| Salt marshes, the species they contain, and the ecological services that they provide are all severely threatened despite abundant scientific support for the importance of these relatively limited coastal habitats. Among the most threatening impacts is the increase in biological invasions, including the rise in common reed [(Phragmites australis) Cav. Trin. ex Steud] within the eastern U.S. For many impacted salt marshes, tidal restoration provides an efficient and sustainable method for deterring P. australis from proliferating, however, the physiological tolerance of this plant across a broad gradient of biogeochemical conditions allows for its persistence despite increased salinity. Following over sixty years of historic tidal restriction, the response of a geologically young, transport-limited salt marsh to tidal restoration was monitored over three growing seasons within the Cape Cod National Sea Shore. The effect of the current restoration management plan on existing plant community structure and pore water biogeochemistry was documented monthly throughout the growing season. Additional manipulations were conducted to determine if rapid and sustained flooding would result in significant changes in pore water chemistry to better achieve restoration goals. Additionally, photo interpretation of historic aerial photography using GIS were combined with palynological inspection of marsh substrate to best determine the species composition and relative distribution of the marsh surface prior to diking to better evaluate the degree of subsequent P. australis invasion. The data suggest that in young, developing, and transport limited salt marshes, characterized by sandy, highly permeable substrates, the return of tidal action and subsequent increase in pore water salinity may not be sufficient to generate biogeochemical conditions sufficient to selectively deter P. australis, as increased tidal flushing precludes development of highly reduced sediments. In the absence of physiologically limiting pore water chemistry, the physical environment is expected to be less significant in the determination of major plant community zones in the tidally restored low marsh. Future tidal restoration projects should distinguish between young, sand-dominated and old, silt/organic matter-dominated salt marsh sediment to more accurately predict the trajectory of pore water response, and therefore, plant community response to flood management strategies. |
