Seasonal Dynamics of Primary Productivity in Gobbur Reservoir, Karnataka.

This study assessed the primary productivity of Gobbur Reservoir in Afzalpur, Kalaburagi District, Karnataka, from January 2024 to December 2024. Gross primary productivity (GPP), net primary productivity (NPP), and community respiration (CR) were measured monthly at four sampling stations using the light-and-dark bottle method. Physico-chemical parameters (temperature, pH, dissolved oxygen, alkalinity, nutrients) were analyzed to evaluate their influence on productivity. The results showed clear seasonal trends: GPP and NPP reached their highest levels in summer (0.65–0.85 gC/m³/hr and 0.40–0.55 gC/m³/hr, respectively) and northeast monsoon periods, whereas their lowest values were observed during the southwest monsoon because of turbid inflows. CR exhibited comparable patterns, showing a strong correlation with dissolved oxygen and temperature. Nutrient ratios (N:P) and morphometric variables (variations in water depth, land use of the catchment) significantly impacted productivity. The reservoir displayed mesotrophic characteristics with moderate productivity, influenced by light access, nutrient contributions from agricultural runoff, and consistent thermal stratification. These results emphasize the susceptibility of Gobbur Reservoir to eutrophication and stress the importance of sustainable land-use methods in its watershed.