Participatory modeling and the dilemma of diffuse nitrogen management in a residential watershed

Whereas point sources of nutrients are well understood and controllable, there is growing concern about non-point sources, especially those that are related to individual property owners. Modeling tools were used to analyze and visualize the fate of nitrogen from three anthropogenic sources: septic tanks, atmospheric deposition, and fertilizer. Our results suggest that septic tanks may be a less significant contributor to surface water nitrogen pollution in the short-term whereas fertilizer used at the home scale is a more significant source than previously thought. Participation in the study was solicited from community stakeholders who were instrumental in understanding how models could be applied to local decision making, in making appropriate model assumptions, and in developing politically feasible scenarios. Stakeholders used the model results to develop recommendations for the Calvert County Board of Commissioners. Recommendations include mandating nitrogen removal septic tanks for some homes, intensive citizen education about fertilizer usage, local regulation of fertilizer sales, reduction in automobile traffic, and cooperation with regional regulatory agencies working to reduce regional NOx emissions. We explore how the participatory process can be used to influence decision-making, management policies, and citizen education in Calvert County, MD, to reduce all anthropogenic sources of nitrogen to local waters.