Mudflats • Saltmarshes • Sea level changes •
Process relationships

Sea level changes

Sea level changes can change saltmarsh accretion rates. In areas of net sea level rise, accretion rates are accelerated due to the increase in water depth and tidal inundation. Provided adequate supplies of sediment are available to the saltmarsh, accretion rates will continue to increase until they equal the rate of sea level rise when a dynamic equilibrium is established (see figure below). Examination of a saltmarsh accretion curve for a period of years can help to predict the outcome of sea level rise.

Theoretical saltmarsh growth curves under rising and steady sea level conditions in the Humber Estuary (from Toft et al., 1995)

An exponentially increasing curve indicates that water depths are deepening over the saltmarsh surface and suggests that the sediment supply is inadequate to compensate for sea level rise; under these conditions the saltmarsh may theoretically eventually 'drown'. However, evidence from Holocene sedimentary sequences has shown that saltmarshes are able to keep pace with rates of sea level rise of up to several tens of centimetres per year, if sufficient sediment is available. A decreasing rate of measured accretion (i.e. vertical elevation change) over time suggests that sedimentation is outpacing sea level rise and will eventually result in a balance being achieved between the two.