Experimental manipulation of drainage in a Georgia saltmarsh: lessons learned

In two separate studies of factors olling primary productivity of Sparti contr na alterniflora, subsurface water movement was increased in stands of intermediate and short Spartina. The objective of the manipulation was to simulate conditions found in creekbank marsh, where productivity was 2-4 times higher than in the experimental areas. The small-scale pilot study had resulted in a two-fold increase in aboveground biomass in one growing season and in shifts in belowground chemical conditions toward those typical of creekbank marsh. In the large-scale experiment, belowground chemistry changed as expected, but although plant biomass increased at all sites during the first growing season, it declined steadily during the next three years. In addition to those contradictory results, substantial site-to-site variation was observed in the large-scale study. These results demonstrate the need for caution in making broad generalizations about salt marshes and their response to disturbance, and the value of long-term studies in determining the effects of disturbance.