Impoundment, environmental variables and temporal scale predict zooplankton beta diversity patterns in an Amazonian river basin

Seasonal management of multiple stressors: Interactive effects of dams and urbanization on pollution loads in the Shaying River Basin, eastern China

With population growth and accelerating urbanization in developing regions, numerous dams have been built to support industrial activities and residential water supply. These developments have exposed rivers to the multiple stressors of dams and urbanization, complicating river restoration and water quality predictions. Understanding of how these stressors interact to influence water quality is crucial for effective river management. Therefore, during the wet and dry seasons, we investigated pollutant concentrations (including EC, COD, TN, NH3-N, and TP) and habitat quality in four river systems across different stressor combinations of dam presence/absence and high- or low-intensity urbanization. The findings suggested that the interaction between dams and urbanization exerted additive effect on pollution load (PL) in the wet season and synergistic effect in the dry season. The generalized linear model (GLM) and structural equation modeling (SEM) results revealed that in the wet season, PL was directly influenced by both dams and urbanization, whereas in the dry season, they were driven indirectly by habitat degradation and directly by urbanization. The results of distance-based redundancy analysis (db-RDA) and variation partitioning analysis (VPA) revealed that the interactive effects contributed more to the variation in the structure of water quality parameters (WQPs) in the dry season (27.9 %) than in the wet season (11.3 %). Moreover, in the wet season, PL in the dam group increased gradually from upstream to downstream, whereas in the dry season, an increase occurred in the urban group. Dam elements (flood control and power generation) explained most of variance (29.7 %) in the WQPs in the wet season, whereas urbanization elements (nightlight intensity and land use index) explained most of the variance (33.8 %) in the dry season. It is recommended that in the wet season, dams should be collectively regulated to prevent pollutant migration via flood discharge, whereas in the dry season, efforts should focus on restoring riparian habitats and reducing urban point source pollution.

Dominant and keystone genera of microorganisms dominate the multi-trophic aquatic ecological integrity of the Yangtze finless porpoise reserve

Aquatic ecological integrity is a critical attribute to sustain a vibrant ecosystem, which reflects of the intricate balance among various trophic levels, ensuring the prosperity of the aquatic fauna. The Yangtze finless porpoise (Neophocaena asiaeorientalis), a flagship species in the Yangtze River ecosystem, has been grappling with the degradation of its aquatic habitat due to anthropogenic activities, but the current state of the ecosystem remains uncertain since the implementation of the initial 10-year period of the fishery ban. In this study, we evaluated the ecological integrity of the Yangtze finless porpoise Tongling Nature Reserve (including core zone, experimental zone, buffer zone, and semi-natural zone (artificial feeding zone)) by using a multi-trophic index of biological integrity (MT-IBI) involving phytoplankton, zooplankton, and microorganism. We found that the ecological status was relatively favorable both in experimental and core zones. However, the ecological conditions in the buffer zone and artificial feeding zone were significantly poorer. Hydraulic conditions, including flow velocity and water depth, along with nutrient concentrations such as chemical oxygen demand, and total nitrogen, were critical drivers influencing the MT-IBI values. It was particularly worth noting that the integrity of the aquatic ecosystem is largely affected from the presence of key microbial genera Pseudarthrobacter and Rhodococcus, which play a pivotal role in shaping polytrophic communities. This study provides a foundational understanding for the conservation of Yangtze finless porpoise habitat, and underscore the potential of the MT-IBI as a valuable tool for assessing ecosystem health across various aquatic environments in the future.

Spatiotemporal dynamics, community assembly and functional potential of sedimentary archaea in reservoirs: coaction of stochasticity and nutrient load

Archaea participate in biogeochemical cycles in aquatic ecosystems, and deciphering their community dynamics and assembly mechanisms is key to understanding their ecological functions. Here, sediments from 12 selected reservoirs from the Wujiang and Pearl River basins in southwest China were investigated using 16S rRNA Illumina sequencing and quantitative PCR for archaeal abundance and richness in all seasons. Generally, archaeal abundance and α-diversity were significantly correlated with temperature; however, β-diversity analysis showed that community structures varied greatly among locations rather than seasons, indicating a distance-decay pattern with geographical variation. The null model revealed the major contribution of stochasticity to archaeal community assembly, which was further confirmed by the neutral community model that could explain 71.7% and 90.2% of the variance in archaeal assembly in the Wujiang and Pearl River basins, respectively. Moreover, sediment total nitrogen and organic carbon levels were significantly correlated with archaeal abundance and α-diversity. Interestingly, these nutrient levels were positively and negatively correlated, respectively, with the abundance of methanogenic and ammonia-oxidized archaea: the dominant sedimentary archaea in these reservoirs. Taken together, this work systematically characterized archaeal community profiles in reservoir sediments and demonstrated the combined action of stochastic processes and nutrient load in shaping archaeal communities in reservoir ecosystems.

Phytoplankton dynamics and implications for eutrophication management in an urban river with a series of rubber dams

Rubber dams are widely used in urban rivers for landscape construction and flood control. However, the increased water residence time by dams usually causes phytoplankton accumulation. Developing a greater understanding of the phytoplankton dynamics and the effecting factors is essential for the eutrophication control of dammed rivers. Here, we investigated the variations in biomass and structure of phytoplankton communities along an urban landscape river with 30 rubber dams, and the main controlling factors during a 2-yr field monitoring. The biomass of phytoplankton significantly increased from 12.7 μg/L-Chl a and 1.14 × 107 ind./L-cells at the natural river part above dams to 65.2 μg/L-Chl a and 1.16 × 108 ind./L-cells at the 30th dam on average. There were different dominant taxa of phytoplankton between river sections with and without dams in different seasons. As Bacillariophyta dominated at the natural river part above dams throughout the year, accounting for 64.6% on average, and dominated at the 13th and 30th dams during the cold seasons (69.6% on average). But during the warm seasons, Cyanophyta and Chlorophyta increased obviously in the dammed river sections and became dominant taxa at the 30th dam, accounting for 55.9% and 34.7% respectively. The α-diversity of phytoplankton decreased along the series of dams. While the β-diversity between river sections with and without dams increased because of species replacement. Redundancy analysis revealed that nutrients, flow velocity and temperature were the main factors influencing the spatial-temporal variation in phytoplankton community structure in this river. High-frequency monitoring data further indicated that phosphorus and discharge explained most of the variations in phytoplankton biomass within the 13th dam impoundment. It suggested that management strategies should focus on reducing the phosphorus input concentration under 0.164 mg/L and increase the discharge higher than 0.64 m3/s during warm seasons, to prevent phytoplankton bloom and further eutrophication problems in this dammed river.

eDNA metabarcoding revealed differential structures of aquatic communities in a dynamic freshwater ecosystem shaped by habitat heterogeneity

Freshwater ecosystems have been threatened by complicated disturbances from both natural and anthropogenic variables, especially in dynamic and complex river basins. The environmental DNA (eDNA)-based approach provides a broader spectrum and higher throughput way of biomonitoring for biodiversity assessment compared with traditional morphological survey. Most eDNA metabarcoding studies have been limited to a few specific taxa/groups and habitat scopes. Here we applied the eDNA metabarcoding to characterize the structures and spatial variations of zooplankton and fish communities among different habitat types in a highly dynamic and complex freshwater ecosystem of the Daqing River basin (DRB). The results showed that varied species spectra of zooplankton and fish communities were identified and unique dominant species occurred across habitats. Additionally, markedly spatial distributions of biotic community structures were observed in areas with different habitat characteristics. Natural variables, including geographic distances and gradient ratio, as well as anthropogenic factors of chemical oxygen demand (COD) and organic chemicals demonstrated significant effects but different outcomes on the structures of zooplankton and fish communities. Moreover, the relative abundances of specific aquatic taxa were associated with the gradient of particular environmental variables. This case study verified the distribution patterns and differentiation mechanisms of biotic communities under habitat heterogeneity could be captured by application of eDNA biomonitoring. And habitat-specific and even species-specific environmental stressors would be diagnosed for improving management of complex river basins.