Effect of climate changing pattern on ecosystem productivity of Bhimtal lake (Kumaun Himalaya), India.

Abstract

Global climate change is recognized as an ecological threat on ecosystem productivity of aquatic ecosystem. Climate can be considered the major factor determining the distribution of species at a continental scale. Climate changes are recognized as important environmental regulatory factors to assess the ecosystem productivity in relation to changing pattern of abiotic and biotic characteristics in aquatic system of lake. Bhimtal lake is a sub-tropical lake located between 290 21’ N latitude and 790 24’ E longitude, at an elevation of 1332 m above mean sea level in Kumaun region of Himalayan zone of Indian sub-continent. The catchment basin of lake is posing a numbers of ecological stresses due to climatic variations, invasive land use pattern, degraded forest zones and changed agriculture pattern. The water surface area is decreasing due to massive infestation of aquatic macrophytes and water depth level showed a decreasing trend due to increased siltation along with sedimentation load. The present study focused on long and short term effect of climate change on ecosystem productivity of Bhimtal lake. The comparative meteorological data of last fifteen years of catchment basin of Bhimtal lake revealed that air temperature has been increased 1.5 to 2.1oC and 0.2 to 0.8oC in summer and winter seasons respectively, relative humidity decreased 4 to 6% annually and rainfall pattern changed erratically in rainy season. The surface water temperature of lake showed an increasing pattern as 0.8 to 2.6 oC, pH value decreased 0.5 to 0.2 in winter and increased 0.4 to 0.6 in summer and dissolved oxygen level showed a decreasing trend as 0.4- 0.7 mg/l in winter. The lake ecosystem productivity mainly depends on species richness, abundance and biomass of phytoplankton, zooplankton, benthos and fish species. A total of 5 groups of phytoplankton, 3 groups of zooplankton, 11 groups of benthos and 14 fish species were recorded in Bhimtal lake. The changing pattern of phytoplankton groups indicated that biomass of Chlorophyceae and Bacilleriophyceae were decreasing as 1.99 and 1.08% respectively in Bhimtal lake but biomass of Cynophyceae group was increasing as 0.45% and contributing the algal blooming in lake surface water during summer season. The biomass of zooplankton and benthos were showed decreasing trend in winter season and increase in summer season. The population of endemic fish species i.e. Tor, Schizothorex, Barilius, and Nemacheilus showed decreasing trend as exotic fish species, Cyprinus carpio, Hypophthalmicthys molitrix showed as dominance in recorded fish catch data from Bhimtal lake. The present research study focused on correlation matrix among different climatic variables, physico-chemical characteristics with population of phytoplankton, zooplankton, benthos and fishes of Bhimtal lake. The present study will be contributed significantly to assess the current changing trend of ecosystem productivity of Bhimtal lake with different time sc