National Park Service

Northeast Coastal and Barrier Network (NCBN)

Salt Marsh Monitoring

Measuring marsh sediments at Gateway NRA
Measuring marsh sediments at Gateway NRA

Salt Marsh Elevation Protocol

For more information contact: James Lynch or
Sara Stevens

Importance / Issues

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.

SET Juicebox photo slider
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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.

Monitoring Objectives

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).

Parks to Be Monitored

  • Assateague National Seashore (ASIS)
  • Cape Cod National Seashore (CACO)
  • Colonial National Historical Park (COLO)
  • Fire Island National Seashore (FIIS)
  • Gateway National Recreation Area (GATE)

Approach

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 Patuxent Wildlife Research Center SET web site.

Collecting data in Big Egg Marsh, Gateway NRA
Collecting data in Big Egg Marsh, Gateway NRA

Salt Marsh Nekton Monitoring Protocol

Resource Briefs

Monitoring Reports

Monitoring Data

For more information contact: Erika Nicosia or
Sara Stevens

Importance / Issues

Nekton (defined as free swimming fishes and crustaceans) are an abundant estuarine fauna that provide an integral link between primary producers, consumers, and top predators. They are likely to respond to either top-down or bottom-up estuarine perturbations. For example, nutrient enrichment (a bottom-up perturbation) could affect nekton by altering submersed vegetative habitats that serve as nursery grounds.

Conversely, removal of predatory fishes through over-fishing (top-down) could induce responses in the forage or prey nekton. Nekton also represent a significant portion of the diets of many fish-eating birds, economically valuable fishes, and (in estuaries) marine mammals.

Monitoring nekton over time will help evaluate both natural and human-induced changes in estuarine nekton over the long-term and will advance our understanding of the interactions between nekton and the dynamic salt marsh and estuarine environment.

Preliminary Monitoring Objectives

Determine long term trends in species composition, abundance and size structure in nekton communities in selected NCBN park salt marshes.

Parks to be Monitored

  • Assateague National Seashore (ASIS)
  • Cape Cod National Seashore(CACO)
  • Colonial National Historic Park (COLO)
  • Fire Island National Seashore (FIIS)
  • Gateway National Recreation Area (GATE)
  • George Washington Birthplace National Monument (GEWA)
  • Sagamore Hill National Historic Site (SAHI)

Approach

At each study marsh, 15 to 25 sampling locations will be established where nekton will be collected, depending on the available habitat. Sampling locations may include marsh pools, creeks, ditches and shoreline areas, depending on the topography of the site.

Depending on the amount and type of open water habitat (pools or ditches) on the marsh, two different sampling techniques (throw trap and ditch net) will be employed. If pools and ditches are both present within the marsh, both habitats will be sampled.

Pools and ditches will be sampled on ebbing tides, when the marsh surface has drained. Sampling will occur twice per year, once in early summer (June-July) and once in late summer-early fall (August – October)

Salt marsh monitoring at Sagamore Hill NHS
Salt marsh monitoring at Sagamore Hill NHS

Salt Marsh Vegetation Protocol Development Summary

Resource Briefs

Monitoring Reports

Monitoring Data

For more information contact: Erika Nicosia or
Sara Stevens

Importance / Issues

Salt marsh communities are sensitive to disturbance and perturbations from natural causes such as storms and geomorphic processes, as well as human induced impacts associated with nutrient loading, watershed development, tidal restrictions, and ditching.

There is a long history of alteration of salt marshes along the Northeast coast, including extensive ditching for mosquito control, salt hay farming, and restriction of tidal exchange by roads, causeways, bridges, and dikes. As the coastal corridor becomes more urbanized, watersheds become increasingly developed, and salt marsh acreage declines and become fragmented. Urbanization leads to nutrient-laden runoff.

By monitoring Salt Marsh vegetation, the Network will be able to provide information to park managers on how park salt marsh communities are changing over time. Detection of species composition change, including the presence of invasive species can provide early warning to park managers that changes in pollution levels, salinity levels, tidal flow and groundwater levels may be occurring within or around the park.

Preliminary Monitoring Objectives

Identify temporal patterns in salt marsh vegetation communities as determined by species composition and abundance (measured by percent cover) within NCBN parks.

Parks to be Monitored

  • Assateague National Seashore (ASIS)
  • Cape Cod National Seashore(CACO)
  • Colonial National Historic Park (COLO)
  • Fire Island National Seashore (FIIS)
  • Gateway National Recreation Area (GATE)
  • George Washington Birthplace National Monument (GEWA)
  • Sagamore Hill National Historic Site (SAGU)

Approach

Two to three study marshes of approximately 10ha in size will be randomly selected from the population of all potential study marshes so that statistical inference can be extended to all salt marshes within each park unit. Vegetation will be sampled within 35, 1m2 plots aligned along a minimum of 7 transects. Once selected, each study marsh site will remain permanent and will be re-sampled in future years; however transects and plots will be randomly re-located within each study marsh each year.

The percent cover of salt marsh vegetation and other covers (e.g., water, bare ground, wrack and litter) within the 1m2 plots will be visually estimated using the Braun-Blanquet scale. Additional data will also be collected using the point intercept method in short canopied (<1m height) vegetation at a subset of selected plots. Other metrics, such as height of species of interest (e.g., Phragmites australis) can also be measured when they occur within the vegetation plots. Salt marsh vegetation is sampled once per year, near the end of growing season.

Last Updated: December 30, 2016 Contact Webmaster