Affiliations: [a] Environmental Studies Division, National Aquatic Resource Research & Development Agency, Crow Island, Colombo-15, Sri Lanka | [b] Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-3-11, Takeda, Kofu, Yamanashi, 400-8511, Japan
Abstract: There has been a considerable amount of research investigating suspended sediment (SS) and water quality in river basins. However, there has been less attention to the suspended sediment behaviour in tropical river basins, especially in Sri Lanka. The Gin river basin is one of the major river basins in Sri Lanka and catchments consist of multi-land use systems. The behaviour of water quality, and suspended sediment with land use pattern is still not well studied in tropical river basin. Therefore, the aim of this study was to elucidate land use effects on suspended sediment and water quality in multi-land use tropical river basins. Elevated nitrate nitrogen concentrations were observed in the upper catchment and greater ammonia nitrogen concentrations were recorded in the lower catchment sampling locations. Also, higher fluxes of nitrate nitrogen and dissolved phosphate were observed during April to June and June to July, respectively. The major land use systems in the upper catchment portion consist of activities related to forest management while the lower catchment region has a higher percentage of agriculture and other land use related functions. Different land use pattern from forest to agriculture was increasing the suspended matter in the river water. Also, there was a very low concentration of suspended sediment and turbidity in the highly forested catchments in upper parts of the basin. This was expected since turbidity and suspended sediments increase with increasing amounts of agriculture and other land use activity. Also, statistical results prove that major physical and chemical water quality parameter means are different with three sub basins. In conclusion, the suspended sediment flux and discharge fits well with the linear regression model (R2 = 0.97) and would imply that the discharge can be used to predict the SS load from runoff.
Keywords: Gin river basin, land use, water quality, suspended sediment
