Evaluating the role of runoff and soil erosion on nutrient loss in the Chenetale Watershed, upper Blue Nile Basin, Ethiopia

Abstract

The non-point source pollution of agricultural nutrients (P and N) by surface water is not well quantified in the Ethiopia highlands. The objective of this study was to quantify soil nutrients (N and P) from an agricultural uplands area in upper Blue Nile basin. A small watershed (104.6 ha) and nested gully catchment were gauged for data collection. Two years (2015 and 2016) data of runoff, sediment, sediment-associated and dissolved soil nutrients loss were collected from two gagging stations. Both dissolved and sediment associated nutrients were computed for 2015 and 2016 rainy seasons. The result indicated that sediment associated nutrient loss was significantly higher than the dissolved nutrient loss. In 2015, the nutrients loss was 8.93 kg ha−1yr−1 N and 0.3 kg ha−1yr−1 P at the outlet of W-1 and 3.04 kg ha−1yr−1 N and 0.14 kg ha−1yr−1 P at the outlet of W-2. In 2016, 7.67 kg ha−1yr−1 N and 0.24 kg ha−1yr−1 P were lost at the outlet of W-1 and 8.44 kg ha−1yr−1 N and 0.57 kg ha−1yr−1 P were lost at the outlet of W-2. Nutrients losses with sediment were 91.3% and 45.6% of N and P, respectively. High amount of nitrogen was lost with sediment than in dissolved form indicating that soil erosion is an important process for soil nutrients losses in the highland. Therefore, soil and water conservation practices are practically significant to control soil nutrients loss.