HS10.6 | Lakes and Inland Seas under Global Change
Lakes and Inland Seas under Global Change
Convener: Georgiy Kirillin | Co-conveners: Timothy W. Lyons, Senlin Zhu, Tom Shatwell, Yi Luo, Virginia Gewin
Orals
| Wed, 17 Apr, 10:45–12:30 (CEST)
 
Room 3.29/30, Thu, 18 Apr, 08:30–12:30 (CEST)
 
Room 3.29/30
Posters on site
| Attendance Wed, 17 Apr, 16:15–18:00 (CEST) | Display Wed, 17 Apr, 14:00–18:00
 
Hall A
Orals |
Wed, 10:45
Wed, 16:15
Lakes, as major components of the hydrosphere, are able to accumulate and transfer energy and matter to and from other spheres of the environment. As confined water bodies with limited exchange, lakes and inland seas are particularly vulnerable to climatic and human impacts accumulated over broad catchment areas. Lakes, especially the largest ones, have higher thermal inertia and longer residence times than those of the other inland water bodies, acting as buffers in the inland waters transport network. Hence, they mirror both the global change effects and anthropogenic pressures, perhaps stronger than any other aquatic bodies. Lakes and inland seas play an important role in the global water cycle and in regulating biodiversity, availability and quality of water resources, and provision of ecosystem services. Research of lakes and inland seas includes many common approaches and techniques. This interdisciplinary session provides a joint forum for limnologists, oceanographers, biogeochemists, and hydrologists interested in processes governing physical, chemical, and biological regimes of lakes and inland seas of the world, as well as their responses to climate change and anthropogenic impacts. The specific topics cover water temperatures, vertical stratification and mixing, ice phenomena, and their responses to climate change, extreme climatic events, lake drying and deteriorating of water quality in the face of intense droughts, increased evaporation, and greater demand on water resources. Other issues include increasing salinity and nutrient levels, increasing dust loads, harmful microbiological/biogeochemical effects, dwindling resource availability (e.g., for agriculture), sociopolitical pressures, ecological degradation within the lakes and beyond, and current and future threats to large human populations, among others. Novel methods to quantify the impact of climate change on lake dynamics are especially welcomed.

Orals: Wed, 17 Apr | Room 3.29/30

Chairpersons: Georgiy Kirillin, Tom Shatwell
10:45–10:50
10:50–11:00
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EGU24-8991
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Highlight
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On-site presentation
Jon Olafsson, Solveig Olafsdottir, and Ingibjörg Jónsdóttir

The caldera Lake Öskjuvatn lies in the remote Dyngjufjöll Mountains in Iceland´s interior. The lake is at 1050 m elevation, it is 11 km2 and 217 m deep. The lake developed after an eruption in 1875. From 1921 to 1926 there were volcanic eruptions in and around the lake. The lake is cold but thermal activity at has been observed at 80 m depth which generally maintains a small opening in the winter ice. There are furthermore several warm marginal springs and seeps (Ólafsson 1980). In February 2012 remote sensing data unexpectedly revealed progressively disappearing ice cover which resulted in Lake Öskjuvatn being totally ice-free by late March. This normally occurs in late June.  We investigated the ice-free lake in early April 2012 and again when the lake was ice covered in April 2013.Using SeaBird Sea Cat CTD instrument and Niskin bottles for water sampling we acquired data to compare the state of the lake under ice-free and ice-covered conditions. From April 2012 to July 2014, we had a moored string of Star-Oddi recording temperature sensors from surface to 60 m depth at a location in the deepest part of the lake. We examined the lake water chemical composition for evidence of active volcanism. The differences in the temperature structure 2012 and 2013 yield signs of circulation and the moored temperature recorders illustrate seasonal variations.  With this data combined we seek to explain why the lake became ice free in 2012 but was mostly covered with 80 cm thick ice at the same time the following year.

Ólafsson, J. (1980). "Temperature structure and water chemistry of the caldera Lake Öskjuvatn, Iceland." Limnology and Oceanography 25: 779-788.

How to cite: Olafsson, J., Olafsdottir, S., and Jónsdóttir, I.: Sudden disappearance of winter ice from Caldera Lake Öskjuvatn, Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8991, https://doi.org/10.5194/egusphere-egu24-8991, 2024.

11:00–11:10
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EGU24-5434
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ECS
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Highlight
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On-site presentation
Weijia Wang, Kun Shi, and Iestyn Woolway

Global lake ecosystems are subjected to an increased occurrence of heat extremes, yet their impact on lake warming remains poorly understood. In this study, we employed a hybrid physically-based/statistical model to assess the contribution of heat extremes to variations in surface water temperature of 2260 lakes in China from 1985 to 2022. Our study indicates that heat extremes are increasing at a rate of about 2.08 days/decade and an intensity of about 0.03 °C/ day·decade in China. The warming rate of lake surface water temperature decreases from 0.16 °C/decade to 0.13 °C/decade after removing heat extremes. Heat extremes exert a considerable influence on long-term lake surface temperature changes, contributing 36.5% of the warming trends within the studied lakes. Given the important influence of heat extremes on the mean warming of lake surface waters, it is imperative that they are adequately accounted for in climate impact studies.

How to cite: Wang, W., Shi, K., and Woolway, I.: The impact of extreme heat on lake warming in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5434, https://doi.org/10.5194/egusphere-egu24-5434, 2024.

11:10–11:20
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EGU24-7193
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ECS
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On-site presentation
Lei Huang, Axel Timmermann, and Sun-Seon Lee

The Caspian Sea and Black Sea are the two earth's largest inland seas. Projections of their temperature, circulation and water balance responses to greenhouse warming remain largely uncertain. We investigated hydrodynamic changes of the two water bodies in a high-resolution CESM1 simulation, in which both the Caspian Sea and Black Sea are simulated by the ocean model (POP2). It turns out the mean surface water temperature of the two seas will increase by about 2.5°C in response to CO2 doubling in the atmosphere. Meanwhile, reduction of wind stress curl will lead to a spin-down of the main gyre circulations particularly in the Black Sea, which was also evidenced by a two-dimensional ocean model with joint effect of baroclinicity and bottom relief being considered. Our results also show that future evaporation enhancement due to surface warming will lead to a negative water balance for both seas, which is equivalent to a mean sea level trend of -0.1 m/year when CO2 concentration in the atmosphere doubles. These hydrodynamic changes are likely to exert large impacts on the aquatic ecosystems, fisheries, and human societies in the coastal areas.

How to cite: Huang, L., Timmermann, A., and Lee, S.-S.: Hydrodynamic responses of the Caspian Sea and Black Sea to greenhouse warming in a high-resolution ocean-atmosphere coupled climate model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7193, https://doi.org/10.5194/egusphere-egu24-7193, 2024.

11:20–11:30
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EGU24-12466
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ECS
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On-site presentation
Margarita Choulga, Gianpaolo Balsamo, Souhail Boussetta, Tom Kimpson, Ekaterina Kurzeneva, Elena Shevnina, and Patricia de Rosnay

Lakes modify the structure of the atmospheric boundary layer. They can intensify winter snowstorms, increase/decrease surface temperature and amount of precipitation. It has been shown that monthly varying lake surface cover has a significant positive impact over regions with prolong rain and dry seasons, especially over Malaysia, Indonesia and Papua New Guinea (see Kimpson et al., 2023).

At European Centre for Medium-Range Weather Forecasts (ECMWF) current lake mask is constant over time and represent permanent water over the period 1984-2018. To meet reanalysis requirements of monthly varying high-resolution lake mask outlined in CERISE project the Joint Research Centre (JRC) Global Surface Water Explorer (GSWE) dataset (Pekel et al., 2016) was used. Applied methodology, its advantages and drawbacks, as well as first results of monthly lake surface cover maps will be presented.

How to cite: Choulga, M., Balsamo, G., Boussetta, S., Kimpson, T., Kurzeneva, E., Shevnina, E., and de Rosnay, P.: Varying lake surface cover for reanalysis application, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12466, https://doi.org/10.5194/egusphere-egu24-12466, 2024.

11:30–11:40
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EGU24-20529
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ECS
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On-site presentation
Brent Heerspink and Anthony Kendall

Changing climate conditions have altered sea and inland lake levels around the globe, including in the world's largest inland lake system, North America's Laurentian Great Lakes. These five lakes span the border between the United States and Canada, holding ~23,000 km3 of freshwater, including ~4,000 km3 of groundwater, which represents ~21% of the world's available freshwater. Rapid interannual changes in lake elevation of 1-2m over the last 25 years have occurred due to changing climatic conditions including precipitation, lake surface temperature and the extent of winter ice cover. Significant effort has been invested to develop predictive models for climate, runoff and lake levels in the Great Lakes region. Recent hydrologic modeling efforts have also investigated interactions between the Great Lakes and the adjacent groundwater aquifers, with a focus on groundwater as a source or sink of water to the lakes. Yet little attention has been given to the coastal hydrologic processes that control the feedback between lake levels and groundwater response. Here, we investigate the effects of lake level changes on terrestrial groundwater elevations with a coupled surface and groundwater hydrology model encompassing the entire State of Michigan, using the Landscape Hydrology Model (LHM). LHM is a gridded, process-based surface and shallow subsurface water balance model coupled to USGS MODFLOW which simulates saturated groundwater processes. We tested the effect of lake levels on terrestrial groundway by running a set of model experiments using consistent climate forcing data and different lake elevations as groundwater model boundary conditions. Results indicate the changing lake levels drive changes in terrestrial groundwater elevations of up to 2m and as far as 20 km inland. Here, we extend this study to consider how these lake-level induced changes in groundwater elevation affect the hydrologic connectivity of coastal wetlands. We explicitly consider both surface connectivity and groundwater connectivity, and how those vary in space and time. Given the predicted impacts of climate change on sea and lake levels globally, it is important to understand how feedbacks between surface and groundwater in coastal regions affect the connectivity of and ecosystem services provided by coastal wetlands. 

How to cite: Heerspink, B. and Kendall, A.: Interactions and Connectivity between Large Inland Lakes, Coastal Wetlands and Groundwater, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20529, https://doi.org/10.5194/egusphere-egu24-20529, 2024.

11:40–11:50
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EGU24-3036
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ECS
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Highlight
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Virtual presentation
Xiwen Wang, Kun Shi, Yunlin Zhang, Boqiang Qin, Yibo Zhang, Weijia Wang, R. Iestyn Woolway, Shilong Piao, and Erik Jeppesen

Climate change could seriously threaten global lake ecosystems by warming lake surface water and increasing the occurrence of lake heatwaves. Yet, there are great uncertainties in quantifying lake temperature changes globally due to a lack of accurate large-scale model simulations. Here, we integrated satellite observations and a numerical model to improve lake temperature modeling and explore the multifaceted characteristics of trends in surface temperatures and lake heatwave occurrence in Chinese lakes from 1980 to 2100. Our model-data integration approach revealed that the lake surface waters have warmed at a rate of 0.11 °C 10a-1 during the period 1980–2021, being only half of the pure model-based estimate. Moreover, our analysis suggested that an asymmetric seasonal warming rate has led to a reduced temperature seasonality in eastern plain lakes but an amplified one in alpine lakes. The durations of lake heatwaves have also increased at a rate of 7.7 d 10a-1. Under the high-greenhouse-gas-emission scenario, lake surface temperature and lake heatwave duration were projected to increase by 2.2 °C and 197 d at the end of the 21st century, respectively. Such drastic changes would worsen the environmental conditions of lakes subjected to high and increasing anthropogenic pressures, posing great threats to aquatic biodiversity and human health.

How to cite: Wang, X., Shi, K., Zhang, Y., Qin, B., Zhang, Y., Wang, W., Woolway, R. I., Piao, S., and Jeppesen, E.: Climate change drives rapid warming and increasing heatwaves of lakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3036, https://doi.org/10.5194/egusphere-egu24-3036, 2024.

11:50–12:00
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EGU24-15301
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ECS
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Virtual presentation
Dieu Anh Dinh, R. Iestyn Woolway, Eleanor Jennings, and Valerie McCarthy

Lake Surface Water Temperature (LSWT) plays a crucial role in aquatic ecosystems, influencing lake physical and biogeochemical processes. LSWT serves as a critical measure of the effects of climate change on lakes. Therefore, analysing LSWT variability is vital for understanding lake response to a warming climate. Lake Titicaca, the largest lake in South America and one of the highest lakes in the world, served as an important water resource in Peru-Bolivia. However, Lake Titicaca is also affected by climate change and anthropogenic activities. In this study, we investigate the historical and future change in LSWT of Lake Titicaca at different timescales (diel, seasonal, and annual). This research used the Global LAke Surface water Temperature (GLAST) dataset for the historical period of 1981-2020 and the future projected period of 2021-2099 for SWT of Lake Titicaca. Model projections were validated with LSWT from the ESA CCI Lakes dataset (2000-2020). The results showed that (1) LSWT has an increasing trend of  +0.16 K decade-1 annually and of +0.01 K decade-1 in diel range from 1981 to 2020, (2) LSWT is expected to warm at a rate of 1-4 K under future climate change scenarios. This finding gives an insight into LSWT and diel temperature range in Lake Titicaca, and LSWT changes in historical and future under climate change. This study could be beneficial for water resource managers and decision-makers to adapt and mitigate the climate change impacts.

How to cite: Dinh, D. A., Woolway, R. I., Jennings, E., and McCarthy, V.: Historic changes and future projections of surface water temperature in Lake Titicaca, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15301, https://doi.org/10.5194/egusphere-egu24-15301, 2024.

12:00–12:10
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EGU24-12006
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ECS
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On-site presentation
Nilo Lima, Denis Ruelland, Marisa Escobar, Antoine Rabatel, Waldo Lavado, and Thomas Condom

For decision making, it is crucial to provide an estimate of the main water balance fluxes to help understand trends and drivers of lake fluctuation in the past and in the future. However, the quantification of fluxes is a complicated task due to the scarcity of hydro-climatic data in space and over time, which hampers addressing all the local and regional hydrological processes at play, notably in the face of multi-decadal climatic and anthropogenic changes. These challenges are addressed at the scale of the Lake Titicaca hydro-system (57000 km2). Lake Titicaca (8400 km2) is located at 3812 m a.s.l. in the Altiplano of South America. Lake water levels measured since the beginning of the last century show extreme fluctuations within a range of approximately 6 m. This study presents an approach to disentangle the climatic and anthropogenic drivers of past  fluctuation of Lake Titicaca. For this, we implemented a conceptual integrated modeling chain that represents the following components: (i) production and routing processes based on a precipitation-runoff model including snow and glacier as well as net water consumption from irrigation in order to estimate lake inflows; and (ii) lake basic functioning according to inflows, direct precipitation and evaporation, bathymetry and outflows. The modeling chain was implemented in the Water Evaluation and Planning System (WEAP) platform at a daily time step over a 30-year period (1985–2015) and was driven by climate inputs derived from ground station data and ERA5 reanalysis. Model calibration and evaluation was based on geodetic mass balance, catchment streamflow, and lake water levels. The results indicate that the estimated annual water balance in the upstream catchments shows that the climate regime is mainly dominated by rainfall since snowfall only represents 1% of total precipitation (716 mm). Ice melt also accounts for 1% of total precipitation. The simulated actual evapotranspiration represents on average 565 mm year-1, of which 3% correspond to net irrigation consumption. Runoff is approximately 173 mm year-1. By scaling this runoff to the lake area, upstream inflow represents 53% of the total inflows into the lake (1818 mm year-1), the remaining 47% corresponding to direct precipitation over the lake. Evaporation losses from the lake are estimated to mean annual value of 1718 mm and downstream outflows 142 mm. Then, the Lake Titicaca is primarily driven by interannual variations in precipitation. The evaporation rate can exacerbate conditions in dry years. The integrated modeling chain will later be used to assess how water levels could be altered by climate change and management options such as water withdrawals and lake releases.

How to cite: Lima, N., Ruelland, D., Escobar, M., Rabatel, A., Lavado, W., and Condom, T.: Integrated water balance reveals that Lake Titicaca is driven by extreme climate variability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12006, https://doi.org/10.5194/egusphere-egu24-12006, 2024.

12:10–12:30

Orals: Thu, 18 Apr | Room 3.29/30

Chairpersons: Timothy W. Lyons, Virginia Gewin
08:30–08:35
08:35–08:45
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EGU24-923
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ECS
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On-site presentation
François Toussaint, Alice Alonso, and Marnik Vanclooster

Lake Tanganyika, one of the world’s largest freshwater body and located in East Africa, is under threat from both anthropogenic activities and climate change. The region strongly depends on it as a vital resource for water and food for the surrounding populations while pollution is increasing and fish catches and size are decreasing.

The characterization of Lake Tanganyika’s hydrodynamics, surface primary productivity and their changes over the past decades has not often benefited from remote sensing observations. In this study, we use satellite-derived estimates of surface chlorophyll-a concentration from ESA’s CCI Lakes dataset to enhance our understanding of Lake Tanganyika's hydrodynamics and more particularly the seasonal spatial patterns. Then, we focus on the analysis of the spatiotemporal changes of this variable over the past two decades with a subsequent effort to discern the underlying factors contributing to these observed changes.

After applying the DINEOF method for spatiotemporal interpolation, we comprehensively described the seasonal dynamics in surface chlorophyll-a concentration. We showed that the main patterns are the contrasting dynamics in the coastal and pelagic regions of the lake, explaining nearly 80% of the variance. The observed 20-year trends in primary productivity confirmed the hypothesis that primary productivity is decreasing in the pelagic regions of Lake Tanganyika, as asserted by earlier studies. This phenomenon can be attributed to the impact of climate change on air temperature and wind velocities in the region. These negative trends were found most dominant between March and June, and amount to around -0.5 mg.m-3.decade-1. We also showed a relative sharp increase in primary productivity (+0.5 to 2 mg.m-3.decade-1) in coastal regions near urban centres and river mouths, most notably in the North near Bujumbura and the outlet of the Ruzizi river. This most certainly illustrates the growing impact of the surrounding populations on the lake’s water quality.

How to cite: Toussaint, F., Alonso, A., and Vanclooster, M.: Assessing the Ecological Dynamics of Lake Tanganyika: Remote Sensing Insights into Seasonal Hydrodynamics and Human or Climate-Induced Changes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-923, https://doi.org/10.5194/egusphere-egu24-923, 2024.

08:45–08:55
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EGU24-12120
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On-site presentation
Huan Li

Climate change is an inevitable phenomenon that has a great impact on the physical, chemical, and biological effects on water bodies, among which water temperature is a key parameter that needs to be closely monitored. As the largest lake in Central Europe, Lake Balaton provides important recreational and ecological values that could be affected by global warming and anthropogenic activities, which lacks comprehensive spatiotemporal analysis. Our study leverages multisource data on Google Earth Engine (GEE) to conduct a temperature variation analysis over two decades and detailed spatial variations across different parts of the lake, with in-situ data serving as both auxiliary and validation source. With an accuracy of 1.6 °C and a seasonal quantile difference within 1 °C, the satellite-based observations are in good agreement with the in-situ measurements. In the inter-annual analysis, water temperature increases at 0.7 ℃/decade, closely paralleling the 0.6 ℃/decade rise in air temperature, with more notable warming in annual minimum and winter temperatures, particularly in the shallowest basin. For intra-annual temperature analysis, we propose a cumulative temperature anomaly method to examine temperature variations in each month, which shows distinct change patterns between different basins. This implies that during warmer months, the western, shallower regions exhibit relatively higher temperatures, while in cooler months, the deeper, eastern areas show elevated temperatures. Water depth has high correlations with seasonal temperature of the entire lake. In near-coast areas, windspeed induces cooling effects, while artificial surfaces contribute to water warming. The GEE user interface provides easy access for scientists and the public, and the open-source code can be readily customized to other lakes.

How to cite: Li, H.: Unveiling Spatio-Temporal Patterns of Water Temperature in Lake Balaton Through Remote Sensing Data Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12120, https://doi.org/10.5194/egusphere-egu24-12120, 2024.

08:55–09:05
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EGU24-17387
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ECS
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On-site presentation
Benjamin Kraemer

Dead zones are commonly associated with marine coastal areas where rivers deposit excessive nutrients leading to local anoxia sometimes stretching for hundreds of kilometers. Marine dead zones are well-recognized for their adverse effects on ecosystems, fisheries, and coastal communities. But in contrast, the global extent and drivers of dead zone formation near inflowing rivers to the world’s lakes remains uncertain despite the importance of lakes for drinking water supplies, recreation, and biodiversity. Here, I used 742 million bias-corrected chlorophyll-a (chl-a) estimates merged over 6 satellite sensors (daily, 1 to 4 km resolution) to map dead zones at the mouths of major inflowing rivers in more than 100 large lakes and asses their changes from 1997 to 2020. Dead zones were present in lakes across geographic and climatic gradients and were associated with a combination of urban and agricultural activities in lake watersheds. Dead zones expanded in some lakes even as water quality offshore improved. This spatiotemporal complexity demonstrates the value of moderate resolution mapping of lake dead zones to inform water management decision-making and to determine the local ecological consequences of human activity. 

How to cite: Kraemer, B.: Global drivers of lake dead zone formation at the mouths of major rivers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17387, https://doi.org/10.5194/egusphere-egu24-17387, 2024.

09:05–09:15
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EGU24-13918
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ECS
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On-site presentation
Jiayue Sun, Jianjun Zhou, and Man Zhang

The Yellow River Delta (YRD) in the Bohai Sea (BS) is one of the most rapidly expanding deltas worldwide, owing to a giant sediment load of 1.2 Bt/a in pre-damming years that emptied into a weak tidal semi-enclosed shallow sea, with 70% of the sediment deposited within the estuarine area. Since 1855, the delta has experienced a land accretion of 20 km2/a, and the channel extends seaward at a rate of 2~3 km/a. These morphological changes have raised the base level of the river, approaching 1 m for every 10 km of the channel elongation. It constitutes one of the two key factors for the peached lower Yellow River. Nevertheless, it is not clear about the impact on the tidal regime under the delta expansion in the BS. Consequently, the long-term sedimentation evolution of the YRD under various tidal dynamics is still not well understood. In this study, tidal responses to the delta evolution were investigated using a hydrodynamic model based on Delft 3D, covering the entire BS and parts of the adjacent Yellow Sea. The historical conditions were simulated with topographic survey data (circa 1855, 1962, 1981, 2003, and 2015), and the future scenarios over the next 200 years were predicted with sediment load data. The results indicate that the main tidal amplitude (M2 tide) has changed by -1.1~3.8 mm/a, which is larger than the mean sea-level rising rate of 2 mm/a, and the flow velocity has changed by -0.42~0.55 m/s. As the YRD protruded seaward, the flow velocity along the delta increased while the increasing rate decelerated over time, historically maintaining maximum flow velocities below 0.86~0.9 m/s. In future scenarios, it gradually increased to a peak of 1.2 m/s, followed by a 10% decrease. The estuarine sediment transport capacity, which is proportional to the cube of the flow velocity, would remain limited or even diminished by around 30%, exacerbating the sedimentation in the delta estuary. With accelerated sea-level rise and limited lifespan of sand control projects, it could be more challenging to sustain the safe development of the river and delta.

How to cite: Sun, J., Zhou, J., and Zhang, M.: Tidal responses in the semi-enclosed Bohai Sea to the delta intrusion of a high sediment-laden river, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13918, https://doi.org/10.5194/egusphere-egu24-13918, 2024.

09:15–09:25
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EGU24-2386
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On-site presentation
Pavel Kishcha, Yury Lechinsky, and Boris Starobinets

Climate model predictions have shown that Lake Kinneret could disappear by the end of the 21st century due to decreasing precipitation and increasing evaporation. Kinneret surface water temperature (SWT) is one of the main factors determining evaporation. During the last several decades, observations and model data showed increasing desert dust pollution over the Eastern Mediterranean. Generally, dust impact on lake SWT has not yet been discussed in previous publications.

    We investigated the impact of an extreme dust intrusion on the diurnal behaviour of SWT in Lake Kinneret, which appeared from September 7 – 9, 2015, when dust aerosol optical depth (AOD) ranged from 0.2 to 1.5. This was carried out using METEOSAT and in-situ observations of SWT. In the presence of dust, METEOSAT showed that SWT decreased along with increasing dust pollution, both in the daytime and nighttime. This contradicted in-situ measurements of SWT at a depth of 20 cm which showed an increase up to 1.2 °C in the daytime and up to 1 °C in the nighttime: this was in comparison to daytime and nighttime SWT on clear-sky Sept. 6. This in-situ SWT was in line with in-situ radiometer measurements of upwelling longwave radiation (ULWR) which is determined by actual SWT. This led us to the conclusion that, in the presence of dust, in-situ SWT measurements were capable of reproducing Kinneret SWT.

    In the daytime, an observed increase in air temperature (Tair) on dusty days Sept. 7 and 9 contributed to an increase in daytime Kinneret SWT. However, a decrease in daytime Tair on Sept. 8 (in the presence of maximal dust pollution) contributed to a decrease in daytime Kinneret SWT.

    As for the nighttime on dusty days Sept. 7–9, in-situ measurements showed that an increase in Tair up to 4.3 °C was accompanied by an increase in SWT up to 1 °C, compared to nighttime Tair and SWT on clear-sky Sept. 6. This was in line with ULWR measurements, which showed that nighttime ULWR on each dusty day under study was higher than nighttime ULWR on clear-sky Sept. 6. This is evidence that dust pollution reflects part of ULWR back to the surface of the lake, leading to a noticeable increase in nighttime SWT.

    During the dust intrusion, a noticeable increase in absolute atmospheric humidity (ρv) over the lake was observed: ρv reached 30%, 20%, and 15% in the presence of maximum, intermediate, and low dust pollution on Sept. 8, 9, and 7 respectively: this was in comparison to ρv on clear-sky Sept. 6. The maximal increase in ρv on Sept. 8 was observed in the absence of moisture advection: this indicates that dust intrusion can cause additional evaporation from Lake Kinneret. This finding implies the following significant point: increasing desert dust pollution over the Eastern Mediterranean can intensify the drying up of Lake Kinneret.

 

Reference: Kishcha et al., Remote Sensing 2023, https://doi.org/10.3390/rs15225297 

How to cite: Kishcha, P., Lechinsky, Y., and Starobinets, B.: Impact of a severe dust intrusion on surface water temperature in subtropical Lake Kinneret, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2386, https://doi.org/10.5194/egusphere-egu24-2386, 2024.

09:25–09:35
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EGU24-3661
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On-site presentation
Giles Wiggs, Natasha Wallum, Robert Bryant, and Richard Reynolds

Dust emissions from ephemeral playas are characterized by considerable spatiotemporal variability.  It has proven extremely difficult to resolve the complex dynamics between climatic conditions and surface crust characteristics that control aeolian dust emissivity.  In this study we used multitemporal satellite remote sensing and model reanalysis data to determine the climatic environments, surface sediment mineralogy, and hydrological context associated with the formation of ‘hot-spots’ of dust emission at Etosha Pan, Namibia. A twenty-year record (2000–2022) of dust source locations was established from MSG-SEVIRI and MODIS data, which enabled the identification of clusters of dust sources (‘hot-spots’). Using a time-series of Landsat 8-9 data we identified the surface mineralogical characteristics associated with the development of these ‘hot-spots’ of dust emission. These analyses were validated using reflectance spectroscopy and XRD analyses of sediment samples collected from the field. Linear spectral unmixing was applied to map the relative proportions of identified evaporite and clay mineral spectral endmembers from pixel spectra of Landsat image time-series. Results show that the development of emissive ‘hot-spot’ dust sources are associated with the formation of evaporite mineral crusts through the process of salt efflorescence initiated by wet season flooding events. Field experimentation using a portable wind tunnel combined with remote sensing analysis demonstrates that high winds in the dry season can break down this mineral crust exposing large quantities of fine and highly emissive sediments that are extremely susceptible to aeolian entrainment. Surface crust geochemistry, influenced by flooding history, therefore offers a first-order control on the development of ‘hot-spots’ of dust emission (Figure 1). The approach described here could be used at other ephemeral playas that are significant dust sources to elucidate hydrological and mineralogical controls on aeolian dust emission and to enhance regional-scale dust emissions modelling.

Figure 1. Landsat 8 OLI image time-series and linear spectral unmixing model outputs showing changes in crust mineralogy (abundance of saponite, montmorillonite, and thenardite) influenced by the flooding history of the surface and determining the location of emissive ‘hot-spots’ of dust emission (outlined) at Etosha Pan for the 2018 winter dust season (May to September).

 

How to cite: Wiggs, G., Wallum, N., Bryant, R., and Reynolds, R.: Surface geochemistry controls 'hot-spots' of dust emission at Etosha Pan, Namibia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3661, https://doi.org/10.5194/egusphere-egu24-3661, 2024.

09:35–09:45
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EGU24-14078
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On-site presentation
William Porter and Yaning Miao

Windblown dust has long been an air quality and public health concern among residents living around California’s Salton Sea, a region characterized by serious socioeconomic and health outcome disparities. Dropping water levels and unique biogeochemistry within the Salton Sea water itself have raised concerns regarding the human health impacts of drying sediments exposed on shrinking shorelines, as well as potential lake spray emissions from the water surface. As particles emitted from different surface types can differ greatly in terms of composition, size distribution, and other properties, variability in the resulting health impacts of particulates reaching communities in the region may likewise be source dependent. Here I will share analyses of surface-specific health outcomes associated with windblown coarse PM around the region, as well as attempts to better understand and mitigate the unique issues linked to these emissions across the basin. I will further explore similarities and differences connecting evaporating inland lakes and seas worldwide, as well as some of the opportunities for sharing knowledge and tools to address air quality changes in the increasingly dry, dusty future facing the Salton Sea basin and other analogous regions.

How to cite: Porter, W. and Miao, Y.: Tracking dust sources and human health impacts around California's shrinking Salton Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14078, https://doi.org/10.5194/egusphere-egu24-14078, 2024.

09:45–09:55
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EGU24-13820
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ECS
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On-site presentation
Caroline Hung, Charles Diamond, and Timothy Lyons

Desiccating arid lakes are a global problem in the face of dwindling water supplies through climate-induced droughts and intensified human activities, including damming, agriculture, and urban expansion. The deleterious consequences of declining water supplies are exacerbated by anthropogenic pollution, which increases rates of ecosystem collapse. The Salton Sea, California’s largest lake with a current maximum depth of only 10 meters, is suffering in these ways. Despite significant investments in the creation of wetlands and planning in-basin restructuring to combat salinity increases, the lake's primary purpose, as stated in the Water Quality Control Plan for the Colorado River Basin, remains drainage collection from irrigated cropland. This long-standing policy allowed unchecked inputs of nutrient-rich agricultural runoff for the last century. Because surface flow from tributaries and agricultural canals is the primary input to this terminal lake, extreme eutrophication results in ecosystem challenges made worse by declining lake level. For example, eutrophication via excessive nitrogen and phosphorus influx and evapoconcentration trigger algal blooms and concomitant suboxia/anoxia and sulfidic conditions in deeper waters. These conditions threaten aquatic life as well as human health through likely pathogen production.

Data spanning the past two decades reveal critical patterns of nutrient cycling and related consequences for basin chemistry and ecologies. Summer is marked by an overall decrease in total phosphate and nitrate concentrations due to increased primary production, which is sustained by the combination of enhanced release of phosphorus from sediments during summer anoxia and surface water inputs. Year-round N:P molar ratios in the water column exceed 50:1 to 100:1, deviating from the Redfield ratio of 16:1. However, phosphorus, which is persistently loaded through surface runoff and release from sediments, is never strongly depleted in the water column, challenging previous studies in the Salton Sea that suggest phosphorus limitation. Rapidly declining lake levels show significant changes in thermo- and chemo- stratification of the water column, including declines in dissolved oxygen and changing seasonal redox patterns. These trends suggest that the Salton Sea will become increasingly unsuitable for wildlife due to worsening water quality, which could undermine at least some habitat restoration efforts planned or already underway, such as those focused primarily on controlling salinity. As such, the more effective approach will require dramatic reduction in nutrient loading, necessitating the establishment and enforcement of Total Maximum Daily Loads (TMDLs) maintained via wetlands and/or treatment facilities at tributary mouths. Beyond regional concerns, the Salton Sea serves as an important example of the many interwoven threats to ecology, regional public health, and overall quality of life for those living in the basins of drying lakes. These are system experiencing complex chemical evolutions driven by direct human activities, such as agricultural runoff, and indirectly through anthropogenic climate change. The Salton Sea serves as an important case study for the importance of comprehensive integration of an atypically broad range of chemical, biological, and physical data and interpretations in policy decisions.

How to cite: Hung, C., Diamond, C., and Lyons, T.: Water quality decline in California’s drying Salton Sea: Relationships between nutrient pollution, water column redox, and regional ecosystem health , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13820, https://doi.org/10.5194/egusphere-egu24-13820, 2024.

09:55–10:05
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EGU24-16484
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Highlight
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On-site presentation
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Namdar Baghaei-Yazdi, Ali Mohseni, and Esmaeil Fallahi

This paper is a literature review of published papers on Lake Urmia. The authors have conducted a literature search on the status of this dying lake, causation of failure, and potential of recovery.

Lake Urmia (LU) is as the largest endorheic and hypersaline lake in Iran and one of the largest saltwater lakes in the world. Anthropogenic drought, along with natural resources mismanagement based on political ideology of Islamic Republic of Iran are the preeminent factors behind the disappearance of LU.

There is a growing interest in restoration of saline lakes around the world. Eco-conscious people around the world have been concern with drying lakes of the world. Likewise in Iran the number of concern scientists and Eco-conscious public has been increasing as well. The outcry for restoration of the drying lakes inundated the scientific communities for restoration of the drying lakes. The published data indicate that LU had the least recorded shrinkage between 1987 to 2000 with less than 2% of the lake surface water area. From 2000 to 2010 LU started shrinking with rapid pace to 28% of the surface area and from 2010 to 2014. The 2 chief contributing factors to the LU shrinkage are the construction of 30 operating dams and 16 more under construction by the IRI government and the second factor is licensing the drilling of 88000 water wells in and around the lake Urmia. After years of the public outcry, finally the Government sanctioned the restoration of LU in 2014. As a part of the restoration process, the researchers using the spatio-temporal technology to detect the land cover changes and salinization progress in Urmia Lake Basin (ULB) during  2014 to 2019. The available data indicates that the area of irrigated lands around the lake increased from 1265 km2 in 1975 to 5525 km2 in 2011, resulting in disappearing of the water surface area of UL from 5982 km2 in 1995 to 586 km2 in 2014 with increased salinization in the basin of LU.  

According to most of the published investigative studies to the cause and effect of the shrinkage of the LU, the natural drought and climate changes were not the main causes of the lake LU shrinkage. We believe, restoration of the lake Urmia demands a multidisciplinary approach through integration of marine biologists, ecologists, botanists, agricultural scientists, engineers, epidemiologists, chemists, geologists, management and governmental policies experts, under the supervision and inspection of the United Nations Environmental agencies.

How to cite: Baghaei-Yazdi, N., Mohseni, A., and Fallahi, E.: An overview of Lake Urmia: a dying lake in Iran, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16484, https://doi.org/10.5194/egusphere-egu24-16484, 2024.

10:05–10:15
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EGU24-4013
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On-site presentation
Stephan Schulz, Sahand Darehshouri, Tanja Schröder, Elmira Hassanzadeh, and Christoph Schüth

Lake Urmia, one of the largest hypersaline lakes on earth, known for its unique biodiversity, has experienced a profound and alarming decline in water levels over the last two decades, posing a huge threat to the lake's complex ecosystems. The causes of this decline are subject to controversy and vary between blaming mismanagement of water resources and attributing it to climate change. In order to find out the reasons for the drying up of Lake Urmia, we have conducted a series of studies to quantify the water balance components of Lake Urmia and analyze their temporal evolution and interaction over the last five decades. These studies encompass various methods, including the development of an improved bathymetric model using remote sensing data (Schröder et al., 2022), laboratory experiments to estimate the evaporation of the dried-up lake bed (Darehshouri et al., 2020, 2023) as well as setting up a water balance model, accompanied by a statistical analysis of lake inflow and meteorological variables (Schulz et al., 2020). Our results show that the fluctuations in the water levels of Lake Urmia during the study period are mainly related to weather conditions. Nevertheless, scenario simulations also revealed that agricultural water extraction, which has even exceeded the residual lake inflow in recent years, is also a decisive factor. The influence of irrigation water withdrawal on the volume of the lake can thus either strengthen the stability of the lake or accelerate its collapse. This differentiated understanding is essential for informed decision-making and sustainable management strategies to preserve or restore the ecological functioning of Lake Urmia.

Darehshouri, S., Michelsen, N., Schüth, C., and Schulz, S.: A low‐cost environmental chamber to simulate warm climatic conditions, Vadose Zone Journal, 19, https://doi.org/10.1002/vzj2.20023, 2020.

Darehshouri, S., Michelsen, N., Schüth, C., Tajrishy, M., and Schulz, S.: Evaporation from the dried-up lake bed of Lake Urmia, Iran, Science of The Total Environment, 858, 159960, https://doi.org/10.1016/j.scitotenv.2022.159960, 2023.

Schröder, T., Hassanzadeh, E., Darehshouri, S., Tajrishy, M., and Schulz, S.: Satellite based lake bed elevation model of Lake Urmia using time series of Landsat imagery, Journal of Great Lakes Research, 48, 1710–1717, https://doi.org/10.1016/j.jglr.2022.08.016, 2022.

Schulz, S., Darehshouri, S., Hassanzadeh, E., Tajrishy, M., and Schüth, C.: Climate change or irrigated agriculture – what drives the water level decline of Lake Urmia, Scientific Reports, 10, 236, https://doi.org/10.1038/s41598-019-57150-y, 2020.

How to cite: Schulz, S., Darehshouri, S., Schröder, T., Hassanzadeh, E., and Schüth, C.: Unraveling the hydrological dynamics of Lake Urmia: A comprehensive analysis of the impact of climatic changes and agricultural water extraction on lake level decline, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4013, https://doi.org/10.5194/egusphere-egu24-4013, 2024.

Coffee break
Chairpersons: Senlin Zhu, Yi Luo
10:45–10:55
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EGU24-5047
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On-site presentation
Nurgul Balci

Under threat from climate change Türkiye's alkaline lakes are alarming

Lakes district of Turkey, located in the southwest, host the majority of the Turkish lakes. These lakes (Acıgol, Yarisli, Burdur and Salda) are not only valuable for their unique water chemistry but also for their role in supporting biodiversity and serving as important habitats for various species, especially birds. The impact of climate change, alongside human activities like uncontrolled land use and agriculture, is visibly altering these crucial ecosystems. The decrease in annual precipitation in the Aegean and Mediterranean regions, coupled with overall global climate changes, is directly affecting the water levels of the lakes. The drying out of approximately 1.5 million hectares of Turkish wetlands over the last century highlights the severity of the situation. Preserving these lakes is crucial not only for their ecological significance but also for their potential analogs, like Lake Salda, which offer invaluable insights into understanding geological landscapes similar to those found on other planets, such as Mars. Addressing these challenges requires urgent action. Strategies to mitigate the impact of climate change and implementing sustainable land use practices, are essential. Additionally, regulate and manage anthropogenic activities (e.g., agriculture and land use) around the lakes can help alleviate the pressure on these fragile ecosystems. Conservation efforts, combined with public awareness and policy changes, can play a vital role in protecting these lakes and preventing further deterioration.

 

How to cite: Balci, N.: Under threat from climate change Türkiye's alkaline lakes are alarming, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5047, https://doi.org/10.5194/egusphere-egu24-5047, 2024.

10:55–11:05
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EGU24-21413
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On-site presentation
Gao Ang, Shiqiang Wu, Xiufeng Wu, Jiangyu Dai, and Fangfang Wang

Water environment pollution and water ecological degradation are the common problems in lake. As the dynamic basis of lake system, lake hydrodynamics has a decisive influence on lake water environment and water ecology. The numerical simulation is an important means to study the characteristics of lake hydrodynamics, water environment and water ecology. For numerical simulation of lakes driven by wind, the drag force of airflow on water is usually represented by wind drag coefficient ( Cd ). Cd reflects the momentum transfer efficiency between water and airflow, and is closely related to the characteristics of wind,waves,flow and their mutual feedback mode, and is the most critical parameter to determine whether the numerical simulation results are reasonable. However, the expression methods of wind drag coefficient widely used at present are mostly proposed based on the ocean. The characteristics of ocean wind, wave, flow and their mutual feedback mode are less affected by the blowing range and water depth. Cd is mainly restricted by wind speed ( u10 ) without considering the influence of the blowing range ( F ) and water depth( d ), which has poor adaptability in lakes.

In this study, theoretical analysis, wind tunnel experiment, in-situ monitoring and numerical simulation were used to propose a model of wind-water interaction in finite water area considering the wind-wave-flow mutual feedback model. Two dimensionless numbers, u10/(gF)0.5and u10F/νw, which can be used to describe the comprehensive strength of wind-wave and wind-flow interaction in finite water area were constructed. A new expression of wind stress coefficient considering wind speed, blow distance and water depth is proposed (expression (1) ), which improves the limitation of the traditional expression considering wind speed only, overcomes the limitation of its application in limited blow distance and water depth, and maintains the overall consistency with the existing expression. When the wind speed is greater than 5m/s, the wind stress coefficient is positively correlated with u10 and F, and negatively correlated with d,the sensitivity of the three factors to the Cd is 0.92, 0.22 and 0.14, respectively. The results of the three dimensional hydrodynamic mathematical model of Lake Tai show that the simulation results of the wind stress coefficient considering the influence of three factors are more consistent with the measured results.

How to cite: Ang, G., Wu, S., Wu, X., Dai, J., and Wang, F.: Fine characterization of wind drag force in shallow lakes based on the wind-wave-flow mutual feedback model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21413, https://doi.org/10.5194/egusphere-egu24-21413, 2024.

11:05–11:15
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EGU24-5495
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ECS
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On-site presentation
Xueqi Cao, Nan Wei, Zhongwang Wei, and Xingjie Lu

Lakes play an important role in the context of climate change response, necessitating accurate simulation of their thermal states to address associated challenges. Despite the progress in lake modeling, the description of several processes within current models require improvement. Traditional 1-D models often neglect the extinction effect of lake ice and oversimplify the extinction coefficient of lake water with a parameterized schemes. Moreover, the radiative transfer scheme adheres to the conventional Beer law. This study aims to enhance the radiative transfer process within the CoLM-Lake (The Common Land Model – Lake scheme). Implementation steps involve integrating observed water extinction coefficients for individual lakes, introducing the ice extinction coefficient, distinguishing radiation calculations between the visible light and infrared band, and replacing the traditional Beer law with a two-stream approximation scheme. The research analyzes simulation results regarding to freeze-thaw cycles, latent heat flux, sensible heat flux, lake surface temperature, and vertical temperature profiles. Results indicate that the simulated European lake surface temperatures driven by ERA5-LAND outperforms those for American lakes by CoLM-Lake. Incorporating observed water extinction coefficients, adding ice extinction, and employing the two-stream approximation scheme results in slight changes to the freeze-thaw date, but significant variations in ice thickness. For lakes with greater depths, the simulated latent and sensible heat flux exhibit substantial improvements, with more consistency with observed data. Validation of vertical temperature profiles for Nam Co (92m) and Sparkling (18m), two representative lakes, reveals that the original CoLM-Lake scheme overestimates/underestimates the upper lake temperature of Nam Co during summer/winter, and underestimates the winter upper temperature and summer lower temperature of Lake Sparkling. However, considering ice extinction and implementing the two-stream approximation mitigates these simulation errors. The study further incorporates ice dynamic processes into CoLM-Lake, distinguishes lake ice ages, and differentiates ice between blue and white ice, with subsequent evaluation. In conclusion, adopting the proposed scheme enhances the physical processes within CoLM-Lake, resulting in improved simulation performance.

How to cite: Cao, X., Wei, N., Wei, Z., and Lu, X.: Improvements of Radiative Transfer Processes in CoLM-Lake based on applications in in-situ lake simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5495, https://doi.org/10.5194/egusphere-egu24-5495, 2024.

11:15–11:25
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EGU24-8417
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On-site presentation
Omarjan Obulkasim, Shulei Zhang, and Yongjiu Dai

Lake thermal processes greatly impact the local climate and environment and are sensitive to climate change and human interference. The Yangtze River Basin has the highest lake density in China, boasting diverse natural and artificial water bodies; however, there is still a lack of comprehensive understanding and effective simulation approaches for the thermal processes of the various lakes in this area. This study, utilizing observed lake surface temperatures, thermal stratification data, and evaporation data from lakes in the region, provides key parameters for three one-dimensional lake models (namely, Simstrat, CoLM-Lake, and Flake) and comprehensively assesses their performance in the region. The findings indicate that all three models demonstrate robust accuracy in simulating shallow lakes (primarily natural lakes) but show substantial differences in performance when simulating deep lakes (mainly reservoir water bodies). Specifically, Simstrat excels in reproducing the thermal stratification of deep lake. It also demonstrates good performance in simulating lake surface temperature and evaporation, which is primarily attributed to the integration of Monin-Obukhov similarity theory into Simstrat. However, its ability to model temperature diffusion during the colder seasons requires further improvement. CoLM-Lake, while capable of simulating thermal stratifications, shows limitations in maintaining stability in deeper stratifications. Flake, on the other hand, encounters substantial challenges in accurately estimating turbulence effects in deeper lakes, particularly in autumn and winter. This study provides valuable insights for improving the simulation of lake thermal processes, particularly for deep artificial water bodies, which will enhance our understanding of lake thermal changes and their impacts in the Yangtze River Basin.

How to cite: Obulkasim, O., Zhang, S., and Dai, Y.: Understanding the performance of three 1-D lake models over Yangtze River Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8417, https://doi.org/10.5194/egusphere-egu24-8417, 2024.

11:25–11:35
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EGU24-10921
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ECS
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On-site presentation
Haoxin Deng, Martina Flörke, Kan Lei, and Qiuhong Tang

Many terminal lakes in Central Asia have witnessed concerning rates of shrinkage in recent decades. These lakes are particularly sensitive to both climate change and human water withdrawals. Although human water withdrawals are acknowledged as a major factor influencing long-term lake changes, previous studies often fail to distinguish the specific contributions of different sectors such as irrigation, livestock, industry, and domestic water usage. This knowledge gap is largely due to the absence of observed multi-sectoral water withdrawals. Recognizing the value of machine learning methods in predicting water withdrawals through complex, non-linear relationships between water uses and potential explanatory factors, we developed an innovative approach that integrates a hydrological model and a machine learning-based water use model. This methodology was applied to simulate the long-term changes in the area of Ebinur Lake, a large terminal lake in Central Asia. Water withdrawals estimated by Random Forest based on meteorological (temperature and precipitation) and socio-economic data (e.g., population, multi-sectoral GDP, per capita income, etc.) and allocated by irrigated area and population were extracted from the river route in the hydrological model which in turn affects the inflow into the lake. Finally, integrated model simulations were validated using remotely sensed lake areas and streamflow data from mountain hydrologic stations. Several experiments, including and excluding different sectoral water uses, were conducted to isolate factors influencing lake dynamics. The results indicated irrigation water withdrawal not only caused lake shrinkage, but also increased seasonal variability, thereby increasing the uncertainty of water supply to lake ecosystems. The proposed modelling approach provided a framework for quantifying the responses of terminal lake area changes to different sectoral water withdrawals in arid basins, especially in the absence of specific water withdrawal data.

How to cite: Deng, H., Flörke, M., Lei, K., and Tang, Q.: Estimating Multi-sectoral Water Withdrawals Through Machine Learning for Attribution in an Ungauged Terminal Lake Basin in Central Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10921, https://doi.org/10.5194/egusphere-egu24-10921, 2024.

11:35–11:45
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EGU24-2505
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ECS
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On-site presentation
Bo Gai, Jian Sun, Binliang Lin, Yuanyi Li, Chenxi Mi, and Tom Shatwell

Phytoplankton blooms in lakes and reservoirs are sensitive to hydrodynamics. Bulk metrics of hydrodynamics are often used to investigate bloom formation, but they may not adequately represent the synergistic hydrodynamic processes in large riverine reservoirs caused by dam operation. Here we examine how complex three-dimensional hydrodynamic processes trigger blooms in Xiangxi Bay, a typical tributary bay of the Three Gorges Reservoir, China, which has suffered phytoplankton blooms of different scales in recent years. We used a 3D ecological-hydrodynamic model, which integrated hydrodynamics with the abiotic factors that limit phytoplankton growth to simulate one whole year (2010). By implementing a scaling criterion, we quantified the contribution of local phytoplankton growth and hydrodynamic processes, including advection transport and vertical mixing, on bloom dynamics. Results indicated vertical mixing was the main process inhibiting blooms in colder months (from October to February) but horizontal advection, which flushed and diluted blooms, was dominant in warmer months (from May to July) when stratification was intense and nutrients were replete. Accordingly, blooms occurred when both vertical mixing and horizontal advection were low. We suggested a potential dam operation strategy to mitigate blooms during stratification, which involves withdrawing the warm surface water from upstream reservoirs to increase horizontal flows in the surface layer. Extending the critical turbulence model, our study shows that not only the rate of vertical mixing, but also horizontal advection controls blooms in highly dynamic riverine systems.

How to cite: Gai, B., Sun, J., Lin, B., Li, Y., Mi, C., and Shatwell, T.: Vertical mixing and horizontal transport determine bloom dynamics in a large riverine reservoir, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2505, https://doi.org/10.5194/egusphere-egu24-2505, 2024.

11:45–11:55
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EGU24-17634
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ECS
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On-site presentation
Hossein Amini, Hossein Masigol, Georgiy Kirillin, and Hans-Peter Grossart

Density stratification is a distinctive feature of lakes characterized by a less dense layer (epilimnion) on top of a denser water (hypolimnion) separated by a strong density jump (pycnocline) between them. While the main driver of thermal lake stratification is temperature, this phenomenon changes the vertical particles distribution, which in turn may affect lake stratification, when suspended particles (including both non-organic and organic ones) cause an overall increase in water column density. Sinking of particles to denser layers changes the sinking rates and may produce particle accumulation at the density interface (pycnocline) having important consequences for organic matter turnover. To investigate the interaction of the physical water properties and distribution of particles as a consequence of the stratification, we used in this study the particle tracking system UVP 6 (Under Vision Profiler) for particle characterization in a stratified Lake Stechlin, Berlin, Germany. The preliminary results, as expected, show that the particle abundance changes in concordance with temperature, which proves the dependency of particle characteristics (size and concentration) on the vertical temperature distribution.

How to cite: Amini, H., Masigol, H., Kirillin, G., and Grossart, H.-P.: Vertical characterization of particles in stratified lakes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17634, https://doi.org/10.5194/egusphere-egu24-17634, 2024.

11:55–12:05
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EGU24-3051
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On-site presentation
Roberto Grilli, Tonya DelSontro, Josette Garnier, Frederick Jacob, and Julien Némery

Inland waters are a significant source of atmospheric methane (CH4), a greenhouse gas (GHG) 34-85 times stronger than carbon dioxide (on 100 to 20-yr timescales) and responsible for ~23% of global radiative forcing. Of the GHGs produced by inland waters (i.e., carbon dioxide, CH4 and nitrous oxide), CH4 is responsible for ~75% of the climatic impact of aquatic GHG emissions with aquatic CH4 emissions comparable to the largest global CH4 emitters - wetlands and agriculture. Considering that aquatic systems contribute up to half of global CH4 emissions and that CH4 is predominantly formed in anoxic environments such as lake sediments, the source and quantification of ubiquitous surface CH4 observed in most aquatic systems are a question of global importance.

In this work we present the first deployment of a novel membrane inlet laser spectrometer (MILS) instrument, composed of a mid-infrared spectrometer for simultaneous detection of CH4, C2H6 and  d13CH4 coupled with a fast response (t90 < 30sec) membrane extraction system. During a 1-day field campaign, we performed a 2D mapping of dissolved CH4, C2H6 and d13CH4 of surface water of Lake Aiguebelette (France) highlighting the advantages of continuous high-resolution mapping of dissolved gases.

The results showed the presence of CH4 sources less enriched in 13C in the littoral zone (presumably the littoral anoxic sediments). The CH4 pool became more enriched in 13C with distance from shore, suggesting that oxidation processes prevailed over epilimnetic CH4 production. The data obtained were in line with recent multi-lake studies.

How to cite: Grilli, R., DelSontro, T., Garnier, J., Jacob, F., and Némery, J.: A novel high-resolution in situ tool for studying biogeochemical processes in aquatic systems: The Lake Aiguebelette case study, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3051, https://doi.org/10.5194/egusphere-egu24-3051, 2024.

12:05–12:15
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EGU24-14427
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ECS
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Virtual presentation
Amit Singh, Sanjeev Kumar Prajapati, and Attila Bai

In the past few decade’s urbanization, changing rainfall patterns, and inadequate precipitation are a few of the major reasons for dried urban lakes. Many such lakes are successfully revived using effluent from nearby sewage treatment plants. However, high nutrient loading and concentrated surface flow leads to problems like eutrophication followed by high greenhouse gas emissions (GHG). Majority of these lakes are shallow which has higher GHG emissions compared to the deeper lakes. India’s urban lakes are suffering from the similar fate. Study conducted in South Delhi, India reflects high phosphate and nitrate concentrations in the lake. Due to this, lakes are highly eutrophic and biomass concentration varies between 2 - 4.5 gL-1. Considering volume and biomass concentration, carbon dioxide sequestration comes out to be 1.2 Kg CO2/Kg of biomass. It was also seen that the average methane yield from microalgae is around 56%. It was found that total GHG potential was 5.856 Kg CO2-equivalent/ Kg of biomass which makes eutrophication a serious environmental issue. It is worth noting that microalgae in lakes decreases CO2, simultaneously increasing CH4 emissionswhich has 27-30 global warming potential (GWP) and relatively harmful for environment. In the past few decades studies reflected CH4 is responsible for 72 % of the climatic change (in CO2-equivalents) from lakes and inland waterbodies. The current study highlights the consequences of eutrophication in urban lakes with treated domestic discharge and suggests proper lake water quality management. Nevertheless, microalgae harvesting, and anaerobic digestion can be used to mitigate GHG and recover energy for a better and sustainable future.

How to cite: Singh, A., Kumar Prajapati, S., and Bai, A.: Potential of greenhouse gas emissions from urban lakes recharged with STP effluent, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14427, https://doi.org/10.5194/egusphere-egu24-14427, 2024.

12:15–12:25
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EGU24-14480
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ECS
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Virtual presentation
Ajayeta Rathi, Siddhartha Sarkar, Abdur Rahman, and Sanjeev Kumar

For over half a century, scientists have endeavoured to measure the rates of primary production (PP) and dinitrogen (N2) fixation in a diverse range of inland waters, spanning from freshwater to saline. There is nearly an equivalent portion of the saline as well as fresh in the world's inland waters, emphasizing their significance within our continental landscapes. Lakes play crucial role in global biogeochemical processes and are fundamental for essential ecosystem functions and services. Nonetheless, swift alterations in lakes have been recognized (i.e., salinization of freshwater ecosystems) on a global scale due to shifts in climate and increasing human interventions, posing risks to the valuable services these habitats offer. While considerable research on saline lakes has occurred in the past years across Africa, Australia, and North America, there remains a substantial amount to explore in Asian lakes and beyond, necessitating investigation into these unique ecosystems worldwide.

            The current study explores rates of PP and N2 fixation within a subtropical saline lake (Sambhar, India) along with its neighbouring brine reservoir and salt pans. Incubation experiments were performed to estimate the PP and N2 fixation rates using 13C and 15N tracer techniques. The study reveals that PP and N2 fixation rates were higher in the lake than the adjacent brine reservoir. Concentrations of particulate and dissolved forms of carbon and nitrogen were also higher in the lake than the brine reservoir. However, salt pans showed huge variation in PP, but N2 fixation rates were quite low. The highest concentration of particulate and dissolved forms of carbon and nitrogen were also found in the salt pans. The high uptake rates in the lake and salt pan may be attributed to high biomass and high nutrient concentrations than the brine reservoir. The difference in the rates is possibly due to variation in salinity, temperature, nutrient concentrations, and runoff to the lake, which can affect primary producers and potentially leading to shifts in community structure and biodiversity in different systems. This study provides insights into the complex interactions of PP and N2 fixation rates with environmental parameters in a subtropical saline environment.

How to cite: Rathi, A., Sarkar, S., Rahman, A., and Kumar, S.: Primary production and dinitrogen fixation in a subtropical inland saline environment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14480, https://doi.org/10.5194/egusphere-egu24-14480, 2024.

12:25–12:30

Posters on site: Wed, 17 Apr, 16:15–18:00 | Hall A

Display time: Wed, 17 Apr 14:00–Wed, 17 Apr 18:00
Chairpersons: Timothy W. Lyons, Senlin Zhu
A.120
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EGU24-8316
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ECS
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Ezgi Asirok, Georgiy Kirillin, Hans-Peter Grossart, and Tobias Goldhammer

Arctic and boreal lakes in the Northern Hemisphere experience annual ice cover lasting 4 to 7 months. Freshwater lakes in cold regions are sensitive to subtle environmental changes and influenced by various physical and biogeochemical factors. Our study focuses on comparative analysis of under-ice metabolism shaped by the thermal and oxygen dynamics of Arctic Lake Kilpisjarvi and Boreal Lake Paajarvi during the late winter. We aim to understand the effect of different trophic levels and light regimes on lake metabolism within cold regions by using high-frequency data on temperature, dissolved oxygen, and solar radiation for Lake Kilpisjarvi in 2019 and 2020, and Lake Paajarvi in 2022. Besides the long-term data, we compared the phytoplankton biomass and chemical parameters obtained from water samples collected from different depths. We studied the changes in the vertical distribution of lake metabolism by diel cycles by considering the strength and influence of internal motions on temperature and oxygen data.

Our results demonstrate that following prolonged darkness, a significant increase in dissolved oxygen occurs in the upper water column of Lake Kilpisjarvi. The depth of the mixed layer increases with depth, ranging from 1.1 m/day to 2.3 m/day for 2019 and 2020 in Kilpisjarvi. In contrast, Lake Paajarvi has a slower and steady rate of deepening at 0.55 m/day, resulting in a comparatively shallow mixed layer.



How to cite: Asirok, E., Kirillin, G., Grossart, H.-P., and Goldhammer, T.: Dissolved Oxygen Dynamics in Arctic and Boreal Lakes in Late Winter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8316, https://doi.org/10.5194/egusphere-egu24-8316, 2024.

A.121
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EGU24-403
Fatemeh Sadat Sharifi, Reinhard Hinkelmann, Tore Hattermann, and Georgiy Kirillin

The effects of freshwater river runoff on dynamics of ice-covered brackish lakes have not been adequately studied to date. Compared to freshwater lakes, the circulation patterns in brackish lakes are complicated by non-linear effects of temperature and salinity on density stratification and mixing, and as a result on the ice melt. Quantifying these effects is essential for understanding circulation of large endorheic lakes in cold regions and their ecological and physical characteristics. We present modeling results on circulation caused by river runoff in a typical ice-covered brackish lake obtained with the Regional Ocean Modeling System (ROMS). The lake water salinity was set to 14 practical salinity units (PSU). In the initial state, the water temperature increased linearly from the freezing point at the surface to the temperature of maximum density, at the bottom, both accounting for the water salinity. Mixing of cold freshwater river inflow with the warmer saline waters produces negative buoyancy and downslope flow of dense currents near the river inlets with a secondary geostrophically-balanced circulation throughout the lake. We use the modeling results to quantify the contribution of this circulation mechanism on deep lake circulation and ventilation of the near-bottom waters.

How to cite: Sharifi, F. S., Hinkelmann, R., Hattermann, T., and Kirillin, G.: The effects of salinity and river runoff on idealized brackish ice-covered lakes , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-403, https://doi.org/10.5194/egusphere-egu24-403, 2024.

A.122
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EGU24-16200
Georgiy Kirillin, Sergey Bogdanov, and Galina Zdorovennova

Convective turbulence driven by gravitational instability is a fundamental mixing mechanism in geophysical flows, but in situ estimation of its characteristics is obscured by the background flows and the relatively slow temporal scales. We present characteristics of the full Reynolds tensor from a convective surface boundary layer of an ice-covered lake. The results were obtained by using an original method of measuring the full set of turbulent stresses by a combined use of two ADCPs. The strong horizontal shear stress was revealed as a characteristic feature of free convection differing from the  "conventional"  turbulent boundary flows. The ratio of normal stresses along vertical and horizontal axes remained below 1/4, demonstrating anisotropic character of turbulence asymptotically approaching the axisymmetric two-component “pancake” form. The vertical r.m.s. velocity fluctuations obeyed the buoyancy flux scaling with the coefficient of 1/3, which is at the lower boundary of previously reported values, while horizontal fluctuations followed the same scaling with a unity coefficient

How to cite: Kirillin, G., Bogdanov, S., and Zdorovennova, G.: Kinetic energy and anisotropy of  convective turbulence under lake ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16200, https://doi.org/10.5194/egusphere-egu24-16200, 2024.

A.123
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EGU24-19062
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Highlight
Tom Shatwell, Daniel Graeber, Jantsje M. van Loon-Steensma, and Annette Janssen

Lakes are a global sink for nutrients and thus supply an important ecosystem service in the form of nutrient retention. However, it is unclear how the relative availability of nitrogen (N) and phosphorus (P) affects nutrient retention. To address this, we performed experiments with the lake model PCLakePlus on 9 lake archetypes that represent lakes of different mixing regimes (mono-, di-, and polymictic) in different climates. We forced the model with stochastically generated inflows and N and P loads to examine how the N:P ratio in inflow affects the N:P ratio in the lake outflow. In these model experiments, lakes tended to amplify imbalances between N and P in the inflow. At intermediate inflow N:P (~30), the outflow N:P was similar. However, at low inflow N:P, the outflow N:P was equal or lower, and at high inflow N:P, the outflow N:P was equal or higher. This amplification effect was most sensitive to high N input loads. This suggests that lakes either maintain or amplify N:P imbalances rather than buffering or compensating them. We explain these differences in nutrient retention with the lake phytoplankton and sedimentation dynamics. When input N:P is imbalanced, the phytoplankton biomass is generally limited by the nutrient in shortest supply, which limits the phytoplankton’s capacity to uptake the non-limiting nutrient. Consequently the nutrient in shortest supply is retained most efficiently, amplifying any stoichiometric imbalances. Since phytoplankton have a higher capacity to uptake and store excess P than excess N, high N:P ratios were amplified more than low N:P ratios. We further analysed a global dataset from the Global River Water Quality Archive and BasinATLAS, using boosted regression trees to identify the effect of different drivers and catchment characteristics on the molar TN:TP ratio in river and stream water. This showed that drivers and catchment characteristics associated with human impact increased N:P ratios, with a stronger effect at high N:P. The lake model subsequently showed that lakes further amplified this anthropogenic increase in N:P ratios, so that human induced stoichiometric imbalances from N pollution resonate through the landscape. These results shed light on the mechanisms behind the widespread phenomenon that lakes retain P preferentially over N. The successful management of P inputs into waterways has probably decreased N retention efficiency. Our research suggests that managers should reduce N inputs, for instance by employing nature-based solutions, to maintain a stoichiometric balance and protect sensitive downstream ecosystems and coastal zones. 

How to cite: Shatwell, T., Graeber, D., van Loon-Steensma, J. M., and Janssen, A.: Lakes amplify nitrogen and phosphorus imbalances in inflows, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19062, https://doi.org/10.5194/egusphere-egu24-19062, 2024.

A.124
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EGU24-10203
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ECS
Assessing Short-Term Variability in Seasonal Patterns: Analysis of Chlorophyll-a Dynamics and Environmental Interactions in Lake Müggelsee
(withdrawn)
Rokhya Bhano Kaligatla, Tallent Dadi, Jan Köhler, Kurt Friese, Karsten Rinke, and Hendrik Schubert
A.125
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EGU24-12193
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ECS
Leeza Pickering, Emma Hocking, Paul Mann, Leanne Wake, Saija Saarni, Timo Saarinen, and Maarten van Hardenbroek van Ammerstol

By 2100AD, it is predicted that approximately 16% of lakes worldwide will experience less frequent mixing and become permanently stratified (meromictic) as a result of climate change. Within the Arctic and subarctic, it is anticipated that increases in global air temperature will be magnified leading to strong feedback effects on the climate system, drastic changes in ecologically sensitive aquatic systems and increasing carbon emissions from lakes. Finland contains a dense network of lakes of differing mixing regimes, including meromictic lakes, enabling the opportunity to understand their response to warming temperatures. Hydroclimatic reconstructions have been undertaken, however they have not been focused on mixing regime changes and they have not been combined with modelling efforts to fully understand changes across past, present, and future timescales. Here, we present preliminary results from reconstructions of lake mixing regimes from sediment cores and initial modelling results from five lakes in the Evo National Park, southern Finland. We take a multi-proxy approach to reconstruct lake mixing regimes, including analysis of geochemistry (micro-XRF), chironomids, bacterial pigments, radiocarbon dating and varve counting. Ultimately understanding how lakes have responded to past changes in climate will enable baselines to be established against which to assess any future changes and will also enable models projecting future mixing regime changes to have appropriate boundary conditions set. The General Lake Model, forced with field data provided by Lammi Biological Research Station and from two fieldwork seasons in 2023, is used to understand contemporary and predict future mixing regimes. This research provides a full chronology of lake mixing regimes from the mid Holocene until 2100 linking climatic events with mixing regime changes through combining palaeoenvironmental reconstructions and modelling efforts.

How to cite: Pickering, L., Hocking, E., Mann, P., Wake, L., Saarni, S., Saarinen, T., and van Hardenbroek van Ammerstol, M.: Reconstructing and modelling lake mixing regimes in southern Finland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12193, https://doi.org/10.5194/egusphere-egu24-12193, 2024.

A.126
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EGU24-12409
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ECS
Mateusz Draga, Maciej Gąbka, Ewa Szczęśniak, Stanisław Rosadziński, Daniel Lisek, and Łukasz Bryl

Freshwater ecosystems are widely recognized as a significant global biodiversity hotspot. Unfortunately, they are also highly vulnerable to the expansion of invasive aquatic species, whose spread is considered among the top threats to these ecosystems. Especially problematic are alien aquatic plants species whose rapid growth often disrupts local communities and may even alter physicochemical conditions of a given freshwater ecosystem. Since most of invasive aquatic plants are native to tropical regions of the world, their occurrence in some Central and Eastern Europe countries was, until relatively recently limited by cold winters typical for this part of the continent. However, in the last two decades, we have observed a sharp increase in these species abundances in this part of Europe, which can be linked to the warmer winters resulting from the ongoing climate change. In our study, we examine the effects of temperature changes resulting from global warming on the development and occurrence of several aquatic alien plant species. Our analysis is based on our unique data base that contains extensive information about all currently known alien vascular aquatic plant species present in Poland as well as their precise location. This data is notable for being the first such database summarizing the current status of aquatic plant invasions for this country. Based on it, as well as temperature data from the last several years, we created generalized additive models (GAM) for temperature response for each of 15 aquatic alien plant species known for Poland. Our results show a strong relationship between rising temperatures and the spread of certain species, i.e. Azolla filiculoides. Furthermore, spread of such species as Elodea nuttallii and Lemna turionifera in Poland does not rely strongly on temperature. Presence of some species was found to be highly dependent on highly thermally altered or thermally contaminated waters, i.e. Vallisneria spiralis, Hygrophila polysperma, and  thus their occurrence is still limited only to such locations. Our results confirm the major role of elevated temperatures and thermal modification of waters in the distribution of alien aquatic plants.

How to cite: Draga, M., Gąbka, M., Szczęśniak, E., Rosadziński, S., Lisek, D., and Bryl, Ł.: New insights into alien aquatic plants ecology - response model to an elevated water temperatures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12409, https://doi.org/10.5194/egusphere-egu24-12409, 2024.

A.127
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EGU24-13897
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ECS
Yulu Li, Gang Zhao, and Qiuhong Tang

The sensitivity of lake surface water temperature (LSWT) to atmospheric warming has been well-established due to rapid sensible heat exchange. However, the specific impact of discrete heatwave events on LSWT dynamics, including their magnitude and persistence, remains poorly understood. To address this gap, we comprehensively analyze changes in LSWT during atmospheric heatwave events across a global network of 16,609 lakes. LSWT data are derived from Landsat 5, 7, 8, and 9 satellite imagery spanning 1985 to 2021, while heatwave intensity is quantified using hourly air temperature data from the ERA5-Land reanalysis. Our analysis identifies and characterizes heatwave events and their associated LSWT changes for each lake during the study period. Key findings reveal: (1) A widespread increase in both heatwave intensity and LSWT change across the majority of lakes, highlighting a concerning intensification of coupled air-water warming trends. (2) Significant spatial heterogeneity in LSWT sensitivity to heatwaves is observed. Notably, a pronounced memory effect is detected in LSWT response to heatwaves, suggesting a lingering influence of atmospheric heat events on lake energy balance, with implications for ecosystem stability and resilience.

How to cite: Li, Y., Zhao, G., and Tang, Q.: The thermal response of lake surface water temperature to atmospheric heatwave, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13897, https://doi.org/10.5194/egusphere-egu24-13897, 2024.

A.128
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EGU24-14564
Pengfei Xue, Xing Zhou, Mark Rowe, Peter Alsip, David Bunnell, Tomas Höök, Spencer Gardner, Edward Rutherford, and Paris Collingsworth

Physical factors such as water temperature, water column mixing, and light are crucial for the phytoplankton abundance and primary production in Lake Michigan. The potential impacts of climate change on these factors could significantly affect the dynamics of Lake Michigan's phytoplankton. In this study, we employed an integrated modeling framework to project the impact of climate change. This framework included a two-way coupled 3D lake-ice–climate system (GLARM), a hydrodynamic model (FVCOM), and a nutrient-phytoplankton-zooplankton-detritus (NPZD) model, further enhanced by a compartment representing the invasive quagga mussel (Dreissena rostriformis bugensis). Our approach encompassed historical simulations for the period 2005–2014, as well as two sets of future projections for the mid-21st century (2041–2049) and the late 21st century (2091–2099), utilizing the Representative Concentration Pathway (RCP) 8.5 scenario. Our findings indicate that changes in water temperature and water column mixing significantly influence the seasonal patterns of phytoplankton abundance and primary production. These changes notably alter the timing and magnitude of the winter-spring phytoplankton bloom and the depth of the chlorophyll layer. Furthermore, the model predicts an increase in primary production under the projected climate scenarios, with significant variations in both spatial and seasonal patterns.

How to cite: Xue, P., Zhou, X., Rowe, M., Alsip, P., Bunnell, D., Höök, T., Gardner, S., Rutherford, E., and Collingsworth, P.: Modeling Study of Phytoplankton Responses in Lake Michigan to a Changing Climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14564, https://doi.org/10.5194/egusphere-egu24-14564, 2024.

A.129
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EGU24-14682
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ECS
Gang Zhao, Huilin Gao, Yao Li, Qiuhong Tang, Iestyn Woolway, Julian Merder, Lorenzo Rosa, and Anna Michalak

The availability of surface water in global drylands is essential for local populations and ecosystems. However, the long-term changes in surface water storage and their underlying causes, particularly from anthropogenic activities, remain largely unknown. Here we utilized optical and altimetric remote sensing data to create monthly time series of storage changes between 1985 and 2020 for 105,400 lakes and reservoirs in global drylands. Our analysis reveals that surface water storage in global drylands has been increasing at a rate of 2.20 km3 per year, primarily due to the addition of new reservoirs. For lakes and older reservoirs constructed before 1983, their long-term storage changes are mainly attributed to anthropogenic activities, including human-induced warming and water management, rather than changes in precipitation. These observation-based findings highlight that anthropogenic activities have decoupled surface water storage from precipitation in global drylands, with significant implications for the sustainability of local society and ecosystems.

How to cite: Zhao, G., Gao, H., Li, Y., Tang, Q., Woolway, I., Merder, J., Rosa, L., and Michalak, A.: Human activity has decoupled surface water storage from precipitation in global drylands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14682, https://doi.org/10.5194/egusphere-egu24-14682, 2024.

A.130
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EGU24-742
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ECS
Hatice Kılıç Germeç and Hasan Yazıcıgil

Lakes are valuable natural indicators, providing insights into the impacts of natural and artificial interventions on the hydrologic system. In arid and semi-arid climates, the global interest in monitoring shrinking lakes is growing to quantitatively reveal the impacts of such interventions. The internationally important Burdur Lake (Ramsar site no. 658), located in the semi-arid Mediterranean region of Turkey, stands out as a noteworthy example, with its water levels decreasing by nearly 17 m since the early 1970s. This study aims to investigate the reasons for the continual decrease in Burdur Lake levels over time and to assess the future impacts of various factors on the lake system, utilizing a 3-D numerical groundwater flow model developed with MODFLOW. The modeling process includes three years of transient calibrations for both initial (1969-1971) and current conditions (2014-2016) by simulating the lake with an incorporated lake package. The successfully calibrated model was then simulated with the future climate change scenarios over a 46-year period. Future climatic data derived from the RCP 4.5 and RCP 8.5 scenarios of the CORDEX Regional Climate Models were incorporated into the simulations to assess the impacts of change in natural climatic conditions. The first scenario was created to assess the impacts of climate change on the lake, whereas the second scenario was simulated to investigate the effects of excessive groundwater pumping under the influence of climate change. The third scenario was generated to simulate the cumulative effects of climate change and the decrease in flows of the streams feeding the lake as a result of the reservoirs constructed. The results indicate that climate change was not the primary driver behind the drop in the lake levels until the end of 2018. However, it may exacerbate the situation in the future, amplifying the negative effects of anthropogenic activities by imposing stress on the lake. An anticipated decline of up to 7 m in Burdur Lake level is projected due to the cumulative effects of climatic variations and excessive pumping. Conversely, despite the influence of climate change, an increase of up to 3 m is expected with the release of surface water flows. These findings underscore the need for a dynamic lake management plan to maintain desired conditions in Burdur Lake and its watershed, ensuring the sustainable management of this vital surface water resource.

How to cite: Kılıç Germeç, H. and Yazıcıgil, H.: Impact of human and natural causes on shrinking Burdur Lake in the semi-arid Mediterranean region of Turkiye, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-742, https://doi.org/10.5194/egusphere-egu24-742, 2024.

A.131
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EGU24-15850
Çağdaş Sağır, Emin Atabey Peker, Koray Kamil Yılmaz, and Mehmet Lütfi Süzen

The impacts of global climate change extend to population dynamics, food security, agricultural activities, and water demand, thus presenting complex and urgent challenges associated particularly with the water resources. Türkiye's Lakes Region is situated in the Mediterranean region, which is recognized as a climate change hotspot and further stressed by ever-increasing water demand arising from rapid population growth. Due to the convergence of these factors, the lakes in the Lakes Region face significant challenges with the phenomenon of shrinking lakes.

This study examines the spatio-temporal changes in lake waters in Türkiye's Lakes Region, consisting of sixteen lakes. Using Landsat 5, 8, 9, and Sentinel-2 satellite images, the surface area changes were analyzed via NDWI in the Google Earth Engine environment from April 1984 to April 2023. To assess hydrological/hydrogeological conditions accurately, water volume calculations were performed in lakes having in-situ bathymetry and water level measurements. We analyzed MODIS Terra Land Cover dataset and climatic variables such as precipitation, and evaporation-transpiration to understand the degree of anthropogenic and climatic drivers effecting the study lakes.

Our results indicated that, for large lakes such as Burdur, Beyşehir and Eğirdir, the period of influence of climatic parameters is close to two years. The effect period varies based on lake bathymetry, size, and hydrodynamic characteristics of the recharge basin. Lake water losses were primarily attributed to climatic factors, with clear links to climatic parameters until 2016. After 2016, a shift of precipitation to the summer season significantly impacted the hydrological system, intensifying the shrinking in the lakes. We conclude that the dominant driver for the shrinking lakes is the climatic effects and the anthropogenic effects for the whole-time interval has been found negligible. Of the lakes considered in this study, only Lake Akşehir should be excluded from this assessment. Lake Akşehir was found to be the only lake where human impact was clearly predominant.

How to cite: Sağır, Ç., Peker, E. A., Yılmaz, K. K., and Süzen, M. L.: Spatiotemporal Changes in Lake Water Extents in the Lakes Region (Türkiye) and the Role of Climateand Land Cover Parameters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15850, https://doi.org/10.5194/egusphere-egu24-15850, 2024.

A.132
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EGU24-22100
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ECS
Charles Diamond, Caroline Hung, and Timothy Lyons

The Salton Sea is California’s largest lake, covering almost 330 square miles of low-lying, inland desert in the Imperial and Eastern Coachella Valleys. Despite the enormous surface area of the lake, it has a maximum depth of only 10.5 meters (an aspect ratio almost identical to that of a sheet of A4 paper), and the region is subject to extreme heat in the summer. Functioning more like an industrial evaporation table, the lake would be very small if not for agricultural and municipal wastewater. Combined, these sources represent the overwhelming majority of annual inflows, with agricultural return flow making the largest contribution by far. This has remained the case for over a century, leading to a host of devastating and predictable consequences—all exacerbated by the fact that the Salton Sea is a closed basin.

Over the past hundred years, the salinity of the Salton Sea has risen steadily, while the lake level has experienced significant fluctuations, both up and down. Due to the extremely low angle of the lakebed, small changes in water level lead to dramatic shifts in the location of the shoreline. Over the past five years, for example, tens of thousands of acres of lakebed have been exposed due to water transfer agreements between local water authorities that have reduced inflow. In addition to the ecological devastation that has occurred as the lake has become saltier, the recent exposure of vast areas of lakebed has created an ongoing public health crisis linked to dust emission.

Hypereutrophication has been a persistent feature of the lake over time, as the primary source of inflow is unchecked agricultural runoff. Coupled with intense thermal stratification in the summer, high rates of algal and bacterial production in the upper meters drive respiration and anoxia below, leading to efficient recycling of nutrients and a host of consequences for the cycling of sulfur, iron, and redox-sensitive trace metals. Sulfate levels in the Salton Sea are very high (~300 mM), and the water column regularly becomes sulfidic. Most of the iron that enters the basin is sequestered into sediments as iron-oxides within the river deltas. The small amount of iron that makes it beyond quickly precipitates as iron-sulfides, leaving sediments throughout the vast interior of the lake very low in iron. Concentrations of redox-sensitive trace metals within sediments vary spatially and with depth in ways that reflect the redox stratification and overall geometry of the lake, the distribution of iron, and the history of accumulation and sequestration that has ocurred over time within a closed basin. This study explores these relationships through the integration of geochemical data from sediment cores and water samples from multiple transects within the basin, as well as major tributaries, building toward a comprehensive model of trace-metal cycling within the lake prior to and since the influence of agriculture and industry in the region began. 

How to cite: Diamond, C., Hung, C., and Lyons, T.: Eutrophication and Trace Metal Cycling in the Salton Sea: A Century of Industrial Impact, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22100, https://doi.org/10.5194/egusphere-egu24-22100, 2024.

A.133
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EGU24-19117
Javier Herrero, Antonio Collados-Lara, Matilde García-Valdecasas, Antonio Sánchez-Membrives, Cintia Ramón, María Jesús Esteban-Parra, David Pulido-Velázquez, and Francisco Rueda

Temperature plays a critical role in the functioning of inland aquatic ecosystems. The metabolic rates of aquatic organisms, their productivity, and, more broadly, the rates of biogeochemical processes are largely determined by water temperature. Hence, understanding the processes that govern temperature in water bodies in response to external factors across daily to multi-year scales is essential. This is particularly urgent in alpine semi-arid basins with substantial human impact and strong influence of snow dynamics, and, especially within the context of global change, where 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 simulation algorithms are tested in the small alpine watershed of the River Genil, upstream of the city of Granada, which includes two water-supply reservoirs (Canales and Quéntar). Urban water demand largely determines withdrawal rates from these reservoirs, thus affecting the thermal dynamics in the water column and downstream reaches. Autonomous temperature sensors have been deployed at different sites and programmed to record hourly data. The model is forced with climate databases (reanalysis, regional climate simulation, and measured data sets) and used in hindcast/forecast exercises to assess the impact of climate change on the thermal regime of inland waters.

How to cite: Herrero, J., Collados-Lara, A., García-Valdecasas, M., Sánchez-Membrives, A., Ramón, C., Esteban-Parra, M. J., Pulido-Velázquez, D., and Rueda, F.: Assessing Impacts of Climate Change on surface water temperatures in semi-arid alpine basins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19117, https://doi.org/10.5194/egusphere-egu24-19117, 2024.