stressors, such as wet and dry deposition of sulfates, nitrates, other sources of acidification, and ammonium, as well as to track changing climatic and forest stand conditions.

Sensitive Surface Waters and Estuarine Systems

Deposition of air pollutants can also perturb the chemistry and ecology of sensitive surface waters. Acid deposition is of concern for acid-sensitive lakes and streams, primarily in the Northeast and the mid-Atlantic high-lands (see discussion in Box 6-6). Further, deposition of nitrates and ammonium has been shown to be a major source of nutrients and associated eutrophication of estuarine systems along the eastern seaboard of the United States (Castro and Driscoll 2002). There is also considerable interest in the effects of atmospheric mercury deposition on coastal and other ecosystems.

A number of programs are in place to monitor aspects of this problem. The most comprehensive atmospheric deposition monitoring networks are NADP/NTN, NADP/MDN, CASTNet, and AIRMoN (for example, see Figure 6-6). However, these networks do not track dry gaseous ammonia (NH3) deposition, which could be important in estuaries that drain agricultural watersheds (for example, Delaware Inland Bay, Chesapeake Bay, and Neuse River Estuary). Another shortcoming of these programs is that they do not measure organic nitrogen deposition, which may account for 10–30% of the total nitrogen budget to East Coast estuaries (Peierls and Paerl 1997; Whitall and Paerl 2001).

In addition to the networks noted above, EPA administers the temporally integrated monitoring of ecosystems (TIME) and long-term monitoring (LTM) programs, which monitor lake and stream chemistry and document changes in response to changing emissions and acidic deposition. There also are several national coastal monitoring networks (for example, the EPA national estuarine program and NOAA’s National Estuarine Research Reserve System [NERRS]), but none directly assesses the effects of atmospheric deposition of pollutants. The NERRS has 20 coastal sites (and one Great Lakes site) and includes a systemwide monitoring program through which data for pH, salinity, dissolved oxygen, temperature, and turbidity are collected (NERRS 2001). No attempt is made to relate the oxygen status of estuaries directly to nutrient loading from either atmospheric or watershed sources except at very basic levels. Similarly, a study that documents estuarine water quality problems related to runoff was published by NOAA’s NERRS (Bricker et al. 1999), but no direct link to atmospheric deposition was made.

The National Estuaries Program (NEP) was established to allow local groups to take responsibility for tracking estuarine function, and perhaps as a result, there is no systemwide effort to document the effects of nitrogen or



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