Large Floodplain Lake Research Articles

Fifty years marshland changes in a large floodplain lake: Natural driving or human impact?

Study region: Poyang Lake, the largest freshwater floodplain lake in China. Study focus: Marshlands in a floodplain, as the typical natural wetland offering vital habitats for various organisms, are sensitive to environmental changes. The spatiotemporal changes of marshlands were investigated and their driving forces from both natural factors and human activities were discussed. The remote sensing image data from 1973 to 2022 was adopted to explore the long-term changes of marshlands exposed in dry season. New hydrological insights for the region: Over the past fifty years, the total area of marshlands in Poyang Lake is around 2540–2718 km2 and has undergone substantial changes. It follows the bell-shaped curve pattern with continuous rise since 1970s and reach the maximum at the end of 20 century and then fluctuating decline. Different evolutionary patterns were identified in different lake regions owing to the combination of human activities and natural processes. The expanding marshlands mainly concentrate in the central lake, while the significant losses of marshlands are observed in the northern lake（By sand mining and dyke constructions）. In the southern lake, sediment input from inflow rivers deposited naturally in the river mouth elevated the lake bed and lead to delta expansion（A 3.1 km expansion has been observed）. The complex geomorphological processes and fishery activities also create the dish-shaped internal sub-lakes in marshlands.

Taxonomic and functional response of fish assemblages to flood-triggered water level fluctuations in a large floodplain lake along the Yangtze River

Taxonomic and functional response of fish assemblages to flood-triggered water level fluctuations in a large floodplain lake along the Yangtze River

Multi-source remote sensing data and image fusion technology reveal significant spatiotemporal heterogeneity of inundation dynamics in a typical large floodplain lake system

Study regionThe Poyang Lake, which is located on the south bank of the middle-lower Yangtze River basin. The lake is the largest freshwater lake in China, and also a typical floodplain lake in the world. Study focusThe spatiotemporal heterogeneity of inundation dynamics of large floodplain lake system has not been paid enough attention. Based on the reconstructed high spatial and temporal resolution inundation dataset using the image fusion model and multi-source remote sensing data, this study systematically analyzed the spatiotemporal heterogeneity of inundation dynamics in the Poyang Lake- floodplain system. New hydrological insights for the regionIt is found that within the same floodplain lake, the inundated area and inundation frequency in different regions of the lake (the main lake region and the adjacent floodplain region) can have asynchronous intra-annual fluctuation and opposite inter-annual change trend. This is highly related to the hydrological complexity of the lake: the relative impacts of catchment inflow and the Yangtze River varies in different regions across the lake. The stage-area relationship at the central station along the flow direction of the lake has the highest linear correlation, which might provide more accurate estimates of lake surface/volume. In addition, this study highlights the importance of reconstructed high spatial-temporal resolution of remote sensing data for the accurate assessment of inundation dynamics in floodplain lakes. All the results enrich the understanding of complex hydrological regime of large floodplain lakes and are valuable for the practice of water resources management and ecological conservation in such lakes.

Epiphytes support aquatic consumers of a large floodplain lake ecosystem in the southern Gulf of Mexico

Epiphytes support aquatic consumers of a large floodplain lake ecosystem in the southern Gulf of Mexico

Influence of Seasonal Water Level Fluctuations on Food Web Structure of a Large Floodplain Lake in China

Seasonal shifts in hydrology are known to alter the abundance and diversity of basal production resources and habitats and hence strongly influence the structure and function of river ecosystems. However, equivalent knowledge of natural lake ecosystems in floodplain regions is lacking. Here, we used stable isotope ratios of carbon and nitrogen to assess available primary production sources and consumer taxa during the dry and wet seasons in a large floodplain lake connected to the Yangtze River. Fish species showed distinct δ13C values between two hydrological periods but only small changes in δ15N values. Most of the fish species had higher estimated trophic levels in the dry season, likely indicating greater carnivory. Results of Bayesian mixing models revealed that benthic algae and benthic organic matter (BOM), combined with C3 vegetation, were the principal food sources supporting the biomass of most fish species during the low-water period, whereas benthic algae and seston were the most important carbon sources during the flood period. Overall, these findings demonstrate that seasonal hydrological changes, such as water-level fluctuations, can affect the trophic structure and ecosystem functioning of floodplain lake food webs in the subtropical zone.

Water level fluctuations associated with hydrological connectivity consolidate the food web stability of the largest Chinese freshwater lake via mediating trophodynamics and trophic structure

Variation in hydrological connectivity (HC) between rivers and lakes gives rise to periodic large water level fluctuation (WLF) in river-connected lakes (RCL). However, how WLF shapes the material cycling and concomitant trophodynamics of RCL remain unclear. Here we evaluated the resource availability, relative contributions of autochthonous and allochthonous carbon sources (by Bayesian mixing models) and trophic structure (using δ13C and δ15N) of Lake Poyang, the largest freshwater lake in China, during different hydrological periods. Terrestrial C3 plants in the aquatic/terrestrial transition zones (ATTZ) were the main supporter of aquatic consumers all year round. Compared with historical data, the contributions of autochthonous production to aquatic food webs were low. This is primarily ascribed to the influences of hydrological regimes in that the operation of Three Gorges Dam and HC changed the rhythm of WLF in Lake Poyang, restricting the production of aquatic vegetation and epiphytic algae. Most common fish species indicated higher trophic positions (TPs) during the dry than wet season, but only eleven of thirty-six common species showed a statistically significant increase (p < 0.05). Our study reveals a relatively consistent trophic diversity of consumer communities (fish and aquatic invertebrates) during dry and wet seasons, but each trophic guild showed specific trophic response to WLF, as they flexibly adjusted feeding strategies and the degree of trophic niche differentiation. Although WLF triggered fluctuations in the resource availability and species composition of lake food webs, and the TPs and trophic niches of aquatic consumers during different hydrological periods, the resource diversity and habitat complexity driven by HC and WLF reduced the strength of trophic interactions, and thus resulted in overall stability of food web trophodynamics and trophic structure of Lake Poyang. Our findings highlighted the importance of HC and natural WLFs in maintaining the ecosystem stability of large floodplain lakes, and that seasonal WLF patterns should be maintained in future floodplain lake management to conserve biodiversity and the resilience of ecological functions.

Submergence in the Dry Season Alters Microbial Nitrogen Transformations in the Root Zone of Carex cinerascens: A Mesocosm Study in One Floodplain Lake.

The online version contains supplementary material available at 10.1007/s13157-022-01656-1.

Impact of hydrological processes on wetland landscapes and wintering migratory birds in a large floodplain lake (Poyang Lake, China)

AbstractHydrological processes are an important factor influencing the wetland landscapes and the quality of wintering migratory birds habitat in Poyang Lake. However, most of the research on a small spatiotemporal scale and there is a lack of studies on the impact of hydrological processes on migratory bird habitats. This study analysed the response of the Poyang Lake wetland landscape to low water levels from 1990 to 2016 and determined the relationship between hydrological processes, wetland landscape characteristics and migratory bird habitats. According to the results, the number of days during the study period when the maximum water level was higher than the current water level (MaxDay) and the average water level from the 40th to 50th day prior to the current day (D50) are two critical factors affecting the area of grassland in Poyang Lake. In particular, a D50 value of 9.5–11.0 m is important for maintaining the grassland area and growth of wetland vegetation. Besides, the water level should not exceed 11 m from mid–late October to early November and should be maintained between 7.58 and 7.97 m in mid–late December that can maximize the habitat area of migratory birds. Furthermore, this study used ecological threshold to propose the optimal inundation period of Cyperus rotundus L. community, Leersia japonica community, Polygonum criopolitanum community, Phragmites australis community, Triarrhena lutarioriparia community, Carex spp. community and Phalaris arundinacea community, which are 124–174, 31–101, 199–249, 65–147, 51–121, 110–190 and 175–253 days, respectively.

Chlorophyll a variations and responses to environmental stressors along hydrological connectivity gradients: Insights from a large floodplain lake

Understanding the key drivers of eutrophication in floodplain lakes has long been a challenge. In this study, the Chlorophyll a (Chla) variations and associated relationships with environmental stressors along the temporal hydrological connectivity gradient were investigated using a 11-year dataset in a large floodplain lake (Poyang Lake). A geostatistical method was firstly used to calculate the hydrological connectivity curves for each sampling campaign that was further classified by K-means technique. Linear mixed effect (LME) models were developed through the inclusion of the site as a random effect to identify the limiting factors of Chla variations. The results identified three clear hydrological connectivity variation patterns with remarkable connecting water area changes in Poyang Lake. Furthermore, hydrological connectivity changes exerted a great influence on environmental variables in Poyang Lake, with a decrease in nutrient concentrations as the hydrological connectivity enhanced. The Chla exhibited contrast variations with nutrient variables along the temporal hydrological connectivity gradient and generally depended on WT, DO, EC and TP, for the entire study period. Nevertheless, the relative roles of nutrient and non-nutrient variables in phytoplankton growth varied with different degrees of hydrological connectivity as confirmed by the LME models. In the low hydrological connectivity phase, the Chla dynamics were controlled only by water temperature with sufficient nutrients available. In the high hydrological connectivity phase, the synergistic influences of both nutrient and physical variables jointly limited the Chla dynamics. In addition, a significant increasing trend was observed for Chla variations from 2008 to 2018 in the HHC phase, which could largely be attributed to the elevated nutrient concentrations. This study confirmed the strong influences of hydrological connectivity on the nutrient and non-nutrient limitation of phytoplankton growth in floodplain lakes. The present study could provide new insights on the driving mechanisms underlying phytoplankton growth in floodplain lakes.

The role of phytoplankton communities on coupled carbon-silicon cycling in a large floodplain lake system

Carbon (C) and silicon (Si) are essential lake ecosystem components, impacting both phytoplankton growth and other available elements and nutrients. In this study, we selected a typical floodplain-lake system to explore the seasonal role of coupled C and Si as matter is imported and exported through lotic water processes. Results showed considerably higher dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and dissolved total carbon (DTC) concentrations during the transitional stage between the dry and wet season (here referred to as TDW) compared to the other seasonal stages (5.81 mg/L–28.80 mg/L), indicating that imported runoff significantly effects the transport of C and Si. Rock weathering was the main source of dissolved silicon (DSi). The dilution effect and water temperature may also impact DIC, DOC, and DTC concentrations. Except for the wet season, Bacillariophyta was the dominant phytoplankton taxon, and diatom growth as well as the growth of other algae taxon may influence DSi and DTC concentrations through several biochemical processes. This study describes effects of coupled C and Si and highlights variation in environmental variables driven by the resident phytoplankton communities in a lake ecosystem.

Modelling past migrations to determine efficient management rules favouring silver eel escapement from a large regulated Floodplain Lake

As human activities caused a dramatic decline of European eel population since the 1970 s, the European Union has set targets to ensure a 40% escapement to the sea of the silver eel biomass by considerably reducing anthropogenic impact. Thus, human obstacles to fish migration like dams and hydropower plants should enable efficient management measures ensuring safe passage for eels during the migration. In order to provide a quick and efficient assessment of eel conservation measure applied to the sluice gates of a large floodplain lake, we implemented a novel evaluation method using predictions on past migration seasons when no management measure were applied. For this purpose, we collected acoustic telemetry monitoring data over three migration seasons and fitted a predictive model based on Boosted Regression Trees (BRTs) to describe the influence of environmental parameters on migration. The water level difference over two days proved to be decisive, along with early migration occasions in the season, as an increase of at least 10 cm water level was associated with a sharp increase of migration probability. We then used the BRT model to predict migration occasions at the dam over 8 past seasons and forecast the impact on escapement of management measures if they had been applied. Thanks to this original prospective assessment of dam management measures, we identified an enhanced opening decision rule, capable of increasing the eel escapement for each year of the study. The management measure is particularly efficient during the years with poor hydrological conditions (i.e. droughts), that is the periods with the lowest initial escapement rates. Finally, efficient management measures to increase silver eel escapement were based on increasing the number of gate opening days by only a few days per year (c.a. 15%). However, the management measure only focused on silver eel migration, so that further investigations should consider the impacts of other threats occurring during the life cycle. This study also provides a highly operational approach for fast evaluation of conservation measures, avoiding lengthy and expensive monitoring campaigns of classical ex-post assessments.

Periphytic algal communities are highly influenced by substrate types in small pond, not large floodplain lake

Periphytic algal communities are highly influenced by substrate types in small pond, not large floodplain lake

Vertically stratified water source characteristics and associated driving mechanisms of particulate organic carbon in a large floodplain lake system

Particulate organic carbon (POC) is an important component of lake organic carbon (C) pools, of which different factors drive vertical distributions and sources. This study used the dual stable isotope (δ13C and δ15N) approach to investigate vertical POC sources and drivers in a large floodplain lake system. Findings showed that POC composition gradually changed from endogenous dominant to exogenous dominant sequentially from the surface layer to the bottom layer of Lake Poyang. Environmental factors associated with phytoplankton photosynthesis as well as nutrient levels primarily drove surface POC. Moreover, soil erosion, sediment deposition, and resuspension strongly affected POC distribution and composition in the middle and bottom layers of the lake. POC sources were also affected by factors associated with vertical mixing, such as wind speed and water depth. Litter from C3 plants significantly contributed to POC concentrations in the middle and bottom layers of the lake. Results from this study can benefit our overall understanding of the potential driving mechanisms of lake C cycling processes, aquatic ecosystem functions, and pollutant migration.

Exploring the spatiotemporal water quality variations and their influencing factors in a large floodplain lake in China

Poyang Lake is the largest freshwater lake in China. It is characterized by dramatic hydrodynamic fluctuations which result in complex water quality variations. To explore the water quality status we used the fuzzy matter-element evaluation (FME) model to integrate key water quality indicators into a rank value. Monthly monitoring data from 18 sampling sites in the main lake and in the inflowing rivers collected during June 2010 to December 2015 were used to evaluate the water quality variations at spatial, seasonal and annual scales in the Poyang Lake. The results showed that the water quality status was generally the best in the wet summer season and the poorest in dry winter season. In addition, two considerably different spatial water status clusters were identified. A significant trend of water quality deterioration was observed during dry winter season for high pollution cluster and during summer for both clusters the lake from 2010 to 2015, which makes the lake more vulnerable to algal blooms. Random forest (RF) model showed that hydrological conditions together with water quality of inflow rivers yield 54% and 51% of the variation in water quality variations for low- and high-polluted clusters, respectively. Importance analysis based on RF indicated that hydrological conditions contributed the most to water quality variations in Poyang Lake, followed by the pollutants from adjacent sub-basins. This study provides new insights into when and where to control pollution sources of Poyang Lake.

Anthropogenic habitat alternation significantly decreases α- and β-diversity of benthopelagic metacommunity in a large floodplain lake

Anthropogenic habitat alternation is one of the leading causes of biodiversity loss, especially in freshwater ecosystems. Understanding the mechanisms of how habitat degradation drives changes in spatial patterns of species assemblages is fundamental to conservation science. We conducted an empirical study to investigate the species richness (α-diversity) and community composition (β-diversity) of benthopelagic biota along the gradient of human modification in West Dongting Lake, China. The study site is a large floodplain lake that has been subjected to long-term intensive human use. For a better understanding of how β-diversity responds to human disturbance, we also distinguished between two patterns of β-diversity, i.e., turnover and nestedness. We found that both α- and β-diversity of the benthopelagic assemblage decreased along the intensity gradient of human modification, indicating the strong homogenizing effect of anthropogenic habitat alternation. Our results also suggested that multiple processes, including environmental filtering, dispersal limitation, and biological interactions, were important in shaping the benthopelagic assemblage structure because spatial turnover other than nestedness dominated the total β-diversity at both the lake and habitat level. These findings support that habitat restoration by removing artificial banks and channels and increasing the landscape naturalness would be the key for this highly modified floodplain lake.

Quantifying the hydrodynamic impacts of cumulative sand mining on a large river-connected floodplain lake: Poyang Lake

Sand mining has significant impacts on the hydrological and hydrodynamic regimes of river-lake systems. Recently, continuous sand mining has occurred in Poyang Lake, a large floodplain lake connected to the Yangtze River. Previous studies on the impact of sand mining in Poyang Lake focused on water level variations. However, the influence of different magnitudes of sand mining on the hydrological and hydrodynamic regimes in such a complex river-lake floodplain system is unclear. The current study aims to address this issue by combining a hydrodynamic model and hydrological data. Based on average conditions (2000–2010), the influences of 1–4 m uniform sand mining in the northern lake on water levels and outflows were quantified, and the spatial and temporal impacts of cumulative sand mining (1998–2010) on current speeds and residence times were further assessed. The results showed that the elevations of the thalwegs in the northern outlet channels decreased unevenly from 1998 to 2010. The water levels decreased cumulatively but nonlinearly with increasing sand mining. Mining 1–4 m of sand caused cumulative water level decreases of 0.55–2.14 m in the northern channels when the water levels were lower than 14 m. Due to cumulative sand mining from 1998 to 2010, the current speeds in the northern mining channels generally decreased, and those in the central channels mostly increased, with the majority varying from −0.4 to 0.4 m/s. The residence time changes were opposite to the current speed changes, with −4 to 10 day variations. The opposite outflow variations between uniform mining and realistic uneven mining indicated that outflow variations depended on the mining magnitudes and bed slope changes. The above results suggested that for this river-connected floodplain lake, sand mining in outlet channels enhanced the spatial and temporal heterogeneity of the lake hydrodynamics and that the blocking effect of the connected large river impacted the hydrodynamic variation patterns. This study leads to better understanding of the effects of different magnitudes of sand mining on the hydrologic and hydrodynamic regimes in Poyang Lake and provides a reference for quantifying similar human activities in complex floodplain lakes.

Large lake gauging using fractional imagery

Large floodplain lakes provide riparian habitat, are sediment and nutrient sinks, help control flow connectivity and flooding along rivers, and are both used by humans and strongly impacted by human activity. However, water level in many remote large floodplain lakes, especially in developing countries, is often monitored inconsistently or not at all. In this study, a novel method for estimating large lake water level using passive, optical remote sensing data combined with any digital elevation model (DEM) is presented. The method obtains water level estimates at 30 m2 resolution using Landsat, in this case in conjunction with SRTM elevation data, nested within a 240 m2 grid “fishnet”. A probabilistic mean of elevation values for all water-designated pixels (between 5% and 95% filled within each grid) produces lake water levels often accurate to within ±50 cm of gauged reference data on Lake Curuai in the Amazon River and Tonle Sap Lake along the Mekong River. The method is relatively insensitive to cloud cover, especially as lake size increases. This study is the first to use solely passive optical remote sensing data for water level estimation and thus could be used to produce accurate, long-term estimations of water level in many large lakes globally. The use of optical sensors to obtain lake water level is both an important complement and potential alternative to methods that use active sensors.

Hydrodynamic and water quality modeling of a large floodplain lake (Poyang Lake) in China.

Floodplain lakes are valuable to humans because of their various functions and are characterized by dramatic hydrological condition variations. In this study, a two-dimensional coupled hydrodynamic and water quality model was applied in a large floodplain lake (i.e., Poyang Lake), to investigate spatial and temporal water quality variations. The model was established based on detailed data such as lake terrain, hydrological, and water quality. Observed lake water level and discharge and water quality parameters (TN, TP, CODMn, and NH4-N) were used to assess model performance. The hydrodynamic model results showed satisfactory results with R2 and MRE values ranging between 0.96 and 0.99 and between 2.45 and 6.14%, respectively, for lake water level simulations. The water quality model basically captured the temporal variations in water quality parameters with R2 of TN, TP, CODMn, and NH4-N simulation ranges of 0.56-0.91, 0.44-0.66, 0.64-0.67, and 0.44-0.57, respectively, with TP of Xingzi Station and CODMn of Duchang Station excluded, which may be further optimized with supplementation of sewage and industrial discharge data. The modeled average TN, TP, CODMn, and NH4-N concentrations across the lake were 1.36, 0.05, 1.99, and 0.48mg/L, respectively. The modeled spatial variations of the lake showed that the main channel of the lake acted as a main pollutant passageway, and the east part of the lake suffered high level of pollution. In addition, consistent with previous water quality evaluations based on field investigations, water quality was the highest (average TN = 1.35mg/L) during high water level periods and the poorest (average TN = 1.96mg/L) during low water level periods. Scenario analysis showed that by decreasing discharge of upstream flow by 20% could result in the increase of TN and TP concentrations by 25.6% and 23.2% respectively. In summary, the model successfully reproduced the complex water and pollutant exchange processes in the systems involving upstream rivers, the Poyang Lake, and the Yangtze River. The model is beneficial for future modeling of the impact of different load reduction and other hydrological regime changes on water quality variation and provides a relevant example for floodplain lake management.

Impacts of pen culture on alpha and beta diversity of fish communities in a large floodplain lake along the Yangtze River

Pen culture is a cumulative factor leading to water quality degradation, competition intensification, habitat alteration and fragmentation. Despite the unprecedented expansion of pen culture areas in Chinese lakes due to the increasing demands on fishery products, little is known about the potential impacts of pen culture on fish communities. Here, we addressed this issue by quantifying changes in alpha and beta diversity with its turnover and nestedness-resultant components between pen culture areas (PA) and non-pen culture areas (NPA) in a large floodplain lake lying on the northern shore of the Yangtze River. Fish communities were sampled seasonally from January 2016 to December 2016 in 16 representative sites (PA, 8; NPA, 8) of Lake Huayanghe using fyke nets. In comparing with fish communities in NPA, we demonstrated an overall loss of fish species and a significant reduction in alpha diversity (richness) in PA, which were probably due to habitat alteration and fragmentation triggered by pen culture. We reported a significantly lower overall beta diversity with its turnover component and a significantly higher nestedness-resultant component in PA. The homogenized and nested trend for fish communities in PA was triggered by the synthesized effects of abiotic and biotic factors. Net pens caused habitat fragmentation and blocked the offset effects by supplementary fish species in nearby habitats, thus resulting in a significantly lower turnover and higher nestedness-resultant component in PA. The introduction of the same cultured fish species and the decrease of the wild native fish species made the fish communities in PA become more homogenized and nested. Pen culture had resulted in a significant decline in alpha diversity and a designed homogenization for fish communities in the lake. Our study highlighted the urgent need for systematic assessment of cultured fish and effective control of pen culture areas to avoid the future fish homogenization and species loss in Chinese lakes.

3D hydrodynamic investigation of thermal regime in a large river-lake-floodplain system (Poyang Lake, China)

Thermal regime and its response to meteorological and hydrological forcings play an important role in controlling water quality and ecosystem of lakes. Many large floodplain lakes are subjected to significant river-lake interactions and could benefit greatly from hydrodynamic modeling. The current work presents a first attempt to use a 3D hydrodynamic model and statistical methods to explore spatiotemporal variations and primary causal factors of thermal stability within a large river-lake-floodplain system (Poyang Lake, China). The hydrodynamic model successfully reproduced the lake hydrodynamics and thermal dynamics through a comparative analysis of field measurements. Simulation results revealed that the thermal stability of Poyang Lake exhibits similar spatial patterns between seasons; however, the lake is generally stratified during summer and early autumn. It is classified as partial mixed and full mixed during winter and spring. The thermal stratification may develop in the center area and eastern bay area of the lake, while the full mixing is likely to occur in the floodplains and the main flow channels. Statistics and simulations indicate that the air temperature, solar radiation and evaporation trigger a positive effect on the thermal stability of Poyang Lake, whereas a negative relationship is recognized due to the catchment river temperature. The responses of thermal stability to the meteorological and hydrological changes are much stronger in summer than other seasons, producing a significant seasonal thermal regime in the floodplain lake. Additionally, the dynamics in the lake water depth and associated hydrological regime are a major factor in maintaining the seasonal thermal stability of Poyang Lake. The findings of this study can support management of Poyang Lake as well as other similar floodplain lakes, by providing information on both water quality and ecosystem succession.