Abstract:
Walawe River Basin, the fourth-largest in Sri Lanka, has emerged as a focal point for the
management of water quality because of its size and population density. The catchment
is highly agricultural and the land use activities in the catchment have the potential of
deteriorating the surface water quality. However, very little research has been carried
out to evaluate the effects of catchment land use on surface water quality in the upper
Walawe basin. Therefore, this study aims to investigate the connection between soil
erosion in the catchment and water quality in the Upper section of the Walawe River
basin. Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) Sediment
Delivery Ratio (SDR) model was used to assess the soil erosion in nine microcatchments
within the upper Walawe River basin. Water quality parameters were recorded in
streams draining through selected micro catchments and the association between soil
erosion and water quality was analyzed using the Pearson correlation test at a 0.05
significance level. The results of the study indicated mean soil erosion of the microcatchments
ranging from 0.84 to 18.1 t ha-1 yr-1 with an annual average of 11.75 t
ha-1 yr-1, which is ∼2.35 times greater than the soil erosion tolerance (5 t ha-1 yr-1) in
Sri Lanka. Pearson correlation test was conducted to assess the relationship between
soil erosion of the microcatchments and water quality variables. The results indicated
a significant positive correlation between soil erosion and potassium (K) levels in the
water. In conclusion, this study provides valuable insights into the complex interactions
between soil erosion, and water quality in the study catchment.
