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Altering the hydrological connectivity between river channels and their riparian wetlands is a significant threat to river ecosystems. Aquatic insects are sensitive to environmental changes. In this study, community composition and functional traits of aquatic insects were investigated in reaches of the Manjiang and Songjiang Rivers, impacted by a water diversion project in northeast China. The species diversity of the flow-reduced reaches was more than twice as much as that of the reservoir riverine wetlands, and the species diversity of the flow-reduced reaches was less than twice as much as that of the natural riverine wetlands. Compared with the natural riverine wetlands, there was a lower abundance of scrapers in the reservoir wetlands, a higher abundance of filter collectors and shredders in the flow-reduced riverine wetlands, higher abundance of swimmers in the reservoir wetlands, and more sprawlers and swimmers in the flow-reduced wetlands. Co-occurrence network showed interspecific relationships of aquatic insect communities differed between the three types of riverine wetlands. Indicator species differed among wetland types. The environmental factors affecting the aquatic insect were water nitrate-nitrogen content, chlorophyll-a content, and electrical conductivity. In conclusion, proper hydrological connectivity between reaches wetlands should maintain to ensure ecological flow and biological connectivity. [ABSTRACT FROM AUTHOR]

Aim: High‐throughput pipelines supported by eDNA metabarcoding have been applied in various freshwater ecosystems. Both eDNA in ethanol (EtOH) samples (ES‐eDNA) and in water samples (WS‐eDNA) can provide comprehensive classification lists with good taxonomic resolution and coverage for determining freshwater biodiversity and biomonitoring. But, the advantages of ES‐eDNA metabarcoding over WS‐eDNA metabarcoding remain unclear for routine assessments of diversity of benthic macroinvertebrates in streams. Location: Qiantang River Basin, China. Methods: Here, we compared ES‐eDNA and WS‐eDNA metabarcoding to evaluate the performance of two eDNA workflows in determining biodiversity and recovery of damaged macroinvertebrate communities. All eDNA samples from the environment and bulk specimen of macroinvertebrates were processed into available molecular operational taxonomic units (MOTUs) and identified to the level of genus. Results: WS‐eDNA detected more exact sequence variants (ESVs) (formerly referred to as operational taxonomic units; OTUs), than did ES‐eDNA (2,866 vs. 2,406), but fewer macroinvertebrate ESVs (381 vs. 481). Among sampling sites, the two eDNA workflows exhibited relatively large dissimilarity on inferred community composition (p <.001). Furthermore, ES‐eDNA metabarcoding exhibited more consistent with morphological identification approaches than did WS‐eDNA metabarcoding (24.24% vs. 17.63%, p =.002), especially for species identified by traditional morphology (morphotaxa). Main conclusions: Based on the attributes of ES‐eDNA and WS‐eDNA, it is suggested that ES‐eDNA metabarcoding performs better than does WS‐eDNA metabarcoding in detecting local biodiversity and was consistent with morphological results, while WS‐eDNA was more suitable for exploring biodiversity patterns on a broad scale, as it is the easiest and most convenient way to collect samples. Results of this study suggest ES‐eDNA metabarcoding could be an option in building molecular measurement biomonitoring programme based on EtOH sample used for preserving biological samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new approach integrating heavy metal- and macrobenthos-based indices to assess benthic EcoQs was tested in Laoshan Bay. • The composite index more closely represents the benthic EcoQs than assessments based on single indices. • The acceptable/unacceptable areas in terms of benthic EcoQs were determined, and the benthic EcoQs was acceptable across ∼ 90% of the bay. • The framework proposed here is a useful tool for evaluating the benthic EcoQs of similar marine ecosystems. Many different indices have been developed to evaluate habitat quality status (EcoQs) in marine ecosystems; however, few studies have concurrently considered both abiotic and biotic indices in their assessments of benthic EcoQs. Here, we propose and test a framework for integrating heavy metal pollution-related indices and macrobenthos-based indices to assess the benthic EcoQs of Laoshan Bay (Yellow Sea, China). This bay is exposed to urbanization, construction, heavy metal pollution, and land- and marine-based culturing operations for commercially valuable species like fish, scallop, and laver (seaweed). We first assessed the EcoQs of Laoshan Bay using four heavy metal pollution-related indices, i.e., the geo-accumulation index (I geo), potential ecological risk index (RI), pollution load index (PLI), and Nemerow pollution index (Pn) and four macrobenthos-based indices, i.e., AZTI's Marine Biotic Index (AMBI), the multivariate AMBI (M−AMBI), BENTIX, and the feeding evenness index (jFD). All indices (except I geo) were then reclassified and combined to assess the overall EcoQs of Laoshan Bay. Our results show that, while some sites in Laoshan Bay have relatively high levels of heavy metal (Hg and Cd) pollution, the benthic EcoQs is acceptable across 88.90% of the bay. Kappa analysis showed that the agreement between any two indices was very low, which suggests that the composite index used here may be more robust for assessing EcoQs and more closely represent the actual status of benthic habitats than assessments based on single indices. In addition, the assessment framework proposed here is relatively flexible and can serve as a useful tool for evaluating the benthic EcoQs of similar marine ecosystems. [ABSTRACT FROM AUTHOR]

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., (© 2023. The Author(s).)

Pesticides from agricultural activities transfer to surrounding waterways, jeopardizing aquatic ecosystem. To better characterize transfer of pesticide residues and toxicity, a batch of pesticides were analyzed in 22 sediment samples collected from the ditches (< 5 m away from field) and receiving streams nearby a vegetable planting area, South China. Sum concentrations of pesticides in ditch sediments (152 ± 121 ng/g dry wt.) were higher than those in stream sediments (24.9 ± 14.9 ng/g dry wt.). Toxicity reduction from ditch to stream was different for two invertebrates. Stream sediment toxicity to Chironomus dilutus decreased considerably but elevated toxicity was still observed (50% mortality on average), while stream sediments exhibited no significant lethality to Hyallela azteca (< 10% mortality). Fipronil and its transformation products (FIPs) were responsible for sediment toxicity to the midges, and pyrethroids contributed significantly to the death of the amphipods. Hydrophobic pyrethroids were tended to stay in the ditches, whereas FIPs were detected in stream sediments at considerable concentrations due their possible transfer to the nearby streams and/or residential use. This physicochemical property-related transfer characteristics and intrinsic toxicity of the major toxicants explained the distinct toxicity reduction patterns for the two species, which highlighted their importance in assessing aquatic transfer and risk of agriculture derived pesticides. [Display omitted] • Vegetable planting activity causes high pesticide pollution in nearby ditches and streams. • Vegetable planting-related pesticides threaten the health of benthic invertebrates. • Toxicity reduction to midges and amphipods from ditch to stream was different. • Persistent and less hydrophobic pesticides are tended to transport to the stream. • Variation in transport and intrinsic toxicity explain different toxicity reduction. [ABSTRACT FROM AUTHOR]

A field experiment using an artificial step-pool system was conducted to restore the Diaoga River, a seriously incised mountain stream in Yunnan-Guizhou Plateau, southwest China. Twenty-four artificial steps, designed to mimic natural step forms, were constructed on three stretches of about 260 m length in the middle reach of the river. Channel topography, hydraulic features, aquatic habitats and stream ecology were monitored for 20 months. Following the construction of the artificial step-pool system, the stream bed development coefficient increased significantly. This indicates that actions helped to dissipate flow energy more effectively, enhancing the stability of the stream bed. The step-pools have effectively controlled the incision and stabilized the river morphology. In addition, they have created multiple habitats for different species and increased the habitat diversity. Improvement of the aquatic ecosystem is confirmed by increased density and taxa richness of benthic macro-invertebrates, which are used as an indicator species to evaluate stream ecology. [ABSTRACT FROM AUTHOR]

• A benthic invertebrate biomass dynamic model (BIBDM) is newly developed. • The effect of riverbed morphology on benthic invertebrate biomass is examined quantitatively for shallow lakes. • The model performs will in simulating the temporal process and spatial distribution of Corbicula fluminea in Lake Taihu. • The model is highly capable of applying to other species with corresponding environmental factor as the major parameter. Benthic invertebrates play important roles in aquatic ecosystems, and their distribution are significantly affected by substrate conditions, such as substrate type, particle size, and riverbed stability. Traditional research mainly uses statistical methods based on field observation to analyze the relationship between benthic invertebrate distribution and environmental factors, while lacking the consideration of growth process mechanism. Meanwhile, the effect of bed surface morphology on benthic invertebrate biomass has rarely been evaluated quantitatively for shallow lakes. This study newly develops a benthic invertebrate biomass dynamic model (BIBDM), which is coupled to hydrodynamic and bed surface morphology models, simultaneously considering the processes of growth, excretion, and predation. The ripple height, which represents bed surface morphology, is adopted as key parameter in the growth equation. The proposed model was applied to Lake Taihu, which is the third largest shallow lake in China. Corbicula fluminea , the largest biomass species of benthic invertebrates in Lake Taihu, was selected as the research object. The model performs well in reproducing the temporal biomass growth process, and the spatial simulation also shows good agreement with the observed data. Meanwhile, results confirm the importance of bed surface morphology on benthic invertebrates, with the correlation coefficient of 0.81 between the biomass and the ripple height. The proposed model could be used to evaluate the effect of environmental factors on the benthic invertebrate growth process. Moreover, the model is highly capable of applying to other species with corresponding environmental factor as the key parameter. [ABSTRACT FROM AUTHOR]