Importance of geomorphology and sedimentation processes for metal dispersion in sediments and soils of the Ganga Plain: identification of geochemical domains

The Ganga Plain, one of the largest alluvial plains of the earth is under severe environmental stress due to rapid industrial and urban development and exploding population growth. Disposal of industrial and urban wastes and the ignorance of their management have resulted severe environmental problems, especially metal pollution. In the present study, an attempt is made to understand the transport and dispersion processes of metal contaminants in sediments and soils in Kanpur–Unnao industrial region of the Ganga Plain. The significance of geomorphology and monsoon rain is assessed in determining the distribution of contaminated sediments in this area. Three regional geomorphic surfaces (T0, T1 and T2) are identified, each with its characteristic river channel patterns and sediment distribution system which influence the dispersion and accumulation of the metal contaminants. The sediment and water distribution regime depends on the nature of geomorphic features and character of the river channels. Geomorphic features, sedimentation processes, the nature of the river channels and distribution of excess rain water of the monsoon season have given the bases to delineate five geochemical domains in the study area. Each geochemical domain is an independently operating system with its own geomorphic and geochemical characters. Chemical parameters (e.g., pH), metal concentrations, and dispersion of metal-contaminated sediments and soils vary from domain to domain. In comparison to reference values, each domain exhibits its own enrichment of elements, namely the Loni River domain has high contents of C-org, Cd, Cr, Zn; the Ganda Nala domain of C-org, Cu, Cr; the Ganga River domain of C-org, Cr, Cu, Pb, Sn, Zn; the Sewage Network domain of C-org, Cd, Cr, Cu, Pb, Ni, Sn, Zn; and the Pandu River domain of C-org, Cd, Cu, Ni, Zn. Patterns of changes in metal concentrations from one monsoon year to the other and in different seasons of a monsoon flood cycle are also domain specific. Each geochemical domain exhibits its own degree of metal enrichment in sediments and soils by anthropogenic activities and physico-chemical processes. Identification of geochemical domains with their specific physico-chemical processes in the fluvial system of the Ganga Plain will certainly help in assessing the environmental problems and land contamination of this region.