The Himalayan region is globally regarded for its rich biodiversity. However, increased agricultural expansion and urbanization have resulted in greater nutrient loading in Himalayan water bodies causing widespread fish kills and shrinking lakes. Despite concerns for environmental degradation, lack of empirical investigations and quantitative data are a major constraint to model these events. To determine the impact of human activities on lakes of urban and rural regions, we investigated Rewalsar, a spring-fed lake (1500m) and Kareri (3000m) a glacial-fed lake and their surrounding ecosystems in the state of Himachal Pradesh. Rewalsar is surrounded by a rapidly growing town and agricultural fields, whereas Kareri Lake is situated in a relatively pristine area. Data was recorded for fall 2012, spring 2013, and winter 2016 and will be recorded for spring 2016. Water samples were collected 1m below surface level and 1m above sediment and analyzed for major ions, nitrates, phosphates, DO, pH, temperature, turbidity, and TDS. Planktonic algal samples were collected after 50 l of water was filtered through a 25μm sieve. Benthic diatom species were collected from scrapings of rocks and boulders in each lake. Species were counted with a compound microscope and identified using standard taxonomic literature.
Results/Conclusions
Kareri Lake had the highest DO (9.77 mg/ml) while Rewalsar showed the lowest DO at 8.23 mg/ml in 2012 and 3.40 mg/ml in 2016. With a total oxygen demand (TOD) of 6.5 mg/ml in Rewalsar, the decreasing DO value is likely the cause of the increasing annual fish kills. Turbidity was highest in Rewalsar Lake at 210.87 NTU in the fall and 283.77 NTU in the spring compared to the turbidity levels of Kareri (4.75 NTU), indicating a high amount of surface runoff from the surrounding area in Rewalsar. Among the planktonic algae only a few pollution tolerant species dominate Rewalsar Lake: Microcystis, Planctonema lauterbornii, Volvocaceae Eudorina, and Desmodesmus subspicatus. In contrast, species observed in Kareri Lake were Spirogyra and Ulothrix indicating a healthy fresh water body. Our time sequence investigations show that the abundance of Microcystis and other pollution indicating taxa is on the rise. This trend is correlated with an increase in water turbidity and high nutrient levels. High relative abundance of pollutant tolerant algal species indicates progressive eutrophication of Rewalsar Lake emanating from anthropogenic impacts as compared to Kareri. These studies confirm that humans are the main drivers of transformation of the natural ecosystems in the Himalaya.