Impact of Industrial Production, Dam Construction, and Agriculture on the Z-IBI in River Ecosystems: A Case Study of the Wanan River Basin in China

Development and validation of the planktonic index of biotic integrity (P-IBI) for Qin River, a main tributary of the Yellow River in China

To evaluate the ecosystem health of Qin River, a main tributary of the Yellow River, a planktonic index of biotic integrity (P-IBI) that includes phytoplankton and zooplankton was established based on five metrics using a dataset covering 61 sampling sites in Qin River and its largest tributary the Dan River from October to November 2020. First, an index based on land use pattern and water quality was constructed to select reference sites and impaired sites. Then, five of an initial 38 candidate metrics (phytoplankton density, Palmer algal genus pollution index, zooplankton biomass/phytoplankton biomass, zooplankton Margalef richness index, and zooplankton Simpson diversity index) were selected to establish P-IBI based on their ranges, sensitivity, and redundancy. Finally, five statuses (excellent, good, fair, poor, and very poor) were classified by ratio score method on the basis of their final P-IBI scores. Sites with "excellent and good" and "poor and very poor" status accounted for 26.2% and 49.2%, respectively. "Very poor" sites were mainly located in the Dan River, and "poor" sites were mainly located in the middle reach of the Qin River and upper-middle reach of the Dan River in Jincheng region. Significantly negative correlations between Cl^-, SO₄^2-, and F^- concentrations and P-IBI values indicated that the P-IBI might reflect domestic and industrial wastewater pollution in the Qin and Dan River in Jincheng region. The P-IBI strongly differentiated reference and impaired sites, suggesting the suitability of the index in the study.

Optimal Method for Biomass Estimation in a Cladoceran Species, Daphnia Magna (Straus, 1820): Evaluating Length–Weight Regression Equations and Deriving Estimation Equations Using Body Length, Width and Lateral Area

Assessing the biomass of zooplankton compensates for the difference between number of individuals and the accumulated body weight of the community, which helps assess aquatic ecosystem food web functions. Daphnia are crustaceans that play an intermediate role in biological interactions within food webs. The morphology and body specification of Daphnia differ during growth; hence, it is essential to apply species-specific equations to estimate biomass. We evaluated the length–weight regression equations used previously to estimate Daphnia magna biomass and conducted regression analyses using various body specifications and biomass measurements taken directly using devices such as a microbalance and microscopic camera. Biomass estimated using an equation from the Environmental Protection Agency was significantly different from the direct measurement: average biomass was lower, indicating that the equation possibly underestimated actual biomass. The biomass of D. magna had a higher multiple R2 value when length was compared with width and area, and a linear regression equation was the most suitable equation for biomass estimation. Because body specifications and biomass are affected by various environmental factors, the development of accurate species-specific biomass estimation equations will contribute to obtaining fundamental data with which the biological responses of zooplankton to aquatic ecosystem changes can be assessed.

Assessment of Aquatic Ecosystem Health with Indices of Biotic Integrity (IBIs) in the Ganjiang River System, China

Indices of biotic integrity (IBIs) are widely used to assess aquatic ecosystem health. However, there are few studies on their relationships. Based on fish, macroinvertebrate and plankton survey data collected in the Ganjiang River system from 2016 to 2017, redundancy analysis (RDA) and canonical correspondence analysis (CCA) were used to analyze how the community structures of these organisms respond to environmental variables. The fish IBI (F-IBI), benthic macroinvertebrate IBI (B-IBI), and phytoplankton IBI (P-IBI) were applied to evaluate the health status of the aquatic ecosystem. A Kruskal–Wallis test (p < 0.05) and Spearman’s correlation coefficient analysis were performed to evaluate the spatiotemporal heterogeneity of the results. Our results suggested that the F-IBI-, B-IBI-, and P-IBI-based assessments indicated good, fair, and healthy Ganjiang River system ecosystem health statuses, respectively, and significant differences existed among these indices (p < 0.05). The main environmental factors affecting F-IBI, B-IBI, and P-IBI were different. At the temporal scale, the F-IBI and B-IBI were stable, while the P-IBI fluctuated obviously. The consistency between the F-IBI and B-IBI results was better than that between each of these indices and the P-IBI results, and the consistency was better on a larger scale. These research results show that comprehensive assessments based on multiple groups rather than a single group can better characterize the impacts of environmental pressures on water ecosystems.