Overview of the Mainland Marsh Inundation Experiment

Robert R. Christian, East Carolina University

Biology Department, Greenville, NC 27858

During 1994, we initiated a field experiment on effects of inundation increase and wrack deposition in the salt marsh near the head of Phillips Creek. The experiment is described in the 1994 renewal proposal for the VCR/LTER and involves (1) pumping of tidal water onto the marsh, (2) placement of wrack on the marsh and (3) their combination. James H. Taylor is the graduate student most responsible for constructing the plots and pumping system and for its maintenance. Patty Tolley and he collected information on plant growth and nitrogen cycling from the plots throughout the growing season of 1994.

Near the head of Phillips Creek there is a strong distinction between the high marsh (dominated by Distichlis spicata and Spartina patens or Juncus roemerianus) with organic soils and the low marsh (Spartina alterniflora) with mineral soils. The former does not flood with the regularity of the latter, and as sea level rises the former areas will go through a transition to low marsh ecosystems. Accompanying the increased inundation frequency is increased probability of wrack deposition. We are interested in the differences between these two ecosystem states and how the postulated transition is controlled.

The experimental design involves 3 blocks, each containing 3 plots of marsh. Each plot is 3 X 4 m positioned such that approximately 3 X 2 m is in a J. roemerianus stand and 3 X 2 m is in a mixed stand of D. spicata and S. patens. Two plots within each block are surrounded by a 4-in (10 cm) high plywood border to retard but not totally stop flow of water into and out of the plot. Each plot within a block represents a separate treatment with respect to flooding: (1) a plot bordered and flooded at each high tide by the pumping of tidal creek water, (2) a bordered control and (3) an unbordered, undisturbed control. Further, to evaluate the effects of wrack deposition, one half of each plot (1.5 X 4 m) was covered with a layer of wrack at the beginning of the growing season. Pumping began in spring and was stopped in fall with occasional interuption from system's failure.

The following presentations by James Taylor and Patty Tolley provide an initial summary of results from our work during 1994. Further analysis is underway. Both students will use their data for their master's theses at East Carolina University.