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Salt Marshes of the Tagus Estuary: Doomed by Rising Sea Levels?

Paper Reviewed
Silva, T.A., Freitas, M.C., Andrade, C., Taborda, R., Freire, P., Schmidt, S. and Antunes, C. 2013. Geomorphological response of the salt-marshes in the Tagus estuary to sea level rise. Journal of Coastal Research Special Issue No. 65: 582-587.

"Salt marshes," according to Silva et al. (2013), "are important ecosystems due to their role in supporting the aquatic food chain, exporting nutrients to surrounding waters and providing nesting areas for migratory birds." They also act as barriers protecting the shoreline by helping to dissipate wave and current energy. Yet the seven scientists note that "sea level rise can place these intertidal zones at risk, reinforcing the need to understand their morphosedimentary and dynamic response" to future projections of sea level rise in response to predicted CO2-induced global warming, which is exactly what they set out to do. More specifically, they examined historical sedimentation data retrieved from four salt marsh locations within the Tagus estuary, which they describe as one of "the largest and most important estuaries of Western Europe," after which they compared it to projections of future sea level rise.

Their results indicate, first of all, that the marshes all "lie under the upper threshold of accretion," meaning there exists room for further sediment deposition in the marshes. With respect to historic sedimentation rates at each of the four locations, they were found to vary between 4 and 22 mm per year, which rates, according to Silva et al., "largely exceed the mean rate of sea level rise (+2.1 mm per year) determined at the [nearby] Cascais tidal gauge by Antunes and Taborda (2009)." Looking to the future, comparisons of historic sedimentation rates with projected rates of sea level rise suggest, according to Silva et al., that the Tagus estuary salt marshes "will not be drowned in the forthcoming decades." Any concerns of their demise, at least from dreaded CO2-induced global warming, would therefore appear to be unsupported by historical data.

Reference
Antunes, C. and Taborda, R. 2009. Sea level at Cascais tide gauge: Data, analysis and results. Journal of Coastal Research Special Issue No.56: 213-217.

Posted 31 December 2014