Over the past twenty years, the primary concern of water quality management in estuaries has switched from control of discharges of toxic substances and organic matter which contributes to biological oxygen demand (BOD) to control of nutrient pollution and eutrophication (NRC, 1993, 2000). In part, this is because of great success in reducing problems with BOD and toxics over this period, in the Hudson estuary and elsewhere (NRC, 1993). In addition, problems from excess nutrient inputs - and particularly nitrogen - have grown dramatically, to the point where nutrients are now considered the greatest pollution threat to coastal marine ecosystems (NRC, 2000; Howarth and Anderson et al., 2000). Some two-thirds of the estuaries in the contiguous United States are nowmod-erately to severely degraded from nutrient over-enrichment (Bricker et al., 1999). Estuaries vary in their sensitivity to nutrient pollution, and the Hudson in the past has been considered to be relatively insensitive (Bricker et al., 1999). However, our recentresearch demonstrates thatprimarypro-ductivity by phytoplankton in the saline regions of the Hudson estuary increased dramatically in the 1990s relative to the 1970s, and the Hudson is now quite eutrophic (Howarth and Swaney et al., 2000).

The Hudson River Estuary is profoundly influenced both by its watershed and by enormous inputs of materials from municipal wastewater

Table 10.1. Physical characteristics of the saline Hudson estuary in comparison to other representative estuaries in the temperate zone.

Data for all estuaries except the Hudson are from the LOICZ web site ( Only estuaries

larger than 15 km2 are included

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