Geographic Targeting of Increases in Nutrient Export Due to Future Urbanization

Abstract

Urbanization replaces the extant natural resource base (e.g., forests, wetlands) with an infrastructure that is capable of supporting humans. One ecological consequence of urbanization is higher concentrations of nitrogen (N) and phosphorous (P) in streams, lakes, and estuaries. When received in excess, N and P are considered pollutants. Continuing urbanization will change the relative distribution of extant natural resources. Characteristics of the landscape can shape its response to disturbances such as urbanization. Changes in landscape characteristics across a region create a geographic pattern of vulnerability to increased N and P as a result of urbanization. We linked nutrient-export risk and urbanization models in order to identify areas most vulnerable to increases in nutrientexport risk due to projected urbanization.A risk-based model of N and P export exceeding specified thresholds was developed based on the extant distribution of forest, agriculture, and urban land cover. An empirical model of urbanization was used to increase urban land cover at the expense of forest and agriculture. The modeled (future) land cover was input into the N and P export risk model, and the ''before'' and ''after'' estimates of N and P export were compared to identify the areas most vulnerable to change. Increase in N and P export had to be equal to or greater than the accumulated uncertainties in the nutrient-export risk and urbanization models for an area to be considered vulnerable.The areas most vulnerable to increased N and P export were not spatially coincident with the areas of greatest urbanization. Vulnerability also depended on the geographic distribution of forest and agriculture. In general, the areas most vulnerable to increased N exports were where the modeled urbanization rate was at least 20% and the amount of forest was about 6 times greater than the amount of agriculture. For P, the most vulnerable areas were where the modeled urbanization rate was at least 20% and the amount of forest was about 2 times greater than the amount of agriculture. Vulnerability to increased N and P export was the result of two interacting spatial patterns, urbanization and the extant distribution of land cover. It could not be predicted from either alone.

A Model Approach for Estimating Colony Size, Trends, and Habitat Associations of Burrow-Nesting Seabirds

“…Compared with more completely forested basins, urban streams exhibited roughly 40% higher nitrogen levels and approximately 110% higher phosphorus levels. They note that though these nutrient discharge levels are lower than what might be observed within agricultural regions (e.g., Wickham et al 2002;Weller et al 2003), the levels have significant non-point source pollution implications.…”

“…This loss affects land cover composition and changes ecosystem processes (Fahrig 1997;Alberti and Marzluff 2004;Wiegand et al 2005;Donnelly and Marzluff 2006). Additionally, fragmentation can introduce sharp ecotones or edges that affect both material flows in ecosystems (Wickham et al 2002; and habitat conditions for species (deMaynadier and Hunter 2000; , particularly when there is a strong contrast between adjacent land cover types (e.g., impervious surface adjacent to forest). Since the vegetation loss and fragmentation are generally correlated and their interactions are difficult to untangle, we discuss their combined effects.…”

“…Most readily apparent are changes in the spatial pattern and configuration of landscapes such as the fragmentation of forests. Landscape fragmentation impacts ecosystems at multiple scales and levels of organization: it affects the distribution and persistence of species (Wiegand et al 2005;Donnelly and Marzluff 2006), as well as fluxes of nutrients and water (Baker et al 2001b;Wickham et al 2002;. Even regions of low-density development, in which a significant percent of the landscape is comprised of forest, can exhibit significant levels of fragmentation due to inclusions of roads, houses, and other structures .…”

“…Changes in the vegetation structure within watersheds alter or remove the water and nutrient retentive capacity associated with intact forests (Tague and Band 2001;Wickham et al 2002;Groffman et al 2004Groffman et al , 2006Kaye et al 2006). Ecological functions performed by remnant urban forest patches are diminished relative to their more connected, structurally and biologically complex exurban counterparts.…”

“…Ecological functions performed by remnant urban forest patches are diminished relative to their more connected, structurally and biologically complex exurban counterparts. Urban forests, for instance, exhibit higher potentials for nitrogen saturation (Wickham et al 2002;Groffman et al 2004;Zhu and Carreiro 2004). Water absorption into soils is also diminished or locally eliminated, particularly with higher levels of imperviousness.…”