UTTAR PRADESH JOURNAL OF ZOOLOGY

Freshwater lakes support diverse plankton communities that play important roles in aquatic ecosystems and can indicate changes in water quality. This study investigated the physicochemical characteristics of Ponneri Lake, Tamil Nadu, India, and assessed monthly variations in phytoplankton and zooplankton occurrence from February to April. Water samples were collected from three sampling sites, and physicochemical parameters, including pH, turbidity, electrical conductivity (EC), total suspended solids (TSS), total dissolved solids (TDS), alkalinity, hardness, calcium, magnesium, iron, chloride, and silica, were analysed. Plankton genera were identified microscopically, and their occurrence was assessed using qualitative abundance categories. The tabulated mean pH values were 7.03, 7.60 and 5.51 in February, March and April, respectively. Mean turbidity decreased from 14.90 NTU in February to 10.67 NTU in April. Mean TDS declined from 371.67 mg/L in February to 310.33 mg/L in March before increasing to 331.67 mg/L in April. Seven phytoplankton genera were recorded: Phacus, Chlamydomonas, Navicula, Euglena, Volvox, Spirulina and Monactinus. Phacus was abundant in February but absent in April, whereas Euglena occurred throughout the study period. The zooplankton community comprised Keratella, Rotaria, Moina, Cyclops and an unidentified copepod. Keratella and Rotaria were recorded in all three months, while the occurrence of other taxa varied. Changes in physicochemical parameters coincided with monthly variations in plankton occurrence. However, the qualitative assessment did not establish direct relationships between individual parameters and plankton distribution. These findings provide baseline information on the physicochemical characteristics and plankton diversity of Ponneri Lake and highlight the importance of continued monitoring to assess changes in this freshwater ecosystem.