September 2014

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Overview

Eelgrass Map (06-07)

Seagrass, a form of Submerged Aquatic Vegetation (SAV), serves as important fish and wildlife habitat and assists with storage and recycling of nutrients and the stabilization of sediments. The predominant seagrass found in Massachusetts coastal waters is eelgrass (Zostera marina). The Massachusetts Department of Environmental Protection (MassDEP) began surveying seagrass in the early 1990s and the MassDEP Eelgrass Mapping Project has produced multiple phases of seagrass mapping along the Massachusetts coastline.

This layer contains features mapped in the sixth phase of the MassDEP Eelgrass Mapping Project. Phase 6 mapping was conducted in 2013 and focused on re-mapping portions of the Massachusetts coastline including Buzzards Bay, west Cape Cod, the Elizabeth Islands, Martha’s Vineyard and Nantucket.

The layer is named EELGRASS2013_POLY.

Methodology

Digital imagery was acquired in late spring 2013 through a contract with GeoVantage Corporation (Peabody, MA). The GeoVantage sensor consists of a digital camera with four bands centered on blue (450nm), green (550nm), red (650nm) and near-infrared (850nm). The output of the camera system are GeoTIFF image products which were created from the true color imagery captured with a 0.5 meter ground sample distance resolution and 8 bit radiometric resolution. The images were orthorectified, terrain corrected (using 7.5m USGS DEMs), georegistered and mosaicked from individual photos with a spatial accuracy of +/- 3 meters (90% of pixels). The digital images were interpreted monoscopically on screen using the same photo-interpretative protocols as previous phases of the MassDEP Eelgrass Mapping Project. The digital imagery was analyzed and interpreted using a high resolution CRT 22 inch monitor.

Polygons of seagrass were hand digitized on-screen using ESRI ArcGIS Desktop software. Much of the Massachusetts coast has a sandy substrate providing a useful color contrast to map the darker seagrass photo-signatures. Nonetheless, there are still uncertainties with signature interpretation that required field verification. Extensive fieldwork was conducted to develop a quantitative understanding of the signatures and gather surface level data where the presence or extent of habitat was not apparent. The fieldwork methods and ground-truthing protocols were similar for this project as were utilized in the earlier two mapping efforts (1995, 2001, 2006-07, 2010 and 2012).

Using a small boat, a total of 893 points were visited as part of fieldwork.  These points were chosen for their mapping relevance all along the coastline of the 2013 project area.  For 620 of these points bottom characteristics were recorded using GPS location data connected to a mapping database on an on-board laptop using ArcGIS 9.3.1.  Navigation to each point in the field was accomplished using DGPS (1 meter accuracy) in Massachusetts State Plane coordinates.

The remaining 273 points were logged onto a spreadsheet using a hand-held GPS using DMS latitude and longitude coordinates, because normal GPS connectivity was unavailable.  These points were later converted to Massachusetts State Plane coordinates.  Their locations are the western coastline of Cape Cod, including Bourne and Wareham, western coastline of Martha’s Vineyard, several off Cape Poge, and Nantucket.

The two databases were combined back in the laboratory, used for the final interpretation, and added to the total inventory of the Seagrass mapping project points.  Questionable areas in the interpreted data were investigated on board the boat to verify the presence or absence of seagrass using an underwater video camera (videography).

Attributes

The attribute fields for this layer are:
FIELD TYPE VALUE(S)
YEAR Char Year of delineation; 2013
HABITAT Char Seagrass type (Eelgrass)
AREA_ACRES Float Area of SAV feature in acres

Maintenance/Availability

This layer is maintained by the MassDEP Wetlands Conservancy Program. For additional information on the MassDEP Eelgrass Mapping Project, visit: http://www.mass.gov/eea/agencies/massdep/water/watersheds/eelgrass-mapping-project.html.

Also see:


Last Updated 7/12/2017