But really, do we know them and what they do: besides smell funny at low tide? Here is a collection of paragraphs from a web survey:
Typical erosion cycle: waves undermine the marsh grass peat by dissolving underlying clay layer, then grass peat sections break off and put the grass below the elevation that it can survive at, and new soil is opened up to waves gnawing at the underlaying clay.
From Wade H. Elmer (Dept of Plant Pathology and Ecology, New Haven, CT):
“…it may be surprising to many that salt marshes are one of the most valuable ecosystems and outrank tropical rainforests and coral reefs for productivity. Carbon sequestration can approach more than 3kg dry matter/m²/year, which outperforms coral reefs by 40% (Bertness, 2007). Furthermore, their value in absorbing excess nitrogen and phosphorous, detoxifying pollutants, and providing habitat for marine animals elevates the salt marsh ecosystem as the most valuable natural ecosystem on the planet for in terms of productivity.”
- alterniflora is noted for its capacity to act as an environmental engineer. It grows out into the water at the seaward edge of a salt marsh, and accumulates sediment and enables other habitat-engineering species, such as mussels, to settle. This accumulation of sediment and other substrate-building species gradually builds up the level of the land at the seaward edge, and other, higher-marsh species move onto the new land. As the marsh accretes, S. alterniflora moves still further out to form a new edge.
Healthy S. Alternaflora (Common Cordgrass) which can resist and attenuate wave energy that surges into or over it with no damage to the grasses.
(S.patens) A healthy salt marsh depends on the presence of plants such as salt hay grass and smooth cordgrass. These grasses provide rich habitat for crustaceans, mollusks, and birds, and serve as a major source of organic nutrients for the entire estuary. Mats of salt hay grass are inhabited by many small animals and are an important food source for ducks and seaside sparrows. Salt meadow cordgrass marshes serve as pollution filters and as buffers against flooding and shoreline erosion.
The grass spreads asexually by means of a subterranean rhizome system. The grass becomes dense and forms a baffle, which encourages the deposition of fine particulate sediment, including organic matter (salt marsh peat). This, in effect, causes a rise of the sediment surface and makes the habitat more terrestrial.
The ribbed mussel Geukenzia demissa often lives among Spartina spp. and its production of nitrogen-rich feces and pseudofeces enhances grass growth.
Marsh mussels can be quite densely packed. Mark Bertness and colleagues demonstrated that this mussel enhances the growth of Spartina. The mechanism may relate to biodeposition of nitrogen-rich feces and pseudofeces. The byssal threads of this mussel also help bind the sediment and may retard erosion. Another common salt marsh resident, the fiddler crab Uca pugnax, also aids in Spartina growth by burrowing and aerating the sediment.
In Virgina, County governments have Wetlands Boards that are composed of citizen volunteers and supported by a county Wetlands Coordinator in the Planning Department. Their charge is essentially to try to prevent marsh grass losses due to human construction activities. If an erosion control project comes up for permitting, they can act to deny the project or fine applicants for wetlands destruction. They can also initiate violation procedures for activities that are destructive to the environment in the intertidal zone.
Newly planted grasses on a 10:1 slope in a space that was an eroded clay scarp. We need the sand to hold the grasses in the short term, but the grass roots to hold the sand over the longer term.
However, there is no legal mandate or mechanism to grow new marsh, other than via the installation of Living Shorelines. With Living Shorelines, sand backfill [behind a sill, such as an oyster reef] is permitted to be pushed out and marsh grass is planted out on it. The backfill over marine bottom land is allowed only to the distance seaward that is “minimally necessary” to achieve a 10:1 slope (5.7°). Still, the value of a living shoreline reversing an erosion situation and adding new square footage of marsh grasses is major win environmentally.
Marsh Grasses planted into Flexamat creating a living shoreline at a 4:1 slope. Note anchoring reefs offshore.