Background/Question/Methods Impervious surfaces associated with exurban ‘sprawl’ alter ecosystem functioning, resulting in potentially dramatic changes in the provision of ecosystem services that support local well-being.  Communities are faced with two future development alternatives, one that is highly desired by society at large (most people want to live in a big house in the suburbs) but with large impacts on water quality, and a more sustainable pattern of urban in-fill that leaves the rest of the watershed to exist in a more natural state, with attendant abilities to provide ES. Currently communities do not have a decision-support capability to assess tradeoffs of development and land use decisions in terms of water-related ecosystem services.  Our objectives, therefore, were to (1) demonstrate the interconnection among landscape, human, and natural systems in an explicit and quantitative way, and (2) develop a user-friendly decision support system that enables even novice users to select various scenarios, change underlying assumptions, examine uncertainties, and make the best possible decisions based on holistic understanding.  We have developed an integrated suite of spatial modeling tools that link economic driving factors to the number of new housing permits, and establish spatially explicit relationships between resultant new impervious surfaces and water quality.

Results/Conclusions To date we have tested the modeling framework in two New York State watersheds.  The Wappinger Creek watershed in Dutchess County demonstrated a typical case of sprawl: (1) population increased by 20%; (2) the number of building permits strongly responded to economic growth variables (e.g., GDP); (3) observed and projected sprawl spread outward from urban centers to rural areas, showing a strong urban-rural gradient; and (4) the stream quality (e.g., chloride concentration and specific conductivity) showed clear temporal and spatial responses with increasing development. The Onondaga Creek watershed in Onondaga County displayed a typical case of sprawl without growth: (1) population was stagnant; (2) the pattern tended to be exurban, i.e. more individual units than housing developments; (3) annual building permits were correlated with increasing Federal aid and decreasing interest earnings; and (4) water quality does not follow a strict rural to urban gradient. Based on our findings, we used our assessment toolbox to project new impervious areas for the next ten years under various economic scenarios, and consequent changes in stream flow, water quality, stream biotic condition and sediment yield. The degree of impact was highly dependent on the economic scenario assumed (e.g., continued economic growth or economic downturn).