Environmental Impact of Long Piers on Tidal Marshes in Maryland-Vegetation, Soil, and Marsh Surface Effects

Abstract

Piers may impact the health of coastal wetlands by altering vegetation, soil organic matter accretion, and sediment deposition or erosion. Permit requests for piers have recently increased in the U.S. leading to concern by environmental regulatory agencies on potential impacts. In response, a project was conducted in Maryland to assess the impacts of long piers on plant communities, soils, and marsh surface characteristics. Twenty sites with piers and 20 control sites were assessed. Control sites and pier sites were similar with respect to soil types, marsh surface characteristics, and plant community composition. Shading consistently reduced vegetation density directly beneath piers and occasionally reduced vegetation density adjacent to piers. Shading favored Spartina alterniflora over Distichlis spicata, and Distichlis spicata over Spartina patens. Distribution of marsh surface components (high marsh, low marsh, mudflats, open water) was unaffected by proximity to piers. Direct evidence of pier effects on erosion or deposition was limited to the immediate vicinity of a few piers. In general, thickness of the organic horizons or that of the root mats was unaffected by proximity to a pier. We concluded that any effects of piers on vegetation or erosion were restricted to the close proximity of the piers.