Lake ecosystem are made up of the physical, chemical and biological properties contained within water bodies. Lakes are superb habitats for the study of ecosystem dynamics. Lakes are important ecosystems because humans depend on it for many services such as drinking water, waste removal, fisheries, agricultural irrigation, industrial activity and recreation. A lake and its watershed are often considered to be a single ecosystem (Likens, 1985).
The Kumaun Himalaya lies in the lesser Himalayas zone from 28○43’55” to 30○49’12” N latitude and from 78○44’30” to 80○5’E longitude with a total area of 21,035km2. It provides an epitome of geological architecture of the whole Himalayan region. Hence, Kumaun is one of the most representative sector of the great mountain system and is blessed with enhanced beauty and varied natural water resources. Nature has bountifully supplied the Kumaun region with a large number of lakes and rivers with an average annual discharge exceeding 2.0 million m3. Himalayan lakes in the mid 20th century raised concern about the consequences of cultural eutrophication for example Nainital, Bhimtal, Naukuchiatal, Sattal, etc.
Lakes in the Kumaon region have undergone ecological changes during the last few decades that have affected water quality, increasing heavy metal content and algal productivity (Chakrapani 2002; Das, 2005; Choudhary et al., 2009). Deterioration of the water quality of Kumaun lakes because of the intense cultural activities in their catchment areas has been recognized recently (Das and Pandey, 1978). In lakes water quality has been highly transformed due to anthropocene.
Impacts of climate change on water quality of lakes
Climate change is recognized as a threat on biological productivity of lakes. Climatic variation affects the hydrological characteristics of lakes. The hydrological and physico-chemical characteristics of lakes are changing due to climatic variations i.e. increasing pattern of air and water temperature, rate of evaporation, precipitation, humidity and solar intensity. Impacts of global warming on lakes include an extended growing period at high latitudes, intensified stratification and nutrient loss from surface waters, decreased hypolimnetic oxygen (below the thermocline) in deep, stratified lakes, and expansion in range for many invasive aquatic weeds (Bates et al. 2008).
Lakes are very vulnerable to climate change. In the lake ecosystem, the impact of climate changes on biological productivity and distributional pattern of aquatic biodiversity has recently been the focus of interest. The diversity of biotic components in the lake ecosystem serves as a reliable index of biological productivity and its trophic status. The temperature structure of lake water mass is one of the major factors modifying the hydro-biological, chemical, sedimentation and physical processes occurring in lakes. Direct effects of climate change on lakes includes changes in temperature, water level, pH, concentration of dissolved gases (dissolved oxygen, free carbon dioxide etc). Elevated temperatures would decrease oxygen solubility and increase the rates of microbial oxygen demand, both leading to a decrease in dissolved oxygen available for biotic communities in different trophic level of lake ecosystem. Climate changes are increasingly recognized as important regulatory factors to assess the primary productivity in relation to changing pattern of biotic communities (phytoplankton, zooplankton, benthos and fish species) in the lake ecosystem. Therefore, the thermal stratification of lake affects the solubility of gases, availability of nutrients and ultimately the biological productivity of lake ecosystem.