Efficiencies of best management practices in reducing nitrate pollution of the Sebdou River, a semi‐arid Mediterranean agricultural catchment (North Africa)

Abstract

AbstractA major problem facing the water sector in Algeria is deteriorating water quality, which is strongly influenced by nutrient inputs to agricultural watersheds. To mitigate the effects of agricultural activities and enhance water quality, this study considered the impact of different best management practices (BMPs) in agriculture. The objective of the research was to evaluate the impacts of various agricultural BMPs on nitrate losses in the Sebdou catchment in north‐west Africa using the Soil and Water Assessment Tool (SWAT) model in order to identify and recommend the most appropriate BMP. The study was carried out in two parts: first, the SWAT model was calibrated and validated to simulate discharge and nitrate losses at the outlet of the catchment, and second, the calibrated model was used to assess the effects of BMPs on nitrate losses. The hydrological modelling fitted well with the observed data for the calibration and validation periods (NSE between 0.63 and 0.65 and R2 between 0.80 and 0.92). Nitrate simulation was also satisfactory (NSE = 0.58 and R2 = 0.58), with the average nitrate exports at the outlet varying between 136 and 149 t N year−1. Agricultural tillage practices were the main N input and plant uptake was the main N output. The simulation results of BMP scenarios (contour farming, strip cropping and terracing) showed a significant decrease in nitrate quantity in soil, nitrate yield in surface run‐off and nitrate exports. The maximum reduction was observed from the use of parallel terraces, which reduced nitrate in soil by 17% (41 kg ha−1) and decreased nitrate flux exportation to below 133 t N year−1 (a reduction of about 11%). This study provided useful information for implementation of the most effective agricultural BMPs in the catchment for stakeholders who are interested in soil and water management.