Integrated Limnological Assessment of Gangasamudra Lake (Karnataka): Physicochemical Characteristics, Plankton Dynamics, and Fish Diversity

Abstract

The present study provides an integrated limnological assessment of Gangasamudra Lake, a semi-arid freshwater ecosystem in Karnataka, India, by evaluating physicochemical characteristics, plankton community dynamics, and ichthyofaunal diversity across five sampling sites during 2024. Monthly analysis of water quality parameters revealed consistently alkaline pH, high turbidity, elevated total dissolved solids, conductivity, biochemical oxygen demand, chemical oxygen demand, magnesium, and iron, indicating meso-eutrophic to eutrophic conditions. Although most toxic heavy metals were absent or below detection limits, elevated iron and occasional lead concentrations suggested localized anthropogenic influences, primarily from agricultural runoff, catchment erosion, and internal nutrient loading. Phytoplankton assemblages comprised 23 genera belonging to Bacillariophyceae, Chlorophyceae, and Cyanophyceae, with diatoms dominating during pre-monsoon and monsoon periods, followed by increased representation of green algae and cyanobacteria during post-monsoon months. Zooplankton communities were represented by Rotifera, Protozoa, Copepoda, and Ostracoda, with rotifers showing marked dominance and seasonal fluctuations, reflecting nutrient enrichment and dynamic trophic interactions. Diversity indices indicated moderate to high plankton diversity during monsoon and post-monsoon periods, while reduced diversity and increased dominance during summer months reflected environmental stress. Ichthyofaunal assessment recorded six fish species belonging to three families (Cichlidae, Cyprinidae, and Clariidae), dominated by hardy and omnivorous taxa such as Oreochromis spp. and Clarias spp. The presence of the endangered Clarias batrachus highlights the conservation significance of the lake despite anthropogenic pressures. Overall, the combined physicochemical and biological evidence suggests that Gangasamudra Lake is a nutrient-enriched but moderately resilient ecosystem, emphasizing the need for regular monitoring, nutrient management, and sustainable fishery practices to preserve its ecological integrity and biodiversity