Abstract:
Soil erosion in river catchments increases sediment deliver to streams causing water quality
deterioration. This study was aimed to determine the relationship between soil erosion and water quality
of intensively cultivated Uma Oya watershed and to assess human-induced factors contributing to soil
erosion in the watershed. The soil erosion rates of ten selected micro-catchments were evaluated using
Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) Sediment Retention Model. The
overall ecological health of the streams associated with micro-catchments was calculated by assessing
physiochemical parameters and benthic macro-invertebrate indices in monthly intervals. A
comprehensive questionnaire survey was conducted to obtain information on farmers' land use practices
and their level of adoption of water and soil conservation practices (n=83). Person’s correlation test and
multiple regression analysis were used to estimate association of water quality and soil erosion, and to
identify human-induced factors that contribute to soil erosion. The estimated average soil loss of selected
micro-catchments varied between 36.4 t/ha/yr to 222.4 t/ha/yr. Correlation analysis indicated average
soil loss of the catchment is having significant (p<0.05) positive relationships with phosphate, Biological
Oxygen Demand (BOD5), Total Dissolved Solids (TDS), alkalinity, %Chrinomidae and a negative
correlation with Percentage Ephemeroptera: Plecoptera: Trichoptera (EPT) taxa in study streams. Results
of the questionnaire survey indicated that the farm-level soil loss was attributed to family size, farmer's
education and their soil conservation adoptions (p<0.05). The findings of the present study suggested
close relations among the stream health and soil erosion, and need for human interventions in catchment
management.
