Disentangling natural and anthropogenic effects on benthic macroinvertebrate assemblages in western US streams

A Study on the Community and Ecological Characteristics of Benthic Invertebrates in the Ulungu River, Xinjiang, via eDNA Metabarcoding and Morphological Methods

eDNA metabarcoding has been used for the biomonitoring of benthic invertebrates, but the correct steps to achieve its effectiveness, the stability of the results, and comparisons with morphological methods are still understudied. In this study, morphology and eDNA were studied for benthic invertebrate samples collected at six sites in the Ulungu River Basin. A Mantel test and NMDS analyses were used to test the correlations of the communities obtained via the two methods, the Shannon index was calculated to evaluate the ecological status, and the correlation of the evaluation results was analyzed. The results revealed that eDNA metabarcoding did not detect a greater number of species than the morphological method, that the results from the two methods shared fewer taxa at the family level and below, and that only five taxa were shared at the genus level. The Mantel test and NMDS analyses revealed very significant differences between the communities monitored by the two methods (PERMANOVA, p = 0.0056), but eDNA metabarcoding provided richness and abundance data for species that are difficult to identify morphologically, and these findings can be used to supplement the morphological data. The cor.test revealed that there was no significant correlation between the diversity and ecological assessment results of the two methods, and the ecological assessment results of eDNA metabarcoding cannot represent accurate and true ecological conditions. The water sample eDNA-based method and morphological method exhibited low consistency and high complementarity in monitoring benthic invertebrate communities and diversity. More research is still needed on the key links of eDNA sampling, the control of the degradation rate, data utilization, and index development to provide more environmentally friendly and effective monitoring methods for ecological protection, more reliable support for ecological decision-making, and to more adequately respond to the challenges of global environmental change.

Hydrogeomorphic conditions drive aquatic macroinvertebrate diversity between depression and slope wetlands in a mountainous region

Aquatic macroinvertebrates inhabiting freshwater wetlands make important contributions to biodiversity. However, environmental characteristics of wetlands is often varied in a specific region, especially in mountainous areas. We investigated 24 depression wetlands and 20 slope wetlands in the Great Xing'an Mountains in Northeast China and aimed to reveal the hydrogeomorphic settings in driving the wetland aquatic macroinvertebrate diversity and offer insights to environmental management. We found that depression wetlands supported higher taxonomic richness and more habitat specialists. Fifteen orders or infraclasses responded positively to depression wetlands, whereas eight orders responded positively to slope wetlands. The composition of aquatic macroinvertebrate assemblages differed significantly between the depression and slope wetlands. Additionally, the variation in species composition in the depression and slope wetlands are largely explained by habitat variables. For community assembly of aquatic macroinvertebrates, both wetland types were largely driven by stochastic processes, with a higher proportion observed in the slope wetlands. Whereas a significant distance-decay relationship and stronger dispersal limitation were detected in the depression wetlands. These findings enhance our understanding of diversity patterns and mechanisms driving aquatic macroinvertebrate community assembly in mountain wetlands. Our research also highlighted the critical need to attach importance to hydrogeomorphic settings and habitat variables in driving aquatic macroinvertebrate diversity for more effective wetland management and conservation.

A method for evaluating sediment-induced macroinvertebrate community composition changes in Idaho streams

Human activities can increase sediment delivery to streams, changing the composition, distribution, and abundance of stream aquatic life. Few U.S. states have numeric water quality standards for streambed sediment under the Clean Water Act, so managers often need to develop local application-specific benchmarks. This study developed stream surface fine sediment <2 mm (sand and fines, SF) and macroinvertebrate fine sediment biotic index (FSBI) benchmarks and an application framework to test for sediment-induced macroinvertebrate community composition changes in 1st-4th order Idaho streams. FSBI reference benchmarks were calculated as the 25th percentile FSBI value among reference sites within three ecoregion-based site classes. Two approaches were used to develop SF benchmarks. Quantile regression was used to define reach-specific SF benchmarks representing an upper bound value expected under reference conditions. In addition, logistic regression was used to predict SF values with 50% and 75% probability that FSBI is worse than reference within each stream order and site class. The strength of association between SF benchmarks and macroinvertebrate community condition was evaluated by calculating relative risk using multiple datasets and examining responses of multiple macroinvertebrate indicators to SF benchmark status. SF reference benchmarks generally had stronger associations with poor macroinvertebrate condition than SF stressor-response benchmarks. Across datasets and macroinvertebrate indicators, poor macroinvertebrate condition was 1.8-3 times more likely when SF reference benchmarks were exceeded than when achieved. We propose rating the strength of evidence for a surface fine sediment-induced macroinvertebrate community composition change at the sample event scale as 'unlikely' if both SF and FSBI reference benchmarks are achieved, having 'mixed evidence' if only one reference benchmark is achieved, and 'likely' if both reference benchmarks are not achieved. We recommend combining ratings with other relevant data in a weight-of-evidence approach to assess if sediment impairs aquatic life.

Elevation-associated pathways mediate aquatic biodiversity at multi-trophic levels along a plateau inland river

Aquatic biodiversity plays a significant role in maintaining the ecological balance and the overall health of riverine ecosystems. Elevation is an important factor influencing biodiversity patterns. However, it is still unclear through which pathway elevation influences riverine biodiversity at different trophic levels. In this study, the elevation-associated pathways affecting aquatic biodiversity at different trophic levels were explored using structural equation modeling (SEM) and taking the Bayin River, China as the case. The results showed that the elevational patterns were different among aquatic organisms at different trophic levels. For macroinvertebrates and bacteria, the pattern was hump-shaped; while for phytoplankton and zooplankton, it was U-shaped. Building upon these observed elevational patterns, our investigation delved into the direct and indirect pathways through which elevation influences aquatic biodiversity. We found that elevation exerts an impact on aquatic biodiversity via indirect pathways. For all aquatic organisms investigated, the major pathway through which elevation influences biodiversity is mediated by water temperature and water quality. For aquatic organisms at higher trophic levels, like macroinvertebrates and zooplankton, the crucial pathway is also mediated by the landscape. The results of this study contributed to understanding the effects of elevation on aquatic organisms at different trophic levels and provided an important basis for the assessment of riverine biodiversity at large scales.