The Ecology of Freshwater Tidal Wetlands

Abstract

ties of less than one percent, but insufficient flow to dampen upstream tidal movement. Odum et al. (1979) conservatively estimate that there are 500,0001,000,000 ha of freshwater tidal wetlands along the Atlantic and Gulf Coasts, of which 100,000-140,000 ha are in New Jersey. Almost all of the major East Coast cities from Trenton, NJ, to Richmond, VA, are near freshwater tidal wetlands. Consequently, these wetlands are greatly affected by human activities. Our discussion of the structure, function, and value of freshwater tidal wetlands is based on studies of three Delaware River wetlands: the Hamilton Marsh near Trenton, NJ, Woodbury Creek Marsh south of Camden, NJ, and Tinicum Marsh near Philadelphia, PA. In freshwater tidal wetlands the major system components-producers, consumers, detritus, sediment, and nutrients-are coupled by biological and physical processes that transfer materials and energy (Figure 1). Materials, such as organic matter, nutrients, heavy metals, and sediment, enter freshwater tidal wetlands from sources including the atmosphere, tides, point-source effluents, non-point-source runoff, groundwater, and consumer immigration. Outputs are via the atmosphere, tides, and consumer emigration. Along the urbanized upper Delaware River estuary, tidal waters provide the most important inputs, although point-source effluent and non-point-source runoff may locally contribute significant quantities of nutrients and heavy metals (Walton and Patrick 1973). Wetland function is ultimately controlled by climate, but hydrologic parameters such as duration and frequency of inundation, and the velocity and source of the water determine the physical and chemical properties of wetland substrates (Gosselink and Turner 1978). In turn, substrate characteristics dictate specific ecosystem responses, including primary production, species diversity, decomposition, and uptake and release of nutrients.