Integrated GIS-based methodology to assess hotspots of sediment sources in Mediterranean watersheds: a valuable tool supporting decision-makers towards a sustainable watershed management

Soil erosion and land degradation are among the main threats to agricultural landscapes such as Mediterranean agroecosystems. Assessing the variety of geomorphic processes at the different spatio-temporal scales must be considered for identifying hotspots of sediment dynamics, as to support decision-makers in a sustainable watershed management. However, there is a lack of integrated methods that combine geomorphic spatial data with a comprehensive approach to sediment dynamic modelling. Therefore, we introduce a novel methodology that integrates geomorphic data derived from a detailed digital mapping with structural and functional components of sediment connectivity. In particular, a new GIS-based model named HOTSED was developed, designed to assess potential hotspots of sediment sources and related dynamics at the watershed scale. We tested our approach in an agricultural-forested watershed in the Northern Apennines (Italy), starting with the elaboration of an Inventory Map of sediment sources. Then, we estimated the geomorphic potential of sediment sources with a relative scoring system. Moreover, we simulated the structural sediment connectivity and the sediment transport potential by combining terrain/hydrological parameters, land use data, and rainfall erosivity. Finally, the integration of these components was achieved through a raster-based calculation method. HOTSED provides a holistic assessment of sediment sources and related dynamics allowing to detect emergent properties of the landscape through a unique and intuitive output. The results show that the model successfully identified hotspots associated with complex and polygenetic geomorphic systems. They are located in areas close to the main channels, which mostly include processes like rill-interrill and badland erosion and/or landslides associated with bank erosion. Moreover, it identified areas prone to store sediments in depositional landforms with low geomorphic potential and low connectivity. HOTSED offers a valuable tool supporting decision-makers towards a sustainable watershed management. Moreover, the identification of hotspots of sediment sources allows for a preliminary evaluation of the contribution of different processes to sediment dynamics using sediment fingerprinting (e.g., unravelling lithological and land use features as controlling factors).