Impact of land use change on wetland water quality in the Keibul Lamjao Conservation Area (a proposed mixed UNESCO World Heritage site) from northeast India

The flood plain wetlands in the Imphal valley are considered as the lifeline of Manipur state in northeast India. However, the wetlands have seen immense anthropogenic pressure and the total area have reduced from 1000 km² (1990) to 564.62 km² (2010), respectively. Hence, as a part of conservation research, a study was carried out to assess the Land Use / Land Cover (LULC) change (between 1988 and 2023) and the water quality status of two prominent wetlands, viz., Pumlen/Khoidum and Ikop/Kharung (during 2022–2023) from the Keibul Lamjao Conservation Area, a proposed Mixed World Heritage site. Satellite data from Landsat 5TM and Landsat 8 were obtained from the United States Geological Survey (USGS) Earth Explorer website for LULC studies. The physico-chemical parameters of water samples were analyzed for Post-Monsoon (PoM) and Pre-Monsoon (PM) seasons. The LULC analysis showed that 28.47 km² of Pumlen/Khoidum and 25.68 km² of Ikop/Kharung were converted into built-up or agriculture/pisciculture land use classes between 1988 and 2023. The water quality analysis showed high electrical conductivity, high turbidity and low dissolved oxygen content, respectively. The Factor Analysis (FA) suggests a common source of major ions such as Na⁺, K⁺, Cl⁻ and NO₃⁻, which is the sewage discharge and agricultural runoff. The Water Quality Index (WQI) values ranged from 30.12 to 62.06 (PM) and 65.87 to 106.6 (PoM) for Ikop/Kharung, and 38.86 to 108.9 (PM) and 52.09 to 182.0 (PoM) for Pumlen/Khoidum, respectively. Further, the irrigation water quality indices calculated showed the risk of salinity and Mg stress. Therefore, the overall results showed the changing land use patterns and deteriorating water quality of the wetlands, which must be addressed using effective wetland management plans.