Impacts from ditching salt marshes in the mid-Atlantic and northeastern United States

Abstract

Tidal inundation extent and duration, and water drainage and retention by marsh peat — marsh hydrology — determine most physical and ecological characteristics of salt marsh systems. Ditching, installed across nearly all marshes on the US east coast by 1940 to control mosquitoes, alters marsh hydrology. Two linchpin papers are used here as springboards to review the literature that describes the resulting effects, which clearly include reduced water table height for most marshes and changes in avian populations. Effects on invertebrate populations, including mosquitoes, are generally less, although to a smaller degree than is sometimes reported. Impacts on nekton are not clear, although probably negative. Tidal range and the degree of tide asymmetry appear to have greater effects on intermarsh variations in effects from ditching than has generally been appreciated or studied. Overall, although changed patterns of nutrient releases and promotion of Phragmites australis invasions are important ecological effects extending beyond individual sites, and salt marsh aesthetics are marred, ditching impacts are less than certain other anthropogenic alterations of coastal processes that affect salt marshes and estuarine ecology to a much greater extent.