Geospatial habitat change analysis in Pacific Northwest coastal estuaries

Abstract

We assessed historical changes in the location and amount of potential estuarine habitat in three of the four largest coastal estuaries in the United States Pacific Northwest (Grays Harbor, Willapa Bay, and Coos Bay) as part of the Pacific Northwest Coastal Ecosystem Regional Study (PNCERS). To accomplish the historical assessment, navigation charts, hydrographic survey data, maps, and published descriptions were used to gain information on the location of the shoreline, bathymetry, and vegetated habitats, which were then digitized and subjected to geospatial analysis using a geographic information system (GIS). We used present-day elevational boundaries for marshes, flats, and eelgrass meadows to help define habitat areas where they were not indicated, on historical maps. The analysis showed that tidal flats have decreased in all study areas, potential eelgrass,Zostera marina L., habitat has increased in Grays Harbor and Willapa Bay and decreased slightly in Coos Bay, tidal wetland area has declined in all three coastal estuaries with increases in localized areas due to filling and sedimentation, and dramatic changes have occurred at the mouths of Grays Harbor and Willapa Bay. These data illustrate that direct physical alteration (filling and diking) has resulted in large changes to habitats. Forest practices in the watershed, as well as variation in climatic factors and oceanographic processes, may also have contributed to changes. The information provides more evidence for managing estuarine habitats in the region and employing historical templates to plan habitat restoration in the future.