Introduction

Scientists, managers, and educators are interested in estuarine wetlands because they are "hotspots" of ecological processes, biological diversity, and human activity and impact within the estuary. Tidal wetlands occur at the land edges of the Hudson River from the Troy Dam to Manhattan, especially from just south of Albany to the New Jersey state line. There are about 2,895 hectares (7,151 acres) of tidal wetland in the estuary, including 443 hectares (ha) of mudflats, 601 ha of broadleaf marsh, 1,236 ha of graminoid marsh (dominated by grasslike plants), and 617 ha of tree or shrub swamp (Picard, 2002). These wetlands are freshwater tidal north of about Constitution Marsh (Cold Spring), and brackish tidal from about Constitution south to Piermont Marsh (Piermont); Piermont is the southernmost major wetland (Fig. 20.1). Except for Piermont Marsh, the cordgrass (Spartina spp.) dominated "salt" marshes are outside the nominal Hudson River in New York Bay, the Arthur Kill, Jamaica Bay, the Hackensack Meadow-lands, and other estuarine areas associated with the mouth of the Hudson.

Low salinity tidal wetlands such as those of the Hudson River have been studied less than salt marshes. Nonetheless, since about 1970, there has been considerable research on fresh-tidal and brackish-tidal wetlands in the Hudson River and elsewhere on the U.S. Atlantic Coast (see Kiviat, 1981 and Yozzo, Smith, and Lewis, 1994 for bibliographies). These studies have discovered that low salinity tidal marshes have different ecological structure and function than salt marshes (Odum, 1988), but are as important to the estuarine landscape, and in many cases are more threatened because low salinity wetlands occur mostly in the upper reaches of tidal rivers and bays where urban, industrial, and transportation uses tend to be concentrated. Many examples in this chapter refer

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