SALT MARSHES

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Context

• Salt marshes have been playing an outsized role in stabilising the environment. But more than 90 per cent of these biologically productive ecosystems may soon succumb to sea level rise by the turn of the century, according to a new research.

Findings of the research

• If the sea level continues to increase at the rates anticipated, there will be no more room for the low marsh plants. They’re just going to be too submerged to survive.
• The only choice for salt marshes then would be to migrate landward. But even this choice can be impacted by anthropogenic activities and other factors.
• Marshes all over the globe experience ‘coastal squeeze,’ where their movement is obstructed by sea level rise, anthropogenic activities and geographical factors. For instance, a seawall that protects a home from inundation will prevent a wetland from naturally migrating to higher ground.

About Salt Marshes

• Salt marshes are salt-tolerant rooted vegetation and present in a low-energy transition zone between submerged and emerged environments, occupying the upper margins of the inter-tidal landscape.
• These plants are able to withstand high salinity and regular submersion due to regular or occasional immersion by the tides.
• They are the major blue carbon ecosystems, with a greater latitudinal extent than mangroves, and are dominated by herbaceous and halophytic shrubs rather than trees.
• Salt marshes provide a unique habitat for a large number of species that cannot survive in other habitats. Therefore, they are an essential element in our ecological structure.

Global Distribution

• The distribution of salt marsh species is linked to variations in soil, elevation, hydro-period or inundation frequency.
• Salt marshes occur worldwide, particularly distributed in temperate and arctic latitudes from 30° to 80°, and are usually restricted to comparatively sheltered locations.
• Salt marshes are estimated to cover roughly 54,951 km2 worldwide, spreading over 43 countries and territories.

Indian Distribution and Species

• In India, salt marshes are distributed in seven coastal states/UTs, Gujarat, Daman and Diu, Maharashtra, Tamil Nadu, Puducherry, Andhra Pradesh and Andaman & Nicobar Islands, covering an approximate area of 1600 km2.
• Gujarat has the highest area cover of 89.5% of total cover, followed by Tamil Nadu (3.8%), Andaman & Nicobar Islands (3.7%), Andhra Pradesh (2.5%), Maharashtra (0.4%), Puducherry (0.04%) and Daman and Diu (0.04%).
• 15 major salt marsh species have been reported so far from general biodiversity studies.

Ecosystem Services of Salt Marsh

• Provide raw material and food: Direct provisioning of raw materials and food from salt marshes are known as in different parts of the world’s marsh lands are used as pasture land.
• Providing a buffer against wave and storm surges: Marsh vegetations help to stabilize the coast by trapping sediment from the runoff. In due course, increased intertidal height and vertical leaf blades provide a form of sea defense by reducing wave energy, velocity, height and duration.
• At times, marshes support to reduce the storm surge duration and height by providing extra water uptake.
• Nursery areas for coastal biota: Salt marsh ecosystems play a major role in maintaining fisheries by providing nursery ground.
• Filters for nutrients and pollutants: Marshes are called natural  filters  as  they  effectively  purify  water entering the estuary.
• Enhances cultural values: The aesthetics of salt marsh and high diversity of migratory and passerine birds found within marshes draws attention to many tourists and bird watchers, giving a scope for recreational activities.
• Salt marsh and other associated ecosystems provide wide possibilities for research.

Salt Marsh Vulnerability

• Coastal ecosystems are some of the most heavily exploited and threatened natural systems globally, as 40% of the world’s population resides on the world’s coasts, which account for just 4% of the land surface.
• The future of these valuable coastal ecosystems is today at risk, as they are exposed to possibly irreversible transformations due to the effects of climate changes and human interferences.
• Globally, 25-50% of salt marshes are either lost or degraded due to intense human activities.
• Major threats to salt marshes include biological invasions, eutrophication, climate change and sea level rise, increasing air and sea surface temperatures, increasing CO2 concentrations, altered hydrologic regimes, marsh reclamation, vegetation disturbance, and pollution.
• Land reclamations and construction of sea walls can also constrain a marsh and limit the potential for marine transgression.
• Grazing on the marsh can be both beneficial or detrimental, depending on the grazing intensity.
• Salt marshes are also prone to trace metal pollution with possibility of its biological uptake.
• Introduction of salt marsh species for coastal defense has led to large-scale invasions of many grasses, mostly Spartina.
• Severe environmental  stress  from  temperature fluctuations,  high  soil  salinity  and  low  oxygen  availability has limited salt marsh plant diversity  to a handful of stress-tolerant, halophytic genera.

https://www.downtoearth.org.in/news/environment/more-than-90-of-the-world-s-salt-marshes-may-soon-succumb-to-sea-level-rise-study-88548