Erik Kiviat, Stuart E. G. Findlay, and W. Charles Nieder abstract There are about 2,900 ha of tidal wetlands in the Hudson River. Tidal flow between wetlands and the "main river" moves sediment, nutrients, organic matter, and organisms in and out of the wetlands. Sediment deposition rates in the tidal wetlands are about 0.05-2.9 cm yr-1. In wetlands separated from the main river by a railroad, scoured pools remain just inside the openings and large tidal creeks radiate into the gradually-filling landward part of the wetland. Although large areas of the estuary have been filled, there has been a net gain of wetland area. Sediments, vegetation, animal communities, and ecosystem functions may be different in the railroad-sheltered wetlands and the wetlands on sandy dredged material than they were in unaltered wetlands. In Hudson River tidal wetlands, the elevation gradient, from near Mean Low Water through the intertidal zone to near Mean High Water, is correlated with increases in sediment organic matter (SOM), plant litter cover and litter mass, and aboveground peak biomass, height, and species richness of vascular plants. Among different marshes, SOM is correlated with abundance and diversity of benthic macroinvertebrates and fish species richness. Tidal waters are the main source of nitrogen for the marshes, whereas phosphorus appears to come from upland tributaries or decay of organic matter in sediments. The lower intertidal zone is nearly bare ofvas-cular vegetation in the more brackish and the more sandy wetlands; in silty freshwater tidal wetlands this zone is occupied by spatterdock and pickerelweed. The middle intertidal zone is occupied by saltmarsh cordgrass in the most brackish marsh, but by a mixture of many broadleaf and grasslike plants in lower salinity wetlands. The upper intertidal zone is most often dominated by cattail or common reed. Areas near
Mean High Water may be dominated by common reed or saltmeadow cordgrass in the most brackish marsh, and in lower salinity wetlands are typically dominated by common reed, shrubs, or trees. Components of the tidal marsh fauna have low to moderate diversity and include a number of rare or habitat-dependent species. Many animals move in and out of the marshes on seasonal, daily, or tidal cycles.
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