Greenhouse mesocosms of freshwater marsh vegetation were exposed to a simulated saltwater intrusion event followed by a recovery period during which water levels and interstitial water salinity were adjusted over a range of conditions. Virtually all above-ground vegetation, including the three dominant species, Sagittaria lancifolia L., Leersia oryzoides (L.) Swartz, and Panicum hemitomon Schultes, was killed by the initial saltwater intrusion event. P. hemitomon did not recover, but S. lancifolia and L. oryzoides, as well as many of the other species initially present, exhibited some ability to recover depending on post-saltwater intrusion conditions. Increasingly harsh recovery conditions (for freshwater marsh vegetation), including more reduced soil conditions, higher interstitial salinities, and higher interstitial sulfide concentrations were associated with decreased live above-ground biomass and species richness. The effect of elevated salinity on vegetative recovery became more pronounced under flooded conditions. This experiment illustrates that the response of a freshwater marsh community to the long-term disturbance effect of a transient saltwater intrusion event will be strongly influenced by post-intrusion salinity and water levels.

The effects of waterlogging and salinity (25 or 325 mol m 3 NaCl) stressors on the anatomy and metabolism of the marsh grasses 5. alterniflora Loisel. and S. patens Aiton (Muhl.) were investigated in a V factorial greenhouse experiment over 30 d. Waterlogging and salinity in combination resulted in anatomical and metabolic responses in both species. Waterlogging reduced soil redox potential and decreased root‐specific gravity significantly in both species. The inadequacy of aerenchyma development under hypoxia to support aerobic root respiration in S. patens was indicated by significant increases in root alcohol dehydrogenase (ADH) activity of 1,752% and 420%, respectively, in the low and high salinity treatments. ADH activity was not increased significantly by flooding of S. alterniflora. Proline concentrations in roots and leaves were low at low salinities and increased significantly at high salinities in both species, but only under drained conditions. Decrease in leaf elongation by high salinity occurred in drained, but not flooded treatments in both species. Under flooded conditions, leaf elongation was significantly greater in S. alterniflora than S. patens. Greatest leaf elongation occurred in flooded low salinity S. alterniflora plants that had the least proline. Although both species are adapted to waterlogging and salinity, S. alterniflora appears to be more tolerant of reducing soil conditions and less responsive to higher salinity than S. patens.

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