Loss of these marshes would be devastating, the researchers say, due to its effect on the food chain, water quality, and the amount of carbon that would be released into the oceans and atmosphere. Marshes act as carbon sinks, holding it in solid form, so it does not emerge as carbon dioxide gas. The study, by Prof. Michael S. Kearney and colleagues, is reported in the April 16 issue of Eos, a publication of the American Geophysical Union.
Kearney describes a new technique he and his colleagues developed, based on 1993 images from the Thematic Mapper instrument on the Landsat satellite, updated with more recent aerial photography and field surveys. The model measures reflectance from the marsh's soil or sediment layer, its vegetation, and the water, in order to determine its Marsh Surface Condition Index (MSCI), which tracks the overall health of the marsh. A key benefit of the MSCI is that it helps scientists focus on the role of long term sea level rise, without regard to annual variations caused by heavy storms and other transitory phenomena.
In Chesapeake Bay, the greatest degradation of marshes has occurred in the middle portion of its eastern shore at Blackwater Wildlife Refuge. The upper reaches of both Chesapeake and Delaware Bays are less degraded than the middle and lower reaches. This, the researchers say, is due to the smaller amount of river sediment, which helps the upward growth of the marsh, reaching the lower parts of the bays.