Lake Response Research Articles

An Isotope Mass Balance Analysis of Evaporative Loss From Lake Turkana, Kenya Using δ18O and δD of Natural Waters

AbstractMeasurements of oxygen and hydrogen stable isotope ratios (δ18O and δD) in meteoric waters provide insight to overlapping effects of evaporation, precipitation, and mixing on basin scale hydrology. This study of waters collected between 2016 and 2021 in the Turkana Basin, northern Kenya, uses δ18O and δD to understand water balance in Lake Turkana, a large, low‐latitude, alkaline desert lake. The Omo River, a major river system in the Ethiopian Highlands, is historically understood to provide approximately 90% of the water input to Lake Turkana. Discharge of the Omo is prohibitively difficult to measure, but stable isotope ratios in the lake may provide a meaningful method for monitoring the lake's response to changes in input. Precipitation in the Turkana Basin is low (<200 mm/year) with negligible rainfall on the lake's surface, and all water loss from the lake is evaporative. We compare new measurements with previous data from the region and records of lake height and precipitation from the same time period. We show that a Bayesian approach to modeling evaporation using atmospheric conditions and river δ18O and δD yields results consistent with published water balance models. Continued sampling of lake and meteoric waters in the Turkana Basin will be a useful way to monitor the lake's response to regional and global climate change.

Diazotrophic community in the sediments of Poyang Lake in response to water level fluctuations.

Water level fluctuations (WLFs) are typical characteristic of floodplain lakes and dominant forces regulating the structure and function of lacustrine ecosystems. The sediment diazotrophs play important roles in contributing bioavailable nitrogen to the aquatic environment. However, the relationship between the diazotrophic community and WLFs in floodplain lakes is unknown. In this paper, we carried out a comprehensive investigation on the alpha diversity, abundance, composition and co-occurrence network of the sediment diazotrophs during different water level phases in Poyang Lake. There were no regular variation patterns in the alpha diversity and abundance of the sediment diazotrophs with the water level phase transitions. The relative abundance of some diazotrophic phyla (including Alphaproteobacteria, Deltaproteobacteri, Euryarchaeota, and Firmicutes) and genera (including Geobacter, Deferrisoma, Desulfuromonas, Rivicola, Paraburkholderia, Methylophilus, Methanothrix, Methanobacterium, and Clostridium) was found to change with the water level phase transitions. The results of ANOSIM, PerMANOVA, and DCA at the OTU level showed that the diazotrophic community structure in the low water level phase was significantly different from that in the two high water level phases, while there was no significant difference between the two high water level phases. These results indicated that the diazotrophic community was affected by the declining water level in terms of the composition, while the rising water level contributed to the recoveries of the diazotrophic community. The diazotrophs co-occurrence network was disrupted by the declining water level, but it was strengthened by the rising water level. Moreover, redundancy analysis showed that the variation of the diazotrophic community composition was mostly related to sediment total nitrogen (TN) and total phosphorous (TP). Interestingly, the levels of sediment TN and TP were also found to vary with the water level phase transitions. Therefore, it might be speculated that the WLFs may influence the sediment TN and TP, and in turn influence the diazotrophic community composition. These data can contribute to broadening our understanding of the ecological impacts of WLFs and the nitrogen fixation process in floodplain lakes.

Increasing fish biodiversity in high elevation Albertan lakes in response to global environmental change over the past 50 years

IntroductionThe diversity of freshwater fishes is threatened by multiple environmental stressors, including climate change, alterations in land use, and introduction of non-native species. However, the quantification of temporal biodiversity in freshwater communities is limited. Here, we asked: i) how has alpha (species richness), beta (changes in freshwater species composition), and gamma diversity (total species diversity in a landscape) changed over time for lakes over a 50 year period?; and ii) What are the climatic, land use, and lake morphological drivers associated with higher diversity?MethodsWe assembled a database of fish species occurrence from 20 lakes across subalpine and alpine regions in Alberta from 1970-2019, in addition to lake morphological, climatic, and land use characteristics of the watersheds. ResultsWe observed an overall increase in alpha, beta, and gamma diversity from the 1970s to 2009s. However, all measures of diversity declined from 2010-2019. We found that more lakes and species assemblages were influenced by species gains, rather than species losses (with the exception of the last decade of sampling). DiscussionGenerally, we found that coolwater species were expanding and coldwater fishes were being lost throughout our study lakes. We highlight temporal heterogeneity in fish biodiversity responses to substantial environmental pressures in this region.

Holocene process-based hydroclimate evolution coupled with human behaviours in Dian Lake basin, Southwest China

Lakes are considered excellent archives for the reconstruction of sedimentary processes and related hydroclimatic variations. Dian Lake in south-western China was selected to demonstrate the impacts of Indian summer monsoon-induced water and sediment availabilities on land surface changes and human behaviours. A new sediment core from Dian Lake in the vicinity of Hebosuo village was analyzed by grain size composition, geochemical content, and minerals to detect land-lake processes that responded to hydroclimatic variations and human impacts through the Holocene. Our data suggest that Dian Lake levels during the last 9.8 cal. ka BP were controlled by the variations of the Indian summer monsoon moisture supply according to the displacements of the Intertropical Convergence Zone. A low lake level stage of ∼ 4 m lower than present was determined between 3.1 and 1.73 cal. ka BP, allowing the residents of the Dian culture to occupy the low terrains for settlement and farmland cultivation. With lake level rise at around 1.73 cal. ka BP (220 CE) the high input of clay-fine silt-sized sediments rich in rubidium and barium indicates intensified soil erosion in the Dian Lake basin. Former paddy farmlands and mountain slopes were drained by artificial and natural channels towards the lake in response to strengthened rainfalls covering low terrains by coarse and red alluvial sediments that fostered the residents to abandon the lowlands in the southern basin until 1368 CE. However, the surface erosion process during this period promoted the elevation of the south-eastern delta so that it could be re-occupied since Ming Dynasty. The Indian summer monsoon influence comparable to the modern pattern was responsible for lake level rise to the present level since then but also triggered high seasonality in flood and drought events to foster manual regulation of flood discharge during the last centuries.

Exploring potential glacial lakes using geo-spatial techniques in Eastern Hindu Kush Region, Pakistan

The study aimed to investigate the potential glacial lakes in response to climate change and the associated risk of glacial lake outburst floods (GLOFs). Remote sensing data and GIS techniques were utilized to analyze glacial lakes, employing empirical models to estimate their area, volume, and depth. The Normalized Difference Water Index (NDWI) was applied to detect changes in glacial lakes using Sentinel imagery. The findings revealed a notable increase in both the number and surface area of glacial lakes over the past two decades. Specifically, the number of glacial lakes rose from 101 in 2000 to 162 in 2020, while their combined surface area expanded from 9.72 km2 to 12.36 km2 during the same period. Among these lakes, 31 were identified as Potentially Dangerous Glacial Lakes (PDGLs), with 6 located in Chitral, 16 in Swat, and 9 in Upper Dir. Two lakes were classified as high potential glacial lakes, with depths estimated at 41.86 ​m and 30.43 ​m. Continued monitoring of these glacial lakes and their susceptibility to GLOFs is crucial in the face of ongoing climate change. Long-term planning and adaptation strategies are necessary to safeguard the well-being and safety of communities residing in these vulnerable regions. By understanding the evolving characteristics of these lakes, researchers and policymakers can better prepare for and mitigate the impacts of GLOFs on downstream communities and infrastructure.

Taxonomic diversity and functional potential of microbial communities in salt lakes Gudzhirganskoe and Nukhe-Nur (Barguzin depression, Baikal Rift Zone)

On the territory of the Barguzin depression (Baikal Rift Zone) there are salt lakes, which are unique natural formations formed in exceptional natural conditions and experiencing extreme shifts in seasonal environmental conditions. This paper presents the results of the study of the microbial communities in the sulfate Lake Gudzhirganskoe and the soda Lake Nukhe-Nur in winter and summer seasons: from the assessment of the taxonomic composition to potential metabolic pathways. For the first time, based on the 16S rRNA gene sequencing data, the diversity of the microbial community of bottom sediments in summer and winter was studied. Environmental conditions such as pH, temperature and mineralization mainly determined the microbial community composition and led to noticeable shifts in the composition of the community at the level of families and genera. The change of the "summer" obligate and moderately alkalphilic and halophilic community to the "winter" alkali-, halotolerant/halophilic microbial community is observed in the winter period in Lake Gudzhirganskoe. In Lake Nukhe-Nur, a change from mesophilic-thermophilic community in summer to mesophilic-psychrophilic microbial community in winter was revealed. The totality of the obtained results gives an idea about the main trends in the seasonal dynamics of extremophilic microbial communities in the studied lakes in response to fluctuations in environmental parameters. The prediction of the metabolic pathways of prokaryotic communities using the Tax4Fun program made it possible to reveal similarities and differences in the metabolic potential of the microbial communities of the studied lakes. Potential functional genes have been found for all stages of the C, N and S cycles, with the exception of nitrification and aerobic CH4 oxidation.Only small qualitative and quantitative variations in the relative abundance of predicted functional genes were found between the microbial communities of the studied lakes. We predicted metabolic pathways that play an important role in the adaptation of microorganisms to changing environmental conditions. In general, it has been shown that there is a change in the dominant taxa at the level of families and genera in the microbial community in the summer and winter seasons, however, the predicted functional potential of microbial communities differed slightly by season and between the studied lakes.

Changes in habitat conditions in a Late Glacial fluviogenic lake in response to climatic fluctuations (Warta River valley, central Poland)

The Warta River valley was greatly influenced by the ice sheet of the Last Glacial Maximum (LGM). A small peatland located in the Warta drainage system is here used as a palaeoarchive of climatic and habitat changes during the Late Glacial (Weichselian). The Ługi sediment profile was investigated using multi-proxy (pollen, Chironomidae, Cladocera and geochemistry) analyses that recorded changes in a fluviogenic sedimentary depression. After the Poznań Phase (LGM), Ługi functioned as an oxbow lake that was cut off from the active river channel as a result of fluvial erosion. Since that time, the Warta River has flowed only along the section now occupied by the Jeziorsko Reservoir. Sedimentation of lacustrine deposits started at the beginning of the Late Glacial. Summer temperature reconstructions indicate cool Oldest and Younger Dryas, but no clear cooling in the Older Dryas. During the Younger Dryas the palaeolake was completely occupied by a peatland (fen), which periodically dried out during the Holocene. Investigation of this site has tracked the reaction of the habitat to climatic, hydrological and geomorphological changes throughout the Late Weichselian.

Detection of surface water temperature variations of Mongolian lakes benefiting from the spatially and temporally gap-filled MODIS data

• We applied an effective spatiotemporal gap-filled method to improve the LSWT from MODIS. • The long-term variations of the annual and seasonal mean LSWTs of Mongolian lakes were provided. • The LSWT of Mongolian lakes confirmed the phenomenon “global warming hiatus”. Lakes provide critical water resources for human activities and ecosystems, particularly in the Mongolian Plateau (MP), which is characterized by a dry climate and a harsh environment. As a region that is sensitive to anthropogenic warming, tracking lake surface water temperature (LSWT) changes in Mongolian lakes is crucial for understanding the consequences of a warming climate on lake ecosystems. However, the long-term monitoring of LSWT is restricted by the spatiotemporal gaps in the raw imagery of remote sensing-based land surface temperature (LST), e.g., the commonly used Moderate Resolution Imaging Spectroradiometer (MODIS) LST products. This study applied an improved gap-filling method by utilizing the discrete cosine transform-based penalized least squares (DCT-PLS) strategy in the spatial domain combined with the linear interpolation (LI) algorithm in the temporal domain. The method was applied to fill gaps in the LSWT imagery of 12 representative lakes across MP. The randomly sampled high-quality MODIS LSWT values in the spatial and temporal domains were excavated as false data gaps and considered “virtual true” validation datasets. The spatial validation results showed that the estimated LSWT for all the lake cases were comparable with the “virtual true” LSWT values, with the average values of the coefficient of determination, mean absolute error, mean square error, and root mean square error being 0.98, 0.38 °C, 0.45 °C, and 0.59 °C, respectively. Meanwhile, the error of nighttime LSWT results was relatively lower than that of daytime LSWT. For temporal interpolation validation, the LI algorithm exhibited relatively better performance and could more objectively indicate the variation in LSWT. Benefiting from the spatially and temporally well-constrained data, we analyzed the interannual and intra-annual change characteristics of the LSWTs of the 12 lakes. The long-term variations of annual and seasonal mean LSWTs in the 12 selected lakes exhibited no evident trends in 2000–2020, while presented apparent interannual fluctuations. The slight changes in the average LSWTs of the 12 selected lakes were in excellent synchronization with the surrounding LST derived from the reanalysis datasets, confirming the widely reported phenomenon of “global warming hiatus” that occurred in the early 21st century. This study improves the understanding of the LSWT variations in Mongolian lakes in response to global climate change. It has the potential to provide an effective approach for monitoring LSWT changes in other large-scale studies.

Physiological and Genetic Regulation for High Lipid Accumulation by Chlorella sorokiniana Strains from Different Environments of an Arctic Glacier, Desert, and Temperate Lake under Nitrogen Deprivation Conditions.

ABSTRACTMicroalgae can adapt to extreme environments with specialized metabolic mechanisms. Here, we report comparative physiological and genetic regulation analyses of Chlorella sorokiniana from different environmental regions of an arctic glacier, desert, and temperate native lake in response to N deprivation, for screening the optimal strain with high lipid accumulation. Strains from the three regions showed different growth and biochemical compositions under N deprivation. The arctic glacier and desert strains produced higher soluble sugar content than strains from the native lake. The arctic glacier strains produced the highest levels of lipid content and neutral lipids under N deprivation compared with strains from desert and native lake. At a molecular level, the arctic strain produced more differentially expressed genes related to fatty acid biosynthesis, glycolysis gluconeogenesis, and glycerolipid metabolism. The important functional genes acetyl coenzyme A (acetyl-CoA) carboxylase (ACCase), fatty acid synthase complex, pyruvate dehydrogenase component, and fatty acyl-acyl carrier protein (acyl-ACP) thioesterase were highly expressed in arctic strains. More acetyl-CoA was produced from glycolysis gluconeogenesis and glycerolipid metabolism, which then produced more fatty acid with the catalytic function of ACCase and acyl-ACP thioesterase in fatty acid biosynthesis. Our results indicated that the C. sorokiniana strains from the arctic region had the fullest potential for biodiesel production due to special genetic regulation related to fatty acid synthesis, glycolysis gluconeogenesis, and glycerolipid metabolism.IMPORTANCE It is important to reveal the physiological and genetic regulation mechanisms of microalgae for screening potential strains with high lipid production. Our results showed that Chlorella sorokiniana strains from arctic glacier, desert, and temperate native lake had different growth, biochemical composition, and genetic expression under N deprivation. The strains from an arctic glacier produced the highest lipid content (including neutral lipid), which was related to the genetic regulation of fatty acid biosynthesis, glycolysis gluconeogenesis, and glycerolipid metabolism. The functional genes for acetyl-CoA carboxylase, fatty acid synthase complex, pyruvate dehydrogenase component, and fatty acyl-ACP thioesterase in the three pathways were highly expressed in arctic strains. The revelation of physiological and genetic regulation of strains from different environmental regions will contribute to the microalgae selection for high lipid accumulation.

Characterization of Long-Time Series Variation of Glacial Lakes in Southwestern Tibet: A Case Study in the Nyalam County

Glacial lakes are important freshwater resources in southern Tibet. However, glacial lake outburst floods have significantly jeopardized the safety of local residents. To better understand the changes in glacial lakes in response to climate change, it is necessary to conduct a long-term evaluation on the areal dynamics of glacial lakes, assisted with local observations. Here, we propose an innovative method of classification and stacking extraction to accurately delineate glacial lakes in southwestern Tibet from 1990 to 2020. Based on Landsat images and meteorological data, we used geographic detectors to detect correlation factors. Multiple regression models were used to analyze the driving factors of the changes in glacier lake area. We combined bathymetric data of the glacial lakes with the changes in climatic variables and utilized HEC-RAS to determine critical circumstances for glacial lake outbursts. The results show that the area of glacial lakes in Nyalam County increased from 27.95 km2 in 1990 to 52.85 km2 in 2020, and eight more glacial lakes were observed in the study area. The glacial lake area expanded by 89.09%, where we found significant growth from 2015 to 2020. The correlation analysis between the glacial lake area and climate change throughout the period shows that temperature and precipitation dominate the expansion of these lakes from 1990 to 2020. We also discover that the progressive increase in water volume of glacial lakes can be attributed to the constant rise in temperature and freeze–thaw of surrounding glaciers. Finally, the critical conditions for the glacial lake’s outburst were predicted by using HEC-RAS combined with the changes in the water volume and climatic factors. It is concluded that GangxiCo endures a maximum water flow of 4.3 × 108 m3, and the glacial lake is in a stable changing stage. This conclusion is consistent with the field investigation and can inform the prediction of glacial lake outbursts in southwestern Tibet in the future.

Environmental Changes and Geomorphological Factors Influencing the Sediment Flux to a Coastal Lake Spanning the Deglacial- Early Holocene Period in East Antarctica

Abstract The geomorphological settings of the lakes in the coastal oases of East Antarctica play a significant role in the lake's response to the local and regional environment. A 63-cm radiocarbon-dated sediment core spanning between 18.7 and 7.2 cal ka BP was retrieved from Discussion Lake, Larsemann Hills of East Antarctica in order to understand the pathways of sediment transport and deposition and the mechanisms involved in response to changing environmental settings. This was achieved by analyzing the sedimentary sequence of this coastal lake for its grain size (sand-silt-clay) and organic matter content variations. Two cluster zones were identified viz., LZ1 (18.7 to 8.2 cal ka BP) and LZ2 (8.2 to 7.7 cal ka BP). LZ1 was dominated by fine-grained sediments (clay-silt), indicating wind and low meltwater influx influenced deposition of higher silt content. In addition, the lake during this period was in a moated or partially ice-free phases. On the other hand, coarser grains (sand) were predominant in LZ2 suggesting increased flux of the meltwater to the ice-free lake. Thus, the distinct shift in the sedimentary grains fractions (finer-to-coarser), indicated a change in environmental conditions of the lacustrine system, i.e., from an ice-covered lake to an ice-free lake in response to the regional warming trends and local geomorphological features. Furthermore, the environmental conditions, proximity of the lakes to coast or the ice-sheet, elevation and area, defines the sedimentological characteristics of the lake.

Prediction of Future Lake Water Availability Using SWAT and Support Vector Regression (SVR)

Lakes are major surface water resource in semi-arid regions, providing water for agriculture and domestic use. Prediction of future water availability in lakes of semi-arid regions is important as they are highly sensitive to climate variability. This study is to examine the water level fluctuations in Pakhal Lake, Telangana, India using a combination of a process-based hydrological model and machine learning technique under climate change scenarios. Pakhal is an artificial lake built to meet the irrigation requirements of the region. Predictions of lake level can help with effective planning and management of water resources. In this study, an integrated approach is adopted to predict future water level fluctuations in Pakhal Lake in response to potential climate change. This study makes use of the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) dataset which contains 21 Global Climate Models (GCMs) at a resolution of 0.25 × 0.25° is used for the study. The Reliability Ensemble Averaging (REA) method is applied to the 21 models to create an ensemble model. The hydrological model outputs from Soil and Water Assessment Tool (SWAT) are used to develop the machine-learning based Support Vector Regression (ν-SVR) model for predicting future water levels in Pakhal Lake. The scores of the three metrics, correlation coefficient (R2), RMSE and MEA are 0.79, 0.018 m, and 0.13 m, respectively for the training period. The values for the validation periods are 0.72, 0.6, and 0.25 m, indicating that the model captures the observed lake water level trends satisfactorily. The SWAT simulation results showed a decrease in surface runoff in the Representative Concentration Pathways (RCP) 4.5 scenario and an increase in the RCP 8.5 scenario. Further, the results from ν-SVR model for the future time period indicate a decrease in future lake levels during crop growth seasons. This study aids in planning of necessary water management options for Pakhal Lake under climate change scenarios. With limited observed datasets, this study can be easily extended to the other lake systems.

Lake microbiome and trophy fluctuations of the ancient hemp rettery

Lake sediments not only store the long-term ecological information including pollen and microfossils but are also a source of sedimentary DNA (sedDNA). Here, by the combination of traditional multi-proxy paleolimnological methods with the whole-metagenome shotgun-sequencing of sedDNA we were able to paint a comprehensive picture of the fluctuations in trophy and bacterial diversity and metabolism of a small temperate lake in response to hemp retting, across the past 2000 years. Hemp retting (HR), a key step in hemp fibre production, was historically carried out in freshwater reservoirs and had a negative impact on the lake ecosystems. In Lake Slone, we identified two HR events, during the late stage of the Roman and Early Medieval periods and correlated these to the increased trophy and imbalanced lake microbiome. The metagenomic analyses showed a higher abundance of Chloroflexi, Planctomycetes and Bacteroidetes and a functional shift towards anaerobic metabolism, including degradation of complex biopolymers such as pectin and cellulose, during HR episodes. The lake eutrophication during HR was linked to the allochthonous, rather than autochthonous carbon supply—hemp straws. We also showed that the identification of HR based on the palynological analysis of hemp pollen may be inconclusive and we suggest the employment of the fibre count analysis as an additional and independent proxy.

Rapid response of the nearshore round goby population to temperature declines associated with upwelling events in Lake Ontario

Upwellings occur in all the Great Lakes in response to prolonged wind events. Several studies have modeled or measured changes in abiotic conditions associated with upwellings, but few direct observations of fish responses have been documented. Video-capture techniques were used in conjunction with moored temperature loggers to link the disappearance of benthic round gobies to temperature declines during upwelling events along the southern Lake Ontario nearshore in summer of 2019. Benthic water temperatures declined by as much as 18 °C within 18 h over as many as nine events. Round goby density estimates were as high as 50/m2 prior to upwellings, but declined to as low as 0/m2 during the events. Using just nine observation dates, ARMA trend analysis suggested a relationship between benthic temperature and round goby abundance (AIC = 78.7, t = 2.21, P = 0.063). Although the actual response of gobies to rapidly declining temperatures was unknown, this population was unobservable in our sample area during upwellings, yet returned to pre-upwelling densities within days. Understanding the magnitude and frequency of fish responses to these events can improve our understanding of the potential for this non-native benthic fish to affect the nearshore environment.

Hydrochemical characteristics and water quality variations in the main area of Lake Baiyangdian under extreme precipitation

极端降水是影响水环境质量的重要气象因素之一，随着全球气候变暖，极端降水事件的频率和量级呈显著上升的趋势，对湖泊水化学和水环境产生了深刻的影响.白洋淀是华北地区重要的湖泊型湿地和生态功能区，为查明极端降水条件下白洋淀主淀区的水化学和水质特征，本研究利用Piper三线图、Gibbs图和多元统计方法阐明了白洋淀极端降雨后的水化学特征、氢氧稳定同位素特征和水质空间变化，揭示了极端降水条件对白洋淀主淀区水化学和水质的影响.结果表明：（1）在极端降水条件下，白洋淀主淀区湖水呈弱碱性，水化学类型主要为Ca-HCO₃·SO₄型，极端降水减弱了蒸发结晶作用和人类活动等因素对白洋淀主淀区湖水水化学组成的影响.极端降水是导致白洋淀主淀区pH、电导率和总溶解性固体发生大幅度变化的原因之一.（2）极端降水条件下白洋淀主淀区湖水的δ²H和δ¹⁸O值的范围分别为-60.86‰~-35.01‰和-8.84‰~-3.45‰，其值均与水深呈显著负相关.极端降水使得白洋淀主淀区湖水的氢、氧稳定同位素贫化，但对其空间分布的影响不大，湖水氢、氧同位素关系受降水本身氢、氧同位素关系的影响更为强烈.强降水引起白洋淀的水深突然增加，导致湖水受到的蒸发分馏作用影响减弱.（3）极端降水增加了面源污染扩散的速度，导致白洋淀主淀区湖水中的氨氮、硝态氮和总磷等营养物质浓度升高，白洋淀大气降水中的氨氮也可能导致极端降水条件下主淀区湖水中氨氮浓度升高，而上游水库为了应对强降雨事件进行的调蓄放水使得白洋淀东北部水质有所改善.该研究为白洋淀的生态修复治理和雄安新区的生态系统管理提供了科学依据.;Extreme precipitation is one of the important meteorological factors affecting water quality. With global warming, the frequency and magnitude of extreme precipitation events have increased significantly, which greatly influenced the hydrochemistry and water environment in lakes. Lake Baiyangdian is an important wetland and ecological area in North China. In order to identify the hydrochemical characteristics and water quality variations in the main area of Lake Baiyangdian under an extreme precipitation event, the Piper diagram, Gibbs diagram, and multivariate statistical methods were used to elucidate the hydrochemical characteristics, hydrogen and oxygen stable isotope characteristics, and spatial variations of water quality in this study. Accordingly, the effects of the extreme precipitation event on the hydrochemistry and water quality were detected in the main area of Lake Baiyangdian. The results showed that (1) Lake water is weakly alkaline, and the hydrochemistry type is Ca-HCO₃·SO₄ under the extreme precipitation event. The extreme precipitation weakened the effects of evapotranspiration and human activities on the chemical compositions of the lake water. The extreme precipitation also led to the large changes in pH, electrical conductivity and total dissolved solid values in the lake water. (2) The hydrogen and oxygen isotopic values (δ²H and δ¹⁸O) respectively ranged from -60.86‰ to -35.01‰ and from -8.84‰ to -3.45‰, showing significant negative correlations with water depths. Although the hydrogen and oxygen stable isotopes of the lake water were depleted by the extreme precipitation, the extreme precipitation did not affect their spatial distribution. The relationship between δ²H and δ¹⁸O values is more strongly influenced by the correlation between δ²H and δ¹⁸O values in precipitation itself. Additionally, the heavy precipitation caused a sudden increase in the water depth of the main area of the lake, which weakened the influence of evaporative fractionation on the lake water. (3) The extreme precipitation raised the diffusion rate of non-point source pollution and increased the concentrations of ammonia nitrogen, nitrate nitrogen and total phosphorus in the lake water. The ammonia nitrogen, in precipitation may also increase the ammonia nitrogen concentration in lake water. Additionally, releasing water from reservoirs located in the upper reaches of the lake in response to extreme precipitation improved the water quality in the northeastern area of the lake. This study provides a scientific basis for the ecological restoration of Lake Baiyangdian and the ecosystem management of Xiong'an New Area.

An availibility of arctic lakes organic sediments to microbial degradation: a laboratory incubation experiment

The water ecosystems of the Arctic region are most vulnerable to modern climatic changes since the global biogeochemical processes mostly occur on the territories of the permafrost zone. Aquatic ecosystems show a high degree of sensitivity to climatic changes; both in these and in other ecosystems, the biogeochemical processes are intense. These water bodies are located in the permafrost zone, which is vulnerable to temperature increases. The paper gives new insights into the fundamental research question of how fast the organic matter of thawing permafrost can be converted to greenhouse gases emitted into the atmosphere (CO2, CH4). We aimed to assess the microbial response and the associated release of CO2 and CH4 from the Arctic lakes in response to temperature increase. We investigated lakes located in the Lena River delta in the Samoylov Island, Russia, at 72° 22′ N, 126° 28′ E. Bottom sediments from three thermokarst and three oxbow lakes were anaerobically incubated in the laboratory at two temperature regimes (at 4 °C and at 25 °C). All the oxbow lakes have shown similar dynamics of methane emission both at low temperatures (4 °C) and at high temperatures (25 °C). The shift of carbon isotopic composition in methane has indicated that methane is emitted in all the oxbow lakes with a similar composition of microbial communities. In the thermokarst lakes, the emission of methane in the sediments proceeded differently at low and at high temperatures. These results have indicated a dissimilar composition of methanogenic / methanotrophic populations in the thermokarst and oxbow lakes. In both cases, the temperature increase caused a growth in methane emission from the sediments of the Arctic lakes. The thermokarst lakes will make a greater contribution to methane emission than the oxbow lakes. Thus, it is believed that the emission of methane from the thermokarst lakes will rise from 6 to 46 times due to ambient temperature increase. Methane emission from the oxbow lakes will grow from 1.8 to 7.6 times. Our results suggest that with the global warming both thermokarst and oxbow lakes could become a great source of methane emission into the atmosphere.

Evaluating the Water Level Variation of a High-Altitude Lake in Response to Environmental Changes on the Southern Tibetan Plateau

AbstractLakes are sensitive to environmental changes, and an example of this change is the decreased water level in the Yamzho Yumco Lake (YYL, in southern Tibetan Plateau), which is opposite of th...

Hydrodynamics and water quality of the Hongze Lake in response to human activities.

The hydrodynamics and water quality of a lake in response to human activities is an important yet poorly understood issue. In this study, the responses of flow field, water level, and water quality of the Hongze Lake to changes in land use, project operation, and pollution accident were investigated using the 2D hydrodynamic model, water quality model, and hydrological model. The results show that project operations have more significant effects on the hydrodynamics and water quality of the Hongze Lake than changes in land use. In addition, the construction and operation of various water conservancy projects could increase pollutant diffusion and water exchange, thus contributing to improve the water quality of the Hongze Lake, but there is a need to solve the problem of rising water level in the Lihe depression lake area. The increase of urban and farmland area can significantly affect the flow of the Hongze Lake that could increase the flood risk. The simulations of the loosely coupled model imply that the coupling among the hydrodynamic model, water quality model, and SWAT model for the lake basin is feasible. Furthermore, a model based on the space grid was proposed in the study and combined with the verified loosely coupled model to assess the flood risk in the Hongze Lake, which could improve water resources and flood retarding basin operations.

Impacts of long-term land use on terrestrial organic matter input to lakes based on lignin phenols in sediment records from a Swedish forest lake

Organic carbon burial in lake sediments plays an important role in the global carbon cycle, and is heavily affected by the terrestrial organic matter input. However, few studies have focused on long-term changes in terrestrial organic matter input to lakes in response to land-use changes. The aim of this study was to assess variations in sedimentary terrestrial organic matter over the last 1000 years based on lignin biomarker records from two sediment cores from Lake Skottenesjön, southwestern Sweden. In combination with pollen-based quantitative land cover reconstruction, we investigated the impacts of centennial-scale land-use changes on terrestrial organic matter input to lake sediments. The results show that human activities in the catchment had significant impacts on terrestrial organic export by modifying the vegetation cover. Intensified use of the forest in the 18th and 19th centuries led to enhanced soil erosion, and increased terrestrial organic matter input to the lake. Although farmland expanded between the 12th and the middle of 14th century, no significant change in terrestrial organic matter input was observed at that time. Much higher export of terrestrial organic and minerogenic matter to the lake was observed during the period of modern forestry in the 20th century as compared to previous periods of minor forest disturbance, such as 11th century. The changes in the vegetation cover in the catchment considerably modified the composition of terrestrial organic matter deposited in the lake sediments, which is reflected by the composition of lignin phenols. This study demonstrates that the combination of lignin phenols analysis and pollen-based quantitative land cover reconstruction is a useful approach for investigating long-term changes in terrestrial organic matter delivery to lake ecosystems.

Establishing Climate Change Resilience in the Great Lakes in Response to Flooding

Over the past decade, both the average rainfall and the frequency of high precipitation storm events in the Great Lakes Basin have been steadily increasing as a consequence of climate change. In this same period, cities and communities along the coasts are experiencing record high water levels and severe flooding events (ECC Canada et al. 2018). When cities are unprepared for these floods, the safety of communities and the water quality of the Great Lakes are jeopardized. For example, coastal flooding increases runoff pollution and contaminates the freshwater resource that 40 million people rely on for drinking water (Lyandres and Welch 2012, Roth 2016). Since the Great Lakes are shared between two nations, the United States and Canada, the region is protected by several international treaties and national compacts, including the Great Lakes Water Quality Agreement (GLWQA) and the Great Lakes Restoration Initiative (GLRI). In order to increase climate change resiliency against flooding in the region, we recommend the United States Environmental Protection Agency (EPA) work with Environment and Climate Change Canada to relocate the GLRI under the GLWQA in order to guarantee consistent funding and protection efforts. We additionally recommend expansion of both agreements in their scope and long-term commitments to engender cooperative efforts to protect the Great Lakes against climate change.