Hydrobiological Changes during the Rainy Season in Upper Manair Dam, Narmala Village, Rajanna Siricilla District, Telangana

Abstract

Freshwater reservoirs support water supply and aquatic food webs, but rainy-season runoff can alter water quality through sediment, nutrient, and organic-matter inputs, affecting plankton communities. This study evaluated rainy-season hydrobiological changes in Upper Manair Dam near Narmala Village, Rajanna Siricilla District, Telangana, during June–August 2026, using physicochemical monitoring and plankton assessment. Water and biological samples were collected monthly at fixed stations, and nine physicochemical parameters were measured using established methods. Phytoplankton were identified and enumerated by group; zooplankton were identified taxonomically, but monthly abundance and diversity indices were unavailable. Rainy-season conditions showed monthly variation: temperature ranged 29.8–32.0°C, pH remained alkaline (8.50–8.65), turbidity peaked in July (34.0 NTU), transparency rose to 111.5 cm by August as TSS declined to 48.0 mg/L, and TDS varied from 410.0 to 522.5 mg/L. DO remained modest (5.35–6.00 mg/L) with high BOD (8.20–8.35 mg/L) and variable COD (5.50–6.00 mg/L), indicating oxygen demand without depletion. Phytoplankton were dominated by Chlorophyceae, and total abundance declined from 7,420.0 in June to 5,547.5 in August; Bacillariophyceae remained stable (~1,142.5–1,166.0). Zooplankton richness comprised 45 taxa. Exploratory correlations from three observations suggested negative associations between total phytoplankton abundance and both turbidity and DO, and a strong positive association with BOD, requiring cautious interpretation. Overall, the results support a rainfall–runoff pathway linking suspended material and oxygen-demand dynamics to shifts in phytoplankton structure, underscoring seasonal monitoring and catchment-focused sediment and agricultural-runoff management.