Altered hydrology effects on Louisiana salt marsh function

A marsh subject to "structural marsh management," which changes natural wet land hydrology, was found to be functionally impaired when compared to an a djacent unimpounded reference marsh. The "managed" marsh had much lower sed imentation rates and tidal amplitude. Also, net annual primary production w as lower in the managed marsh relative to the reference marsh. In light of the great importance of sedimentation, as well as primary production, to ve rtical accretion and maintenance of the salt marsh surface, our findings su pport the contention that structural marsh management (SMM) inhibits marsh surface accretion. Even so, much of the Louisiana coast has been proposed f or this form of management in an effort to protect it from loss. However, o ur results show such management activities in the salt marsh could likely i ncrease sediment aggradation deficits and wetland loss, especially in areas subject to high rates of subsidence or sea-level rise, such as Louisiana. Further research is needed to evaluate whether the results shown here are t ypical for saline SMM sites. In the absence of such research, the use of SM M in salt marshes is not presently recommended.