POD! Landscape indicators of urban stressors on aquatic ecosystems in the Upper San Francisco Estuary, California, by Hydrodynamic Subregion
Land use is an ultimate driver of many of the stressors on the Upper San Francisco Estuary, but the magnitude and pattern of land use change has not previously been analyzed. I attempted to fill this knowledge gap through a screening-level risk assessment in which ancillary data were used to quantify measures such as impervious cover, housing density, road density and road crossings.
With a mask set for land area, use the ArcGIS ZonalStatistics tool with Hydrodynamic Subregions as the zones and the National Land Cover Dataset Impervious Cover raster as the value grid. Each grid cell in the Impervious Cover raster has a percent impervious cover value between 0-100. The mean value of the ZonalStatistics output is the summary statistic for each subregion.
Housing density 2000
Housing count data from the 2000 US Census by census block was resampled by Patrick Jantz to 500 m grid cells. The ArcGIS Zonalstatistics tool was used to calculate the mean density of each hydrodynamic subregion.
Median distance of urban land to water
The straightline distance of each grid cell in the Estuary region from open water was calculated with ArcGIS Spatial Analyst. Then the distances were summarzed for all urban and built-up cells in the 2000 Farmland Mapping and Monitoring Program land use map.
The US Census TIGER files road data were converted to ArcGIS shapefiles using Bruce Ralston's tgr2shp tool. All road features except trails were selected. A LENGTH field was added and the length of each road segment was calculated with the ArcGIS Calculate Geometry tool in kilometers. The roads layer was intersected with the subregions layer, and the lengths of all roads was summed with the Frequency tool. Total length was divided by land area in each subregion.
Density of road-stream crossings
A new shapefile was created to contain points where roads and streams(also from the2000 US Census TIGER files) intersected. In the ArcMap Editor, the roads and streams were selected. The macro AddLines.UseHighlightedLayers was run after adding the AddPointsatCrossings.bas script to the VBA Editor. An X-coord and Y-coord field were added to the shapefile and filled with the Calculate Geometry tool. This layer was then Dissolved by the X-coord and Y-coord. The points were allocated to subregions using the Identify tool. The count of points in each subregion was tallied.
Data Set Usage Rights
These data may be freely shared within the public scientific domain. They are intended to provide a general estimate of urban land use attributes within the Upper San Francisco Estuary as a first level approximation of environmental effects. They are not intended to make any land use or regulatory decisions. The boundaries of the hydrodynamic subregions are approximations.