Will sediment buildup save the marshes?

Salt marshes are among the most vulnerable ecosystems on Earth. Because they only occur within narrowly defined elevational ranges relative to mean sea level, they are under increasing threat from accelerating sea level rise.

While salt marshes can respond to sea level rise by slowly creeping inland when that possibility exists, research has shown that some salt marshes are gaining elevation through the vertical accumulation of sediment and organic matter, a process that appears to make them resilient. to the rising of the seas.

However, assessments of this resilience have revealed conflicting results showing variations between different locations and between contemporary instrument observations and Holocene geological data.

The root cause of these discrepancies is not fully understood, but it is important to understand in order to predict the fate of salt marshes in the face of future sea level rise.

By comparing salt marsh elevation adjustment data from 97 locations on four continents, the team of Neil Saintilan of Macquarie University in Australia has discovered a relationship between sediment accumulation and marsh subsidence, which helps explain the observed variable response to sea level rise.

Saintilan and colleagues have found that although salt marshes can gradually accrete more sediment to gain elevation and keep pace with relatively slow sea level rise, they can also reach a point where the rate of accretion becomes too high, leading to compaction of sediments and subsidence of the marsh.

A marsh. (Photo: NOAA Restoration Center, Jed Brown)

According to the authors of the new study, sediment subsidence increases nonlinearly with sediment accumulation, so that at higher rates of sea level rise, salt marshes begin to sink rather than gain elevation. In this way, elevation gain of salt marshes is limited relative to sea level rise and mechanisms that can promote resilience of salt marshes to low rates of sea level rise may result in failure in the context. accelerated rates projected for the future.

The study is titled “Constraints on the adjustment of tidal marshes to accelerating sea level rise.” And it has been published in the academic journal Science. (Source: AAAS)