The influence of prolonged flooding on the growth of Spartina alterniflora in Cape Cod (Massachusetts, USA).
The tolerance of Spartina alterniflora L. to prolonged flooding is a subject of considerable debate. Understanding how this species responds to extended periods of continuous flooding in the field is crucial for making decisions about its management where it is exotic and in predicting losses due to sea level rise where it is native. In this study, plots of S. alterniflora within poorly-drained areas of four salt marshes in Cape Cod National Seashore (CCNS; Massachusetts, USA) were lowered to create conditions of continuous flooding over the duration of one growing season. These were compared to control plots where Spartina was removed and put back in place at the same elevation and un-manipulated plots. The density of plants in the lowered treatment was significantly reduced by 86%, whereas the manipulated and un-manipulated controls declined only marginally by 28% and 11%, respectively. Lowering also reduced the extent of height growth, although not significantly compared to manipulated controls. Porewater sulfide concentrations were initially over fourfold higher in lowered plots than the other treatments, and in the range toxic to S. alterniflora growth, whereas there was no effect on salinity. The results suggest that prolonged flooding in its natural setting over the course of several months may be enough to eliminate S. alterniflora. Thus, when areas of S. alterniflora in marshes become continuously flooded as a result of sea level rise, they may undergo substantial decline. Moreover, in controlling S. alterniflora as an exotic species hydrologic manipulation may be a useful management tool.