Modeling the effect of best management practices on sediment yield in a Mediterranean watershed

To counteract the threat of soil erosion, the most widespread form of soil degradation, European policies (PAC, 2014-2020) incentive the implementation of Best Management Practices (BMPs). Therefore, European countries are called to identify the areas at a high risk of soil erosion and to adopt conservation measures. In this study, the Soil and Water Assessment Tool (SWAT) was used to quantify the soil erosion rates for the current management options and to identify the critical source areas in the Carapelle watershed, an agricultural watershed located in the Puglia region (Southern Italy). The model was calibrated and validated for streamflow and sediment load at a daily time scale (2007-2011). The results showed that in the Carapelle basin the average annual sediment load is 5.95 t ha-1 yr-1. The areas under severe soil erosion rate (10 t ha-1 yr-1) were identified resulting in 59 HRUs located in the mountainous part of the watershed and characterized by agricultural land use. Different BMPs scenarios, based on the regional policies, were modelled in the areas under severe soil erosion: contour farming (BMP1), no-tillage (BMP2), reforestation (BMP3), and the combination of contour farming and reforestation (BMP4). Results showed that BMP4 was the most effective for soil erosion control (38%; 5.95 to 3.70 t ha-1 yr1 ), followed by BMP2 (29 %; from 5.95 to 4.20 t ha-1 yr-1), BMP1 (22 %; from 5.95 to 4.61 t ha-1 yr-1) and BMP3 (15 %; from 5.95 to 5.04 t ha-1 yr-1). An analysis of the farmer return-production cost ratio (FR/PC) indicated that the baseline (conventional tillage) and BMP1 were both economically sustainable in areas with slope < 20 % (FR/PC = 1.12 and 1.11, respectively). BMP2 received the highest FR/PC rating of 1.67 in areas with slope < 20 %. The baseline scenario had no economic advantage (FR/PC = 0.93) in steep slope areas. BMP3 was ranked at the top (FR/PC = 1.49) followed by BMP2 (FR/PC = 1.41) in areas with slope > 20 %. The results show that a program of measures can be effective for controlling soil erosion but it must be implemented over long time frames and it requires relevant investments from the public and private sectors.