Largest Freshwater Lake Research Articles

Physicochemical Properties and Environmental Effects of Suspended Sediment Particles in the Largest Freshwater Lake, China

Suspended sediment particles (SSPs) act as a potential source of and sink for aquatic pollution. This study sampled six sites in Poyang Lake in August and November 2019. Changes in the physicochemical properties of SSPs were analyzed using scanning electron microscope energy-dispersive spectrometry (SEM-EDS). The results showed that SSPs consisted mainly of clay and chalk, with an average content of 39.71% and 57.52%, respectively. The average particle size distribution of SSPs in the study area ranged from 5.54 to 15.97 μm and the spatial distribution pattern showed the north lake area (I) > west lake area (II) > east lake area (III). The angle (K) of morphological indicators varied widely, with coefficients of variation between 0.25 and 1.23. Water-flow velocity was negatively correlated with SSP size, while suspended-solid concentration was positively correlated with SSP surface roughness. Morphological parameters, chemical composition, and correlation between each SSP form were analyzed to identify morphological distribution characteristics. Linear regression equations estimated endogenous phosphorus load in zones I, II, and III as 1027.202 mg/kg, 1265.343 mg/kg, and 1013.111 mg/kg respectively. Therefore, we conclude that the morphological differences in particulate matter, the interaction between chemical fractions, and the aqueous environment affecting the distribution of phosphorus fugitive forms, may contribute to endogenous lake pollution. These results are essential for revealing the intrinsic relationship between SSP physicochemical properties and lake eutrophication and studying other water–sediment interface processes of lake pollutants.

Distinct seasonal variations of dissolved organic matter across two large freshwater lakes in China: Lability profiles and predictive modeling

Biological lability of dissolved organic matter (DOM) is a crucial indicator of carbon cycle and contaminant attenuation in freshwater lakes. In this study, we employed a multi-stage plug-flow bioreactor and spectrofluorometric indices to characterize the seasonal variations in DOM composition and lability across Poyang Lake (PY) and Lake Taihu (TH), two large freshwater lakes in China with distinct hydrological seasonality. Our findings showed that the export of floodplain-derived organics and river-lake interaction led to a remarkable increase in terrestrial aromatic and humic-like DOM with high molecular weights and long turnover times in PY. Consequently, the labile fraction was extremely low (average LDOC% of 3%) during the rising-to-flood season (spring and summer). Conversely, autochthonous production in TH considerably enriched semi-labile (average SDOC% of 26%) and biodegradable DOM (average BDOC% of 34%) during the phytoplankton bloom to post-bloom season (summer and autumn). This was reflected by the accumulation of low-light-absorbing and protein-like components with high biological and fluorescence indices. In the dry and non-bloom season (winter), the better preservation of humic substances maintained the high molecular weight and humic degree of DOM in PY, while the decay of aquatic plants strengthened autochthonous production, resulting in a similar BDOC% of PY samples (23%–34%) to TH samples (18%–33%). We further applied partial least squares regression using DOM optical indices as predictive proxies, which generated a greater prediction strength for BDOC% (R2 = 0.80) compared to SDOC% (R2 = 0.57) and LDOC% (R2 = 0.28). The regression model identified aromaticity (SUVA254) as the most effective and negative predictor and low molecular weight (A250/A365) as the highly and positively influential factor. Our study provides new evidence that the seasonality of DOM lability profiles is regulated by the trade-off between flow-related variation and phytoplankton production, and presents an approach to describe and predict DOM lability across freshwater lakes.

Non-native species in Poyang Lake Basin: status, threats and management

Poyang Lake is the largest freshwater lake in China and sustains a high level of biodiversity in the mid-reach area of the Yangtze River watershed. Poyang Lake is also one of the most important aquaculture regions in China, and a great number of non-native species have been introduced into it. We present a current and well-documented list of the non-native species of plants, molluscs, crustaceans, fishes, reptiles, and amphibians currently found in Lake. We found that there are 103 non-native species (83 vascular plants, 12 fishes, three crustacea, two molluscs, two reptiles and one amphibian) that have invaded Poyang Lake Basin, of which 96 non-native species were introduced after 2000. The invasion rate of non-native species reached 4.36 species year-1, which is the highest invasion rate recorded in freshwater ecosystems. The primary pathways of introduction are through the ornamental trade and unintentional escapes (30 species each, respectively), followed by food (19), aquaculture (15), forage grass (four), medicinal and oil (two, respectively), and biocontrol (one). The origins of non-native species are North America (29.12%), Asia (25.24%), South America (20.38%), Africa (18.44%), Europe (5.82%) and Oceania (0.97%). Many non-native species provide significant support for the rapid development of the local economy (such as aquaculture). However, many non-native species pose a great threat to local biodiversity and societal development. More studies that include monitoring and the development of strategies for managing and eliminating non-native species in Poyang Lake are needed.

Checklist of the diatoms (Bacillariophyta) from Lake Naivasha, Kenya, with some historical notes.

Lake Naivasha is one of only two large freshwater lakes in the Eastern Rift Valley of Kenya, East Africa. Together with its satellite lakes Crescent Island Crater, Oloidien and Sonachi, it comprises a great variety of pelagic and benthic habitats for aquatic biota, and its sediment record represents a unique archive of past climate change and long-term ecosystem dynamics in equatorial East Africa. This is particularly so because local paleoenvironmental reconstructions can be checked against historical data on the composition of aquatic fauna and flora collected in Lake Naivasha since the early 20th century. Some of the most prominent biological proxies for reconstructing past changes in lakes are diatoms (Bacillariophyta), a group of unicellular autotrophic eukaryotes of which the siliceous skeletons (valves) preserve well in lake sediments and are good indicators for, among others, climate-driven changes in salinity. However, diatom taxonomy and species concepts have changed a lot in recent decades, making it sometimes difficult for non-taxonomists to know which species are concerned in different published studies. This paper provides the currently accepted taxonomic names of the 310 specific and infraspecific diatom taxa reported from Lake Naivasha and its satellite lakes to date, together with their synonyms used in literature concerning these lakes as well as other, commonly used synonyms. Further, a short overview is given of the history of diatom research conducted on materials from Lake Naivasha and its satellite lakes. The present checklist may facilitate the identification and interpretation aspects of future diatom studies on the wider Lake Naivasha ecosystem and on other East African lakes that are less well studied.

Inter-Species and Inter-Organ Differences in Stable C and N Isotope Signatures of Macrophytes from the Largest Freshwater Lake in China

Macrophytes play important roles in shallow aquatic ecosystems. Stable isotope signatures of macrophytes indicate the environmental conditions and macrophyte contributions to food webs. However, macrophyte isotope signatures have been studied less than isotope signatures of other organisms. We determined the stable C and N isotope signatures of 10 aquatic plant species from Poyang Lake wetland (Wucheng, Yongxiu County) and Nanji wetland (Nanjishan, Xinjian County) in Jiangxi Province, which are Chinese national nature reserves, among different seasons. The isotope signatures for different species and seasons were significantly different. The dominant macrophyte species were Potamogeton malaianus and Nymphoides peltatum. The isotope signatures for different organs of these two species were determined. Both δ13C and δ15N values were higher for P. malaianus than for N. peltatum stems, roots and leaves, and δ13C varied less for N. peltatum than for P. malaianus organs. The δ13C and δ15N values for P. malaianus organs increased in the order roots<stems<leaves. δ13C values for N. peltatum organs decreased in the order roots>stems>leaves, and δ15N values for N. peltatum organs increased in the order roots<stems<leaves. The stable C and N isotope signatures for P. malaianus and N. peltatum may be controlled by various factors including macrophyte life history, external sources of C/N, and the amount of water in the wetland. These results provided a theoretical reference and experimental data support for detecting the flow trend of C & N elements and environment changes in the lake by the δ13C and δ15N values of euhydrophytes.

Microeukaryotic Communities of the Long-Term Ice-Covered Freshwater Lakes in the Subarctic Region of Yakutia, Russia

Currently, microeukaryotic communities of the freshwater arctic and subarctic ecosystems are poorly studied. Still, these are of considerable interest due to the species biogeography and autecology as well as global climate change. Here, we used high-throughput 18S rRNA amplicon sequencing to study the microeukaryotic communities of the large subarctic freshwater lakes Labynkyr and Vorota in Yakutia, Russia, during the end of the ice cover period, from April to June. By applying the statistical methods, we coupled the microeukaryotic community structure profiles with available discrete factor variables and hydrophysical, hydrochemical, and environmental parameters. The sub-ice layer and the water column communities were differentiated due to the temporal change in environmental conditions, particularly temperature regime and electric conductivity. Additionally, the community composition of unicellular eukaryotes in lakes Labynkyr and Vorota was changing due to seasonal environmental factors, with these alterations having similar patterns in both sites. We suggest the community developed in the sub-ice layer in April serves as a primer for summer freshwater microeukaryotes. Our results extend the current knowledge on the community composition and seasonal succession of unicellular eukaryotes within subarctic freshwater ecosystems.

Estimating Effects of Natural and Anthropogenic Activities on Trophic Level of Inland Water: Analysis of Poyang Lake Basin, China, with Landsat-8 Observations

The intensification of anthropogenic activities has led to the infiltration of enormous quantities of pollutants into rivers and lakes, resulting in significant deterioration in water quality and a more prominent occurrence of eutrophication. Poyang Lake, the largest freshwater lake in China, is facing a severe challenge related to eutrophication, which seriously threatens the delivery of the ecosystem service and the safety of drinking water. To address this challenge, Landsat-8 Operational Land Imager (OLI) data for the Poyang Lake Basin (PLB) from May 2013 to December 2020 were used. Since inland water bodies with complex optical characteristics, we developed a semi-analytical algorithm to assess the trophic state of the water based on two cruise field measurements in 2016 and 2019. Combining the semi-analytical trophic level index (TLI) with an atmospheric correction model is the most suitable model for OLI images of the PLB, this model was then applied to Landsat-8 time series observations. The trends of the trophic state of water bodies in PLB were revealed, and the annual, quarterly and monthly percentages of eutrophic water bodies were calculated. Natural and anthropogenic factors were then used to explain the changes in the trophic state of the PLB waters. The main findings are as follows: (1) From the 8-year observation results, it can be seen that the variation of trophic level of water in PLB showed obviously spatial and temporal variations, characterized by higher in the north than in the south and higher in winter than in summer. (2) Temperature promoted the growth of harmful algae and plays an essential role in affecting changes in the trophic level of the water. (3) Changes in the trophic level of water bodies in PLB were mainly affected by human activities. The results of spatial and temporal variation of the trophic level of water and the driving factors in PLB can extend our knowledge of water quality degradation and provide essential references for relevant policy-making institutions.

Spatial-temporal pattern of desertification in the Selenge River Basin of Mongolia from 1990 to 2020

Land degradation is the most serious environmental challenge in the Mongolian Plateau, an important arid and semiarid region east of the Eurasian continent. The Selenge River Basin is not only the main catchment area of Baikal Lake, the largest fresh water lake, but also the main concentration area of agriculture and animal husbandry in Mongolia. Under the common influence of global warming and human activities, desertification has become more prominent in this basin, threatening the ecological security and sustainable development of the Mongolian Plateau. In this study, we selected NDVI, Modified Soil Adjusted Vegetation Index, topsoil grain size index and Albedo as feature space indicators, and retrieved the desertification process from 1990 to 2020 in the Selenge River Basin of Mongolia based on a novel feature space monitoring index. A 30-m resolution desertification map of the Selenge River Basin was retrieved based on optimal feature space models for 1990, 1995, 2000, 2005, 2010, 2015, and 2020. Then, the spatial-temporal dynamic changes and driving mechanism of desertification. The results show that: 1) Compared with the other four feature space models, the point-to-line Albedo-MSAVI feature space model has the highest recognition accuracy of 84.89% for desertification in the basin. 2) The desertification level of the Selenge River basin is mainly low and medium on the whole, the high desertification is mainly located in BULGAN and HOVSGOL provinces in the middle-upper reaches of the basin, and the severe desertification is mainly located in TOV province and Ulaanbaatar in the middle-lower reaches of the basin. 3) From 1990–2020, desertification degree in the Selenge River Basin has further deteriorated, and the area of high and serve desertified land has expanded significantly. Within the stage, 1990–2015 was a period of rapid increase in desertification. However, from 2015–2020, recovery takes the dominant position. The regions with high conversion frequency of desertification degree are mainly concentrated in the central and southeastern of the Selenge River basin. The joint effects of large fluctuations in temperature, overgrazing and population migration aggravate the desertification degree in this region. The research results can provide the desertification retrieving method recommendation and land degradation nutrition measures decision support in the Selenge River Basin and the whole Mongolian Plateau.

Effects of Fe(II) and organic carbon on nitrate reduction in surficial sediments of a large shallow freshwater lake

Nitrate-reducing ferrous [Fe(II)]-oxidizing (NRFO) has been reported from lake sediments as a natural reduction pathway. However, the effects of the contents of Fe(II) and sediment organic carbon (SOC) on the NRFO process still remain unclear. In this study, the influences of Fe(II) and organic carbon on nitrate reduction were analyzed quantitatively at two typical seasonal temperatures (25 °C representing summers and 5 °C for winters) by conducting a series of batch incubation experiments, using surficial sediments at the western zone of Lake Taihu (Eastern China). Results showed that Fe(II) greatly promoted NO3‾-N reduction by denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) processes at high-temperature (25 °C, representing summer season). As Fe (II) increased (e.g., Fe(II)/NO3‾ = 4), the promotion effect on NO3‾-N reduction was weakened, but on the other side, the DNRA process was enhanced. In comparison, the NO3‾-N reduction rate obviously decreased at low-temperature (5 °C, representing the winter season). NRFO in sediments mainly belongs to biological rather than abiotic processes. A relatively high SOC content apparently increased the rate of NO3‾-N reduction (r = 0.023–0.053 mM/d), particularly on the heterotrophic NRFO. It is interesting that the Fe(II) consistently remained active in the nitrate reduction processes no matter whether SOC was sufficient in the sediment, particularly at high-temperature. Overall, the combining effects of both Fe(II) and SOC in surficial sediments made a great contribution towards NO3‾-N reduction and N removal in a lake system. These results provide a better understanding and estimation of N transformation in sediments of the aquatic ecosystem under different environmental conditions.

Influence of spatial and temporal variation on establishing stable isotope baselines of δ15N, δ13C, and δ34S in a large freshwater lake

Abstract It is essential to establish a baseline in studies using stable isotopes to interpret trophic relationships across ecosystems and through time. Studies in freshwater ecosystems struggle to quantify baseline stable isotopes due to difficulties collecting representative samples, particularly from pelagic habitats. We assessed temporal and spatial variation in δ13C, δ15N, and δ34S in a commonly used pelagic baseline, seston (n = 156), in Lake Erie to understand mechanisms that correlate with baseline stable isotope dynamics in large lakes. Seston contains a wide range of material which can confound stable isotope interpretation, and we examined the utility of element content and ratios to account for variation in sample source. Seston was collected in each of the three basins of Lake Erie from May to October in 2017–2019 at nearshore (<10 m depth) and offshore (>10 m depth) sites. General linear models were conducted on each stable isotope (δ15N, δ13C, and δ34S) and sample composition (variables: %N, %C, %S, C:N, C:S, and N:S) to assess how basin, month, and collection year influenced seston stable isotopes and composition. Sample composition (variables: %N, %C, %S, C:N, C:S, and N:S), which is rarely reported for organisms in stable isotope studies, was constant throughout the sample period with no temporal or spatial trends except for small variations in %C, C:N, C:S, and N:S. This indicated that the temporal and spatial trends observed within the stable isotopes were related to seasonal changes in system processes and plankton community dynamics, with few or minimal changes in the amount of detrital and inorganic material within seston. Values and trends of δ15N, δ13C, and δ34S in seston were comparable to those measured previously in Lake Erie and other Laurentian Great Lakes. All three isotopes increased from May to October of each sample year and varied spatially, δ15N was higher, δ34S was lower, and δ13C was the same in the west basin compared to the central and eastern basins of Lake Erie, which did not differ. These trends probably reflect seasonal changes in plankton community composition and nutrient cycling throughout the lake and are potentially linked to the presence of Microcystis blooms in the western basin during the late summer and autumn. Seston turns over quickly, as shown by the rapid changes in stable isotope values throughout the study, which confounds the investigation of stable isotopes in upper trophic levels, and especially in organisms that have slower tissue turnover and move throughout the lake seasonally. Additionally, the variable composition of seston (e.g., % C, % N, % S, C:N, C:S, N:S) necessitates analysing sample composition to determine the degree of abiotic (e.g., detritus, sediment, particulate organic matter) and biotic (e.g., phytoplankton, zooplankton) content in it.

Observing the recent floods and drought in the Lake Victoria Basin using Earth observations and hydrological anomalies

The Lake Victoria Basin, home of Africa’s largest freshwater lake, experienced extensive floods in 2019–2020 and anomalous drought conditions in early 2022. Both antithetical hydrological events raised concerns for an estimated 35 million people within the basin who are vulnerable to these continually recurrent hydrometeorological extremes. While there is a need for high-resolution spatial and temporal hydrological monitoring, in-situ observations are limited and insufficient within the basin. This study assesses the capability of publicly available Earth observations and models to capture the occurrence of recent hydrological extremes within the Lake Victoria Basin. Spatial and temporal comparisons of the following hydrological variables are conducted within the Lake Victoria Basin from June 2002 – June 2022: precipitation, evapotranspiration, runoff, soil moisture, lake height, and total water storage anomaly (TWSA). Results from the time series and spatial analyses confirm that the anomalous wet and dry events respectively occurred from October 2019 – March 2020 and November 2021 – March 2021. The observations also indicated a quick recovery from the drought event by June 2022. Additionally, a comparison of 9-km soil moisture and 1-km downscaled near-surface soil moisture products improves understanding of wetness spatial variability within the basin. These results were validated using in-situ soil moisture data available through the International Soil Moisture Network, making this the first study to validate the downscaled 1-km soil moil moisture product within the African continent. Methods from this study demonstrate the utility of a diverse array of publicly available Earth observation and model data to improve understanding of recent hydrological anomalies and extreme events within the Lake Victoria Basin. This can be applied to water resources management, particularly in regions lacking sufficient in-situ hydrological data.

Abundance, Distribution Patterns, and the Contribution of Transparent Exopolymer Particles and Dissolved Acidic Polysaccharides to Organic Carbon in Lake Taihu, China

Transparent exopolymer particles (TEP) are essential for the carbon cycle in aquatic environments. However, the distribution of TEP, its precursor, and the contribution to the organic carbon pool in the large freshwater lake remain inadequately understood. Here, we focused on the spatial distribution of TEP and dissolved acidic polysaccharides (dAPS) in four typical seasons in Lake Taihu, the third-largest lake in China. TEP concentrations in Lake Taihu ranged from 0.05 to 5.19 mg Xeq/L, with a mean value of 1.31 ± 1.08 mg Xeq/L. The concentration of dAPS in the lake averaged 3.7 ± 2.19 mg Xeq/L (range, 0.19–13.12 mg Xeq/L). Higher content of TEP and dAPS was found in summer, and their distributions appeared to be influenced by the cyanobacterial blooms, as they showed significant correlations with chlorophyll-a content in Lake Taihu in summer. In addition, TEP accounted for an average of 24.3% of particulate organic carbon, and dAPS represented 25.9% of dissolved organic carbon. These results provide valuable insights into the contribution of TEP to organic carbon pools in inland waters and highlight the role of TEP in the carbon cycling of large freshwater lakes.

Assessment of impacts of water transfer on lake flow and water quality in Lake Chaohu using a three-dimensional hydrodynamic-ecological model

Study regionLake Chaohu is a typically large shallow freshwater lake in China, experiencing long-term eutrophication and a short period of drought. Study focusThis study employs a three-dimensional (3-D) hydrodynamic-ecological model to assess the impacts of water transfer on lake flow, water quality, and their relationship, and then reveals optimal strategies for achieving improved water quality in Lake Chaohu. New hydrological insights for the regionResults indicated that clean water transfer could dramatically increase flow rate and decrease nutrient concentrations near the water transfer inlets, while the grade level of lake water quality is not changed. The degree of improvement in water quality parameters is not always proportional to lake flow rate. A clean water transfer through the eastern route (ZH) has the largest improvement effect on the average flow rate and water quality (total nitrogen (TN) and total phosphorus (TP)) of the entire lake. Winter water transfer improves TN and TP better than summer, while the opposite for ammonia nitrogen (NH3-N). Decrease of wind speed is essential for mitigating nutrient accumulation in western lake’s heavily polluted bay through weakening the reverse circulation and the northwest flow. Water transfer operations are revealed to improve water quality in Lake Chaohu: conduct water transfer through ZH in winter, strictly control NH3-N concentration in the donating water, and combine the effects of the low east wind.

Local-scale impacts of water hyacinth on water quality in a hypereutrophic lake

Increased nutrient concentrations have been linked to water quality impairments across the world. In Lake Victoria, the second largest freshwater lake in the world, decades of eutrophication have challenged water quality management and led to conditions with compromising levels of cyanobacteria and cyanotoxins. Our study focuses on Winam Gulf, where a resurgence of water hyacinth has led to renewed challenges with navigation and anoxia, but also may present a local-scale opportunity for water quality improvements. Over the course of 1.5 years, we conducted three, in situ experiments to vary levels of water hyacinth density and determined its effects on lake water nutrient composition, biochemical parameters (chlorophyll a, cyanotoxins), and fecal indicators (fecal coliforms and Escherchia coli). While our study did not show overwhelming improvements in water quality with increasing water hyacinth density, we did find that small-scale removal of water hyacinth led to decreases in coliforms (F1, 11 = 11.14, p < 0.01), E. coli (F1, 11 = 22.95, p < 0.001), and total microcystins (F1, 9 = 3.47, p = 0.095). Throughout the experiment, the majority of samples collected had both E. coli and microcystin concentrations, notably exceeding World Health Organization guidelines for drinking water. Our data suggest that magnitude of scale, as well as season considerations such as rainfall and background level of water hyacinth, will strongly influence the phytoremediation potential of water hyacinth. The data encourages further exploration of remediation potential of native and introduced macrophytes.

Water Area Variation and River–Lake Interactions in the Poyang Lake from 1977–2021

Lakes are an important part of the Earth’s surface. Poyang Lake is China’s largest freshwater lake with complex hydrological relationships and unique rhythmic changes. There is no systematic understanding of the relationship between lake watershed area and river–lake connectivity. In this study, using remote sensing imagery, hydrological data, meteorological data, and land use surveys, we investigated changes in the Poyang Lake water area from 1977–2021. In addition, we examined the relationship between the lake water area and potential impact factors and analyzed the influence of river–lake interactions on the lake water area. The results showed that the water area of Poyang Lake decreased during the study period. River runoff and sediment load changes in the Poyang Lake basin are the main factors affecting the lake water area. Additionally, the Three Gorges Dam water impoundment situated in the upper reaches of the Yangtze River weakened and eliminated the block and reverse flow of the Yangtze River into the Poyang Lake, causing the water area to decrease toward the end of the flood season in 2005 and in the dry season in 2003. Changes in the lakebed elevation caused by sedimentation and anthropogenic activities have also accelerated the shrinkage of the water area. Overall, the results of this study indicate that variations in the river–lake interactions are the primary cause of the significant changes observed in the Poyang Lake water area in the last five decades.

Spatial ecology of translocated American Eel (Anguilla rostrata) in a large freshwater lake

American Eel (Anguilla rostrata) undertake extensive migrations from their rearing grounds to spawn in the Sargasso Sea, and historically the upper St. Lawrence River and Lake Ontario provided an important source for large, fecund female eel. Following declines in the Lake Ontario population, glass eel were translocated from eastern Canada from 2006 to 2010. From 2016 to 2018, large, presumably translocated yellow eel (N = 230) with the potential to begin maturing and out-migrating within their year of capture were collected in spring and fall and tagged with acoustic transmitters. Eel were released into eastern Lake Ontario and tracked to better understand their movement patterns prior to and during migration, and the timing of migration. Most eels successfully migrated out of Lake Ontario (64%). Timing of migration was consistent regardless of year or tagging season and primarily occurred in late summer or fall, with cooling water temperatures and decreasing sky illumination associated with initiation for fall tagged eel. Eels were mostly detected in eastern Lake Ontario and those in western Lake Ontario were mostly detected in shallow waters (< 20 m) close to shore. Eels were detected on fewer receivers in the winter, suggesting reduced movements during this season. Finally, larger individuals spent less time in the system, particularly when tagged in the fall. These findings confirm that translocated eels can migrate out of Lake Ontario; however, the weeks when migration occurred were more aligned with timing in their natal range (i.e., eastern Canada) than with naturally recruited eels from Lake Ontario. This temporal mismatch requires further consideration, since it may influence arrival times of translocated eel to the spawning grounds and their recruitment potential. These results can be used to inform future assessments of eel translocation efficacy and can also aid in the design of future tracking studies to more completely explore the downstream migration success of eel translocated into the highly productive waters of Lake Ontario.

A conditional copula model to identify the response of runoff probability to climatic factors

Understanding the response of runoff to climate drivers is important to ensure rational water allocation and address the risk of drought. Many models that assess the effect of climate factors on the response of runoff volume have been developed and widely used. However, models that assess the response of the probability of runoff occurrence (runoff probability) are lacking. In this study, we developed a model by integrating a conditional probability distribution (CPD) and a copula function model to assess the effect of climate conditions on variation of the probability of runoff occurrence. The developed model was applied to the basin of Poyang Lake, the largest freshwater lake in China. The study showed that Frank copula was the copula that had the best-fitted effect to identify the impact of climate factors (except for precipitation and air temperature [AT] in low flow period [LFP]) on the probability of runoff occurrence. The copulas with the best-fitted effect of precipitation and AT is the Gumbel copula and Clayton copula during LFP, respectively. Precipitation, relative humidity (RH), and water vapor pressure (WP) were positive with streamflow variation, while wind speed (WS), potential evapotranspiration (ET0), and sunshine duration (SD) were negative with runoff, but AT had an inverse relation with the streamflow during high flow period (HFP) and LFP. Sensitivity analysis indicated that precipitation has a weaker effect on the likelihood of extreme hydrological events than many other climate factors (such as RH and SD). Moreover, the sensitivity of runoff probability to climatic factors tended to be relatively stable during HFP, which was in contrast to that during LFP. This research highlights the significance of considering change conditions when evaluating runoff response to climate drivers, which is consistent with the objective of achieving more accurate runoff predictions to combat climate change and extreme weather conditions.

2000 years of lake-level fluctuations and human adaptation around China's largest freshwater lake

The human society is facing growing flood risks due to the rapidly-changing global climate. Understanding how early human coped with flooding will shed light on the increase of contemporary social resilience to projected intensified extreme climate change. However, assessment of such ancient human response to hydrological changes remains difficult due to the paucity of records for flood risk coupled with ancient human activities. Here, we present a two-millennium continuous reconstruction of water level changes for Poyang Lake, China's largest freshwater body, using microbial tetraethers extracted from a well-dated sedimentary core. The rising trend of lake water level over the past 2000 years indicates an increase in flood risks for this fertile region that has long been populated by ancient human settlements. A comparison with spatial-temporal distribution of ancient cities and towns in the lake basin reveals that, during the first millennium, human settlements passively retreated outwards and upwards away from the lake to minimize flood risk due to the rising lake water. However, a reversal pattern occurred at ∼1000 CE, witnessing human settlements to moving closer to lakeshore during the second millennium despite of the high water table. The strategic shift, accompanied by a booming economy in southern China during the Song Dynasty, was possibly facilitated by technology innovations, such as intensified water conservancy construction and enhanced shipbuilding, in and around the lake basin. Such an enhanced social resilience in responding to flood risks as early as 1000 years ago remains as a common practice today although the unprecedented scale of anthropogenic climate change in the near future may post additional and unexpected challenges.

Do Geographically Isolated Grasslands Follow the Principle of Island Biogeography in a Landscape Scale? Taking Poyang Lake Grassland as an Example

As one of the basic theories of biodiversity conservation, island biogeography has been widely accepted in the past decades. Originally, island biogeography was put forward and applied in oceanic environments. But later on, it was found out that the application was not only limited to oceanic islands, but also in terrestrial environments with relatively isolated conditions. In terms of biodiversity level, island biogeography generally focuses on a small scale, such as species diversity and genetic diversity. The studies of biodiversity on a large-scale based on island biogeography, such as ecosystem and landscape scales, were seldomly conducted. Taking Poyang Lake, the largest fresh water lake in China as case study area, 30 grasslands were randomly selected to study whether island biogeography can be applied to grasslands at a landscape level from three island attributes (area, distance and shape), and the most important ecological variable (flooding) in Poyang Lake. The results showed that in general, grasslands have the property of an island, and follow the basic principle of island biogeography. We found the area and flooding duration were the two most important determinants of landscape diversity. There was a significant positive correlation between the grassland area and the landscape diversity, which could be well expressed by logarithmic function model (R2 = 0.73). There was a negative correlation between flooding duration and landscape diversity, which could be described by an inverse model (R2 = 0.206). The distance to mainland and the shape of grassland were correlated with landscape diversity, but the fitting result of the models was not as good as expected. The possible reason could be that Poyang Lake is a seasonal lake, the water level varies with hydrological conditions, so that the grasslands are not strongly isolated and their shape is not stable enough required by island biogeography. Furthermore, it indicates that besides area, distance and shape attributes, flooding strongly affects the biodiversity of grassland vegetation, and should not be ignored when applying island biogeography theory to Poyang Lake. This study is expected to be a supplement for island biogeography in terrestrial environments, and the results are expected to benefit for the biodiversity conservation in Poyang Lake.

Validation of ICESat-2 Derived Data Products on Freshwater Lakes: Bathymetry, Diffuse Attenuation Coefficient for Downwelling Irradiance (Kd ), and Particulate Backscatter Coefficient (b bp)

Monitoring large bodies of water, such as the Laurentian Great Lakes in North America, can be challenging and costly. The bathymetry, the diffuse attenuation coefficient for downwelling irradiance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K_d</i> ), and the particulate backscattering coefficient ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b_bp</i> ) are important metrics in monitoring water quality in lakes and have typically been measured in two ways: 1) via in situ sampling campaigns, which are expensive, time-consuming, and have low spatial resolution, and 2) via passive optical imagery, which can have errors in excess of 50%. Recently, ICESat-2, an active LiDAR-based satellite, has proven effective in deriving the bathymetry, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K_d</i> , and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b_bp</i> in the global oceans. However, validation of such metrics has never been done on satellite flyovers taken on the same day as in situ measurements. Likewise, studies on freshwater environments have been limited. Here, we compare in situ data sampled from Lake Michigan and Big Glen Lake between August 13th and 14th, 2021, and results derived from an ICESat-2 flyover in the same region on August 14th, 2021.We find excellent agreement between the in situ values and the satellite-derived values for all three metrics. This suggests that ICESat-2 and other future LiDAR-based satellites will be powerful tools in monitoring large freshwater lakes.