Soil Leaching Behaviour of Different Urban Landscapes

Abstract

Leaching behaviour of soil has an significant role in influencing composition of water and it is important to study the soil leaching behaviour to understand their role in modifying water composition. Guwahati, the capital city of Assam exhibits high soil erosion rate from its urbanized hilly catchments leading to their subsequent role in leaching of ionic species to water. In this paper, soil and sediment samples from 11 different sites representative of hilly and valley areas of the Guwahati City were collected and their leaching behaviour was studied using the standard Toxicity Characteristic Leaching Procedure (TCLP) developed by US EPA (Townsend et al. 2003). The study evaluated the total leachable amounts of some cations (Na, K and Ca) and trace metals of concern (Pb, Fe, Ni, Mn, Cr and Cd) and their role in influencing the surface water chemistry. The average leaching was observed in the following order: Ca > Fe > K > Na > Mn > Pb > Ni. Leaching of Cr and Cd was below detectable limit. The study indicated that the leaching of dissolved nutrients and trace metals varies with site condition, background condition and level of saturation. While there may not be a generalized leaching behaviour for these soils, characterization at local level may be possible by the current approach. Overall analysis of all the samples revealed that the soil samples with high initial concentration of ions can leach out higher ionic species. Since a more or less linear trend was observed between the ions present in soil and their subsequent amount of leaching, it is likely that increased toxic contamination of urban soils due to anthropogenic sources can lead to higher water contamination.