Trophic state assessment of a freshwater Himalayan lake using Landsat 8
OLI satellite imagery: A case study of Wular Lake
Abstract
A new version of Trophic State Index for freshwater Himalayan lake
(TSIFHL) has been derived from Landsat 8 OLI to determine the aquatic
health of the lake ecosystem. TSIFHL is based on chlorophyll-a
concentration (CChl-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 (ZSD)
in a freshwater Himalayan lake (FHL). The derived CChl-a exhibited lower
and upper limit of 25.81 µg/L and 207.96 µg/L respectively. The modelled
ZSD values ranged between 0.18 m to 0.66 m with an average depth of 0.50
m. The best-fitted regression model, developed for CChl-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 ZSD, 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.