Determining limiting factors influencing fish kills at Rewalsar Lake: a case study with reference to Dal Lake (Mcleodganj), western Himalaya, India

Abstract

The present study at Rewalsar Lake situated within the outer Himalayan rocks of western Himalaya determines the limiting factors causing fish kills, repeatedly during the summer season. The Dal Lake situated in Kangra re-entrant is selected as a reference lake to compare the physiochemical parameters of two lakes. During the month of April, the concentrations of Ca2+, Mg2+, Na+, K+, F−, Br−, and HCO3− were found to be dominant at the Rewalsar, rather than the Dal Lake. However, the SO42− and Cl− were noticed more at Dal Lake which may be due to the lithological abundance of dolomite and gypsum minerals. The box and scatter plots indicated similar pattern of variations in the physiochemical parameters from these lakes. Although the dissolved oxygen (DO) at Dal Lake was observed lowest from May to June (5.3–5.4 mg l−1), and it was above the stress level for fishes. The temperature during April in the Rewalsar Lake increased to 25 °C, which decreased the oxygen holding capacity of water; therefore, DO level dropped to 1.5 mg l−1. The bottom deposited and floating organic material degradation, induced by rise in temperature further promoted the dissolved oxygen depletion and turned the lake greenish as well as blackish colored. The Rewalsar Lake thus turned hypoxic, and an extensive mass of fishes abruptly perished from the lake in April, which may further be considered a main limiting factor for the fish kills, repetitively ever since a long time period from April to June.