Publications

Document Type

Report

Publication Date

2008

Abstract

During the spring and summer of 2007 a survey of the fringing marshes existing along the mainland coast of Casco Bay was commissioned by the Casco Bay Estuary Partnership and the U.S. Environmental Protection Agency. The work was performed by personnel supervised by the Wells National Estuarine Research Reserve (WNERR) in Wells, Maine.

A delineation of fringing marshes based on aerial photography was performed during the spring and early summer months. This delineation, based upon aerial imagery taken in 2003, identified approximately 1,160 marsh units along the mainland coast of Casco Bay (islands were omitted from this study). Later in the summer, after maturation of marsh vegetation, survey teams were dispatched in two separate efforts in support of the image-based identification. Boat transects were taken along representative shorelines and fringing marshes detected were marked at each end with a GPS point allowing an approximation of marsh location, and extent, to be recorded. Survey teams on foot visited a number of randomly-selected sample points and performed on-site measurement of marsh area (total, high marsh, low marsh, and major invasive patches), an estimate (based on elevation differences) of potential total marsh area after a forty centimeter (40 cm) rise in average sea level, and performed a 'rapid assessment' of marsh characteristics and degradation condition.

Based on the estimated average fringing marsh area, there is approximately 41 hectares of marsh covering nearly 150 km of the mainland coastline of Casco Bay. While some marsh is very healthy, development and other factors have taken their toll. The average impact assessment score was 73% (100% would be a 'perfect' score, with no problems); the median was just slightly higher at 75%. The average degradation score was 0.17 (with unity, '1', being the worst possible 1 score and '0' the best); similarly, the median was slightly better at 0.15.

The image-based identification performed well in identifying marshes. Based on 2007 'surface truth' provided by the boat transects, the image delineation (from 2003 imagery) identified between 50% and 70% (depending on the radius of tolerance used to define detection of a single marsh) of the marshes. When changes to the marshes over time are considered, this reflects favorably on its use. The marshes identified can serve as a basis for further efforts to find, assess, improve, and protect marshes in Casco Bay.

Comments

Funded through grants from the Casco Bay Estuary Partnership and the U.S. Environmental Protection Agency Region 1.

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