Integrated Assessment of Water Physico-Chemistry and Algal Diversity in the Pranhita River, Gadchiroli District, Maharashtra, India: A Baseline Study for Ecosystem Health

Abstract

Freshwater algae are important components of riverine ecosystems and respond sensitively to changes in physicochemical and hydrological conditions. The present study assessed seasonal variation in algal diversity and abundance and examined their association with physicochemical characteristics of the Pranhita River in Chamorshi and Aheri Tehsils of Gadchiroli District, Maharashtra, India. Three sampling sites, Chaprala (S1), Wangepalli (S2) and Devalmari (S3), were examined during the pre-monsoon, monsoon and post-monsoon seasons of 2025–26. A total of 30 algal taxa belonging to four major classes, Chlorophyceae, Bacillariophyceae, Cyanophyceae and Euglenophyceae, were recorded. Twenty-nine taxa were observed during the pre-monsoon and monsoon seasons, while all 30 taxa were recorded during the post-monsoon season. Quantitative abundance was estimated from 1000 mL whole-water samples and expressed as units per 1000 mL. Total standardized abundance increased from 58,100 units/1000 mL in the pre-monsoon to 148,100 units/1000 mL in the monsoon and 148,400 units/1000 mL in the post-monsoon. Chlorophyceae was the dominant group throughout the study, followed by Bacillariophyceae, Cyanophyceae and Euglenophyceae. Prominent taxa included Pinnularia sp., Diatoma sp., Spirogyra sp., Zygnema sp., Oedogonium sp. and Cymbella sp.
Shannon–Wiener, Simpson's, Pielou's evenness and Margalef's richness indices ranged from 1.146–1.178, 0.630–0.647, 0.827–0.850 and 0.252–0.274, respectively. Physicochemical parameters showed marked seasonal variation, with comparatively higher temperature, TDS, EC, hardness, calcium, alkalinity, chloride and BOD during the pre-monsoon period, increased turbidity during the monsoon, and lower temperature with higher dissolved oxygen during the post-monsoon period. Seasonal changes in algal communities appeared to reflect the combined influence of temperature, water movement, turbidity, dissolved substances and oxygen availability. Cyanobacterial taxa were recorded, but cyanotoxins were not analyzed; therefore, their occurrence does not establish toxin contamination or human-health risk. The study provides baseline information for future ecological and water-quality assessments of the Pranhita River.