The thermal strati?cation of the lakes impedes the transfer of atmospheric oxygen into the lower layers of the lake. In lakes which are af fected by diverse anthropogenic in?uences, the increasing organic matter amoun...The thermal strati?cation of the lakes impedes the transfer of atmospheric oxygen into the lower layers of the lake. In lakes which are af fected by diverse anthropogenic in?uences, the increasing organic matter amounts lead to a sharp decrease in hypolimnetic oxygen amounts, aided by thermal strati?cation,and anaerobic conditions arise. The determination of hypolimnetic oxygen demand(HOD) and areal hypolimnetic oxygen demand(AHOD) and their monitoring represent an integrated approach to investigate the oxygenation of lakes, the nutrient conditions, and the physicochemical dynamics. In this study, two lakes dif fering by size and af fected by dif ferent anthropogenic sources, are investigated in this respect. At?rst, bathymetric studies were conducted to determine the depth, surface area, and volume relationships.Then, based on monitoring studies conducted in 2013 and 2014, the thermal strati?cation dynamics and layer properties were established using the relative thermal resistance to mixing(RTRM) index based on temperature and density pro?les. Following this, the oxygen depletion rates were determined by oxygen and temperature pro?ling in the hypolimnion. For the years of 2013 and 2014, the AHOD values for the Borabey Pond which is far from anthropogenic in?uences, were found to be 0.848 and 0.569 g O 2/(m·d), respectively.The AHOD values for the Porsuk Reservoir which was overburdened for years by industrial and domestic pollution were found to be 4.263 and 5.099 g O 2/(m·d), larger than its counterpart by almost sevenfold. The HOD and AHOD monitoring can be considered to a valuable tool for assessing the ecological and chemical status of lakes within Annex 5 of the Water Framework Directive and as an integrated approach to assess and monitor the status of lakes.展开更多
Water-level reduction frequently occurs in deep reservoirs,but its effect on dissolved oxygen concentration is not well understood.In this study we used a well-established water qual-itymodel to illustrate effects of ...Water-level reduction frequently occurs in deep reservoirs,but its effect on dissolved oxygen concentration is not well understood.In this study we used a well-established water qual-itymodel to illustrate effects of water level dynamics on oxygen concentration in Rappbode Reservoir,Germany.We then systematically elucidated the potential of selectivewithdrawal to control hypoxia under changing water levels.Our results documented a gradual decrease of hypolimnetic oxygen concentration under decreasing water level,and hypoxia occurred when the initial level was lower than 410 m a.s.l(71 m relative to the reservoir bottom).We also suggested that changes of hypoxic region,under increasing hypolimnetic withdrawal discharge,followed a unimodal trajectory with themaximum hypoxic area projected under the discharge between 3 m^(3)/sec and 4 m^(3)/sec.Besides,our results illustrated the extent of hypoxia was most effectively inhibited if the withdrawal strategy was applied at the end of stratification with the outlet elevation at the deepest part of the reservoir.Moreover,hy-poxia can be totally avoided under a hybrid elevation withdrawal strategy using surface withdrawal during early and mid stratification,and deep withdrawal at the end of strat-ification.We further confirmed the decisive role of thermal structure in the formation of hypoxia under water-level reduction and withdrawal strategies.We believe the conclusions from this study can be applied to many deep waters in the temperate zone,and the results should guide stakeholders to mitigate negative impacts of hypoxia on aquatic ecosystems.展开更多
Eutrophication is one of the primary factors causing harmful cyanobacteria blooms in freshwater lakes.This study investigated the long-term changes in water quality and summer phytoplankton assemblages in Oswego Lake,...Eutrophication is one of the primary factors causing harmful cyanobacteria blooms in freshwater lakes.This study investigated the long-term changes in water quality and summer phytoplankton assemblages in Oswego Lake,OR,USA,in relation to phosphorus reduction through hypolimnetic aeration and alum applications.Both water quality and phytoplankton assemblages were sampled biweekly during the summers from 2001 to 2013.The concentrations of total phosphorus,soluble reactive phosphorus,and total nitrogen decreased 66%,93%and 31%,respectively,in response to the hypolimnetic aeration and alum treatments since 2005.Summer phytoplankton assemblages showed a 62%reduction of cyanobacteria biovolume and a shift from cyanobacteria dominance(2001–2005)to diatom and chlorophyte dominance(2006–2013).Cluster analysis identified four statistically different groups of summer phytoplankton assemblages(denoted Groups 1–4).Nonmetric multidimensional scaling analysis indicated that the four groups were associated with different water quality conditions.Group 1 occurred prior to hypolimnetic aeration and was primarily comprised of cyanobacteria,associated with water conditions of high nutrients and high primary production.Group 2,dominated by cyanobacteria and chlorophytes,occurred between hypolimnetic aeration and alum surface application.Group 3 was dominated by diatoms and occurred after alum surface application.Group 4 included R-strategist phytoplankton that quickly respond to environmental changes and occurred in the years following alum injection,drawdown,and inflow alum treatment.Both Group 3 and 4 were associated with reduced nutrients in the lake.We conclude that these lake management practices had strong effects on both production and community compositions of phytoplankton,and advocate for future studies on large-scale climate impacts on lake ecosystems and to identify corresponding best management practices.展开更多
基金Supported by the Anadolu University Scientific Research Project(No.1208F129)(Project Coordinator:S.GONCü)
文摘The thermal strati?cation of the lakes impedes the transfer of atmospheric oxygen into the lower layers of the lake. In lakes which are af fected by diverse anthropogenic in?uences, the increasing organic matter amounts lead to a sharp decrease in hypolimnetic oxygen amounts, aided by thermal strati?cation,and anaerobic conditions arise. The determination of hypolimnetic oxygen demand(HOD) and areal hypolimnetic oxygen demand(AHOD) and their monitoring represent an integrated approach to investigate the oxygenation of lakes, the nutrient conditions, and the physicochemical dynamics. In this study, two lakes dif fering by size and af fected by dif ferent anthropogenic sources, are investigated in this respect. At?rst, bathymetric studies were conducted to determine the depth, surface area, and volume relationships.Then, based on monitoring studies conducted in 2013 and 2014, the thermal strati?cation dynamics and layer properties were established using the relative thermal resistance to mixing(RTRM) index based on temperature and density pro?les. Following this, the oxygen depletion rates were determined by oxygen and temperature pro?ling in the hypolimnion. For the years of 2013 and 2014, the AHOD values for the Borabey Pond which is far from anthropogenic in?uences, were found to be 0.848 and 0.569 g O 2/(m·d), respectively.The AHOD values for the Porsuk Reservoir which was overburdened for years by industrial and domestic pollution were found to be 4.263 and 5.099 g O 2/(m·d), larger than its counterpart by almost sevenfold. The HOD and AHOD monitoring can be considered to a valuable tool for assessing the ecological and chemical status of lakes within Annex 5 of the Water Framework Directive and as an integrated approach to assess and monitor the status of lakes.
基金supported by the German Research Founda-tion(DFG,grant RI 2040/4-1)the InventWater ITN(Inventive forecasting tools for adapting water quality management to a new climate)through the European Union’s Horizon 2020 research,innovation program under the Marie Skłodowska-Curie grant agreement No.956623 and UFZ Program Integra-tion Budget+3 种基金Chenxi Mi acknowledges the financial support from the National Natural Science Foundation of China(No.42107060)Liaoning Provincial Doctoral Research Startup Fund Project(No.2022-BS-174)supported by the“Xingliao Talents Plan”science and technology in-novation leading talents project of Liaoning Province(No.XLYC2002054)the National Key Research and Develop-ment Program of China(NO.2022YFF1301000-4).
文摘Water-level reduction frequently occurs in deep reservoirs,but its effect on dissolved oxygen concentration is not well understood.In this study we used a well-established water qual-itymodel to illustrate effects of water level dynamics on oxygen concentration in Rappbode Reservoir,Germany.We then systematically elucidated the potential of selectivewithdrawal to control hypoxia under changing water levels.Our results documented a gradual decrease of hypolimnetic oxygen concentration under decreasing water level,and hypoxia occurred when the initial level was lower than 410 m a.s.l(71 m relative to the reservoir bottom).We also suggested that changes of hypoxic region,under increasing hypolimnetic withdrawal discharge,followed a unimodal trajectory with themaximum hypoxic area projected under the discharge between 3 m^(3)/sec and 4 m^(3)/sec.Besides,our results illustrated the extent of hypoxia was most effectively inhibited if the withdrawal strategy was applied at the end of stratification with the outlet elevation at the deepest part of the reservoir.Moreover,hy-poxia can be totally avoided under a hybrid elevation withdrawal strategy using surface withdrawal during early and mid stratification,and deep withdrawal at the end of strat-ification.We further confirmed the decisive role of thermal structure in the formation of hypoxia under water-level reduction and withdrawal strategies.We believe the conclusions from this study can be applied to many deep waters in the temperate zone,and the results should guide stakeholders to mitigate negative impacts of hypoxia on aquatic ecosystems.
文摘Eutrophication is one of the primary factors causing harmful cyanobacteria blooms in freshwater lakes.This study investigated the long-term changes in water quality and summer phytoplankton assemblages in Oswego Lake,OR,USA,in relation to phosphorus reduction through hypolimnetic aeration and alum applications.Both water quality and phytoplankton assemblages were sampled biweekly during the summers from 2001 to 2013.The concentrations of total phosphorus,soluble reactive phosphorus,and total nitrogen decreased 66%,93%and 31%,respectively,in response to the hypolimnetic aeration and alum treatments since 2005.Summer phytoplankton assemblages showed a 62%reduction of cyanobacteria biovolume and a shift from cyanobacteria dominance(2001–2005)to diatom and chlorophyte dominance(2006–2013).Cluster analysis identified four statistically different groups of summer phytoplankton assemblages(denoted Groups 1–4).Nonmetric multidimensional scaling analysis indicated that the four groups were associated with different water quality conditions.Group 1 occurred prior to hypolimnetic aeration and was primarily comprised of cyanobacteria,associated with water conditions of high nutrients and high primary production.Group 2,dominated by cyanobacteria and chlorophytes,occurred between hypolimnetic aeration and alum surface application.Group 3 was dominated by diatoms and occurred after alum surface application.Group 4 included R-strategist phytoplankton that quickly respond to environmental changes and occurred in the years following alum injection,drawdown,and inflow alum treatment.Both Group 3 and 4 were associated with reduced nutrients in the lake.We conclude that these lake management practices had strong effects on both production and community compositions of phytoplankton,and advocate for future studies on large-scale climate impacts on lake ecosystems and to identify corresponding best management practices.
