Urban pollution has a stronger influence than monsoon changes on microscopic life in the Mula-Mutha river, a study by Pune’s Agharkar Research Institute found. Researchers said, "sewage pollution appears to be masking much of this natural seasonal variation." Pollution-tolerant species now dominate the river’s midstream and downstream stretches instead.
Urban pollution is having a stronger influence than seasonal monsoon changes on microscopic, aquatic life in the Mula-Mutha river system with pollution-tolerant species increasingly dominating the system's more polluted stretches; according to a study by researchers at Pune's Agharkar Research Institute (ARI).
Published recently in the journal, River Research and Applications, the study found that though the overall diversity of diatoms -- microscopic algae that play a crucial role in freshwater ecosystems -- remained relatively stable across seasons and river stretches, the composition of species varied significantly from one stretch to another. The findings suggest that persistent pressures from urbanisation and pollution are reshaping aquatic communities, overshadowing much of the natural seasonal variation caused by monsoon rainfall.
Researchers Pratyasha Nayak and Balasubramanian Karthick studied diatom communities at 17 monitoring sites across the Mula-Mutha river basin over two years: 2022 and 2023. They collected 70 samples during three hydrological periods -- pre-monsoon, monsoon and post-monsoon -- to assess how seasonal changes and human activities influence these organisms. The researchers identified 170 diatom species across the study sites. However, their distribution followed a distinct geographical pattern. Upstream stretches, characterised largely by forest cover and relatively undisturbed conditions, supported more pollution-sensitive species. By contrast, midstream and downstream stretches, exposed to greater urban and other human-induced pressures, had a higher prevalence of pollution-tolerant species.
Karthick, senior scientist at ARI, said, "Through this study, we found three distinct diatom communities across the Mula-Mutha river basin, with pollution-sensitive species dominating upstream stretches, while pollution-tolerant species were more prevalent in the midstream and downstream regions. Normally, diatom communities undergo seasonal changes, with different species dominating during the pre-monsoon, monsoon and post-monsoon periods. However, in the Mula-Mutha, sewage pollution appears to be masking much of this natural seasonal variation and altering the composition of these communities. This is a long-term study, and our findings underline the need to address pollution in the river to protect its aquatic biodiversity."
The study concluded that diatom communities can serve as indicators of persistent environmental stress, helping identify pollution-related changes that may not be evident through seasonal observations or conventional measures of species diversity. The study also underscores the need for long-term biological monitoring to assess the impact of urbanisation on freshwater ecosystems.