Westport Salt Marsh Loss Study

NEP Technical Report Documenting Salt Marsh Loss in Westport, MA

Figure from the Westport salt marsh loss technical report.

Figure from the Westport salt marsh loss technical report.

The Buzzards Bay NEP has released a technical report documenting the loss of salt marsh on six islands in the West Branch of the Westport River.  The analysis was undertaken in partnership with the Buzzards Bay Coalition, the Westport River Fisherman’s Association, and scientists at the Woods Hole Research Center. The collaborative study was initiated because of reports of apparent rapid salt marsh loss in the West Branch of the Westport River. The Buzzards Bay NEP was the lead on the historical analysis, which included an evaluation of aerial photographs between 1938 and 2016, a 2016 unmanned aerial vehicle survey in October 2016, and a 1934 nautical chart. The NEP provided both training to Buzzards Bay Coalition staff in digitizing salt marsh boundaries, and performed the GIS analysis of the historical changes. The report describes in detail the GIS methodologies used, and their limitations. This work complimented a companion study of field studies of marsh biomass, and evaluation of water quality trends, to better understand the causes of the recent salt marsh losses. The Buzzards Bay NEP report is available at this link: Costa & Weiner, 2017.

Since the end of the last ice age, over long periods, rising sea level has caused salt marshes to migrate into uplands. In the case of marsh islands studied, except for one, there is no upland area for the marsh to migrate into. The Costa and Weiner study found that while the rate of salt mash loss on the islands was generally linear for much of the twentieth century, there appeared to be an acceleration of marsh loss during the past decade. In addition, the rates of loss varied among the islands, likely due to initial marsh elevations, proximity to river channels, and other factors.  The report estimates the approximate dates of when each of the islands may disappear if recent rates of loss continue.

Jakuba et at. (2017, unpublished) incorporated the data from the Costa and Weiner study into a more comprehensive analysis of potential causes of marsh loss that included field data of salt marsh above and below ground biomass, water quality data, and other field observations. The authors concluded that nitrogen pollution in the Westport River was a contributing factor to the loss of salt marsh area on the islands. A summary of the findings of the Jakuba study is at the Buzzards Bay Coalition Website, and their report to the public is at this link: Salt-Marsh-Loss-in-the-Westport-Rivers.pdf.

Loss in area of the salt marsh island Bailey Flat in the west Branch of the Westport River, 1934-2016.

Loss in area of the salt marsh island Bailey Flat between 1934 and 2016.

About Joe

Joe Costa is the Executive Director of the Buzzards Bay National Estuary Program.