Trophic State Assessment of a Freshwater Himalayan Lake Using Landsat 8 OLI Satellite Imagery: A Case Study of Wular Lake, Jammu and Kashmir (India)

A new version of Trophic State Index for freshwater Himalayan Lake (TSI_FHL) has been derived from Landsat 8 OLI to determine the aquatic health of the lake ecosystem. TSI_FHL is based on chlorophyll-a concentration (C_Chl-a) which has been retrieved from Landsat 8 OLI data and laboratory measurements using an empirical approach. Further, in situ measurements have also been taken with Secchi disk depth (Z_SD) in a freshwater Himalayan Lake (FHL). The derived C_Chl-a exhibited lower and upper limit of 25.81 and 207.96 μg/L, respectively. The modeled Z_SD values ranged between 0.18 and 0.66 m with an average depth of 0.50 m. The best-fitted regression model, developed for C_Chl-a with R² = 0.89, exhibited model error of 0.77 μg/L for the standard error of estimate (SEE). The mean absolute percentage error (MAPE), and Nash-Sutcliffe coefficient (E) values were 5.83% and 0.98 μg/L, respectively. For the Z_SD, the best-fitted model showed errors of 0.11 μg/L (SEE), 13.93% (MAPE), and 0.77 μg/L (E) with R² = 0.84. The proposed model is useful for bio-optical studies of Himalayan Lake ecosystems and could provide potential support for inland water management. Long term strategies like multisector monitoring and control of nutrient load entering the lake can be developed to alleviate problems of eutrophication.