An Investigation of Salt Marsh Dieback in Georgia Using Field Transplants

In 2001 and 2002, Georgia salt marshes experienced a dieback event that affected more than 800 ha throughout the coastal zone. The dieback event was unprecedented in the state and affected both Spartina alterniflora and Juncus roemerianus. A transplant study was conducted from May to October 2003 to determine if healthy plants could survive in dieback areas. Transplants were carried out at two locations on the Georgia coast in areas of S. alterniflora dieback along the banks of tidal creeks, an area of S. alterniflora dieback in the mid marsh, and a J. roemerianus dieback area in the mid marsh. Transplant survival was nearly 100% and growth (measured as increases in the height of the 5 tallest stems and the number of stems per experimental pot) was observed in both healthy (control) and dieback areas. J. roemerianus grew more slowly than S. alterniflora, with no observed increase in stem height and an average 38% increase in stem density as compared to an average 57% increase in stem height and 137% increase in stem density in S. alterniflora. Differences in growth were inconsistent but in most cases no significant differences were observed between healthy and dieback areas. Soil characteristics measured over the course of the experiment were generally comparable between healthy and dieback areas (redox potential averaged 69 6 123 [SD] across all observations at all sites, pH averaged 6.7 6 0.3, and salinity averaged 24.9 6 4.4), but porewater ammonium (NH4) concentration was often higher in dieback areas (overall mean NH4 concentration was 138 6 127 mM in dieback areas versus 33 6 40 mM in healthy areas). These results suggest that the cause of dieback was no longer present at the time of this study and that transplants are a possibility for restoring affected areas.