Salt marsh

Birds may raise their young among the high grasses, because the marsh provides both sanctuary from predators and abundant food sources which include fish trapped in pools, insects, shellfish, and worms.

[12] The most extensive saltmarshes worldwide are found outside the tropics, notably including the low-lying, ice-free coasts, bays and estuaries of the North Atlantic which are well represented in their global polygon dataset.

[13] The arrival of propagules of pioneer species such as seeds or rhizome portions are combined with the development of suitable conditions for their germination and establishment in the process of colonisation.

As a result, competitive species that prefer higher elevations relative to sea level can inhabit the area and often a succession of plant communities develops.

[13] Current velocities can be reduced as the stems of tall marsh species induce hydraulic drag, with the effect of minimising re-suspension of sediment and encouraging deposition.

As of 2002, over half of the world's population was estimated to being living within 60 km of the coastal shoreline,[2] making coastlines highly vulnerable to human impacts from daily activities that put pressure on these surrounding natural environments.

A study published in 2022 estimates that 22% of saltmarsh loss from 1999–2019 was due to direct human drivers, defined as observable activities occurring at the location of the detected change, such as conversion to aquaculture, agriculture, coastal development, or other physical structures.

[12] Additionally, 30% of saltmarsh gain over this same time period were also due to direct drivers, such as restoration activities or coastal modifications to promote tidal exchange.

[1][29] Land reclamation for agriculture has resulted in many changes such as shifts in vegetation structure, sedimentation, salinity, water flow, biodiversity loss and high nutrient inputs.

There have been many attempts made to eradicate these problems for example, in New Zealand, the cordgrass Spartina anglica was introduced from England into the Manawatū River mouth in 1913 to try and reclaim the estuary land for farming.

In the Blyth estuary in Suffolk in eastern England, the mid-estuary reclamations (Angel and Bulcamp marshes) that were abandoned in the 1940s have been replaced by tidal flats with compacted soils from agricultural use overlain with a thin veneer of mud.

Little vegetation colonisation has occurred in the last 60–75 years and has been attributed to a combination of surface elevations too low for pioneer species to develop, and poor drainage from the compacted agricultural soils acting as an aquiclude.

[34] The remaining marshes surrounding these urban areas are also under immense pressure from the human population as human-induced nitrogen enrichment enters these habitats.

[47] The bare areas left by the intense grazing of cordgrass by Sesarma reticulatum at Cape Cod are suitable for occupation by another burrowing crab, Uca pugnax, which are not known to consume live macrophytes.

In New Zealand, the tunnelling mud crab Helice crassa has been given the stately name of an 'ecosystem engineer' for its ability to construct new habitats and alter the access of nutrients to other species.

[49] The variable salinity, climate, nutrient levels and anaerobic conditions of salt marshes provide strong selective pressures on the microorganisms inhabiting them.

The results from an experiment that was done in a salt marsh in the Yangtze estuary in China,[55] suggested that both the species richness and total abundance of sulfate-reducing bacterial communities increased when a new plant, S. alterniflora, with a higher C-input to the ecosystem was introduced.

[55] Although chemolithotrophs produce their own carbon, they still depend on the C-input from salt marshes because of the indirect impact it has on the amount of viable electron donors, such as reduced sulfur compounds.

Therefore if the ecosystem contains more decomposing organic matter, as with plants with high photosynthetic and littering rates, there will be more electron donors available to the bacteria, and thus more sulfate reduction is possible.

[69][70] In anoxic environments, like salt marshes, many microbes have to use sulfate as an electron acceptor during cellular respiration instead of oxygen, producing lots of hydrogen sulfide as a byproduct.

[74] Examining 16S ribosomal DNA found in Yangtze River Estuary, the most common bacteria in the rhizosphere were Proteobacteria such as Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, and Epsilonproteobacteria.

In Jiangsu, China, Actinobacteria from the suborders Pseudonocardineae, Corynebacterineae, Propionibacterineae, Streptomycineae, Micromonosporineae, Streptosporangineae and Micrococcineae were cultured and isolated from rhizosphere soil.

Studies on the decomposition of a salt marsh cordgrass, Spartina alterniflora, have shown that fungal colonization begins the degradation process, which is then finished by the bacterial community.

These types of restoration projects are often unsuccessful as vegetation tends to struggle to revert to its original structure and the natural tidal cycles are shifted due to land changes.

[37] As a result, the marsh shifted to a freshwater state and became dominated by the invasive species P. australis, Typha angustifolia and T. latifolia that have little ecological connection to the area.

Information on all components of the salt marsh ecosystem should be understood and monitored from sedimentation, nutrient, and tidal influences, to behaviour patterns and tolerances of both flora and fauna species.

Dredging, pipelines for offshore petroleum resources, highway construction, accidental toxic spills or just plain carelessness are examples that will for some time now and into the future be the major influences of salt marsh degradation.

[82] In addition to restoring and managing salt marsh systems based on scientific principles, the opportunity should be taken to educate public audiences of their importance biologically and their purpose as serving as a natural buffer for flood protection.

The project involved removing of invasive species and replanting with native ones, along with public talks to other locals, frequent bird walks and clean-up events.

These circular traps consist of pre-weighed filters that are anchored to the marsh surface, then dried in a laboratory and re-weighed to determine the total deposited sediment.