The objective of this research is to assess the impact of future land cover changes on nutrient enrichment of streams. It applies cellular automata (CA) Markov chain model to simulate future land cover change and a GIS-based distributed cell-based model to predict non-point source nitrogen loadings to streams. The integration of the two models provides site-specific information on how the spatial location and extent of urban development can affect nitrogen pollution under dry, normal and wet conditions.
Two scenarios of land cover change, in particular, were examined. The baseline scenario (Scenario 1) involved only minor protection of environmentally sensitive areas. The open space conservation network scenario (Scenario 2) incorporated the principles of "green" infrastructure as outlined by the relevant literature. Scenario 2 was based on protection of riparian areas, floodplains, wetlands, urban open space, and areas with exceedingly shallow depth to seasonally high water table and bedrock. Increased setbacks, where appropriate, were considered. The impact of the projected land cover change under different development scenarios was then examined in terms of nitrogen delivery ratios, total loads and contributing areas. A spatial hydrological model of the watershed was developed under dry, normal and wet conditions. A non-linear regression model was applied to estimate nitrogen trapping efficiencies and delivery ratios based on field characteristics such as slope, saturated hydraulic conductivity, soil mean particle diameter, Manning's roughness coefficient and length of flow. An attenuation factor taking into account cost distance to streams and decay constant was also incorporated into the model to account for transmission losses. Contributing areas of nitrogen delivery to streams were delineated based on the model results.