Assessment of the reliable pollution indicators in the continental aquatic systems of a developing country in the context of global environmental sustainability: insights into the sedimentology and geochemistry of the Karuvannur River, India

Rivers in tropical regions are highly sensitive to natural weathering and anthropogenic pressures, making sediment studies vital for understanding environmental health. This study assesses the geochemical features and pollution status of sediments in the Karuvannur River (KR), Kerala, India, which drains into the ecologically significant Kole Wetlands, a Ramsar site renowned for its biodiversity, rice production, and flood regulation. Major oxide composition is dominated by SiO₂ (58.94%), reflecting intense weathering and quartz enrichment, while elevated Al₂O₃ (16.32%), Fe₂O₃ (7.46%), TiO₂ (1.18%), and P₂O₅ (0.34%) indicate prolonged chemical weathering under tropical environmental conditions. The depletion of Na₂O, K₂O, CaO, and MgO further underscores the leaching process under humid tropical conditions. Trace metal enrichment of V (255.11 ppm), Cr (114.33 ppm), Cu (48.52 ppm), Ga (30 ppm), Zr (301.78 ppm), and Sr (344.22 ppm) suggests contamination from both geogenic and agricultural sources. Contamination indices [Enrichment Factor (EF), Geoaccumulation Index (I_geo), Contamination Factor (CF), Degree of Contamination (C_deg), and Pollution Load Index (PLI)] suggest moderate sediment degradation, with V, Cr, Cu, Ga, Zr, and Sr being key contributors. Sediment Quality Guidelines (SQGs) identified Cr and Ni as priority contaminants, exceeding both Threshold Effect Concentration (TEC) and Probable Effect Concentration (PEC) thresholds and posing probable risks to benthic organisms, while Cu indicates moderate concern. Sediment carbon stocks were moderate compared with other ecosystems, reflecting the dynamic nature of the riverine system. These findings provide vital insights into sediment quality in KR, with significant implications for the ecological survival of the Kole Wetlands and the livelihoods that depend on them. They also have global agricultural implications, as many tropical river basins support intensive farming systems that rely on river sediments and floodplain soils to sustain crop yields. The study highlights the importance of watershed management and sustainable agricultural practices in mitigating contamination and achieving sustainability goals, particularly in tropical agricultural regions.