Monitoring water spread and aquatic vegetation using earth observational data for Nani-High Altitude Lake (N-HAL) of Uttarakhand State, India

The lakes are facing anthropogenic pressure and losing its natural characteristics. Hence, the evaluation of lake water quality is a thrust area of research. The Nani-High Altitude Lake (N-HAL) was aimed to study during pre- and post-monsoon (March and October) period (2017–2022) using earth observation data based on false color composite (FCC) and spectral indices. The Sentinel-2 A/B data of 10 m spatial resolution was considered for monitoring and mapping of high-altitude lake. The FCC images were used to map and monitor changes in water spread and aquatic vegetation. Further, three spectral indices, namely, Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), and Normalized Difference Turbidity Index (NDTI), were applied to delineate water bodies and aquatic macrophytic vegetation (recorded are the Potamogeton pectinatus, Potamogeton crispus, Polygonum glabrum, Polygonum amphibium and Polygonum hydropiper (Water pepper). Results reveal that the water surface extent has changed from 2017 to 2022, depending on the pre- and post-monsoon rainfall pattern during the study period. During a flood year on 18-20, October 2021, in the area resulting into a drastic reduction in the aquatic vegetation and suspended particles. This lake needs immediate conservation and management policies.