EFFECTS OF DREDGED MATERIAL DISPOSAL ON TIDAL MARSH PROCESSES

Coastal marsh systems are a critical natural resource that provide significant economic and social benefits. Continued existence of marsh habitat depends on the marsh's ability to maintain its elevation relative to sea level. Marsh loss occurs when surficial deposition and vertical accretion rates are insufficient to keep pace with local rates of sea level rise. Anthropogenic practices, such as coastal development, inlet stabilization, and post-storm bulldozing, disrupt the natural processes of marsh accretion by limiting sediment inputs.

The purpose of this study is to investigate if the addition of dredged material to the surface of sediment-starved marshes can offset submergence without negatively impacting marsh function. The study is being conducted in tidal marshes located in the Masonboro Island component of the North Carolina Estuarine Research Reserve. The experiment consists of four vegetated sites (2 deteriorated and 2 non-deteriorated) each of which has been covered by a wedge of dredged-fill sands ranging in thickness from 0 to 10 cm.

Sediment traps deployed in the plots indicate that accumulation rates in non-deteriorated sites (16.1 g m^-2) are less then those measured in deteriorated sites 62.9 g m^-2). Vascular plant biomass in non-deteriorated sites (312 stems m^-2) exceeds biomass in the deteriorated sites (140 stems m^-2). Marsh soils in the non-deteriorated plots are less reduced than soils in the deteriorated plots.

Thus far, sediment placement has had little effect on sedimentation rates, plant biomass, and soil redox potentials. Presently, the outcome of this project is unclear. However once complete, this study will provide data critical to the development of marsh management and dredged material disposal practices.