Community structure of zoobenthos and its relationship with environmental factors in Zhelin Reservoir

To investigate the community structure of zoobenthos and its relationship with environmental factors in Zhelin Reservoir, seasonal surveys were conducted at 11 sampling sites during September 2020 and January, April, and July 2021. Zoobenthos were collected using a Petersen grab, while major physicochemical parameters, including water temperature, dissolved oxygen, pH, conductivity, and nutrient concentrations (total nitrogen, total phosphorus, ammonia nitrogen, nitrate, nitrite, and phosphate), were concurrently measured. A total of 16 species, representing 4 phyla and 5 families, were identified. The dominant species comprised Limnodrilus hoffmeisteri, Branchiura sowerbyi, Procladius sp. and Aulodrilus sp. The results indicated that the zoobenthos community was predominantly composed of aquatic oligochaetes and chironomid larvae. In terms of biomass, the taxa were ranked in descending order as follows: aquatic oligochaetes, insect larvae, mollusks, and nematodes. Zoobenthos density exhibited low seasonal variability. The highest mean density (440±323) ind./m² was observed at sampling site S5 (located upstream near bay), whereas the lowest density (44±41) ind./m² was recorded at sampling site S7 (located downstream near the Zhelin dam). Significant seasonal variations were observed in the diversity indices. The Shannon-Wiener, Margalef richness, and Simpson indices were lowest in autumn and peaked in winter. Conversely, the Pielou evenness index was lowest in autumn and highest in spring. Canonical correspondence analysis revealed that water depth, suspended solids, and dissolved oxygen were the primary environmental factors driving the distribution of zoobenthos. We concluded that thermal stratification and hypolimnetic hypoxia were the main reasons for the dominance of oligochaetes and chironomid larvae in Zhelin Reservoir.