Impacts of sea level rise on tidal wetlands and shallow water habitats: A case study from Chesapeake Bay

Along with greenhouse gases and temperature, sea level has also increased globally over the last century. In the Chesapeake Bay, where there is postglacial fore-bulge collapse, the rate has increased from 0.5 mm per year, from 1000 to 1850 AD, to more than 3.2 mm per year during the 20th century. Moreover, the decadal rate in the 1990s was very high, more than 1.3 cm per year. This unprecedented rate triggered marsh losses in the Chesapeake and Delaware bays. Evidence from Thematic Mapper satellite imagery suggests that more than half of the tidal marsh area of the Chesapeake Bay now shows signs of degradation. As marshes erode, the resulting open water is marginal habitat for most biota. Among the problems for fish are the periodic hypoxia events in late spring. Contrary to expectations, landward migration of marshes is inadequate to replace marshes lost because sea level is rising faster than the plants can colonize new substrates and create new peat. Although they are complex and highly dependent on shoreline sediment type, sea grasses usually do not replace lost marshes at the seaward edge. It is hypothesized that excess wave action, turbidity, and deposition of fine-grain all interact to make the shallows less hospitable for luxuriant sea grass development. In conclusion, massive marsh erosion spurred by rising sea level will have large impacts in a variety of coastal environments that once supported significant fisheries.