Trophic classification and assessment of lake health using indexing approach and geostatistical methods for sustainable management of water resources

This study aims to analyse the spatio-temporal trends in water quality, trophic state, and organic contamination of an alpine lake in the Darjeeling Himalaya through field investigations and to portray a comprehensive picture using multivariate analysis. Analysed water parameters have shown notable seasonal variations and were within the acceptable range for inland surface water. Water quality index (WQI) and organic pollution index (OPI) values have displayed ‘poor’ to ‘heavily polluted’ status in the pre-monsoon season, with marginally better conditions during the post-monsoon studies. Trophic state indices (TSIs) values revealed ‘eutrophic to highly eutrophic’ conditions during the investigation period. The results of the PCA have depicted three major determining factors (i.e., anthropogenic contribution, geogenic or weathering, and seasonal/climatic factors) that control the overall pollution level in the lake water system. The current study can potentially be a benchmark for assessing and undertaking management and restoration measures for this nascent alpine ecosystem. HIGHLIGHTS Assessment of water quality and trophic state of the lake on a spatio-temporal scale.; Geospatial appraisal of lake health using indexing approach, i.e., WQI, OPI, and NI.; Application of multivariate statistics to delineate influencing factors and pollution sources.; The findings will assist in the sustainable management of the lake water system.;