Influence of Water Quality on Macrozoobenthos Community Structure in Bengawan Solo Sub-Watershed

Abstract

Water quality degradation is one of the major factors affecting the ecological integrity of river ecosystems and the structure of macrozoobenthos communities. This study aimed to evaluate the water quality status and analyze the influence of water quality parameters on macrozoobenthos community structure in the Bengawan Solo sub-watershed. A snapshot field sampling approach was conducted once in May 2025 at nine observation stations distributed across three locations: Gajah Mungkur Reservoir (agricultural and aquaculture pressures), Kyai Mojo Bridge (batik industrial wastewater via Premulung River), and Jurug Bridge (dense urban domestic wastewater), representing a gradient of anthropogenic pressures in Central Java, Indonesia. Water quality was assessed using in situ measurements and laboratory analyses of physicochemical parameters, including dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), nitrate, phosphate, phenol, water transparency, and flow velocity, which were subsequently used to calculate the Pollution Index (PI) based on Government Regulation No. 22 of 2021. Macrozoobenthos were collected from each station, preserved, and identified to family level; community structure was then evaluated using the Shannon–Wiener diversity index (H'), Pielou's evenness index (E'), Simpson dominance index (C), and Functional Feeding Group (FFG) classification. Multiple linear regression and Canonical Correspondence Analysis (CCA) were applied to assess relationships between water quality parameters and macrozoobenthos community composition. The Pollution Index ranged from 3.64 to 47.26, indicating that most sampling stations were classified as heavily polluted, primarily due to elevated phenol and phosphate concentrations. Multiple linear regression showed that water quality parameters had no statistically significant influence on H', E', and C (p > 0.05), suggesting that macrozoobenthos community structure was affected by multiple interacting environmental factors. CCA revealed that dissolved oxygen, organic pollution, nutrient concentrations, and habitat characteristics jointly influenced the spatial distribution of macrozoobenthos families. Habitat heterogeneity, substrate composition, and riparian vegetation were identified as important factors supporting diverse and balanced macrozoobenthos communities. These findings demonstrate that although water quality is closely associated with macrozoobenthos distribution, habitat characteristics play an important role in determining community structure and should be considered in river ecosystem management.