A brief review article on monitoring the eutrophication of high-altitude lakes (HAL) of Uttarakhand, remote sensing, and GIS perspective

Abstract

Water, the most significant element of natural resource available on earth supports liquidity to the life cycle. Their changing status enables the hydrophilic and hydrophobic polarity among the elementary ecosystem which further explains the peculiarity by components, pollutants concentration, and increasing anthropogenic load. In terrestrial/ or inland water bodies, the cyclic affection of rapid urbanization and rising cumulate demands pose a continuous and direct threat to fresh water and its nutritional status. Continuous affection of these resources starts degradation in terms of water quality and it leads to the eutrophication processes. The eutrophication process starts with the enrichment of nutrients as plants and algae bloom to grow in the hydro-ecosystem and then turn the water unfit for aquatic organisms and consumption by humans and other living organisms. The present study concerns the degrading state of High-altitude lakes (HAL)'s and their compromising conditions in the region of Nainital, Uttarakhand. It is critically reviewed that, the regional hydro- ecosystem is under stress. The continuous over-stress affects the aesthetic importance and is primarily controlled by the surrounding 'Architecture with nature'. Observation depicts, the amalgamation does not fit and support its sensitive topography and impact in terms of abnormal responses including enrichment of algal (cyanobacterial) bloom, microbial biomass, and changing geochemical characteristics. The bibliography indicates the practices along the lake environment in the last many decades but is inconsistent in terms of time and position-based analysis. Recent advancement in remote sensing and GIS and directional development in such areas gives space for their continuous monitoring and mapping efficiently and cost-effectively. With the current issue, an urgent need is to monitor the reservoirs and lakes of the territory to check the processes whether rapidly changing or any influence affecting them. Landuse-Landcover (LULC) and their impact on water bodies, Spectral indices like Normalized difference water index (NDWI), Maximum chlorophyll index (M-Chl), Green normalized difference vegetation index (G-NDVI), Normalized Difference turbidity index (NDTI), Topographic State Index (TSI), etc. are some extensively used indices for the water quality estimation. However, recent time developments in merging techniques with drone and unmanned aerial vehicles can attribute the research to a more precise and finer scale. The present review article describes the use of remote sensing techniques to retrieve information on water quality and using land and space-based derived quality indicators and their co-relationships for model development. The retrieval strategies for various specific water quality indicators, such as chlorophyll-a, total suspended matter (TSM), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus, are summarized in this article. (TP). Considerable difficulties associated with the resolution and retrieval models in the contexts or focusing on specific geographic bound, temporal, and water complexity have also been discussed. Finally, potential answers to these problems have been suggested. The review can offer thorough references for upcoming work in retrieving water quality development and research.