New Ephemeral Gully, Riparian Buffer, and Wetland Components within the USDA Annualized Agricultural Non-Point Source (AnnAGNPS) Watershed Pollution Management Model.

The development of watershed conservation management plans involves many decisions that affect various aspects of a watershed system, with consequences that are difficult to measure.  In addition, the efficient placement of practices throughout a watershed as part of an integrated management plan can be difficult without the use of watershed modeling technology to adequately describe where the source of pollutants comes from and their impact on water quality.  New features have been implemented within the USDA Annualized Agricultural Non-point Source (AnnAGNPS) model describing ephemeral gully erosion processes, riparian buffers as they impact sediment and nutrient transport, and wetlands as they may be implemented within watershed systems.  Examples illustrating the new features will be provided from watershed studies developed to evaluate water quality effects from ephemeral gullies and riparian buffers as part of a comprehensive watershed conservation management plan in the German Branch of the Choptank River Basin in Maryland that is part of the USDA-ARS Benchmark CEAP-Watershed Assessment Study project.  The results show that significant loads are produced from ephemeral gullies as well as from overland flow, but loads can be significantly reduced using riparian buffers combined with conservation tillage and grassed waterways to control gully erosion. Examples will also be discussed on the use of the wetland feature based on a 125,000 ha watershed located in North-Central Illinois.  Wetlands in series or individually can be evaluated using the model for their effect on downstream pollutant loadings. The integration of field-scale sheet and rill erosion, gully erosion, riparian buffer and wetland pollutant loading components with watershed-scale modeling tools can provide a more accurate and applied approach for decision-making on where to apply conservation practices for erosion control, as well as riparian buffer or wetland conservation management practices and in determining their effectiveness in reducing pollutant loads.