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Abstract

This study investigates the environmental drivers influencing the spatial and seasonal distribution of macrobenthic communities in the Jajrood River, Iran. Seasonal sampling was conducted at five geographically distributed stations during autumn and winter of 2014 and spring and summer of 2015. Key environmental parameters, including water temperature and dissolved oxygen levels, were recorded in conjunction with biological data on species diversity and abundance. A total of 19 species belonging to five taxonomic orders were identified, with Insecta dominating across all seasons. Diversity indices indicated that macrobenthic richness was highest during spring and lowest during winter, corresponding to variations in temperature and dissolved oxygen. Downstream stations exposed to urban effluents exhibited lower diversity and were dominated by pollution-tolerant species such as Chironomus and Tubificidae. These findings underscore the role of macrobenthos as reliable biological indicators for assessing riverine ecosystem health and highlight the impact of anthropogenic activities on aquatic biodiversity. The study also demonstrates how seasonal fluctuations and spatial gradients reflect natural ecological cycles alongside human-induced pressures. By emphasizing the integration of biological indicators with environmental parameters, the results provide valuable insights for monitoring programs and reinforce the importance of sustainable management of freshwater resources to preserve biodiversity and ecosystem integrity in vulnerable river systems.

Keywords: Macrobenthos, Diversity indices, Seasonal variation, Water quality, Jajrood river, Pollution indicators