River-Corridor Land Use/Land Cover Associations with the Spatial and Seasonal Distribution of Heavy Metals in the Jamuna, Padma, and Meghna Rivers of Bangladesh

<title>Abstract</title> <p>Monsoon-dominated river systems experience heavy-metal contamination through interactions among land use, seasonal hydrology, sediment transport, and local pollution sources. The Jamuna, Padma, and Meghna rivers of Bangladesh were investigated using wet- and dry-season river-corridor land use/land cover (LULC) mapping, physicochemical measurements, inductively coupled plasma-mass spectrometry, and multivariate statistics. Water samples from 12 locations were analyzed for Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, and Pb in wet and dry seasons. Within the 25-km river-adjacent corridors, the wet season was characterized by agriculture as the largest mapped class in all three corridors (Jamuna 53.41%; Padma 56.36%; Meghna 44.59%), with water coverage of 12.19%, 10.75%, and 29.83%, respectively, and barren land of only 1.16%, 0.76%, and 0.14%. In the dry season, agriculture dominated the Jamuna (45.10%) and Padma (43.24%), whereas vegetation was the largest mapped class in the Meghna (35.57%), where water bodies occupied 22.86%. Classification performance was high in both seasons (wet: overall accuracy 99.61%, Kappa 0.950; dry: overall accuracy 94.36%, Kappa 0.915). Seasonal map differences are interpreted as changes in mapped surface-cover state under contrasting hydrological and phenological conditions rather than as permanent land-use conversion. Fe, Cu, Zn, and Pb were strongly enriched in the wet season; mean Fe was 22505.98 µg L-1 in the wet season compared with 2796.66 µg L-1 in the dry season. Significant river-system differences were observed for As, Cr, and Ni but not for Fe, Mn, Cu, Zn, Cd, or Pb. Spearman correlations, principal component analysis, and hierarchical clustering indicated a consistent Fe-Mn-Cu-Zn-Pb assemblage associated with sediment-related transport and mixed geogenic-anthropogenic inputs, together with a distinct Cr-Ni/Cd signature suggesting more localized controls. For most metals, seasonal mobilisation and site-specific effects were more important than broad river identity. The seasonal LULC patterns provide spatial context for these processes, while causal LULC-metal relationships require station-specific modelling.</p>