This data release presents eelgrass distributions and bathymetric data from repeated surveys performed on the Nisqually River delta to document interannual changes in eelgrass abundance and coastal morphology following the removal of dikes in 2009 that restored tidal processes to over 300 ha of former freshwater wetlands. Survey operations were conducted by a team of scientists from the U.S. Geological Survey Pacific Coastal and Marine Science Center and Washington State Department of Ecology. Eelgrass distributions and bathymetric data were collected along a series of shore-perpendicular transects spaced primarily at 25-50 m intervals from the R/V George Davidson equipped with a single-beam sonar system and global navigation satellite system (GNSS) receiver (fig. 1). Acoustic backscatter data were analyzed using a custom graphical user interface that implements a signal processing algorithm applied to each sonar sounding that differentiates and extracts the location of the seafloor apart from the presence of vegetation (Stevens and others, 2008). A towed underwater video camera was used identify the presence or absence of eelgrass along a limited number of survey transects to evaluate the classification of the single beam sonar data.
This data release currently contains eelgrass distributions and bathymetric data from 3 surveys performed on the Nisqually River delta between 2012 and 2017 and will be updated as data from future surveys become available. Links containing eelgrass distributions derived from acoustic and towed underwater video surveys, bathymetric data, and associated metadata are provided in the child pages listed below.
Figure 1. Photographs of equipment used during surveys of eelgrass distributions and bathymetry on the Nisqually River delta, Washington between 2012 and 2017.
Stevens, Andrew W., Lacy, Jessica R., Finlayson, David P., and Gelfenbaum, Guy, 2008, Evaluation of a single-beam sonar system to map seagrass at two sites in northern Puget Sound, Washington: U.S. Geological Survey Scientific Investigations Report 2008-5009, 45 p.