Impacts of habitat alteration on macroinvertebrates in large shallow lakes: An application of a macroinvertebrate-based multimetric index.

Habitat plays a crucial role in shaping the macroinvertebrate community structure in large shallow lakes. In the pursuit of improving the health of freshwater ecosystems, it is imperative to consider their habitat characteristics. To evaluate the impact of habitat variations on lake ecological health, we developed a macroinvertebrate-based multimetric index (MMI) for both the pelagic and littoral zones of Lake Hongze. Additionally, we employed structural equation models to explore the influence of utilization or phytoplankton biomass on ecological health. Historical data served as reference conditions for the pelagic. Seven key attributes were selected for the pelagic MMI, that is, Biological Monitoring Working Party (BMWP), the percentage of Mollusca taxa, the percentage of filter-collector taxa, the percentage of predator taxa, the percentage of gather-collector taxa, and the percentage of sensitive taxa and functional dispersion. The least minimally disturbed conditions and the best attainable conditions were used to develop the littoral. Four key metrics, that is, the percentage of scraper abundance, Mollusca taxa, Biological Pollution Index, and BMWP, were integrated into the littoral MMI. The assessment based on MMI revealed a "poor" health status for the pelagic zone and a "fair" health status for the littoral zone. These findings underscore the high applicability and efficacy of MMIs in assessing and monitoring ecological health in Lake Hongze. Notably, functional feeding groups exhibited heightened sensitivity to disturbance in both zones. Moreover, sediment organic matter strongly influenced the pelagic ecological health, while chlorophyll a and transparency emerged as primary factors influencing the littoral zone, attributable to varying littoral zone utilization. Integr Environ Assess Manag 2024;00:1-11. © 2024 SETAC.

Effects of different hydrological conditions on the taxonomic structure and functional traits of mollusk communities in a large floodplain wetland.

Floodplain wetlands are critical to the conservation of aquatic biodiversity and the ecological integrity of river networks. However, increasing drought severity and frequency caused by climate change can reduce floodplain wetlands' resistance and recovery capacities. Mollusks, which are common inhabitants of floodplain wetlands, are among the most vulnerable species to drought. However, the response of mollusk communities to drought has received little attention. Here, we investigated how the structure and functional traits of mollusk communities changed in response to varying hydrological conditions, including a flash drought (FD) in the Poyang Lake floodplain wetland. Our findings showed that FD strongly reduced mollusk abundance and biomass, decreased both α- and ß-diversity, and resulted in the extinction of bivalve taxa. A sudden shift in community trait structure was discovered due to the extinction of many species. These traits, which include deposit feeding, crawling, scraping, aerial respiration, and dormancy, help mollusks survive in FD and tolerate completely dry out of their Changhuchi habitat. Finally, we discovered that dissolved oxygen was an important controlling variable for mollusk communities during drought. Our findings provide a scientific basis for the management and conservation of floodplain wetland biodiversity in the context of increasing drought frequency and intensity.

Restore polder and aquaculture enclosure to the lake: Balancing environmental protection and economic growth for sustainable development.

The restoration of lakes and their buffer zones is crucial for understanding the intricate interplay between human activities and natural ecosystems resulting from the implementation of environmental policies. In this study, we investigated the ecological restoration of shallow lakes and buffer zones in the Yangtze-Huaihe River Basin, specifically focusing on the removal of polder and aquaculture enclosure areas within the lakes. By examining data from eight shallow lakes and their corresponding buffer zones, encompassing lake morphology, water quality parameters, and land use/land cover (LULC) data spanning from 2008 to 2022, which shed light on the complex relationships involved. During the process of restoring polder and aquaculture enclosure areas, we observed a general decrease in the extent of polders and aquaculture enclosures within the lakes. Notably, the removal of aquaculture enclosures had a more pronounced effect (reduction rate of 83.37 %) compared to the withdrawal of polders (reduction rate of 48.76 %). Linear regression analysis revealed a significant decrease in the concentrations of seven water quality parameters, including COD, CODMn, TN, TP, NH3-N, Chl-a, and F, while pH and DO factors exhibit a distinct increasing trend. The results of redundancy analysis and Pearson correlation analysis demonstrated significant correlations between the area of polders and aquaculture enclosures and the changes in lake water quality. Encouragingly, the withdrawal of polders and the removal of aquaculture enclosures had a positive impact on the lake water quality improvement. In contrast, the LULC in the buffer zones of the lakes experienced a gradual decline owing to land degradation, resulting in a reduction in ecosystem service value (ESV). These results offer valuable support for policymakers in their endeavors to restore lake water quality, mitigate the degradation of buffer zones land, and promote the sustainable development of land and water resources.

Risk assessment of China's Eastern Route of the South-to-north Water Diversion Project from the perspective of Phthalate Esters occurrence in the impounded lakes.

Phthalate esters (PAEs) are widely utilized and can accumulate in lacustrine ecosystems, posing significant ecological and human health hazards. Most studies on PAEs focus on individual lakes, lacking a comprehensive and systematic perspective. In response, we have focused our investigation on characteristic lakes situated along the Eastern Route of the South-to-north Water Diversion Project (SNWDP-ER) in China. We have detected 16 PAE compounds in the impounded lakes of the SNWDP-ER by collecting surface water samples using solid-phase extraction followed by gas chromatography analysis. The concentration of PAEs were found to between 0.80 to 12.92 µg L-1. Among them, Bis (2-ethylhexyl) phthalate (DEHP) was the most prevalent, with mean concentration of 1.56 ±â€¯0.62 µg L-1 (48.44%), followed by Diisobutyl phthalate (DIBP), 0.64 ±â€¯1.40 µg L-1 (19.87%). Spatial distribution showed an increasing trend in the direction of water flow. Retention of DEHP and DIBP has led to increased environmental risks. DEHP, Dimethyl phthalate (DMP) etc. determined by agriculture and human activities. Additionally, Dibutyl phthalate (DBP) and DIBP mainly related to the use of agricultural products. To mitigate the PAEs risk, focusing on integrated management of the lakes, along with the implementation of stringent regulations to control the use of plasticizes in products.

Hydro-meteorological factors and inflowing nutrients drive water quality in an impounded lake of China's South-to-North Water Diversion Project.

Freshwater lakes play a vital role in global hydrological and biogeochemical cycles, serving various functions and maintaining ecological balance. However, freshwater resources are more vulnerable to deterioration due to multiple stressors. Gaoyou Lake is one of the impounded lakes of the Eastern route of South-to-North Water Diversion Project in China, and as an important source of drinking water, the lake has been routinely monitored. Long-term monitoring of water quality in Gaoyou Lake showed that concentrations of nutrients and chlorophyll a as well as trophic state in the water column increased while water transparency decreased, indicating that the water quality has declined during the last 12 years. Specifically, there was a notable and statistically significant increase in chlorophyll a concentrations, averaging an annual rate of 9.9%. Despite a slight decline in trophic level index until 2014, subsequent years saw an upward trend, ranging from 50.7 to 56.4 and indicating a light eutrophic state. Spatially, the western area displayed higher nutrient and chlorophyll a concentrations. Changes in hydro-meteorological variables and nutrients from inflowing rivers were the main factors correlated with water quality in Gaoyou Lake. Thus, pollution source apportionment and management within Huaihe River basin should be considered to reduce the external loadings of nutrients in order to improve and sustain long-term water quality.

Climate-associated variation in the drivers of benthic macroinvertebrate species-area relationships across shallow freshwater lakes.

The island species-area relationship (ISAR) describes how species richness increases with increasing area of a given island or island-like habitat, such as freshwater lakes. While the ISAR is one of the most common phenomena observed in ecology, there is variation in both the form of the relationship and its underlying mechanisms. We compiled a global data set of benthic macroinvertebrates from 524 shallow freshwater lakes, ranging from 1 to 293,300 ha in area. We used individual-based rarefaction to determine the degree to which ISAR was influenced by mechanisms other than passive sampling (larger islands passively sample more individuals from the regional pool and, therefore, have more species than smaller islands), which would bias results away from expected relationships between rarefied species richness (and other measures that capture relative abundances) and lake area. We also examined how climate may alter the shape of the ISARs. We found that both rarefied species richness (the number of species standardized by area or number of individuals) and a measure of evenness emphasizing common species exhibit shallow slopes in relationships with lake area, suggesting that the expected ISARs in these lakes most likely result from passive sampling. While there was considerable variation among ISARs across the investigated lakes, we found an overall positive rarefied ISAR for lakes in warm (i.e. tropical/subtropical) regions (n = 195), and in contrast, an overall negative rarefied ISAR in cool (i.e. north temperate) lakes (n = 329). This suggested that mechanisms beyond passive sampling (e.g. colonization-extinction dynamics and/or heterogeneity) were more likely to operate in warm lakes. One possible reason for this difference is that the area-dependent intensity of fish predation, which can lead to flatter ISARs, is weaker in warmer relative to cooler lakes. Our study illustrates the importance of understanding both the pattern and potential processes underlying the ISARs of freshwater lakes in different climatic regions. Furthermore, it provides a baseline for understanding how further changes to the ecosystem (i.e. in lake area or climate) might influence biodiversity patterns.

Spatial and temporal variation in lake macroinvertebrate communities is decreased by eutrophication.

Eutrophication impacts freshwater ecosystems and biodiversity across the world. While temporal monitoring has shown changes in the nutrient inputs in many areas, how spatial and temporal beta diversity change along the eutrophication gradient under a changing context remains unclear. In this regard, analyses based on time series spanning multiple years are particularly scarce. We sampled benthic macroinvertebrates in 32 sites across three lake habitat types (MACROPHYTE, OPEN WATER, PHYTOPLANKTON) along the eutrophication gradient of Lake Taihu in four seasons from 2007 to 2019. Our purpose was to identify the relative contributions of spatial and temporal dissimilarity (i.e., inter-annual dissimilarity and seasonal dissimilarity) to overall benthic biodiversity. We also examined spatio-temporal patterns in community assembly mechanisms and how associated variation in benthic macroinvertebrate communities responded to nutrient indicators. Results showed that eutrophication caused macroinvertebrate community homogenization both along spatial and temporal gradients. Though spatial variability dominated the variation of species richness, abundance and community dissimilarity, seasons within years dissimilarity, inter-annual dissimilarity and seasonal dissimilarity were much more sensitive to eutrophication. Moreover, eutrophication inhibited a strong environmental control in benthic macroinvertebrate community assembly, including a dominant role of deterministic process in the spatial variation of macroinvertebrate communities and transition from stochastic to deterministic process in the temporal assembly of macroinvertebrate communities along the eutrophication gradient. In addition, some sites in PHYTOPLANKTON habitats showed similar spatial dissimilarity and spatial SES as sites in MACROPHYTE habitats, and the decreased spatial dissimilarity of three habitats implying that lake ecosystem recovery projects have achieved their goal at least to a certain degree.

The Multifaceted Effects of Short-Term Acute Hypoxia Stress: Insights into the Tolerance Mechanism of Propsilocerus akamusi (Diptera: Chironomidae).

Plenty of freshwater species, especially macroinvertebrates that are essential to the provision of numerous ecosystem functions, encounter higher mortality due to acute hypoxia. However, within the family Chironomidae, a wide range of tolerance to hypoxia/anoxia is displayed. Propsilocerus akamusi depends on this great tolerance to become a dominant species in eutrophic lakes. To further understand how P. akamusi responds to acute hypoxic stress, we used multi-omics analysis in combination with histomorphological characteristics and physiological indicators. Thus, we set up two groups-a control group (DO 8.4 mg/L) and a hypoxic group (DO 0.39 mg/L)-to evaluate enzyme activity and the transcriptome, metabolome, and histomorphological characteristics. With blue-black chromatin, cell tightness, cell membrane invagination, and the production of apoptotic vesicles, tissue cells displayed typical apoptotic features in the hypoxic group. Although lactate dehydrogenase (LDH), alcohol dehydrogenase (ADH), catalase (CAT), and Na+/K+ -ATPase (NKA) activities were dramatically enhanced under hypoxic stress, glycogen content, and superoxide dismutase (SOD) activities were significantly reduced compared to the control group. The combined analysis of the transcriptome and metabolome, which further demonstrated, in addition to carbohydrates, including glycogen, the involvement of energy metabolism pathways, including fatty acid, protein, trehalose, and glyoxylate cycles, provided additional support for the aforementioned findings. Lactate is the end product of glycogen degradation, and HIF-1 plays an important role in promoting glycogenolysis in acute hypoxic conditions. However, we discovered that the ethanol tested under hypoxic stress likely originates from the symbiodinium of P. akamusi. These results imply that some parameters related to energy metabolism, antioxidant enzyme activities, and histomorphological features may be used as biomarkers of eutrophic lakes in Chironomus riparius larvae. The study also provides a scientific reference for assessing toxicity and favoring policies to reduce their impact on the environment.

Macroinvertebrate Response to Internal Nutrient Loading Increases in Shallow Eutrophic Lakes.

In eutrophic lakes, even if external loading is controlled, internal nutrient loading delays the recovery of lake eutrophication. When the input of external pollutants is reduced, the dissolved oxygen environment at the sediment interface improves in a season without algal blooms. As an important part of lake ecosystems, macroinvertebrates are sensitive to hypoxia caused by eutrophication; however, how this change affects macroinvertebrates is still unknown. In this study, we analysed the monitoring data of northern Lake Taihu from 2007 to 2019. After 2007, the external loading of Lake Taihu was relatively stable, but eutrophication began to intensify after 2013, and the nutrients in the sediments also began to decline, which was related to the efficient use of nutrients by algal blooms. The community structure and population density of macroinvertebrates showed different responses in different stages. In particular, the density of oligochaetes and the Shannon-Wiener index showed significant differences in their response to different stages, and their sensitivity to eutrophication was significantly reduced. Under eutrophication conditions dominated by internal loading, frequent hypoxia occurs at the sediment interface only when an algal bloom erupts. When there is no bloom, the probability of sediment hypoxia is significantly reduced under the disturbance of wind. Our results indicate that the current method for evaluating lake eutrophication based on oligochaetes and the Shannon-Wiener diversity index may lose its sensitivity.

[Long-term Succession Patterns and Driving Factors of Water Quality in a Flood-pulse System Lake: A Case Study of Lake Luoma, Jiangsu Province].

Lake Luoma is an important storage lake for the Eastern route of the South-to-North Water Diversion Project (NSBD), which has many functions including flood control and irrigation, drinking water supply, and ecological maintenance. In order to understand the succession patterns and driving factors of water quality in Lake Luoma, we used monthly monitoring data from 2009 to 2020 in combination with historical data from 1996 to 2008. The long-term succession patterns, seasonal dynamics, and spatial patterns of total nitrogen (TN), total phosphorus (TP), permanganate index, and ammonia nitrogen (NH+4-N) were examined, and the influence of meteorological and hydrological factors on water quality was explored through correlation analyses and generalized additive models. The results showed that it remained in the status of grade Ⅳ-inferior Ⅴ over the past 25 years. The concentration of TN, which was the main pollutant, changed significantly (1.06-3.49 mg·L-1), experiencing three stages of gradual decline (1996-2002), significant interannual fluctuation (2002-2015), and significant increase (2015-2020). Permanganate index decreased significantly (2.97-6.38 mg·L-1), whereas TP and NH+4-N concentration fluctuated slightly, ranging from 0.024-0.076 mg·L-1 and 0.11-0.69 mg·L-1, respectively. The concentration of TN and TP increased abnormally in the summer of 2017-2020, reaching 3.30 mg·L-1 and 0.14 mg·L-1 in August, respectively, which was approximately 1.5 and 2.4 times the annual average. In terms of seasonal dynamics, the seasonal variation in water quality between summer/autumn and winter/spring reversed after 2015, with water quality in summer/autumn being worse than that in winter and spring, indicating the exacerbation of eutrophication. The water quality in the southern area was obviously better than that in the northern area. The input of pollutants from the Yihe River and Middle Canal increased with water quantity since 2015, which drove the water quality deterioration through nutrients. Our results suggested that the water quality of Lake Luoma should be improved by strengthening exogenous pollution reduction, endogenous control, polder dismantling, and ecological restoration.

Effects of nutrient reduction and habitat heterogeneity on benthic macroinvertebrate assemblages in a large shallow eutrophic lake.

The Taihu Lake ecosystem has been subjected to numerous anthropogenic stressors during the past decades, leading to substantial changes in nutrient dynamics and habitat quality. For instance, the northwestern lake bays receive large amounts of nutrient-rich wastewater and have frequently experienced algal blooms, while the eastern lake region is still dominated by submersed macrophytes. Such changes in environmental characteristics can greatly impact benthic macroinvertebrate communities. We used a 15-year monitoring data series collected by the Taihu Laboratory for Lake Ecosystem Research to examine the spatial and temporal variations of the benthic invertebrate fauna and evaluate its status and trends. We found that three major communities could be distinguished based on taxonomic group composition and abundance, and these corresponded well with three lake habitat types: algal-dominated, macrophyte-dominated, and open-lake zone. An analysis of temporal trends showed major changes in the macroinvertebrates during the study period, largely driven by a lake-wide and significant decline in the abundance of pollution-tolerant taxa. The spatial and temporal variations of macroinvertebrate communities were mainly explained by nutrients (e.g., total nitrogen and ammonium concentrations) and habitat factors (e.g., sediment substrates and macrophyte biomass) as indicated by Random Forests regression, but the major drivers of macroinvertebrate density differed among the three lake zones at the temporal scale. Moreover, our findings suggest that benthic invertebrates were more sensitive to the improvement of the lake's environmental conditions than the pelagic community was. This study provides insights into the responses of macroinvertebrates to ecological dynamics in lakes and highlights the importance of continued monitoring for tracking long-term changes.

Macroinvertebrate diversity and ecosystem functioning across the eutrophication gradients of the middle and lower reaches of Yangtze River lakes (China).

Biodiversity, which strengthens ecosystem stability, ecosystem function, and ecosystem services, is threatened by anthropogenic perturbation and climate change worldwide. However, despite the study of the role of biodiversity in multiple facets of freshwater ecosystems, the linkages between macroinvertebrates diversity and ecosystem functioning have not yet been well-assessed in eutrophication gradients of lowland river-floodplain systems. In this study, we have examined the relationship between macroinvertebrates diversity (species diversity, functional diversity, phylogenetic diversity) and macroinvertebrates biomass across the three typically featured eutrophication gradients: "MACROPHYTE," "TRANSITION," and "PHYTOPLANKTON," of floodplain lakes in the middle and lower reaches of the Yangtze River (China). Our results suggest that macroinvertebrates diversity in three different lacustrine conditions, biomass, and the relationship between diversity and biomass varied along eutrophication gradients. Functional richness and variance (divergence in taxon community) were the two important macroinvertebrate diversity indices, which accounted for the largest amount of variation in the biomass (63% in PHYTOPLANKTON lakes and 57% in MACROPHYTE lakes, respectively). We also found that the macrophyte coverage is more important than the relative abundance in maintaining the macroinvertebrates diversity and biomass in lowland Yangtze floodplain lake systems, while the relative abundance of macrophyte would change the BEF relationship. Our results demonstrate the functional performance of Yangtze River lakes, which would change with increased nutrient loading and decreased macrophyte coverage and would highlight the significance of the restoration of macrophytes to reduce nutrient loads.

Decrease in macrofauna density increases the sediment phosphorus release and maintains the high phosphorus level of water column in Lake Taihu: A case study on Grandidierella taihuensis.

Internal phosphorus (P) loading can increase the P level in the water column and further sustains cyanobacterial blooms. This study focused on the role of benthic fauna bioturbation in affecting the sediment P release and the P level of water column in a eutrophic lake, Lake Taihu. The macrofauna density decreased from 4766.56 ± 10541.80 ind/m2 in 2007 to 345 ± 447.63 ind/m2 in 2020 due to the frequent bottom-water hypoxia in Lake Taihu. The reduced macrofauna density majorly resulted from Grandidierella taihuensis, Limnodrilus hoffmeisteri, and Tanypus chinensis larvae, and their total density decreased by approximately 97% in 2020 compared to 2007. G. taihuensis, one of the major benthic faunas, was further used as a representative to investigate the effects of bioturbation on sediment P release using high-resolution sampling and imaging techniques. The results show that G. taihuensis can increase the O2 penetration depth by more than 20 mm through bio-irrigation, and causes the redox conditions in burrows and surrounding sediments to change dramatically within a few minutes due to the intermittent ventilation. Subsequent oxidation of the soluble Fe(II) led to the formation of Fe-oxide bound P in the surface sediments, thereby increasing the P retention in the sediments. When the G. taihuensis density was 1563 ind/m2 at the sampling site, approximately 0.12 g m-2 yr-1 P can be retained in sediments. As previous studies have shown that L. hoffmeisteri and T. chinensis played a similar role in increasing the P retention in sediments through their bioturbation activities, the sharp decline in benthic fauna density and burrowing activities in Lake Taihu should be an important reason for maintaining the high P level in the water column by decreasing the P retention in sediments.

Determining heavy metal pollution in sediments from the largest impounded lake in the eastern route of China's South-to-North Water Diversion Project: Ecological risks, sources, and implications for lake management.

The eastern route of the South-to-North Water Diversion Project (ER-SNWDP) is a major human health project designed to alleviate the water scarcity in the Beijing-Tianjin-Hebei region in China. Impounded lake water security is directly related to the water diversion project effectiveness. At present, there is not a thorough understanding of the sediment heavy metals in Lake Hongze, the largest impounded lake of the ER-SNWDP. Consequently, this study reports a distribution analysis of Cu, Zn, Pb, Cr, Cd, As, Hg, and Ni in 101 sediment samples from Lake Hongze; we, utilized the enrichment factor, geoaccumulation index, and potential ecological risk index for the are to determine the ecological risk of heavy metals. The heavy metal source was examined with correlation analysis and principal component analysis-multiple linear regressions. The results showed that the average heavy metal content (Cu, Zn, Pb, Cr, Cd, As, Hg, Ni) were 0.03-1.57 times greater than the Jiangsu Province background values. Cd, As, and Hg were the main contributors to the Lake Hongze ecological risk. Spatially, the open water area was the most polluted among the four lake parts, and most of the flushing area had a low ecological risk. Chengzi bay and the western lake area have similar risk profiles, but are lower than the open water area risk. Source analysis showed that nonpoint-source agricultural pollution and industrial production were important pollution sources, while a considerable portion of the heavy metal content came from atmospheric deposition and natural sources. This study identified the main contamination areas and revealed the possible sources of each heavy metal; as such, this study can serve as a reference for the remediation and management of Lake Hongze to ensure the water safety of the ER-SNWDP.

[Community Structure of Phytoplankton and Environmental Impact Factors in Lake Hongze from 2015 to 2020].

Lake Hongze is an essential storage lake for the "Eastern Route of the South-North Water Diversion Project" and plays an important role in climate adjustment and flood prevention and control. To study the structural evolution of phytoplankton communities in Lake Hongze and their relationship with environmental factors and to understand the status of the ecosystem of Lake Hongze before the "ten-year fishing ban," monthly monitoring was carried out from 2015 to 2020. During the study period, total nitrogen showed a significant downward trend starting in 2017, the total phosphorus and chemical oxygen demand declined slightly, the water temperature had no obvious change trend, and the water depth and transparency increased from 2015 to 2018 and then declined significantly. A total of 102 genera of phytoplankton in eight phyla were identified, with a total of 310 species. The dominant phytoplankton phyla mainly included Chlorophyta and Bacillariophyta, followed by Cyanophyta and Pyrrophyta. The dominant genera were Scenedesmus, Aulacoseira, Cryptomonas, Cyclotella, Tetraedron, Microcystis, and Dolichospermum. The results of non-metric multidimensional scaling (NMDS) showed that the structural composition of the phytoplankton community differed significantly among years, seasons, and sampling areas, mainly due to the redistribution among dominant genera. NMDS analysis also indicated that variation in the phytoplankton community in Lake Hongze was mainly related to water temperature, total nitrogen, total phosphorus, water depth, and transparency. Total nitrogen, water depth, and phytoplankton community structure were significantly correlated with interannual succession, whereas water temperature, total nitrogen, and phytoplankton seasonal succession were also significantly correlated. Combined with the measures taken by the management department in recent years, the changes in the structure of the phytoplankton community may be related to the removal of the fence and other management and restoration measures in Lake Hongze.

[Spatio-temporal Distribution Characteristics and Driving Factors of Zooplankton in Hongze Lake].

Hongze Lake is the fourth largest freshwater lake in China and is an important source of water for surrounding industrial and agricultural processes and fishery resources. Analyzing the changes in the zooplankton community structure in Hongze Lake can provide scientific support for the scientific management of its ecology and environment. A one-year monthly monitoring study was conducted from March 2017 to February 2018 to analyze the temporal and spatial changes in species composition, density, and biomass of zooplankton in Hongze Lake, as well as the seasonal changes in community diversity and dominant species. Canonical correspondence analysis was employed to explore the relationships between the temporal and spatial changes in zooplankton and the environmental factors of Hongze Lake. The results showed that the average annual density of zooplankton in Hongze Lake was 383.87 ind ·L-1, and the average annual biomass was 1.36 mg ·L-1. The community structure of zooplankton in Hongze Lake varied greatly across time and space. Community structure varied greatly in summer, and zooplankton density and biomass reached a maximum in autumn. The community structure of the zooplankton was the simplest in winter. Chengzi Bay and Lihewa Bay exhibited an abundance of many different zooplankton species with limited spatial differentiation, whereas the zooplankton in the overflow area comprised fewer species but exhibited greater spatial variation. In summer, water level and temperature are the dominant factors, whereas in autumn and winter, the dominant factors are water temperature, nutrients, and chlorophyll. Canonical correspondence analysis showed that the temporal and spatial changes in zooplankton community structure in Hongze Lake were mainly determined by water level, total phosphorus, water temperature, and total nitrogen content. Water level fluctuation has the greatest direct impact on zooplankton community structure, and water quality regulation has indirect impact.

Agricultural activities compromise ecosystem health and functioning of rivers: Insights from multivariate and multimetric analyses of macroinvertebrate assemblages.

Agricultural activities often lead to nutrient enrichment and habitat modification in rivers, possibly altering macroinvertebrate assemblages and hence ecosystem functioning. For the sake of environmental management and conservation, therefore, assessing the impacts of agricultural activities becomes indispensable, especially when these activities are predicted to be intensified in the future. In this study, the plain river network in the Lake Chaohu Basin was chosen to examine how agricultural activities influence the functioning of rivers by assessing land use, water quality, habitat condition and macroinvertebrate assemblages, followed by calculating the macroinvertebrate-based multimetric index (MMI) to indicate overall ecosystem health of the rivers. We found that agricultural activities lowered the diversity of macroinvertebrates (e.g. total number of taxa and Simpson index) primarily due to elevated ammonium concentrations in water and reduced microhabitat types, thereby impairing the habitat integrity and nutrient cycling of rivers. The macroinvertebrate-based MMI was positively correlated with increasing habitat quality but negatively with increasing nutrient concentrations, suggesting its high reliability for indicating the impacts of agricultural activities, which was further substantiated by classification and regression tree (CART) analysis. We recommend analyzing macroinvertebrate assemblages using both multivariate and multimetric approaches to offer a more comprehensive evaluation of the impacts of agricultural activities on ecosystem health. Some environmental (CODMn, NH4+-N and PO43--P) and biological parameters (total number of taxa), however, can be used as good proxies for MMI, when time and resources for gathering information to develop MMI are limited.

Riverine transport and water-sediment exchange of polycyclic aromatic hydrocarbons (PAHs) along the middle-lower Yangtze River, China.

We examined the riverine transport of polycyclic aromatic hydrocarbons (PAHs) based on their spatial-temporal distributions in water and sediments from the mainstream along the middle and lower Yangtze River. According to the fugacity fraction (ff) estimation, sediments performed as a secondary emission source of two-, three-, and four-ringed PAHs and as a sink for five- and six-ringed congeners, leading to higher ecological and human health risks especially towards the lower reaches. The higher PAH levels observed in the more developed delta and megacities were highly linked to economic parameters. This was further supported by the source apportionment performed using the principal component analysis-multiple linear regression (PCA-MLR) model, which showed major contributions of coal and coke combustions along with vehicle emissions. The spatial-temporal distribution revealed that water runoff was the major contribution to PAHs transport along the middle-lower Yangtze River, whereas a sharp decrease in sediment discharge due to the dam impoundment along the upper reaches would lead to an increase in the catchment retention effect of PAHs. Hence, the biogeochemical processes of PAHs and their impacts on the fragile ecosystems as a consequence of the further modification of the sedimentary system in rivers need to be fully explored.

Lakes in the era of global change: moving beyond single-lake thinking in maintaining biodiversity and ecosystem services.

The Anthropocene presents formidable threats to freshwater ecosystems. Lakes are especially vulnerable and important at the same time. They cover only a small area worldwide but harbour high levels of biodiversity and contribute disproportionately to ecosystem services. Lakes differ with respect to their general type (e.g. land-locked, drainage, floodplain and large lakes) and position in the landscape (e.g. highland versus lowland lakes), which contribute to the dynamics of these systems. Lakes should be generally viewed as 'meta-systems', whereby biodiversity is strongly affected by species dispersal, and ecosystem dynamics are contributed by the flow of matter and substances among locations in a broader waterscape context. Lake connectivity in the waterscape and position in the landscape determine the degree to which a lake is prone to invasion by non-native species and accumulation of harmful substances. Highly connected lakes low in the landscape accumulate nutrients and pollutants originating from ecosystems higher in the landscape. The monitoring and restoration of lake biodiversity and ecosystem services should consider the fact that a high degree of dynamism is present at local, regional and global scales. However, local and regional monitoring may be plagued by the unpredictability of ecological phenomena, hindering adaptive management of lakes. Although monitoring data are increasingly becoming available to study responses of lakes to global change, we still lack suitable integration of models for entire waterscapes. Research across disciplinary boundaries is needed to address the challenges that lakes face in the Anthropocene because they may play an increasingly important role in harbouring unique aquatic biota as well as providing ecosystem goods and services in the future.

The direct and indirect effects of land use and water quality on phytoplankton communities in an agriculture-dominated basin.

Understanding the factors that control biodiversity in rivers is challenging due to the variety of potential sources, linkages, and processes. This research assesses the effects of land use on phytoplankton communities across water quality gradients. By employing abiotic and biotic datasets of 149 catchments in Lake Chaohu basin, China, and a structural equation model (SEM), the direct and indirect effects of land use and water quality on phytoplankton dynamic were analyzed. Both land use and water quality had statistically significant direct effects on phytoplankton community attribute and diversity, although these effects differed among these indices. For instance, farmland was found to positively affect the abundance and diversity indices, while total nitrogen (TN) had significant positive effects on species richness and abundance. Importantly, the average indirect effects strengthened the effects of land use (e.g., built-up land and woodland) up to 82.4% mainly through nutrients, while the average indirect effects weakened the effects of land use (e.g., farmland) by as much as 49.9% mainly due to nutrients, thus indicating the prevailing role of the effects of land use on phytoplankton based on nutrient concentrations. The results suggest that nutrients can regulate the effect of land use on phytoplankton community attribute and diversity indices. This study highlights the advantages of using an SEM because the potential linkages for phytoplankton diversities are more likely to be identified with this method than with a classical linear regression model. Therefore, SEM has wide application prospects in the field of the conservation of biodiversity in freshwater rivers.