerical modelling attempts.

How to cite: Dominović, I., Marguš, M., Dutour Sikirić, M., and Ciglenečki, I.: Regime shifts in a euxinic marine lake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14467, https://doi.org/10.5194/egusphere-egu23-14467, 2023.

17:00–17:10
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EGU23-68
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ECS
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On-site presentation
Fatemeh Sadat Sharifi, Reinhard Hinkelmann, Tore Hattermann, and Georgiy Kirillin

The combined effect of gravity and viscosity forces produces a flow along any inclined solid lateral wall in a density-stratified fluid. The flow becomes an important driver of circulation in ice-covered lakes isolated from wind forcing. We present numerical results from the Regional Ocean Modeling System (ROMS) investigating three-dimensional buoyancy-driven circulation in an ice-covered lake of simplified symmetric shape. The numerical results revealed vertical current velocities of 10-6 m s-1 and horizontal current velocities of 10-3 m s-1. The model simulated an upward current along sloping boundaries, with downwelling return flow throughout the bulk of the lake's water column. For the typical internal Rossby radius of 14 km, basin-scale circulation in a lake with a horizontal dimension of 45 km turns to a counterclockwise gyre in the lake half depth. We investigated the dependence of the boundary flow and the residual lake-wide circulation on the lake size, bottom slope inclination, and earth rotation. The obtained magnitudes of the boundary flow were compared against known simplified analytical solutions. The outcomes demonstrated that the ROMS model, on the basis of the Boussinesq hydrostatic equation, is able to simulate weakly energetic flows governed by viscous forces and rotation in enclosed thermally stratified ice-covered domains. The results contribute to a better understanding of the processes driving the under-ice freshwater circulation with wider applications, including dynamics of buoyancy-driven flows affected by nonlinear effects, such as freshwater density anomaly.

How to cite: Sharifi, F. S., Hinkelmann, R., Hattermann, T., and Kirillin, G.: Three-dimensional gravity flows in an idealized stratified ice-covered lake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-68, https://doi.org/10.5194/egusphere-egu23-68, 2023.

17:10–17:20
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EGU23-366
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ECS
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Highlight
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On-site presentation
Ezgi Asirok, Georgiy Kirillin, and Hans-Peter Grossart

Polar nights are unique periods to understand metabolism in ice-covered lakes from physical and biological perspectives. Despite the nearly zero primary production, polar nights cannot be disregarded as periods of biological stagnation, and recent data on biological processes and biogeochemical interactions are not yet fully understood, but can provide valuable information on lake ecosystem functioning in the absence of sunlight. Seasonally ice-covered Arctic Lake Kilpisjärvi at the latitude of 69° N experiences night time conditions from December to mid-January. Here, we use the continuous high-frequency time series of high-resolution temperature and oxygen from Kilpisjärvi to understand temperature and depth-related changes in respiration levels for three years from 2019 to 2022. In parallel, we aim to derive vertical microbial community composition by analysing water samples from different depths during the ice-covered period and correlate the outputs with oxygen dynamics to understand bacterial adaptations along biogeochemical gradients in Lake Kilpisjarvi.



How to cite: Asirok, E., Kirillin, G., and Grossart, H.-P.: Breathing at Sleep: Respiration in Arctic Lakes During Polar Nights, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-366, https://doi.org/10.5194/egusphere-egu23-366, 2023.

17:20–17:30
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EGU23-6834
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ECS
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On-site presentation
Liuming Wang, Junxiao Wang, and Xingong Li

Lake evaporation (EW) is an important component of both basin evapotranspiration (ETB) and lake water balance for lake-basins on the inner Tibetan Plateau (IB), and it greatly influences lake water storage change (ΔSW). However, the effects of EW on ETB and ΔSW at lake-basin scale have never been reported for most basins on the IB. In this study, the EW of 117 large lakes (area > 50 km2) in 95 closed lake-basins (area > 1000 km2) were estimated, and its effects on ETB and ΔSW over 2001-2018 were examined using several newly derived diagnostic equations from the aspects of EW amount, rate, trend slope and inter-annual variability. During the study period, mean annual EW rate and total EW amount for the lakes are 994.25 ± 20.48 mm, and 24.83 ± 0.52 km3 respectively. The significant increasing trend (0.29 ± 0.04 km3/a) in annual EW amount is mainly caused by the increase (224.65 km2/a) in lake area (82.13%), and the increase (2.12 ± 1.28 mm/a) in EW rate is responsible for the rest (17.87%). EW accounts for 23.16% ± 4.94% of the ETB (107.24 ± 21.90 km3) for the 95 basins, and its impact has increased significantly (0.20% ± 0.09%/a) over the period. The increasing trends of EW rate and lake area ratio (0.06%, P < 0.05) contributed 14.49% and 52.69% to the increase trend in ETB (0.85 mm/a), and their variances contributed 1.60% ~ 4.79% and 1.64% ~ 6.50% to ETB variance (155.44 ± 107.97 mm2), respectively. The contribution of EW, quasi lake inflow (RL, 23.48 km3), and lake surface precipitation (PW, 9.18 km3) to mean ΔSW (7.82 km3) are -43.02%, 40.84% and 15.96%, respectively. And the increasing trends of the three components (EW, RL and PW) account for -58.02%, 29.59% and 12.39% of the decrease trend in annual ΔSW (-0.81 × 10 km3/a, P > 0.05), respectively. Basin RL, derived based on lake water balance, is significantly correlated with two independent land surface net precipitation estimates (0.57 < R < 0.86), and basin lake area ratio is a good indicator of basin EW and lake inflow in the IB.

How to cite: Wang, L., Wang, J., and Li, X.: Lake evaporation and its effects on basin evapotranspiration and lake water storage on the inner Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6834, https://doi.org/10.5194/egusphere-egu23-6834, 2023.

17:30–17:50
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EGU23-15065
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ECS
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solicited
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On-site presentation
Elisa Calamita, Michael Brechbühler, Iestyn Woolway, Clement Albergel, and Daniel Odermatt

Lakes are responding rapidly to climate change and one of the most tangible responses is the increase in lake surface water temperature. Such an increase can intensify thermal stratification and dampen the intensity of vertical mixing. In turn, surface warming has the potential to alter the mixing regime of lakes, potentially leading to abrupt shifts in ecosystem functioning. Reduced mixing between the surface and bottom waters can indeed decrease the upwelling of essential nutrients from deep water to the lake surface and the oxygen transport in the opposite direction. This can result in a decrease in lake productivity and can increase the risk of anoxia at depth, respectively.

Despite the important consequences of such lake mixing anomalies, we lack a systematic overview of their occurrence, mainly due to the lack of systematic data to detect and analyze them worldwide. Remotely sensed lake surface water temperature available from ESA CCI (Climate Change Initiative) and similar sources represent spatial skin temperature gradients, but they do not resolve vertical gradients. They are hence often used to prove the lakes’ long-term warming in terms of spatial average. However, the horizontal gradients of such data could help us better understand the internal processes of lakes and the identification of lake mixing anomalies. Given that seasonal overturning often occurs at different times across the lake, the spatial character of remotely sensed data can reveal important processes in freshwater systems and can help assess the long-term variability in the overturning behaviour of large lakes in the context of climate change. Within our project, we use the spatial component of satellite Earth Observation data to reveal information about lake mixing and mixing anomalies. We apply a thermal front tracking method, a technique much more exploited in oceanography than limnology, to identify mixing anomalies in dimictic lakes worldwide.

Our study suggests that the spatially distributed property of Earth Observation can be useful to spot lake mixing anomalies in dimictic lakes worldwide. Thus, we present the first global-scale assessment of lake mixing anomalies occurrence in the last 20 years. Earth Observation data can also be used to calculate how susceptible lakes are to undergo a mixing regime shift. Interestingly, we found that lakes experiencing more mixing anomalies are also those more susceptible to undergoing a mixing regime shift. Moreover, using Earth Observation, we detected mixing anomalies that have already been documented and, more interestingly, we spotted mixing anomalies occurring in unstudied remote lakes. Although further investigations would be needed to specifically assess the impact of climate change on these remote lakes, these cases highlight that remote sensing can be used as a first screening tool to spot lake mixing anomalies worldwide. Thus, Earth Observation and our methodology can be potentially used as an early warning system for lake mixing regime shifts.

How to cite: Calamita, E., Brechbühler, M., Woolway, I., Albergel, C., and Odermatt, D.: Detecting lake mixing anomalies using Earth Observation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15065, https://doi.org/10.5194/egusphere-egu23-15065, 2023.

Posters on site: Fri, 28 Apr, 10:45–12:30 | Hall A

Chairpersons: Giulia Valerio, Damien Bouffard, Georgiy Kirillin
A.187
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EGU23-6178
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Highlight
Damien Bouffard, Tomy Doda, Cintia Ramón, and Hugo Ulloa

We present the results of a project on differential cooling in lakes. This project aimed at quantifying the cross-shore convective circulation induced by differential cooling, also known as the thermal siphon (TS). Our case study was a small peri-alpine wind-sheltered lake (Rotsee, CH), where we studied the seasonal evolution of  TS over a year using a combination of field observations and high-resolution RANS and LES models. We found that TS  is a frequent cross-shore transport process which can be predicted using laboratory-based scaling formulae. We also observed that penetrative convection modifies the dynamics of the cross-shore flow, which has implications for the littoral-pelagic connectivity. In addition, we quantified the TS-induced lateral transport of dissolved gases, including oxygen and methane. We extended our findings to other lakes in order to improve the prediction of TS occurrence and intensity and we developed a procedure for predicting TS-induced transport based on factors such as lake bathymetry, meteorological forcing (including wind and cooling), and the vertical thermal structure of the lake.

How to cite: Bouffard, D., Doda, T., Ramón, C., and Ulloa, H.: Differential cooling in lakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6178, https://doi.org/10.5194/egusphere-egu23-6178, 2023.

A.188
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EGU23-2074
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ECS
Carolina Rosca, Annett Junginger, Simon Kübler, and Ronny Schoenberg

Continuous lake sediment archives integrate valuable information of geodynamic transformations, climatic fluctuations and anthropogenic environmental forcing through time. In many parts of the world, such as sub-Saharan Africa, lake ecosystems are important pillars of biodiversity and wildlife preservation and evolution, as well as political and economic stability, especially with regard to the rapid population growth and increasing food and water demand.

Located in the central part of the rift valley region, lake Naivasha is the second largest freshwater lake in Kenya, covers a catchment area of ca. 3400 km2 and is considered a “wetland of international importance” (RAMSAR convention, 2011). Previous studies and real-time observations documented a rapid intensification of agricultural activities ranging from subsidy economy (upper catchment) to industrial-sized horticulture practices (lower catchment) from the second half of the 20th century towards the present. These were suggested to have significantly influenced the drainage systems of the catchment and hydrochemistry of the lake, with potentially negative effects on the entire ecosystem. In addition, potential anthropogenic metal influx from other modern, diffuse sources (such as fossil fuel combustion) due to the increasing anthropogenic density and activities in the immediate vicinity of the lake remain poorly constrained.

We analysed major- and trace elements and Pb isotope compositions of lake sediments covering the past ca. 150 years, as well as the surrounding lithologies in order to reconstruct the pathway(s) and source(s) of elemental influx and accumulation into the lake. The characterization of the geological background in this tectonically and volcanologically active region was primarily set on the northern part of the catchment where, the two main lake-feeding rivers Malewa and Gilgil discharge into the lake. Element correlation indices point to i) a strong influence of the local geological background and, ii) a relatively stable catchment for this time-period as seen from sub-parallel REE+Y patterns along the monolith. Lead isotope compositions, on the other hand, show more radiogenic values in the sediment deposited before the 1900’s (206Pb/204Pb: 19.502 – 19.546) and a significant shift towards less radiogenic isotopic ratios from the second half of the 20th century (206Pb/204Pb: 19.228 – 19.304), which persists towards the top of the core. We combine our extended geochemical data with geospatial projections of the land use to build a time-integrated cause-and-effect assessment of metals into lake Naivasha and disentangle the cause for the change in the Pb isotope composition.

How to cite: Rosca, C., Junginger, A., Kübler, S., and Schoenberg, R.: Trace element- and Pb isotope fingerprints of natural vs. anthropogenically induced geochemical changes in tropical lake catchments: A case study from lake Naivasha, Kenya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2074, https://doi.org/10.5194/egusphere-egu23-2074, 2023.

A.189
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EGU23-2637
Pi-Ju Tsou, Huei-Fen Chen, and Zih-Wei Tang

Considering the carbon sinks and carbon sequestration, people often think of forests, trees, oceans. However, the carbon sequestration capacity of the lake was underestimated, until now the change of carbon accumulation in Sun Moon Lake has not been accurately estimated. Sun Moon Lake is the largest natural lake in Taiwan. After the dam was built in 1934, the water source of Sun Moon Lake came from Zhuoshui River from the storage in Wujie Dam . The water depth of the lake increased from 4 meters to 27 meters deep, which makes the lake area to expand suddenly and the sedimentary rate was accelerated. Changes in the environment and human behaviors had caused huge changes in the organic matter of Sun Moon Lake. In this study, the carbon element content was mainly analyzed through sediment cores  in Sun Lake and Moon Lake.  Before the construction of the dam, there were many records of charcoal layers left by the aboriginal people burning forests for reclamation in the core.  The carbon content of the lake can be estimated by the formula CO2e=3.67 * TOC% * BD (g/cm3) * D (cm) * Area (ha). Therefore, we can use this formula to estimate the accumulated carbon sink content in Sun Moon Lake sediments. We try to estimate the carbon storage methods based on inorganic and organic carbon during different periods in the future work. To determine the age control is a critical point in core sediments, so we will use XRF data to reconstruct the timing of typhoon events and human contaminations. The volume of lake sediment can be estimated by the sedimentary rates of cores and seismic profile. Now, we need to measure contents of organic and inorganic carbon for the core sediments. 

Key words: lake, sediments, carbon, organic, inorganic

How to cite: Tsou, P.-J., Chen, H.-F., and Tang, Z.-W.: A preliminary test to estimate the carbon sequestration from lake sediments of Sun Moon Lake in Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2637, https://doi.org/10.5194/egusphere-egu23-2637, 2023.

A.190
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EGU23-6893
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ECS
Hannes Nevermann, Milad Aminzadeh, Kaveh Madani, and Nima Shokri

Reliable projection of evaporative fluxes from lakes is at the core of a wide range of hydrological, climatological, and environmental modeling processes. Evaporation results in losses of blue water from lakes in regions with limited freshwater resources and affects aquatic and terrestrial biodiversity. While current estimates of evaporative losses from lakes remain largely empirical depending on locally calibrated heat and mass transfer coefficients or remotely sensed surface temperature data, we propose a physically-based framework that builds on inherent lake characteristics (e.g., bathymetry, light attenuation characteristics) and atmospheric forcing variables to quantify energy dynamics of the water body and surface evaporative fluxes from the largest lakes across different climatic zones on a global scale. To evaluate the performance of the model, the modelling results determining the seasonal variation of vertical temperature profiles and latent heat loss were compared with in situ measurements of water temperature and surface heat fluxes measured in Lake Mead, in the Southwestern USA. We found good agreements between the physically-based estimations and the measured data. We then quantified evaporative losses from 30 lakes in 30 different climate zone sub-types with an average depth ranging from 1.1 m to 577 m and a surface area of 45 km² to 82,000 km². Our preliminary findings for 2020 indicate that variation of first-order atmospheric parameters (i.e., wind, radiation, air temperature, and humidity) across climatic zones and the change in lake bathymetry altering local vertical temperature profiles within the water body significantly affect evaporative losses. The energy-constrained model enables quantifying the extent of evaporative water losses from lakes and provides a theoretical basis for delineating potential impacts on water management and ecological and climatological processes under different climate change scenarios.

How to cite: Nevermann, H., Aminzadeh, M., Madani, K., and Shokri, N.: Global scale estimation of evaporative losses from large lakes located in different climatic zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6893, https://doi.org/10.5194/egusphere-egu23-6893, 2023.

A.191
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EGU23-7068
Georgiy Kirillin, Alexander Izhitsky, and Abilgazi Kurbaniyazov

Rapid desiccation of the Aral Sea, the former 4th largest lake worldwide, attracts continuous attention of researchers as an example of fast anthropogenically driven change of a large aquatic ecosystem on unprecedentedly large spatial scales. As a countermeasure preventing further desiccation, a dam was constructed in 2005 separating the northern part of the Aral Sea from the rest of the basin. The effort led to stabilization of the North Aral volume and salinity and was widely recognized as an exceptional success in large-scale water management and restoration. The “restarted” ecosystem developed within several years to a highly productive large lake. Owing to the cold arid climate, the lake is covered by ice for several months in winter while gaining significantly higher amount of solar radiation than temperate and polar ice-covered lakes. We present new results revealing characteristic features of large low-latitude brackish lake dynamics under ice cover: strong internal basin-scale waves with long periods, heating of the water column by solar light penetrating the ice cover, and arresting of vertical convective mixing by freshening of upper waters during the ice melt. The under-ice dissolved oxygen content was analyzed in terms of whole-lake metabolism and demonstrated primary production taking place during the entire ice-covered period with a strong intensification in spring months after the snow melt increased the photosynthetically active radiation level under ice.

How to cite: Kirillin, G., Izhitsky, A., and Kurbaniyazov, A.: Thermal conditions and lake metabolism in the ice-covered North Aral Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7068, https://doi.org/10.5194/egusphere-egu23-7068, 2023.

A.192
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EGU23-7208
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ECS
Lingqi Li

Desert terminal lakes are important signals to discern ecological degradation crises, partic- ularly in arid areas where an artificial project of ecological water diversion has designated a quota of river water to prevent lake body shrinkage and protect the ecosystem. Knowledge of the minimum ecological water demand (EWD) is thus necessary to ensure the basic health of lake ecosystems. This study analyzed the spatiotemporal evolution of water boundaries using Landsat satellites data via remote sensing technology from 2002 to 2017 in East Juyan Lake, an inland desert terminal lake of the Heihe River in northwest China. The minimum lake water demand was determined using two estimation methods: the lake-evaporation-oriented EWD method and the minimum water level method. In the latter method, both lake topography (using water-level area curves) and biological survival demands (using bighead carps as indicators) were considered to derive the minimum lake EWD. Water diversion to the lake over the past 15 years has increased the lake’s area, but there are still marked intra-annual seasonal variations. The annual minimum lake water demand was suggested to be 54 × 106 m3/year by comparing the different methods; however, it was not satisfied, and the lake survival was endangered when the occurrence frequency of the annual runoff in the Zhengyixia hydrological station exceeded 65%. This study offered promising directions for inland lake water resource management.

How to cite: Li, L.: Ecological Water Demand Estimations for Desert Terminal Lake Survival under Inland River Water Diversion Regulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7208, https://doi.org/10.5194/egusphere-egu23-7208, 2023.

A.193
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EGU23-9867
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ECS
Accumulation of labile phosphorus in sediments in the zone of influence of the trout farm (Lake Ladoga)
(withdrawn)
Artem Lapenkov, Alina Guzeva, Ksenia Zaripova, and Anfisa Berezina
A.194
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EGU23-10445
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ECS
Meimei Zhang and Fang Chen

Glacial lake outburst floods (GLOFs) are among the most serious natural hazards in mountainous regions in the last several decades. The recent global warming has caused dramatic glacial lake changes and increased potential GLOF risk, particularly in High Mountain Asia (HMA) region. Thus, there is a pressing need to detect and monitor lake area changes and spatial distribution of glacial lakes in this region. In this research, we produce more accurate and complete maps of glacial lake extent in the HMA in 2008, 2012 and 2016 with consistent time intervals using Landsat satellite images and the Google Earth Engine (GEE) cloud computing platform, and further study the formation, distribution and dynamics of the glacial lakes. In total 17016 and 21249 glacial lakes were detected in 2008 and 2016, respectively, covering an area of 1420.15±232.76 km2 and 1577.38±288.82 km2; the lakes were mainly located at altitudes between 4400 m and 5600 m. The annual areal expansion rate was approximately 1.38 % from 2008 to 2016. To explore the cause of the rapid expansion of individual glacial lake, we investigate their long-term expansion rates by measuring changes in shoreline positions. The results show that glacial lakes are expanding rapidly in areas close to glaciers, had a high expansion rate of larger than 20 m/yr from 2008 to 2016. Glacial lakes in the Himalayas show the highest expansion rate of more than 2m/yr, followed by the Karakoram Mountains (1.61 m/yr) and the Tianshan Mountains (1.52 m/yr). The accelerating rate of glacier ice and snow melting caused by global warming is the primary contributor to glacial lake growth. These results may provide information that will help in the understanding of lake detailed dynamics and the mechanism, and also facilitate the scientific recognition of the potential hazards associated with glacial lakes.

How to cite: Zhang, M. and Chen, F.: Monitoring Glacial Lakes in High Mountain Asia from 2008 to 2016, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10445, https://doi.org/10.5194/egusphere-egu23-10445, 2023.

A.195
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EGU23-15524
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Highlight
Giulia Valerio, Stella Volpini, and Elena Benvenuti

Lakes and their biodiversity are threatened by global warming, responding rapidly to climatic change and incorporating the effects occurring in the drained catchments. The thermal characteristics of lakes have undergone substantial alterations in response to the progressive increased air temperature. Surface waters have worldwide warmed, with a global average rate of 0.34°C per decade between 1985 and 2009 during summer. Over the last few years, increased attention is given to the response of lakes to extreme events, such as storms and heatwaves. There is evidence that climate change is leading to longer and more frequent marine heatwaves at the surface of the ocean, while much less is known about heatwaves in lakes, where field studies are generally lacking.

According to the C3S ERA5 dataset, August 2022 globally tied as the third warmest on record, 0.30°C warmer than the 1991-2020 average for August and 0.42°C warmer than the 1981-2010 average in this data record. The month of August was particularly warm over Europe and was also remarkable in terms of hydrological variables with drier than normal conditions over western Europe, sustained by heatwaves with significant impacts on economy and society. In this contribution, we show the thermal response of two deep Italian lakes (Lake Garda and Lake Iseo) under the extreme meteorological conditions occurred in summer 2022. In both these lakes, a floating station measured at a 1/min sampling rate the meteorological forcing at the lake surface as well as water temperature down to 100 m of depth with 0.01 °C accuracy. Thanks to the temperature data, we identified and characterized, in terms of intensity and duration, several long-lasting heatwaves and we compared their characteristics with past observations, showing evidence of an exceptional surface warming over the last 20 years. The overall high-resolution dataset allowed us to compute the thermal balance of the two lakes, comparing the relative importance of the different forcing and that of the morphological and hydrological characteristics of the two water bodies, and to discuss the impact of the internal hydrodynamics on the surface heating. This analysis underlined the fundamental role played by the wind, which affects both the thermal fluxes at the water surface and the vertical distribution of temperature. This result raises the issue about the degree of reliability of the prediction of extreme events in lakes under climate change due to the uncertainties of the wind predictions, especially in geographical context, such as pre-alpine or alpine regions, where the wind fields provided by large-scale resolution models are less accurate. 

How to cite: Valerio, G., Volpini, S., and Benvenuti, E.: Evidence of heatwaves in two deep Italian lakes in summer 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15524, https://doi.org/10.5194/egusphere-egu23-15524, 2023.

A.196
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EGU23-16527
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Highlight
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Birgit Heim, Mareike Wieczorek, Kathleen Stoof-Leichsenring, Boris K. Biskaborn, Anne Morgenstern, Paul P. Overduin, Antje Eulenburg, Izabella Baisheva, Stefan Kruse, Evgenii S. Zakharov, Luidmila A. Pestryakova, Kirsten Elger, and Ulrike Herzschuh

We present a long-year data collection of freshwater chemistry from 590 high latitude lakes based on water sampling during our past expeditions in the Central and Eastern Siberian continuous permafrost regions. We compiled and standardised all acquired seasonal limnological data on major ions, alkalinity, pH and Electrical Conductivity including time series of data from lakes that we sampled repeatedly. The data collection encompasses diverse Siberian regions with numerous lakes along climate and vegetation gradients in the Khatanga and central Yakutian lowlands, to the glacial lakes of the Chukotka mountain region in Eastern Siberia and the central Lena Delta in the Arctic zone. 

The data collection is rich in standardised metadata following the metadata schema of the International Generic Sample Number (IGSN), which provides a unique and persistent identifier for physical objects (samples). Within the project FAIR Workflows to establish IGSN for Samples in the Helmholtz Association (FAIR WISH), funded by the Helmholtz Metadata Collaboration Platform (HMC), we customised the GFZ-specific IGSN schema to better describe lakes and water samples in a hierarchical (parent and child) scheme with standardised metadata on lake and sample characteristics, ecoregions, principal investigators and many more.

This standardised data collection will be made available in the PANGAEA data repository (www.pangaea.de) to enable analyses of land-to-lake geochemical fluxes and will support biodiversity, biogeochemical, bioindicator and many more analyses. In this presentation, we visualize the data in form of Piper and Schoeller plots in order to categorize the water bodies and investigate their geographic distribution and links to catchment vegetation, active layer depth, permafrost disturbances and lithology.

How to cite: Heim, B., Wieczorek, M., Stoof-Leichsenring, K., Biskaborn, B. K., Morgenstern, A., Overduin, P. P., Eulenburg, A., Baisheva, I., Kruse, S., Zakharov, E. S., Pestryakova, L. A., Elger, K., and Herzschuh, U.: Central and Eastern Siberian High Latitude Lake Hydrochemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16527, https://doi.org/10.5194/egusphere-egu23-16527, 2023.

A.197
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EGU23-17259
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ECS
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Jonas Wydler, Mortimer Werther, Camille Minaudo, Alexander Damm, and Daniel Odermatt

Lakes are highly biodiverse ecosystems and are providing a wide range of ecosystem services to human wellbeing such as drinking water, water for irrigation, access to fisheries and recreational areas. Anthropogenic activities threaten these services both through local impacts on water bodies (e.g. eutrophication) and globally (e.g. climate change). The trophic state and the aquatic carbon cycle are sensitive indicators to evaluate the state and health of lake ecosystems. Monitoring the spatial and temporal dynamics of primary production is therefore a high priority in lake research.
Primary production can be assessed in several ways. The most common approach involves the incubation and measurement of labelled carbon isotopes in lake water samples that are exposed to certain light conditions. Alternatively, primary production can be estimated using diel variations in oxygen concentration or fast repetition rate fluorometry. Both approaches are accurate but can hardly be used to cover large spatial heterogeneities. For global assessments, only bio-optical primary production models based on remote sensing data allow a consistent upscaling in a cost-efficient manner.
A wide range of bio-optical primary production models exist and have been applied to lakes. Generally, these models describe the availability of light in the water column and the efficiency of the algae particles to absorb photon energy and to use this energy for subsequent carbon assimilation. The main challenges related to such approaches are to accurately the retrieve required information from satellite data and to precisely estimate sensible model parameters. The upcoming hyperspectral mission Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) by NASA will help to improve the accuracy of primary productivity estimates.
This contribution aims to improve understanding of sensitivities and validity of available bio-optical primary production models to eventually maximise the benefits of improved information retrievals from PACE. We particularly reviewed state-of-the-art primary production models for remote sensing data of oceans and lakes, provided an overview of relevant model inputs and calculated Sobol sensitivity indices for a range of input parameters and models. Our results facilitate future applications of primary production models to hyperspectral PACE data and will particularly help to identify most sensitive input variables, to improve empirical model parameterizations and to guide the selection of suited models for freshwater systems.

How to cite: Wydler, J., Werther, M., Minaudo, C., Damm, A., and Odermatt, D.: Intercomparison and sensitivity assessment of lake primary production models for remote sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17259, https://doi.org/10.5194/egusphere-egu23-17259, 2023.