Geochemical processes of the Mahaweli River Sri Lanka using bulk sediments and its 180-2000μm and <180μm fractions

With the issue that tributaries, climatic conditions and dissolution can have a significant impact on geochemical processes the river sediments of Mahaweli, Sri Lanka was studied where it showed a clear variation upon the change of the climatic conditions; for the wet, intermediate and the dry zones. Thus, XRF analysis was carried to determine 19 elements for the 54 bulk river sediments and the fine (<180μm) and large (180-2000μm) fractions of the river sediments. Since the bulk river sediments showed a clear clustering with the change of the climatic zones the Enrichment Factor (EF) was calculated by normalizing the fine fraction with the large fraction of the river sediment which enhances the changes of the bulk sediments. Based on the similar behaviors for the EF the elements were grouped as (a) Ca, P Sr (b) Ti, Fe, Sc, Y (c) V, Cr, Ni (d) Zr, Th, Nb and (d) As, Pb, Zn and Cu. The tributaries entering the main channel are enriched in almost all elements and also clear downstream accumulation was observed. On the other hand, weathering in the wet zone seem to be high and less in the downstream while dilution due to dissolution of the fine fraction also may be occurring in Ni, Cu, Pb, P and Cr along the stream. Thus, the effect of climatic conditions with heavy rain falls may influence weathering in the upstream (wet zone) causing enrichments where the high concentrated detrital material is brought to the main river via the tributaries and dissolution may be taking place causing the depletions. Thus, this implies that climate, weathering, dilution and tributaries are the main geochemical issues affecting the geochemistry of the Mahaweli River. Key words: Climate, Weathering, Dissolution, Tributaries.