Salt marsh aids in fight against climate change

NMU researchers study role of ‘nature’s kidneys’

Nelson Mandela University researchers are studying how the salt marsh in the Swartkops estuary is helping to combat climate change.
The marsh sequestrates carbon by trapping and stabilising leaf litter, mud and sticks in the water.
This sediment built up among the marsh plants and as long as the system was left intact it inhibited the release of carbon dioxide, a key driver of climate change, study co-ordinator and shallow water ecosystems research chair Prof Janine Adams said.
“So-called ‘blue carbon’ is contained in the salt marsh sediment as well as in the actual roots, stems, branches and leaves of the marsh plants.
“The global loss of these coastal salt marsh ecosystems reduces the capacity of natural carbon sinks.
“When we degrade or disturb them . . . carbon gets released back into the atmosphere as carbon dioxide.”
Adams and her team have been sampling and analysing salt marsh plants and sediment material to quantify their carbon sequestration ability.
News of their work coincides with World Wetlands Day on February 2, which marks the signing of the Ramsar Convention on Wetlands of International Importance in Ramsar, Iran, in 1997.
The NMU study established that about 27% of salt marsh habitat has been lost countrywide due to encroaching development and agriculture.
It revealed a vicious circle where increased degradation would reduce carbon sequestration capacity still further and raise the threat of high sea level rise which, in turn, would inundate the marshes and diminish their value.
This value was multifold and interlinked, Adams said.
“Loss of salt marsh habitat and diversity because of sealevel rise reduces the available area for wading birds, devaluing activities such as bird and wildlife viewing.”
Like all wetlands, salt marshes acted as “nature’s kidneys” by filtering out pollutants but this role was also undermined if they were degraded, she said.
This function is particularly useful in the Swartkops, where the marsh absorbs pollution from the wastewater treatment plants upstream.
Salt marshes also provided coastal protection because of the stability they brought and therefore reduced the duration of storm surges, another threat of climate change, Adams said.
Salt marshes served as habitats for birds including herons, gulls, waders, terns and cormorants, which preyed on prawns, marsh crabs, pencil bait and fish, she said.
“Peringuey’s leaf-toed gecko is the only gecko in the world that lives in salt marshes, and is known only from the Kromme estuary and a few sites near Port Elizabeth.
“As salt marshes disappear under bulldozers, so will [it].”
Salt marshes were also important for the production of fisheries species, she said.
“Due to their complex and rigid plant structure, salt marshes make it difficult for large fish to enter and thus provide protection for juvenile fish, shrimp and shellfish.”
An important next step would be to place a monetary value on these ecosystem services provided by the salt marsh, she said.
“Although this approach is often questioned, government departments and other decision-makers in South Africa are calling for this information.
“SA is economically divided and the vulnerable majority of the population has a high reliance on ecosystem services.
“Thus, the value of ecosystems to society should be communicated using monetary and non-monetary means for improved decision making.”

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