Abstract:
Badulu Oya catchment is an intensively cultivated landscape in Sri Lanka. Soil erosion due to agricultural
practices can reduce soil fertility and deteriorates of surface water quality. However, empirical evidence
on soil erosion rates of the catchment and their association with surface water quality is less documented
in Sri Lanka. The soil erosion rates of the 10 selected micro catchments within Badulu Oya catchment
were evaluated using, Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) Sediment
Retention Model. Physical, chemical water quality parameters and benthic macro invertebrate indices EPT
percentage taxa and Chironomidae percentage were calculated to evaluate the overall ecological health of
the streams associated with micro- catchments. Pearson's correlation test was conducted to estimate the
association between water quality and sediment delivery data of the micro catchments. A comprehensive
household (HH) questionnaire survey was conducted to obtain the information from the farming
community (n=71), on their land use, knowledge on soil and water conservation practices and the degree
of interventions in catchment management. The average soil loss of ten micro catchments varied between
66.0t/ha/yr to 165.9t/ha/yr. Correlation analysis of average soil loss and average water quality
parameters at micro-catchments indicated significant (p<0.05) positive relationships suggesting soil
erosion in the catchment is affecting the stream water quality. Results of the questionnaire survey
indicated that the soil erosion rates of the catchment are related to farmer's education level and their level
of soil conservation adaptations (p<=0.05). The finding of the present study emphasized the need of
human interventions in catchment management.
