Trophic status and its regulating factor determination at the Rewalsar Lake, northwest Himalaya (HP), India, based on selected parameters and multivariate statistical analysis

The present study at Rewalsar Lake demonstrates trophic status and its regulating factor based on the selected physiochemical parameters and multivariate statistical analysis. The chlorophyll-a in the lake was found to be 15.85 ± 4.16 mg L−1, whereas total phosphorus as 0.21 ± 0.11 mg L−1. Secchi disk indicated low visibility (0.57 ± 0.01 m) in the lake that may be due to increased turbidity, phytoplankton, organic color and other suspended particles. The value of trophic state index (TSI) determined in the range of 78.76–87.89 (avg. 83.62 ± 3.09) specified that the Rewalsar Lake is hyper-eutrophic in status. The scatter plot of TSI(Chl-a)–TSI(SD) and TSI(Chl-a)–TSI(TP) revealed the increased nutrient (TP) as a main regulating factor for the higher value of TSI in the lake. The presence of NO3− (6.97 ± 1.56 mg L−1) and NH4+ (18.93 ± 5.02 mg L−1) in the lake may be owing to the use of nitrogenous fertilizers in the surrounding region and entry of other organic substances. Instead, these compounds may also be associated with the natural processes, like as the nitrification and ammonification. The principal component analysis from the data set of 12 variables indicated a total of 59.69% variance, i.e., PC1-27.35, PC2-17.48 and PC3-14.67%. The study further confirmed that the Rewalsar Lake is mainly influenced by the natural sources, whereas the regulating factor for the trophic status via anthropogenic activities. The water sampling sites in the lake are found to be grouped among various clusters and showed the spatial variability of different parameters.