- Vionov, Alexey
Guns Institute for Ecological Economies & Computer Science Department, University of Vermont
Diffuse pollution from urban stormwater and agricultural runoff are among the leading causes of water pollution in the United States. Currently, most management plans that address diffuse pollution are driven by dissociated economic, political and ecological interests that are difficult to reconcile. Integrated watershed management, best achieved through a process-oriented and participatory research approach, aims to protect and improve water resources while considering economic and social concerns in the community.
Such an approach was implemented in the small heterogeneous watershed of St. Albans Bay, Vermont to determine the relative load of phosphorus from all sources and identify the most cost-effective interventions to achieve target reductions, as outlined by a Total Maximum Daily Load. The approach provided a transparent modeling process that involved a representative group of stakeholders throughout the two year research process at multiple levels of engagement—water quality monitoring, soil phosphorus sampling, model development, scenario analysis, and future policy development. Statistical, mass-balance, and dynamic landscape simulation models were used to assess the state of the watershed, the long-term accumulation of phosphorus in the watershed, and to describe the distribution of the average annual phosphorus load to streams (10.57 mtP/year) in terms of space, time, and transport process. Watershed interventions, matched to the most significant phosphorus sources and transport processes, were developed with stakeholders and evaluated with the framework.
The St. Albans Bay watershed has a long-term net accumulation of phosphorus that ranges between 76 and 170 mtP/year, most of which accumulates in agricultural soils. Dissolved phosphorus in surface runoff from the agricultural landscape accounts for 41% of the total load to watershed streams. Direct discharge from farmsteads and stormwater loads, primarily from road sand washoff, are also significant sources.
The most effective combination of scenarios to achieve target reductions in the short-term is reduction in soil phosphorus runoff from farm fields, treatment of farmstead runoff and reduction of road sand washoff using road sweepers. Achievement of long-term nutrient balance in the watershed requires reduction of fertilizer usage in agricultural and urban areas, and reduced manure application rates throughout the watershed.
The participatory modeling approach employed in this study has led to identification of different solutions than stakeholders had previously assumed would be required to reduce phosphorus load to streams and St. Albans Bay. The approach has led to greater community acceptance and usefulness of model results as evidenced by local decision makers now moving forward to implement solutions identified to be most cost-effective.