River Lake Research Articles

A coupled model applied to complex river–lake systems

ABSTRACTSimulating river–lake systems while accounting for climate change and human activity is challenging, particularly when dealing with the complex interactions between rivers and lakes. In this study, we developed an integrated model coupling long short-term memory (LSTM), a two-dimensional hydrodynamic model (NewFlood), and the time-variant gain model (TVGM). We applied and validated this model using the Yangtze River–Poyang Lake system. The coupled model accurately and efficiently simulated the water levels, streamflow, and water exchange between the Yangtze River and Poyang Lake. The average Nash-Sutcliffe efficiency coefficient of the coupled model reached 0.92, indicating high simulation accuracy. The coupled model holistically accounts for the impacts of climate change and human activities on the spatiotemporal dynamics of river–lake systems, providing a robust scientific basis for quantifying the relative contributions of different factors influencing river–lake interactions.

Quantification of sedimentary organic carbon sources in a land–river–lake continuum combined with multi-fingerprint and un-mixing models

Identifying organic carbon (OC) sources in lake sediment is essential for elucidating biogeochemical cycling processes and effectively supporting watershed management. However, the complexity of sources as well as environments in the land–river–lake continuum makes it challenging to accurately identify OC sources. Accordingly, the current study utilized a systematic approach to identify and validate OC sources in a typical land–river–lake continuum. Two tracer groups (group 1: δ13C and δ15N; group 2: fluorescence index and biotic index, respectively (where C is carbon and N is nitrogen)) and one model (MixSIAR) were eventually selected from five tracer groups and two models to identify the OC sources in a land–river–lake continuum according to a consistency evaluation and virtual mixing test. The results showed that the distribution of OC sources in lake sediment was spatially heterogeneous. Closer to the lake center (from sampling site S1 to S3), the autochthonous contributions increased while the allochthonous contributions decreased. Downstream of the inlet river (site S1) was dominated by allochthonous contributions (78.6%), especially cropland (28.7% ± 0.5%, where ± indicates a standard deviation range) and urban land (30.5% ± 2.5%). From site S1 to S2, the allochthonous contribution decreased 11.4%. Autochthonous OC gradually became the major source closer to the lake center (site S3: phragmites: 48% ± 4.5%). This distribution of OC sources in the land–river–lake system was attributed to the mixing effect of the autochthonous sources, selective transport of sediment, and human activities. The current findings may aid in validating the ability of different tracers and models to identify OC sources in complex ecosystems and also provide a theoretical basis for watershed management.

Chiropterans (Chiroptera) in Lake–River Systems of Northern European Russia

Chiropterans (Chiroptera) in Lake–River Systems of Northern European Russia

A framework based on spectral similarity to estimate hydrological connectivity in Juruá River floodplain lakes using 3-m PlanetScope data

Hydrological connectivity based on water surface connectivity controls the water exchange between large rivers and their floodplain lakes, which occurs by channelized flow through floodplain areas and overbank flow, and it is relevant to sustain the ecosystem’s health and biodiversity of floodplain waterbodies. Given the climate change impacts on floodplain aquatic habitats, further studies are needed to understand and quantify the river–lake connectivity and its temporal dynamics. However, few studies are dedicated to objectively estimating hydrological connectivity, and new commercial satellite datasets and machine learning approaches can advance the understanding of this important topic. This paper proposes a new framework for computing the hydrological connectivity of small floodplain lakes (river-Lake CONNECTivity or L-CONNECT) in the Amazon Juruá River. The L-CONNECT framework consists of spectral similarity analysis with machine learning in the river–lake system and three steps were implemented: (i) sampling process based on independent satellite-imagery visual interpretation; (ii) automated similarity features extraction from river-lake system; and (iii) training and validation of machine learning algorithm. A total of 552 3-m PlanetScope SuperDove imagery were acquired in 2020 and 2021 to perform our approach. In general, the L-CONNECT framework achieved 88% overall accuracy. However, not-connected lakes were not easily estimated. We found that the L-CONNECT framework managed to perform accurately over all lakes investigated independent on their distance to Juruá River channel (average accuracy of ∼ 86%), and that there was a low discordance (less than 30%) between the lakes’ hydrological connectivity responses acquired by Sentinel-2 against PlanetScope data. The mapping results showed that lakes were more connected to the Juruá River during the 2021 (not-connected lakes rate of 28%) compared to 2020, which was explained by higher cumulative precipitation during January, February, and March of 2021. Finally, the new L-CONNECT framework proposed here can support hydrological connectivity mapping of small floodplain lakes by considering assumptions relative to the similarity between river and water spectra as a proxy for that.

Analysis on the Current Situation of Phytoplankton in the Typical River-Lake Ecotone of Lake Poyang

The typical river-lake ecotone (tail end area) of Poyang Lake, which is a sensitive area and prone to outbreaks of cyanobacteria bloom, is vulnerable to frequent human activities. To explore the diversity of phytoplankton community structure and the relevant driving mechanism in the typical river lake junction area of Poyang Lake, the water quality and phytoplankton at seven sampling points in the typical river lake junction area of Poyang Lake, at six sampling points in the middle section of Poyang Lake River, and at one sampling point in the main lake area were investigated in the field from 2019 to 2020 (dry season), April (flood season), July (wet season), and October (recession period). The results showed that there were seven phyla and 64 genera of phytoplankton in the typical river-lake ecotone of Poyang Lake, and the biomass and relative abundance of phytoplankton were dominated by diatoms and cyanobacteria. The biomass and abundance in the east of the typical river-lake ecotone of Poyang Lake were generally higher than those in the west, and the biomass and abundance in the river-lake ecotone were higher than those in the middle of the river. The dominant degree of cyanobacteria in the lake area and the river-lake ecotone was large, and the dominant degree of diatoms in the middle section of the river was large. The Monte Carlo test results showed that total nitrogen (TN), total phosphorus (TP), orthophosphate phosphorus (PO43--P), water depth (WD), water temperature (WT), and transparency (SD) were significantly related environmental factors affecting the distribution of the phytoplankton community. Redundancy analysis results showed that the typical river-lake ecotone in the west of Poyang Lake was highly affected by the hydration factors (TN, TP, and PO43--P), and the hydrological factors (WT, WD, and SD) in the typical river-lake ecotone in the east were highly significant. The impact factors of phytoplankton in the typical river-lake ecotone of Poyang Lake were seasonal, being greatly affected by hydration factors in winter and hydrological factors in summer.

Fecal-related anthropogenic sources are key determinants of lake microbiomes through microbial source tracking

Lake microbiomes are essential indicators of lake health and are strongly influenced by allochthonous microbial communities from various sources within the watershed. However, quantifying the contributions of multiple inputs to lake microbiomes is challenging because of the complex nature of river‒lake systems and the presence of many untraceable sources. Here, Jianhu Lake‒‒a geographically simple and closed plateau lake in southwestern China, was surveyed to disentangle the contributions of five distinct sources (three input rivers that receive town sewage, stormwater runoff, and creek spring water, as well as two nonpoint sources, duck ponds and dry farmland) to the overall lake microbiomes. We found that feces-loading sources, namely town sewage and duck aquaculture, accounted for 48.7% of the total variations in lake microbiomes. In contrast, the combined contribution of the remaining three sources amounted to 13.21%, despite these less-influential sources (e.g., stormwater runoff) may introduce an even larger volume of allochthonous materials into the lake. In addition, approximately 38.1% of the variations in the lake microbiomes were attributed to unknown sources. Sewage effluents also caused a significant loss of lake microbial diversity, and there was a tendency for large-scale microbial homogeneity in lake sediments that resembled those from duck ponds. We then used a targeted approach to track host-specific fecal pollution, and found that human feces were the primary source, followed by ruminant and chicken/duck feces, all of which can be successfully traced back to the feces-loading sources. In our further modelling of sediment transport from three rivers into the whole lake, we observed a significant relationship between sediment accumulation and adsorbed microorganisms only for the sewage-receiving river. Together, lines of evidence indicate that both point and nonpoint fecal-related anthropogenic sources possess discriminatory power for shaping microbial geographic patterns of the lake, posing threats to the survival of local indigenous lake microbiomes.

Population Structure of European Whitefish Coregonus lavaretus (Salmonidae: Coregoninae) from the Lake–River System of the Subpolar Urals

This paper presents the first description of the population structure of sparsely rakered whitefish Coregonus lavaretus, which lives in the mountain lake–river system of the middle reaches of the Maly Patok River (a second order tributary of the Pechora River). It has been established that European whitefish has formed a complex system of local groups here, which are associated with small lakes of different types, located on the catchment area of this river. A relatively isolated whitefish lacustrine group, which differs in the pattern of the population dynamics and a rapid linear growth of individuals, has been formed in one of the water bodies. There is a temporary aggregation of whitefish in a small endorheic lake, which is recruited only in years with a very high water level during floods. The results of the study of the linear growth indicate the interrelationship between different groups of floodplain–river whitefish from the Maly Patok River basin.

Asymmetry of blue and green water changes in the Yangtze river basin, China, examined by multi-water-variable calibrated SWAT model

Renewable freshwater is a fundamental natural resource for sustaining human social development and the health of terrestrial ecosystems. While blue water (BW), which can be directly utilized by human beings, has received significant attention, the importance of green water (GW), crucial for ecosystem safety, has often been overlooked in water resource assessments. To date, there has been a lack of integrated research incorporating the detection and attribution of changes in both BW and GW in the Yangtze River basin (YRB), China’s largest river basin, resulting in a deficiency of comparative and interactive analyses between them. In this study, we examined the historical trends and long-term memory of BW and GW flows across 272 sub-basins of the YRB using a multi-water-variable calibrated SWAT model, which was validated by streamflow, evapotranspiration, and terrestrial water storage change. We determined the individual contributions of climate variability and land use changes to BW and GW changes. Additionally, we identified the responses characteristics of BW and GW changes in four different ecosystems primarily characterized by alpine grasslands, cropland, forests, and river–lake systems, respectively. The results indicate a non-significant decreasing trend in precipitation and BW in most regions, while an increasing trend is observed in GW, which is expected to persist in the future. Climate variability played a predominant role in BW and GW changes, while land use change also appeared to have significant impact on monthly GW changes. GW showed a positive correlation with precipitation/humidity index in relatively dry and moderately humid areas, but a negative correlation in highly humid areas. Moreover, a stronger correlation was found between the gross primary production (GPP) of terrestrial ecosystems and GW compared to GPP and BW. The findings contribute to guiding the harmonious utilization of water resources between humans and ecosystems in the YRB, as well as optimizing water allocation.

Nonstationary frequency analysis and uncertainty quantification for extreme low lake levels in a large river-lake-catchment system

Extreme hydrological events have become increasingly frequent on a global scale. The middle Yangtze River also faces a substantial challenge in dealing with extreme flooding and drought. However, the long-term characteristics of the extreme hydrological regime have not yet been adequately recognized. Moreover, there is uncertainty in the extreme value estimation, and this uncertainty needs to be distinguished and quantified. In this study, we investigated the nonstationary frequency characteristics of extreme low lake levels (ELLLs), taking the Poyang Lake as an example. Daily lake levels from 1960 to 2022 were utilized to estimate the return level using the generalized Pareto distribution (GPD). The uncertainty from three sources, i.e., the parameter estimator, threshold selection, and covariate, was quantified via variance decomposition. The results indicate that (1) the parameter estimator is the predominant source of uncertainty, with a contribution rate of approximately 87 %. The total uncertainty of the covariate, threshold, and interaction term is only 13 %. (2) Two indexes, namely the annual minimum water level (WLmin) and the days with peak over the 90 % threshold per year (DPOT90), decreased (0.01–0.03 m/year) and increased (0.17–1.39 days/year), respectively, indicating a progressively severe drought trend for Poyang Lake. (3) The return level with return period of 5 to 100 years significantly decreased after the early 21st century. A large spatial heterogeneity was identified for the variation in the return level, and the change rate of the return level with a 100-year return period ranged from 5 % to 40 % for the whole lake. (4) The ELLLs had a stronger correlation with the catchment discharge than with the Yangtze River discharge and the large-scale atmospheric circulation indices. This study provides a methodology with reduced uncertainty for nonstationary frequency analysis (NFA) of ELLLs exemplified in large river–lake systems.

Spatiotemporal Variation Characteristics of Main Pollutant Fluxes in the Yangtze River Basin from 2017 to 2020

Based on the monitoring data of various pollutants at important water system points in the Yangtze River Basin from 2017 to 2020, research on the flux change law of the main and tributary water systems in the Yangtze River Basin was carried out at the spatiotemporal scale, and the spatial change response, interannual change trend, and flux correlation analysis were analyzed from the aspects of water quantity, quality, and flux so as to reveal the spatial-temporal contribution characteristics of pollutant flux in the upper, middle, and lower reaches of the Yangtze River Basin. The results showed that over the past four years, the concentration of major pollutants in the Yangtze River Basin showed an overall downward trend. The concentration of total phosphorus (TP) and ammonia (NH+4-N) decreased significantly. The concentration of total nitrogen (TN) and total phosphorus (TP) in the main stream gradually increased from west to east. The annual concentration of permanganate index in the upper, middle, and lower reaches decreased by 18.5%, 16.0%, and 14.0%, respectively, from 2017 to 2020, with the highest decline in the upper reaches. The four-year average value of the spatial distribution of runoff significantly increased from 466×108 m3 to 9923×108 m3. The two lake basins in the tributary river lake water system had the largest contribution to the water volume. The fluxes of permanganate index, total phosphorus (TP), and total nitrogen (TN) among the main pollutants showed an annual increase and then decrease trend. The pollutant fluxes in the Minjiang River, Tuojiang River, Jialing River, and the middle reaches of the two lakes contributed greatly to the river inflow. There were differences in fluxes in different regional water environments. The results of correlation and hierarchical cluster analysis showed that the permanganate index and TP fluxes were highly significantly correlated with water volume, and there was a significant correlation between biochemical oxygen demand (BOD5) and total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD). The main pollutants showed strong differences in the flood and non-flood periods and had a significant response in the flood season from July to September. The research results can provide scientific basis and theoretical support for the integrated management and precise prevention and control of the aquatic environment in the Yangtze River Basin.

Lake-TopoCat: a global lake drainage topology and catchment database

Abstract. Lakes and reservoirs are ubiquitous across global landscapes, functioning as the largest repository of liquid surface freshwater, hotspots of carbon cycling, and sentinels of climate change. Although typically considered lentic (hydrologically stationary) environments, lakes are an integral part of global drainage networks. Through perennial and intermittent hydrological connections, lakes often interact with each other, and these connections actively affect water mass, quality, and energy balances in both lacustrine and fluvial systems. Deciphering how global lakes are hydrologically interconnected (or the so-called “lake drainage topology”) is not only important for lake change attribution but also increasingly critical for discharge, sediment, and carbon modeling. Despite the proliferation of river hydrography data, lakes remain poorly represented in routing models, partially because there has been no global-scale hydrography dataset tailored to lake drainage basins and networks. Here, we introduce the global Lake drainage Topology and Catchment database (Lake-TopoCat), which reveals detailed lake hydrography information with careful consideration of possible multifurcation. Lake-TopoCat contains the outlet(s) and catchment(s) of each lake; the interconnecting reaches among lakes; and a wide suite of attributes depicting lake drainage topology such as upstream and downstream relationship, drainage distance between lakes, and a priori drainage type and connectivity with river networks. Using the HydroLAKES v1.0 (Messager et al., 2016) global lake mask, Lake-TopoCat identifies ∼ 1.46 million outlets for ∼ 1.43 million lakes larger than 10 ha and delineates 77.5×106 km2 of lake catchments covering 57 % of the Earth's landmass except Antarctica. The global lakes are interconnected by ∼ 3 million reaches, derived from MERIT Hydro v1.0.1 (Yamazaki et al., 2019), stretching a total distance of ∼10×106 km, of which ∼ 80 % are shorter than 10 km. With such unprecedented lake hydrography details, Lake-TopoCat contributes towards a globally coupled lake–river routing model. It may also facilitate a variety of limnological applications such as attributing water quality from lake scale to basin scale, tracing inter-lake fish migration due to changing climate, monitoring fluvial–lacustrine connectivity, and improving estimates of terrestrial carbon fluxes. Lake-TopoCat is freely accessible at https://doi.org/10.5281/zenodo.7916729 (Sikder et al., 2023).

The Influence of Education and Training and Competency Through the Curriculum on Performance Improvement

The purpose of this study was to determine and analyze the effect of education and training on increasing performance, the effect of competence on increasing performance, the effect of curriculum on increasing performance, the effect of education and training on competence, the effect of curriculum on moderating education and training on increasing performance and the influence of curriculum on moderating competency on improving the performance of auxiliary Syahbandar. In this study using primary data and secondary data, primary data was obtained through distributing questionnaires with a sample of 210 people who were alumni of the Training of Fundamentals of Armed Forces of the Palembang River Lake and Ferry Transportation Polytechnic. The data analysis technique used is Partial Least Square Structural Equation Modeling (PLS SEM) using the SMARTPLS application. From the results of data analysis, it was found that education and training variables and curriculum variables did not have a significant direct effect on performance, competency variables directly had a significant effect on performance, education and training variables had a significant effect on competence, and curriculum variables did not strengthen in moderating the influence of education and training variables. training on performance improvement as well as curriculum variables did not strengthen in moderating the effect of competency variables on improving the performance of the auxiliary Syahbandar.

The Mechanisms Controlling the CO2 Outgassing of a Karst Spring–River–Lake Continuum: Evidence from Baotuquan Spring Drainage Area, Jinan City, Northern China

The significance of CO2 emissions at the water–air interface from inland water bodies in the global carbon cycle has been recognized and is being studied more and more. Although it is important to accurately assess CO2 emission flux in a catchment, little research has been carried out to investigate the spatio-temporal variations in CO2 emissions in view of a water continuum. Here, we systematically compared the differences and control factors of CO2 degassing across the water–air interface of a spring–river–lake continuum in the discharge area of Baotuquan Spring in July 2017, which is a typical temperate karst spring area in Jinan city, northern China, using hydrogeochemical parameters, stable carbon isotope values, and CO2 degassing flux. Affected by the pCO2 concentration gradient between the water and ambient air, the spring water showed a high CO2 degassing flux (166.19 ± 91.91 mmol/(m2 d)). After the spring outlet, the CO2 degassing flux in the spring-fed river showed a slight increase (181.05 ± 155.61 mmol/(m2 d)) due to river flow rate disturbance. The river flow rate was significantly reduced by the “blockage” of the lake, which promoted the survival and reproduction of phytoplankton and provided favorable conditions for aquatic plant photosynthesis, increasing the plankton biomass in the lake to 3383.79 × 104/L. In addition, the significant decrease in the dissolved inorganic carbon (DIC) concentration and the increase in the δ13CDIC values in the lake also indicated that the photosynthesis of the lake’s aquatic plants resulted in a significant decrease in the pCO2 concentration, thus limiting the amount of CO2 off-gassing (90.56 ± 55.03 mmol/(m2 d)).

Reconstructing river flows remotely on Earth, Titan, and Mars

Alluvial rivers are conveyor belts of fluid and sediment that provide a record of upstream climate and erosion on Earth, Titan, and Mars. However, many of Earth's rivers remain unsurveyed, Titan's rivers are not well resolved by current spacecraft data, and Mars' rivers are no longer active, hindering reconstructions of planetary surface conditions. To overcome these problems, we use dimensionless hydraulic geometry relations-scaling laws that relate river channel dimensions to flow and sediment transport rates-to calculate in-channel conditions using only remote sensing measurements of channel width and slope. On Earth, this offers a way to predict flow and sediment flux in rivers that lack field measurements and shows that the distinct dynamics of bedload-dominated, suspended load-dominated, and bedrock rivers give rise to distinct channel characteristics. On Mars, this approach not only predicts grain sizes at Gale Crater and Jezero Crater that overlap with those measured by the Curiosity and Perseverance rovers, it enables reconstructions of past flow conditions that are consistent with proposed long-lived hydrologic activity at both craters. On Titan, our predicted sediment fluxes to the coast of Ontario Lacus could build the lake's river delta in as little as ~1,000 y, and our scaling relationships suggest that Titan's rivers may be wider, slope more gently, and transport sediment at lower flows than rivers on Earth or Mars. Our approach provides a template for predicting channel properties remotely for alluvial rivers across Earth, along with interpreting spacecraft observations of rivers on Titan and Mars.

Exploring invertebrate indicators of ecosystem health by focusing on the flow transitional zones in a large, shallow eutrophic lake

The river–lake transitional zone provides a unique environment for the biological community and can reduce pollution inputs in lake ecosystems from their catchments. To explore environmental conditions with high purification potential in Lake Taihu and indicator species, we examined the river-to-lake changes in water and sediment quality and benthic invertebrate communities in the transitional zone of four regions. The spatial variations in the environment and invertebrate community observed in this study followed the previously reported patterns in Taihu; the northern and western regions were characterized by higher nutrient concentrations in water, higher heavy metal concentrations in sediment, and higher total invertebrate density and biomass dominated by pollution-tolerant oligochaetes and chironomids. Although nutrient concentrations were low and transparency was high in the eastern region, the taxon richness was the lowest there, which disagreed with the previous findings and might be due to a poor cover of macrophytes in this study. The river-to-lake change was large in the southern region for water quality and the invertebrate community. Water circulation induced by strong wind-wave actions in the lake sites of the southern region is assumed to have promoted photosynthetic and nutrient uptake activities and favored invertebrates that require well-aerated conditions such as polychaetes and burrowing crustaceans. Invertebrates usually adapted to brackish and saline environments are suggested to be indicators of a well-circulated environment with active biogeochemical processes and a less eutrophic state in Taihu, and wind-wave actions are key to maintaining such a community and natural purifying processes.

Spatiotemporal Patterns of Ammonia Nitrogen and Chemical Oxygen Demand in the Huaihe River–Hongze Lake System (Eastern China)

Understanding variations in contaminant concentrations and exploring their driving factors are essential for pollution control and water environment improvement. The Huaihe River Basin, as an important region in the eastern region of China, has attracted much attention to its water environment issues in recent years. Therefore, an in-depth analysis of spatiotemporal patterns of water quality parameters was carried out on the Huaihe River–Hongze Lake system, for the period 1998–2018, using the Mann–Kendall test (MKT) and wavelet transforms (WTs). Significant decrease trends of ammonia nitrogen (AN) and chemical oxygen demand (COD) concentrations were detected in the Huaihe River (HR) before 2008 using the MKT. High concentration in the contaminant load was a result of the effect of increased construction and decreased forest on increasing input of pollutants during this period. The results of the WT showed how factors (e.g., streamflow and water temperature), except land use, affect the variations in AN and COD concentrations. The comparison of spatiotemporal patterns of AN and COD between the HR and Hongze Lake (HL) showed their differences in contaminant transport regimes. The contaminants were rapidly transported downstream along the HR with high streamflow during the wet season, while these in the HL were less responsive due to the long residence time of the water body. In addition, rebounds of contaminant concentrations occurred many times at the confluence between the HR and the HL due to strong river–lake interactions, especially in the flood season. These results have implications for future water environment management in the Huaihe River Basin and in similar settings worldwide.

Influences of increasing water release of the Three Gorges Reservoir during dry season on water regimes of downstream lake

AbstractThe severe and frequent drought in Poyang Lake, the largest freshwater lake in China, has seriously affected the local water resources security and wetland ecological security. Especially, the impoundment of the Three Gorges Reservoir (TGR) in the Yangtze River further aggravated the drought in lake. To explore the approaches to alleviate drought in Poyang Lake, this study simulated and quantified the influences of increasing water release of the TGR during the dry periods on water regimes of Poyang Lake, including the lake water level, duration of low water, flow velocity, flow field of lake, as well as potential suitable habitat area of migratory birds, based on a hydrodynamic model. Major results showed that the increase of water release of the TGR raised the lake water level, especially in the northern lake area, with the average lake level increase of 0.2–1.08 m and the lowest lake level increase of 0.16–0.68 m. Meanwhile, the duration of low water was significantly shortened, from 127 days to 87–116 days (threshold lake level of 12.0 m) at Xingzi station. In addition, the hydrodynamic simulations revealed that the increasing water release of the TGR reduced the lake flow velocity and discharge of Poyang Lake, which decreased the outflow of lake by 1.66–17.87 × 108 m3, accounting for about 0.47%–5.11% of the total outflow in the dry season. Finally, the potential suitable habitat area with 0.2–0.6 m water depth increased by 1.7–27.9 km2 in December–February, and showed a significant expansion trend in the central area of Poyang Lake. Outcomes of the study are useful for understanding the influences of water release of the TGR on water regimes of downstream lakes, and can provide valuable references for mitigating lake droughts in complex river–lake system.

Genetic Diversity and Population Structure of Coilia nasus Revealed by 2b-RAD Sequencing.

Coilia nasus is a threatened migratory species in the Yangtze River Basin. To reveal the genetic diversity of natural and farmed populations of C. nasus and the status of germplasm resources in the Yangtze River, the genetic diversity and structure of two wild populations (Yezhi Lake: YZ; Poyang Lake: PY) and two farmed populations (Zhenjiang: ZJ; Wuhan: WH) of C. nasus were analyzed using 44,718 SNPs obtained via 2b-RAD sequencing. The results indicate that both the wild and farmed populations had low genetic diversity, and germplasm resources have undergone varying degrees of degradation. Population genetic structure analyses indicated that the four populations may have come from two ancestral groups. Different amounts of gene flow were identified among WH, ZJ, and PY populations, but gene flow among YZ and other populations was low. It is speculated that the river-lake isolation of Yezhi Lake is the main cause of this phenomenon. In conclusion, this study revealed that genetic diversity reduction and germplasm resource degradation had occurred in both wild and farmed C. nasus, suggesting that conservation of its resources is of great urgency. This study provides a theoretical basis for the conservation and rational exploitation of germplasm resources for C. nasus.

Lakes protect downstream riverine habitats from chloride toxicity

AbstractFreshwater salinization from anthropogenic activities threatens water quality and habitat suitability for many lakes and rivers in North America. Recognizing that salinization is a stress on freshwater environments globally, research on watershed salt transport is necessary for informed management strategies. Prior to this research, there were few studies that examined salt export regimes along a river–lake continuum to investigate the drivers, temporal dynamics, and modulators of freshwater salinization. Here, we use high‐frequency in situ monitoring to assess specific conductance–discharge (cQ) relationships, chloride concentrations and fluxes, and the role of lakes in downstream salt transport. The Upper Yahara River Watershed in southern Wisconsin, USA, is a mixed urban and agricultural watershed where the lakes' chloride concentrations have risen from < 5 mg L−1 in the 1940s to > 50–80 mg L−1 in 2021. Our results suggest cQ behavior depends on land use, with urban areas exhibiting more frequent mobilization events during stormflow and agricultural areas exhibiting predominantly dilution dynamics. In addition, chloride loading is driven by hydrology and watershed size whereas concentrations and yields are a function of anthropogenic drivers like urbanization. We demonstrate how an in‐network lake attenuates downstream salinity, dampening the hydrologic, anthropogenic, and seasonal patterns observed in rivers upstream of the lake. Importantly, biogeochemical processes in lakes overlay a seasonal signal on salinity that must be considered when investigating temporal dynamics of anthropogenic salinization. This research contributes to understanding of temporal dynamics of salt export through watersheds and can be used to inform management strategies for habitat protection.

Synergistic changes in river-lake runoff systems in the Yangtze River basin and their driving force differences

Climate change and human activities simultaneously alter river–lake relationships. Determining the dynamics of river–lake runoff systems on multiple time scales and their differences in response to driving forces can provide insights into hydrological processes and water resource management. This study investigates the synergistic evolution of river–lake runoff systems in the middle and lower reaches of the Yangtze River basin (MLYR) using the cross-wavelet transform method. The effects of different driving force changes on river–lake runoff regimes are quantified based on the Budyko hypothesis, and an InVEST model is developed to assess the spatial and temporal patterns of habitat quality. The results indicate that during the variation period, the runoff distributions of the Yangtze River–Dongting Lake and Yangtze River–-Poyang Lake runoff systems are both skewed towards lower values in the flood seasons compared with those in the base period. The storage of lakes mitigates the extent of human disturbance to the mainstream hydrological regime, particularly under extremely low conditions. From 1960 to 2021, five significant resonance periods are indicated in the river–lake runoff system, and the phase–angle relationships indicate a positive phase coupling between the lake and mainstream hydrological regimes, with the lake lagging behind the mainstream; however, this interaction tends to weaken. In the mainstream and Dongting Lake basins, subsurface conditions are the dominant factor contributing to runoff variability, with contributions ranging from 50.9% to 72.6%; in the Poyang Lake basin, precipitation is the dominant factor, with a contribution of 50.6%; and in the Han River basin, changes in the potential evapotranspiration contribute to 50.6% of runoff variability. The proportion of high habitat quality in the MLYR is approximately 52%, the Dongting and Poyang Lake basins indicate a high habitat quality rating. However, frequent human activity is the main reason of conversion from higher habitats to lower ones, which may result in wetland habitat degradation.