Assessing the effect of BMPs in reducing nutrients and sediment loads in a Mediterranean basin

Tillages and the inappropriate use of mineral fertilizers are the main drivers of diffuse pollution and soil erosion. The European Green Deal (EUGD) and the "Farm to Fork" strategy target to re-establish the natural functions of ground and surface soil by 2030. Mitigation measures, known as Best Management Practices (BMPs), should be adopted in EU Member States' management programs to achieve the policies' objectives. In this work, the Soil and Water Assessment Tool (SWAT) was set up in the Carapelle basin (Apulia, Italy) in order to assess the impact of soil erosion-oriented BMPs in reducing nutrient loads. Moreover, their economic convenience was evaluated for both the public and the private sector. Five BMPs scenarios were simulated with the SWAT model within the high-risk erosion areas: Contour farming (CF), no-tillage (NT), reforestation (RF), and two additional scenarios, including 20% reduction of fertilizers in CF and NT, (CFR) and (NTR), following the Farm to Fork strategy. With the current land management, total nitrogen (TN) was ~49 kg ha-1y-1, while total phosphorous (TP) was ~0.044 kg ha-1y-1. NT and CT showed an increment of N-NO3 load in both surface runoff and leaching. Contrarily, RF, CFR and NTR showed a reduction of N-NO3 losses. In particular, CFR and NTR abated about the 20% of surface runoff and leached N-NO3 loads. From the economical point of view, results showed that BMP implementation requires important investments (public and private). RF was profitable in steep slopes areas while CFR and NTR were the best solutions in hilly and flat areas. This study provides fundamental insights for decision-making for agriculture and watershed management.