Historical floodplain transformation of the Kashmir Valley recorded by sedimentological and geochemical analyses of Lake Ahansar sediments

Over centuries, growing land reclamation pressures, driven by agriculture and urban expansion, have profoundly modified floodplains, reshaping hydrological networks and ecosystems. In the present study, we investigated how anthropogenic watershed transformation influenced the limnological trajectory of Lake Ahansar, located in a distal position within the floodplain of the Jhelum basin draining the Kashmir Valley, western Himalaya. Our multiproxy records (sediment core lithology, chronology, and geochemical signatures, including stable carbon and nitrogen isotope ratios) reveal two significant phases of lake-system change over the last 750 years, with a regime shift occurring at ∼1600 cal. CE (±2 SD: 1510–1635 cal. CE). Phase I (1285–1600 cal. CE) is characterized by sedimentation dominated by detrital inputs and soil erosion, reflecting strong connectivity with the watershed and abundant minerogenic supply. Phase II (1600–2023 cal. CE) is characterized by organic matter-dominated sedimentation, indicating enhanced in-situ productivity under hydrologically isolated, human-modified catchment conditions. Intensified landscape transformations recorded at 1600–1770 cal. CE coincided with the Mughal period, marked by advanced hydroengineering and agricultural expansion in the Kashmir Valley. Our records provide historical controls of external factors on trophic evolution and driving mechanisms, and invite embracing the patrimonial and environmental values of the low-altitude Himalayan lake systems. The records support more informed sustainable management of lake systems characterized by agriculture-oriented and densely populated watersheds.