Eelgrass Mapping Great Bay Estuary for 1981

The methods for this project followed the procedures specified in the approved QA Project Plan (Short and Trowbridge, 2003). Eelgrass meadow polygons for 1981 were mapped from USDA black-and-white aerial photographs, on file at the Strafford County and Rockingham County (NH) offices. The photographs were scanned and analyzed digitally after “rubber sheeting” the images to fit the Great Bay Estuary base map. The 1981 photographs were not ortho-photographs and some distortion across each photograph was evident. To minimize this effect, multiple photographs for each area were used to geo-reference actual locations on the eelgrass distribution map. Some areas of the estuary did not have adequate 1981 images to allow mapping; these areas are marked in red on the map (Figure 1). Ground truth verification of distribution was done by comparison to eelgrass mapping done by NH Fish and Game (Nelson, 1981). Eelgrass cover classes were determined using the standard protocol (Short and Trowbridge, 2003) with the added limitations of black-and-white photograph