The mean elevation of salt marsh surfaces must increase to keep pace with the annual rise in sea level and subsidence of salt marsh organic substrates. If the sedimentation rates in a salt marsh do not equal or exceed the net loss in elevation due to the steady increase in sea level and salt marsh subsidence, it will “drown”. When a salt marsh “drowns”, the surface of the marsh becomes sub-tidal which can cause drastic habitat changes such as the conversion of vegetated salt marsh to unvegetated mud flat.
Understanding changes in relative salt marsh elevation is important for interpreting changes in salt marsh vegetation communities. Salt marsh erosion and accretion are also important parameters for measuring the response of formerly impounded marshes to restoration of tidal influence, and will be particularly critical if the rate of sea level rise accelerates as predicted. This project is also part of a worldwide effort to monitor sea level rise with sediment erosion tables (SETs) and cryogenic coring devices. These two techniques measure the amount of erosion and accretion on salt marsh surfaces.
Determine long term trends in salt marsh elevation at selected sites in NCBN parks and factors contributing to the observed changes (sediment deposition or erosion).
This protocol is being developed for the Cape Cod National Seashore Prototype Monitoring Program, but will be adopted by the Network for implementation in four of the Network’s parks.
The CACO protocol is currently under review.
Salt marsh sediment elevation change is measured using sediment erosion tables (SETs).
Sediment accretion is measured using marker horizons and either cryogenic corers or the "marsh plug" method. Both these techniques are described in detail at the USGS SET web sitehere.