Long term conservation practice effects on agricultural soil loss from concentrated and distributed sources

Conservation practices have been recognized as an important mitigation tool to reduce soil loss and sediment transport from agricultural fields. Multiple conservation structures and farming practices have been proposed to target erosional processes with varying results of sediment trapping efficiency. The quantification of their performance at the watershed scale when multiple integrated and spatiotemporal varying processes occur, remains a challenge. In this study, the impact of conservation practices on erosion from sheet/rill and ephemeral gully sources at field and watershed scales were investigated on a USDA Conservation Effects Assessment Project (CEAP) watershed draining into the Chesapeake Bay. Three periods were identified: 1990-2000, 2010-2020, and 2000-2010 representing before, after, and a transition period of conservation practices implementation, respectively. Ephemeral gullies and conservation practices were characterized at raster grid scale and evaluated at field and watershed scales. The AnnAGNPS watershed pollution model was used to quantify sediment loads before and after actual conservation practices were implemented. Simulation results indicated a potential reduction from implemented conservation practices of approximately 10% from ephemeral gully sources and 30% from sheet/rill sources in annual average sediment loads, or by 60% overall when comparing annual averages expressed as sediment concentration. Analysis of sediment loads indicates that the implemented practices are less effective in deterring sediments from ephemeral gully sources. Two significant precipitation events with an estimated recurrence interval greater than 250 years were estimated to be responsible for adding 25% (151.73 Mg) to the 11-year annual average sediment load prompting the need for future research on the impact of extreme events on soil loss. Using customized soil erosion prediction technology designed for the quantification of diverse source and sink of sediment is a valuable resource for stakeholders seeking to develop erosion mitigation strategies.