Riparian Vegetation as Bioindicator of Heavy Metal Contamination and Soil Nutrient Dynamics in Vamanapuram River, Kerala

This study examines the relationship between riparian vegetation, soil nutrient dynamics, and heavy metal contamination along a 15 km stretch of the Vamanapuram River, Kerala. Six sites representing a gradient of anthropogenic disturbance were assessed through quadrat-based vegetation surveys and comprehensive soil chemical analysis, including macro- and micronutrients (K, Ca, Mg, B, Mn, Cu, Zn) and heavy metals (Hg, Pb, As, Ni, Cd, Cr, Bi, Ga) using ICP-MS. A total of 102 plant species belonging to 45 families were recorded, with Fabaceae and Poaceae dominating across the vegetated sites. Species diversity and abundance were highest at moderately disturbed sites Maveli Nagar (Site 2) and Vamanapuram Bridge (Site 3), which coincided with balanced soil nutrient profiles and lower levels of heavy metals. Conversely, Site 6 (Melattumoozhi), heavily impacted by soil dumping, exhibited minimal vegetation and the highest concentrations of mercury (0.41 mg/kg), arsenic (74.8 mg/kg), and gallium (133 mg/kg). Principal Component Analysis (PCA) revealed that PC1 (45.2% variance) was associated with heavy metal concentrations, while PC2 (27.6%) captured nutrient variability, particularly boron and calcium. Vegetated sites clustered distinctly from polluted sites in the PCA biplot, emphasizing a strong inverse relationship between vegetation cover and metal contamination. The study underscores the role of riparian vegetation as a bioindicator of soil quality and a regulator of contamination. Restoration and conservation of riparian buffers are essential for sustaining soil health and mitigating the ecological impacts of anthropogenic activities along tropical riverine systems.