Land use and river-lake connectivity: Biodiversity determinants of lake ecosystems.

Lake ecosystems confront escalating challenges to their stability and resilience, most intuitively leading to biodiversity loss, necessitating effective preservation strategies to safeguard aquatic environments. However, the complexity of ecological processes governing lake biodiversity under multi-stressor interactions remains an ongoing concern, primarily due to insufficient long-term bioindicator data, particularly concerning macroinvertebrate biodiversity. Here we utilize a unique, continuous, and in situ biomonitoring dataset spanning from 2011 to 2019 to investigate the spatio-temporal variation of macroinvertebrate communities. We assess the impact of four crucial environmental parameters on Lake Dongting and Lake Taihu, i.e., water quality, hydrology, climate change, and land use. These two systems are representative of lakes with Yangtze-connected and disconnected subtropical floodplains in China. We find an alarming trend of declining taxonomic and functional diversities among macroinvertebrate communities despite improvements in water quality. Primary contributing factors to this decline include persistent anthropogenic pressures, particularly alterations in human land use around the lakes, including intensified nutrient loads and reduced habitat heterogeneity. Notably, river-lake connectivity is pivotal in shaping differential responses to multiple stressors. Our results highlight a strong correlation between biodiversity alterations and land use within a 2-5 km radius and 0.05-2.5 km from the shorelines of Lakes Dongting and Taihu, respectively. These findings highlight the importance of implementing land buffer zones with specific spatial scales to enhance taxonomic and functional diversity, securing essential ecosystem services and enhancing the resilience of crucial lake ecosystems.

Historical and dispersal processes drive community assembly of multiple aquatic taxa in glacierized catchments in the Qinghai-Tibet plateau.

Understanding the relative role of dispersal dynamics and niche constraints is not only a core task in community ecology, but also becomes an important prerequisite for bioassessment. Despite the recent progress in our knowledge of community assembly in space and time, patterns and processes underlying biotic communities in alpine glacierized catchments remain mostly ignored. To fill this knowledge gap, we combined the recently proposed dispersal-niche continuum index (DNCI) with traditional constrained ordinations and idealized patterns of species distributions to unravel community assembly mechanisms of different key groups of primary producers and consumers (i.e., phytoplankton, epiphytic algae, zooplankton, macroinvertebrates, and fishes) in rivers in the Qinghai-Tibet Plateau, the World's Third Pole. We tested whether organismal groups with contrasting body sizes differed in their assembly processes, and discussed their applicability in bioassessment in alpine zones. We found that community structure of alpine river biotas was always predominantly explained in terms of dispersal dynamics and historical biogeography. These patterns are most likely the result of differences in species-specific functional attributes, the stochastic colonization-extinction dynamics driven by multi-year glacier disturbances and the repeated hydrodynamic separation among alpine catchments after the rising of the Qilian mountains. Additionally, we found that the strength of dispersal dynamics and niche constraints was partially mediated by organismal body sizes, with dispersal processes being more influential for microscopic primary producers. Finding that zooplankton and macroinvertebrate communities followed clumped species replacement structures (i.e., Clementsian gradients) supports the notion that environmental filtering also contributes to the structure of high-altitude animal communities in glacierized catchments. In terms of the applied fields, we argue that freshwater bioassessment in glacierized catchments can benefit from incorporating the metacommunity perspective and applying novel approaches to (i) detect the optimal spatial scale for species sorting and (ii) identify and eliminate the species that are sensitive to dispersal-related processes.

Improvement in water pollution control alters nutrient stoichiometry of Guanting Reservoir near Beijing, North China.

Significant improvement in wastewater treatment is the most effective way for eutrophication control, especially in semiarid regions. However, its effect on the nutrient status and stoichiometry of the receiving water body has remained poorly considered and understood at broad temporal scales. Taking Guanting Reservoir (GR) in Hebei-Beijing (P. R. China) as an example, we present a study that links a continuous monitoring dataset for GR with corresponding estimates of human-induced nutrient discharges in its watershed from the year 2006 to 2019. We find that current GR belongs to strict P limitation and the faster decrease of TP than TN concentrations and continuous increase of TN/TP mass ratios in GR are attributed to the water restoration investment-induced declining of nutrient loadings. The improved municipal wastewater treatment capacity is mainly responsible for these significant changes, due to the higher removal efficiency of TP than TN in municipal wastewater. Given the potential ecological impact on aquatic biodiversity as well as ecosystem function of changes in TN/TP ratios and higher retention rate of TP (97.4%) compared with TN (93.1%) in GR, our findings highlight that future strategy for water pollution control should not only concentrate on more nutrient reduction efficiencies but attach importance to their stoichiometric balance to reduce the potential risk of phytoplankton blooms and toxin production during the water quality recovery of lakes or reservoirs.

Quantitative analysis of ecological suitability and stability of meandering rivers.

BACKGROUND: As the most widely distributed river form in the world, meandering river is of great significance for stabilizing the physical structure of the river and maintaining ecosystem. To quantitatively study the positive effects of meandering rivers, the Chishui River, a natural tributary of the Yangtze River in Southwest China, is selected as the research area, and two typical river sections with different meandering degrees are selected as the research objects. METHODS: Based on the field survey data, the local endemic fish Procypris rabaudi (Tchang) is considered the object fish, and a hydrodynamic model was used to simulate the distribution of water depth and flow velocity in certain river reaches at different flows. By introducing the weighted usable area (WUA) and hydraulic unit diversity index, combined with the suitability curves of the study species, the hydraulic characteristics and habitat suitability changes of two river reaches under different flows are summarized and analyzed, and the hydrogeomorphological process of the studied river section is generalized. RESULTS: With the change in discharge, a positive correlation is observed between the maximum velocity and depth of the meandering river and the discharge, whereas the WUA and hydraulic unit index of the meandering river have relatively small changes. Under low discharge, the distribution of pool-riffle sequences can be seen in the meandering reach, which is essential to improve the ecological suitability and stability of the river. CONCLUSIONS: This study provides scientific sustentation for river restoration and fish conservation.

Microplastic contamination assessment in water and economic fishes in different trophic guilds from an urban water supply reservoir after flooding.

Rain and floods events are responsible for the transport of microplastics in freshwater ecosystems, yet to date, rare study has examined microplastics pollution in urban water supply reservoirs during such events. In this study, we investigated the concentrations and characteristics of microplastic in water and economic fish species with different feeding guilds in the Dafangying Reservoir, an important source of drinking water for Hefei city. Microplastic concentrations in water were relatively higher than that in natural lakes, indicating abundant microplastic contaminants input through overland runoff triggered by flooding. Our results detected five types (fiber, debris, film, microbead and particle) and six colors (black, transparent, blue, yellow, red and green) of microplastics in water samples. Fiber accounted for the dominant shape, which may result from the household sewage from washing clothes and desquamated fiber transported by wind and overland runoff. Meanwhile, transparent was the predominant microplastic color, which can be ascribe to the widely use of intentionally manufactured transparent disposable plastic commodities in cities. Then in fish samples, the microplastic concentrations ranged from 8.75 to 51.3 items/individual in fish guts, and 9.5-52.6 items/individual in fish gills. Our results demonstrated significant higher microplastic concentrations in planktivorous and herbivorous species. The filter feeding capture mode, i.e., engulfing floating prey through frequently drawing in large volume of water confused with microplastics, may result in the higher microplastic concentrations of planktivorous fishes. Due to the dense microplastics adhering on plant surface, herbivorous fishes can concentrate higher microplastics abundance through the ingestion of macrophytes. According to the biological concentration factor (BCF), all the determined microplastics gave BCF far below 1, suggesting the low bioaccumulation capacity of microplastics in fish species.

Effects of algae proliferation and density current on the vertical distribution of odor compounds in drinking water reservoirs in summer.

Reservoirs are an important type of drinking water source for megacities, while lots of reservoirs are threatened by odor problems during certain seasons. The influencing factors of odor compounds in reservoirs are still unclear. During August 2019, a nationwide survey investigating the distribution of odor compounds in reservoirs used as drinking water sources was conducted on seven reservoirs. 2-methylisoborneol (2-MIB) and geosmin were detected in almost every reservoir, and some odor compound concentrations even exceeded the odor threshold concentration. The average concentration of 2-MIB was 2.68 ng/L, and geosmin was 3.63 ng/L. The average chlorophyll a concentration was 8.25 µg/L. The dominant genera of phytoplankton in these reservoirs belonged to cyanobacteria and diatom. Statistical analysis showed that odor compound concentration was significantly related to the chlorophyll a concentration and indicated that the odor compounds mainly came from phytoplankton. The concentration of odor compounds in the euphotic zone was significantly related to phytoplankton species and biomass. Therefore, the odor compound concentrations in the subsurface chlorophyll maxima layer was generally higher than in the surface layer. However, the odor compounds in the hypolimnion layer were related to the density current. This research suggests that both phytoplankton proliferation events and heavy storm events are important risk factors increasing odor compounds in reservoirs. Control of algal bloom, in-situ profile monitoring system and depth-adjustable pumping system will greatly reduce the risk of odor problems in reservoirs using as water supplies for large cities.

Molecular biogeography of planktonic and benthic diatoms in the Yangtze River.

BACKGROUND: Diatoms are of great significance to primary productivity in oceans, yet little is known about their biogeographic distribution in oligotrophic rivers. RESULTS: With the help of metabarcoding analysis of 279 samples from the Yangtze River, we provided the first integral biogeographic pattern of planktonic and benthic diatoms over a 6030 km continuum along the world's third largest river. Our study revealed spatial dissimilarity of diatoms under varying landforms, including plateau, mountain, foothill, basin, foothill-mountain, and plain regions, from the river source to the estuary. Environmental drivers of diatom communities were interpreted in terms of photosynthetically active radiation, temperature, channel slope and nutrients, and human interference. Typical benthic diatoms, such as Pinnularia, Paralia, and Aulacoseira, experienced considerable reduction in relative abundance downstream of the Three Gorges Dam and the Xiluodu Dam, two of the world's largest dams. CONCLUSIONS: Our study revealed that benthic diatoms are of particular significance in characterizing motile guild in riverine environments, which provides insights into diatom biogeography and biogeochemical cycles in large river ecosystems.

Macroinvertebrate communities and the relationships with biotic factors in river-connected lakes in the lower reaches of Yangtze River, China.

The relationships of macroinvertebrate communities with abiotic factors in lake and river system were well documented, but their relationships with biotic factors were few explored. The macroinvertebrate communities in two river-disconnected lakes (Poyang Lake and Shijiu Lake) and the rivers connected to Shijiu Lake were investigated to reveal the differences in communities and explore the relationships with biotic factors. A total of 34 species were recorded in the three water bodies. Combined with the previous study results, the dominant species in Poyang Lake is almost unchanged since 1997. Mollusks were dominated in abundance in Poyang Lake and the rivers connected to Shijiu Lake, while oligochaetes dominated the communities in Shijiu Lake. The alpha diversity indices of macroinvertebrates in Poyang Lake and the rivers connected to Shijiu Lake were distinctly higher than that of Shijiu Lake, and the beta diversity index of Shijiu Lake was the highest, supporting the rules that alpha diversity of macroinvertebrates achieves a maximum at a moderate level of connectivity and beta diversity seems to be higher when the connectivity is weaker. The differences in communities were significant between the Poyang Lake and Shijiu Lake, while the differences in the Poyang Lake and the rivers connected to Shijiu Lake were not significant. According to the results of canonical correspondence analysis (CCA), protozoon densities and phytoplankton biomass affected the distribution of macroinvertebrates in Shijiu Lake. Species number of planktonic crustaceans influenced the distribution of macroinvertebrates in rivers connected to Shijiu Lake, while species number of rotifer and densities of phytoplankton distinctly impacted on the distribution of macroinvertebrates in Poyang Lake.

[Succession of Phytoplankton Assemblages and Its Influencing Factors in Tangpu Reservoir, Zhejiang Province].

In order to explore the spatial-temporal dynamics of phytoplankton assemblages and its influencing factors in Tangpu Reservoir, phytoplankton and environmental variables were monthly monitored in 2011. The results showed that a total of 115 species of phytoplankton were identified, which belonged to 7 phyla and 62 genera. Phytoplankton abundance varied monthly with the maximum value (20.88×106 cells·L-1) in April and minimum (0.59×106 cells·L-1) in June. Variation partitioning of species data matrix showed that the variation of phytoplankton communities among months (account for 72.3%) was much larger than that among sampling sites (account for 2.5%), which indicated that phytoplankton communities had a high temporal but low spatial heterogeneity. Dominant species showed a marked seasonal succession pattern: diatom and blue-green algae species in spring, blue-green algae and green algae species in summer, diatom and cryptomonads species in autumn and winter. Result of multivariate analysis (RDA) indicated that HRT was the key factor affecting the shift between hydrological disturbance sensitive and tolerant species, and the formation of spring algal bloom; SiO2, WT and N:P were the key factors affecting the shift from diatom and cryptomonads species to blue-green algae and green algae species.

Toward holistic evaluation and assessment: linking ecosystems and human well-being for the three gorges dam.

A significant challenge exists in assessing the social and ecological impacts of development projects in a holistic and comprehensive manner. Our objective is to elucidate the linkages between ecological change and human well-being, and its importance in integrated assessment policy for development projects, using the Three Gorges Dam (China) as a case study. A collaborative research initiative was undertaken to review and synthesize published information on the ecological and human health effects of the Three Gorges Dam. Our synthesis suggests that the Three Gorges Dam has altered social-ecological dynamics of human health and ecosystem function in the Yangtze River basin with significant consequences for human well-being. Direct impacts to human well-being were grouped into four primary categories, including: (1) toxicological impacts; (2) shifting infectious disease dynamics; (3) natural hazards; and (4) social health. Social-ecological relationships were altered in complex ways, with both direct and indirect effects, positive and negative interactions, and chronic and acute impacts on human well-being. Our synthesis supports a comprehensive evaluation of development projects via integrated assessments of human and environmental consequences. This is probably best achieved through a coupled social-environmental impact assessment to ensure holistic and comprehensive analyses of expected costs and benefits. The role of research can thereby be to elucidate the linkages between ecosystems and human health to better inform the assessment process. A synthesis of the existing information on the Three Gorges suggests that this is best achieved through institutional collaboration and transdisciplinary integration of expertise.