Using GIS to Examine the Effect of Scale in Assessing the Relationship Between Land Use and Stream Condition

Landscape modifications due to agricultural needs, urban sprawl, and intensive population growth have seriously reshaped the stream hydrology and ecology in Southern California. This study examines the effects of dominant land uses on stream condition in the Calleguas Creek Watershed. To understand the effects of land use on the stream ecology, analysts evaluated how the observed field condition (e.g., fish, benthic macro invertebrates, and riparian habitat) corresponds to landscape indicators such as land cover percentages (urban, agriculture, and open space), population density, and road density.

They first defined the associated land use to each stream site by describing the type of land use encountered immediately adjacent to the sites. It is clear that exclusively describing the adjacent land uses to a stream site will not encompass all land use activities affecting the sampling site (e.g., agricultural field irrigation discharging into the stream way flows through all downstream tributaries). This study explores how scale and different land use definitions may affect landscape indicator estimation.