Geochemical Assessment of Upper Mahaweli River and Polgolla Reservoir Sediments, Sri Lanka

The river Mahaweli which receives discharges of agricultural fields and urban runoff was investigated using geochemical analysis. The present study focuses on the levels of As, Pb, Zn, Cu, Fe, P, Ca, Ni and Cr in order to assess environmental pollution in this area. Thirty six surface sediments of the upper catchment of the river and one core (28 cm) from the Polgolla reservoir were analyzed on XRF. Pollution assessment was carried out using the geoaccumulation index (GAI). The GIA indicates that all the analyzed sediments are very highly polluted for phosphorus, Zn and Cr, moderate for Pb and Ni. Fe and As are moderate to unpolluted. Cu is moderate to high in the Polgolla reservoir and surface sediments. High phosphorus with high organic matter indicates that it derived from biogenic processes. The strong enrichments of Zn, Cr, Ni, Pb and Cu are due to the association of Fe and sulfur in an oxic environment. The lacing of the geochemical variation of the core sample implies that there is no considerable anthropogenic input in this area but controlled by natural processes. The geochemical characteristics of the core show that temporal changes of the study area are insignificant.