Sediment deposition patterns in Phragmites australiscommunities: Implications for coastal areas threatened by rising sea-level

The explosive expansion of the common reed Phragmites australisover the last 50 years in thewetlands of the U.S. mid-Atlantic has been of concernto biologists, resource managers and the generalpublic. The replacement of Spartinaspp.communities by the invasive P. australishasbeen widely reported, but the ecosystem effect of thisreplacement is poorly understood, especially withregard to sediment accretion processes and elevationchange. It is hypothesized that a more detailedunderstanding of individual plant species and theirrole in marsh accretion may provide an improvedability to predict the effect of projected sea-levelrise in coastal wetlands. Two coastal salt marsh siteson the Eastern Shore of Chesapeake Bay in Maryland(USA) were studied to quantify depositionalenvironments associated with P. australis.Short-term sediment deposition (24 hr) and stormdeposition (17 d) were measured using filter paperplates, and vertical accretion and elevation change (6mo.) were measured using a marker horizon coupled witha sedimentation erosion table (SET). Greater rates ofmineral and organic sediment trapping were associatedwith the P. australiscommunity in both asubsiding creek bank marsh (34 g·m^-2· day^-1in P. australisvs. 18 g·m^-2· day^-1in Spartinaspp.) and a laterally eroding marsh(24 g·m^-2· day^-1in P. australisvs.15 g·m^-2· day^-1in Spartinaspp.).Litter accumulation in P. australisstands isresponsible for the higher depositional patternobserved. Additionally, below ground accumulation inP. australiscommunities (as much as 3 mm in 6months) appears to substantially increase substrateelevation over relatively short time periods. ThusP. australismay provide resource managers witha strategy of combating sea-level rise and currentcontrol measures fail to take this intoconsideration.