LAND USE / LAND COVER CHANGES AND ECOLOGICAL HEALTH INDICATORS IN THE BLACKBIRD CREEK WATERSHED: WITH RECOMMENDATIONS FOR RESTORATION

The objectives of this study were to 1) assess changes in land use and land cover of the Blackbird Creek watershed (New Castle County, Delaware) from 1937 to 1997, 2) present landscape metrics which can be applied to land cover data derived from remotely-sensed imagery, in order to assess landscape ecological integrity, 3) identify areas with degraded ecological conditions, 4) develop recommendations for ecological restoration, and 5) make data available to decision-makers to aid in setting priorities for non-point source pollution control and wildlife habitat restoration efforts. 1937 aerial photography was obtained, scanned and rectified, and land use / land cover (LULC) polygons were on-screen digitized and converted to a grid (ARC/INFO v. 7.1.2). 1997 LULC data were developed by merging 1992 LULC with 1992 State Wetlands Mapping Program (SWMP) data and 1997 updates mapped from Digital Ortho Quarter Quads (DOQQs). The 1937 and 1997 data sets were compared. Between 1937 and 1997, there was a 12.5% increase in development. As of 1997, developed land represented nearly 22% of the upland portion of the watershed. Cultivated land decreased by 16%, but still accounted for over 47% of the upland portion of the watershed in 1997. Deciduous forest increased by 5%, but accounted for less than 30% of the upland portion of the watershed, with nearly 70% devoted to human uses. Another change involved the conversion of a large portion of tidal marsh to open water and mud flats, contributing to a 120-ha increase in these classes. Estuarine impoundments increased from 0 to 11 ha, and palustrine ponds and open water impoundments increased by 14 ha. As of 1997 there were at least 116 ha of farmed wetlands. GIS Landscape metrics were applied to the LULC data in order to demonstrate various approaches to assessing landscape ecological health, and to assess some of the present-day (i.e., 1997) ecological health conditions of the Blackbird Creek watershed, from a remote sensing perspective. Forest interior habitat availability, riparian forest width and degree of forest patch isolation were evaluated, and the results compared with results from bird surveys aimed at detecting forest fragmentation-sensitive birds. The forests of the Blackbird Creek watershed appear to support some fragmentation-sensitive species, but the most sensitive species do not appear to be supported. Forest patch isolation appears to be a limiting factor for at least some rare or endangered species. In addition, 34% of a 30-m zone, along the perimeters of all forest patches, is developed, thus affecting the habitat suitability of the adjacent forest and eliminating opportunities for forest expansion and reduction in fragmentation. A GIS layer of coastal plain ponds, unique wetland features supporting several rare species, was evaluated in terms of percentage of forest cover within 165 m. This buffer distance is important for the conservation of rare and endangered salamanders. Approximately 51% of the ponds were found to have > 75% forest cover within 165 m. Nineteen percent had < 50% forest cover within 165 m, and are in need of buffer