From cedar cemeteries to marsh lakes: a case study of sea-level rise and habitat change in a northeastern US salt marsh.
Evidence for relative sea-level rise in the Mullica River-Great Bay, a relatively undisturbed watershed in southern New Jersey, stretches over hundreds of years. The increase in global sea-level rise in the region is enhanced by subsidence and results in rates that are approximately double the global average. In recent decades, the occurrence of "ghost forests," standing dead forests, especially of the salt-intolerant Atlantic White Cedar, is becoming increasingly obvious as tidal inundation of salty waters increases further inland, especially in the upper portions of the Mullica River and its tributaries. Even older evidence of sea-level rise in the watershed is the subtidal and intertidal occurrence of "cedar cemeteries," i.e., buried accumulations of Atlantic white cedar stumps and timbers that have been radiocarbon-dated from the fifteenth to the sixteenth centuries to as old as the fifth century. Some of these are being exposed as rising water extends intertidal creeks into adjacent wetlands and uncovers this rot-resistant wood. Sea-level rise is perhaps the most significant threat to the persistence of salt marshes over the coming century. Sea-level rise decreases salt marsh area by erosion at the marsh edge, drowning of the marsh surface, and the expansion of marsh pools into larger marsh "lakes." In some instances, this loss of salt marshes is compensated for by expansion landward into ghost forests, but in this watershed and others, the expansion is by invasive plant species such as Phragmites australis, which is suboptimal habitat for fishes, crabs, and other invertebrates. The combination of a fast rate of sea-level rise in an area relatively free from recent human intervention makes the Mullica Valley watershed an ideal location to continue to evaluate the effects of sea-level rise on salt marsh ecosystems.