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authors => protected'Bärenbold, F.; Kipfer, R.; Schmid, M.' (53 chars)
title => protected'Dynamic modelling provides new insights into development and maintenance of Lake Kivu's density stratification' (110 chars)
journal => protected'Environmental Modelling and Software' (36 chars)
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startpage => protected'105251 (15 pp.)' (15 chars)
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categories => protected'Lake Kivu; Simstrat-AED2; 1d modelling; gas accumulation; hydrothermal groun dwater' (82 chars)
description => protected'Lake Kivu is a 485 m deep, Central-East African rift lake with huge amounts of carbon dioxide and methane dissolved in its stably stratified deep waters . In view of future large-scale methane extraction, one-dimensional numerica l modelling is an important and computationally inexpensive tool to analyze the evolution of stratification and the content of gases in Lake Kivu. For t his purpose, we coupled the physical lake model Simstrat to the biogeochemic al library AED2. Compared to an earlier modelling approach, this coupled app roach offers several key improvements, most importantly the dynamic evaluati on of mixing processes over the whole water column, including a parameteriza tion for double-diffusive transport, and the density-dependent stratificatio n of groundwater inflows. The coupled model successfully reproduces today's near steady-state of Lake Kivu, and we demonstrate that a complete mixing ev ent ∼2000 years ago is compatible with today's physical and biogeochemical state.' (995 chars)
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authors => protected'Calamita, E.; Vanzo, D.; Wehrli, B.; Schmid, M.' (67 chars)
title => protected'Lake modeling reveals management opportunities for improving water quality d ownstream of transboundary tropical dams' (116 chars)
journal => protected'Water Resources Research' (24 chars)
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description => protected'Water quality in tropical rivers is changing rapidly. The ongoing boom of da m construction for hydropower is one of the drivers for this change. In part icular, the stratification in tropical reservoirs induces oxygen deficits in their deep waters and warmer surface water temperatures, which often transl ate into altered thermal and oxygen regimes of downstream river systems, wit h cascading consequences for the entire aquatic ecosystem. Operation rules o f reservoirs, involving water intakes at different levels, could mitigate th e consequences for downstream water quality. However, optimized water manage ment of deep reservoirs relies on predictive models for water quality, but s uch predictive capability is often lacking for tropical dams. Here we focus on the Zambezi River Basin (southern Africa) to address this gap. Using the one-dimensional General Lake Model, we reproduced the internal dynamics of t he transboundary Lake Kariba, the world’s largest artificial lake by volum e, created by damming the Zambezi River at the border between Zambia and Zim babwe. Through this modeling approach, we assessed and quantified the therma l and oxygen alteration in the Zambezi River downstream of the reservoir. Re sults suggest that these alterations depend directly on Kariba’s stratific ation dynamics, its water level and the transboundary policies for water wit hdrawal from the reservoir. Scenario calculations indicate a large potential for mitigating downstream water quality alterations by implementing a hypot hetical selective withdrawal technology. However, we show that a different a nd cooperative management of the existing infrastructure of Kariba Dam has t he potential to mitigate most of the actual water quality alterations.' (1742 chars)
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authors => protected'Kobler, U. G.; Wüest, A.; Schmid, M.' (57 chars)
title => protected'Effects of lake – reservoir pumped-storage operations on temperature and w ater quality' (88 chars)
journal => protected'Sustainability' (14 chars)
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startpage => protected'1968 (15 pp.)' (13 chars)
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categories => protected'hydropower; stratification; reservoir modeling; recommissioning' (63 chars)
description => protected'Pumped-storage (PS) hydropower plants are expected to make an important cont ribution to energy storage in the next decades with growing market shares of new renewable electricity. PS operations affect the water quality of the co nnected water bodies by exchanging water between them but also by deep water withdrawal from the upper water body. Here, we assess the importance of the se two processes in the context of recommissioning a PS hydropower plant by simulating different scenarios with the numerical hydrodynamic and water qua lity model CE-QUAL-W2. For extended PS operations, the results show signific ant impacts of the water exchange between the two water bodies on the season al dynamics of temperatures, stratification, nutrients, and ice cover, espec ially in the smaller upper reservoir. Deep water withdrawal was shown to str ongly decrease the strength of summer stratification in the upper reservoir, shortening its duration by ~1.5 months, consequently improving oxygen avail ability, and reducing the accumulation of nutrients in the hypolimnion. Thes e findings highlight the importance of assessing the effects of different op tions for water withdrawal depths in the design of PS hydropower plants, as well as the relevance of defining a reference state when a PS facility is to be recommissioned.' (1311 chars)
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doi => protected'10.3390/su10061968' (18 chars)
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authors => protected'Schmid, M.; Ostrovsky, I.; McGinnis, D. F.' (62 chars)
title => protected'Role of gas ebullition in the methane budget of a deep subtropical lake: Wha t can we learn from process-based modeling?' (119 chars)
journal => protected'Limnology and Oceanography' (26 chars)
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startpage => protected'2674' (4 chars)
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description => protected'We analyzed the processes affecting the methane (CH<sub>4</sub>) budget in L ake Kinneret, a deep subtropical lake, using a suite of three models: (1) a bubble model to determine the fate of CH<sub>4</sub> bubbles released from t he sediment; (2) the one-dimensional physical lake model Simstrat to calcula te the mixing dynamics; and (3) a biogeochemical model implemented in Aquasi m to quantify the CH<sub>4</sub> sources and sinks. The key pathways modeled include diffusive and bubble release of CH<sub>4</sub> from the sediment, a erobic CH<sub>4</sub> oxidation, and atmospheric gas exchange. The temporal and spatial dynamics of dissolved CH<sub>4</sub> concentrations observed in the lake during 3 years could be well represented by the combined models. Re markably, the relative contributions of ebullition and diffusive transport t o the accumulation of CH<sub>4</sub> in the hypolimnion during the stratifie d period could not be accurately constrained based only on the observed evol ution of CH<sub>4</sub> concentrations in the water column. Importantly, how ever, our analysis showed that most (∼99%) of the CH<sub>4</sub> supplied to the water column by bubble dissolution and diffusive transport from the s ediment is aerobically oxidized, whereas a substantial fraction (∼60%) of the sediment-released bubble CH<sub>4</sub> is directly transported to the a tmosphere. Ebullition is thus responsible for the bulk of the emissions from Lake Kinneret to the atmosphere. Therefore, as in all freshwaters, ebulliti on quantification is crucial for accurately assessing CH<sub>4</sub> emissio ns to the atmosphere. This task remains challenging due to high spatio-tempo ral variability, but combining in situ measurements with a process-based mod eling can help to better constrain flux estimates.' (1798 chars)
serialnumber => protected'0024-3590' (9 chars)
doi => protected'10.1002/lno.10598' (17 chars)
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Dynamic modelling provides new insights into development and maintenance of Lake Kivu's density stratification
Lake Kivu is a 485 m deep, Central-East African rift lake with huge amounts of carbon dioxide and methane dissolved in its stably stratified deep waters. In view of future large-scale methane extraction, one-dimensional numerical modelling is an important and computationally inexpensive tool to analyze the evolution of stratification and the content of gases in Lake Kivu. For this purpose, we coupled the physical lake model Simstrat to the biogeochemical library AED2. Compared to an earlier modelling approach, this coupled approach offers several key improvements, most importantly the dynamic evaluation of mixing processes over the whole water column, including a parameterization for double-diffusive transport, and the density-dependent stratification of groundwater inflows. The coupled model successfully reproduces today's near steady-state of Lake Kivu, and we demonstrate that a complete mixing event ∼2000 years ago is compatible with today's physical and biogeochemical state.
Bärenbold, F.; Kipfer, R.; Schmid, M. (2022) Dynamic modelling provides new insights into development and maintenance of Lake Kivu's density stratification, Environmental Modelling and Software, 147, 105251 (15 pp.), doi:10.1016/j.envsoft.2021.105251, Institutional Repository
Lake modeling reveals management opportunities for improving water quality downstream of transboundary tropical dams
Water quality in tropical rivers is changing rapidly. The ongoing boom of dam construction for hydropower is one of the drivers for this change. In particular, the stratification in tropical reservoirs induces oxygen deficits in their deep waters and warmer surface water temperatures, which often translate into altered thermal and oxygen regimes of downstream river systems, with cascading consequences for the entire aquatic ecosystem. Operation rules of reservoirs, involving water intakes at different levels, could mitigate the consequences for downstream water quality. However, optimized water management of deep reservoirs relies on predictive models for water quality, but such predictive capability is often lacking for tropical dams. Here we focus on the Zambezi River Basin (southern Africa) to address this gap. Using the one-dimensional General Lake Model, we reproduced the internal dynamics of the transboundary Lake Kariba, the world’s largest artificial lake by volume, created by damming the Zambezi River at the border between Zambia and Zimbabwe. Through this modeling approach, we assessed and quantified the thermal and oxygen alteration in the Zambezi River downstream of the reservoir. Results suggest that these alterations depend directly on Kariba’s stratification dynamics, its water level and the transboundary policies for water withdrawal from the reservoir. Scenario calculations indicate a large potential for mitigating downstream water quality alterations by implementing a hypothetical selective withdrawal technology. However, we show that a different and cooperative management of the existing infrastructure of Kariba Dam has the potential to mitigate most of the actual water quality alterations.
Calamita, E.; Vanzo, D.; Wehrli, B.; Schmid, M. (2021) Lake modeling reveals management opportunities for improving water quality downstream of transboundary tropical dams, Water Resources Research, 57(4), e2020WR027465 (20 pp.), doi:10.1029/2020WR027465, Institutional Repository
Effects of lake – reservoir pumped-storage operations on temperature and water quality
Pumped-storage (PS) hydropower plants are expected to make an important contribution to energy storage in the next decades with growing market shares of new renewable electricity. PS operations affect the water quality of the connected water bodies by exchanging water between them but also by deep water withdrawal from the upper water body. Here, we assess the importance of these two processes in the context of recommissioning a PS hydropower plant by simulating different scenarios with the numerical hydrodynamic and water quality model CE-QUAL-W2. For extended PS operations, the results show significant impacts of the water exchange between the two water bodies on the seasonal dynamics of temperatures, stratification, nutrients, and ice cover, especially in the smaller upper reservoir. Deep water withdrawal was shown to strongly decrease the strength of summer stratification in the upper reservoir, shortening its duration by ~1.5 months, consequently improving oxygen availability, and reducing the accumulation of nutrients in the hypolimnion. These findings highlight the importance of assessing the effects of different options for water withdrawal depths in the design of PS hydropower plants, as well as the relevance of defining a reference state when a PS facility is to be recommissioned.
Kobler, U. G.; Wüest, A.; Schmid, M. (2018) Effects of lake – reservoir pumped-storage operations on temperature and water quality, Sustainability, 10(6), 1968 (15 pp.), doi:10.3390/su10061968, Institutional Repository
Role of gas ebullition in the methane budget of a deep subtropical lake: What can we learn from process-based modeling?
We analyzed the processes affecting the methane (CH4) budget in Lake Kinneret, a deep subtropical lake, using a suite of three models: (1) a bubble model to determine the fate of CH4 bubbles released from the sediment; (2) the one-dimensional physical lake model Simstrat to calculate the mixing dynamics; and (3) a biogeochemical model implemented in Aquasim to quantify the CH4 sources and sinks. The key pathways modeled include diffusive and bubble release of CH4 from the sediment, aerobic CH4 oxidation, and atmospheric gas exchange. The temporal and spatial dynamics of dissolved CH4 concentrations observed in the lake during 3 years could be well represented by the combined models. Remarkably, the relative contributions of ebullition and diffusive transport to the accumulation of CH4 in the hypolimnion during the stratified period could not be accurately constrained based only on the observed evolution of CH4 concentrations in the water column. Importantly, however, our analysis showed that most (∼99%) of the CH4 supplied to the water column by bubble dissolution and diffusive transport from the sediment is aerobically oxidized, whereas a substantial fraction (∼60%) of the sediment-released bubble CH4 is directly transported to the atmosphere. Ebullition is thus responsible for the bulk of the emissions from Lake Kinneret to the atmosphere. Therefore, as in all freshwaters, ebullition quantification is crucial for accurately assessing CH4 emissions to the atmosphere. This task remains challenging due to high spatio-temporal variability, but combining in situ measurements with a process-based modeling can help to better constrain flux estimates.
Schmid, M.; Ostrovsky, I.; McGinnis, D. F. (2017) Role of gas ebullition in the methane budget of a deep subtropical lake: What can we learn from process-based modeling?, Limnology and Oceanography, 62(6), 2674-2698, doi:10.1002/lno.10598, Institutional Repository
