Field patterns as game changers of the sediment connectivity

In Northwestern Europe, sediment transport from agricultural fields to rivers has significant off-site impacts, influenced by connectivity between landscape elements. Sediment connectivity, assessed using the index of connectivity (IC) developed by Borselli et al. (2008), is shaped by landscape configuration, including features like field boundaries that divide land parcels. Effective management requires understanding these interactions to mitigate soil erosion. IC depends on factors enhancing (upstream area and slope) or impeding (downstream distance and impedance) connectivity, with impedance estimation being particularly challenging to quantify due to vegetation effects. This study proposes to refine the IC weighting factor by incorporating parcel connectivity, better reflecting agricultural landscape fragmentation's impact. Focusing on the Dyle sub-catchment in Belgium, we applied the Revised IC using high-resolution data (1 m × 1 m). Fragmented landscapes yield lower connectivity values, indicating greater sediment disconnection. This is especially pronounced along concentrated flow paths, where up to 49 % of the least connected flow paths are disconnected compared to non-fragmented setups. Isoline-based parcel fragmentation emerged as highly effective, promoting larger parcel sizes and better disconnection on concentrated flow paths. These results emphasize the opportunities for improved management of agricultural landscapes in order to reduce sediment connectivity through appropriate land use practices and parcel configurations. Furthermore, by identifying potential vegetation barriers at the intersection of concentrated flow paths and field boundaries, our analysis shows that around 40 % of these barriers consist of adjacent fields with the same crop. It highlights opportunities for more effective crop rotations strategies.