Environmental Monitoring & Assessment Program

John L. Stoddard 1 and Richard A. Haeuber 2

1 U.S. Environmental Protection Agency, National Health and Environmental Effects Laboratory, Western Ecology Division
2 U.S. Environmental Protection Agency, Office of Air and Radiation, Clean Air Markets Division

Title IV of the 1990 Clean Air Act Amendments (CAAA) of 1990 set target reductions for sulfur and nitrogen emissions from industrial sources as a means of reducing the acidity in deposition. One of the intended effects of the reductions was to decrease the acidity of low alkalinity waters and thereby improve their biological condition.

To track the response of surface waters to the CAAA, the U.S. EPA coordinates the Long-Term Monitoring (LTM) network (which has been collecting temporally-intensive chemical data since 1983), and the Temporally Integrated Monitoring of Ecosystems (TIME) network (which has been conducting annual probability surveys since 1991). The goal of these projects is to track whether the CAAA have been effective in reducing the acidity of surface waters in New England, the Adirondack Mountains, the Northern Appalachian Plateau, the Ridge and Blue Ridge provinces, and the Upper Midwest.

Periodic reports, and a major Congressional Report in 2003 (Stoddard et al. 2003) , have indicated widespread declines in surface water sulfate in all regions except the Ridge/Blue Ridge, and some regional declines in nitrate concentrations. Acid neutralizing capacity (ANC), a key indicator of recovery, has increased in three of the regions (Adirondacks, Northern Appalachian Plateau and Upper Midwest), but has not changed significantly in New England or in the Ridge/Blue Ridge. Because of the probability design of the TIME project, we can also quantify how the number and proportion of acidic lakes and streams has changed since the CAAA of 1990. New Rules (the Clean Air Interstate Rule, and the Clean Air Mercury Rule) have increased the need for TIME/LTM to monitor and report on the status and trends of surface waters in sensitive regions.

Long-term networks, like TIME/LTM, are the sentinels of environmental change, sometimes in surprising and unintended ways. Despite their seemingly routine emphasis on accountability, TIME/LTM data have recently been used to document unexpected trends in Dissolved Organic Carbon (DOC). Increasing DOC values, commonly attributed to climate change, are now being observed across major portions of North America and Europe (Monteith et al. In Press) , and appear to be related to recovery from acidification, rather than changing climate. Without data like those collected in TIME/LTM, we would be unable to document unanticipated trends (like those in DOC), let alone identify a mechanism for them.

Stoddard, J. L., J. S. Kahl, F. A. Deviney, D. R. DeWalle, C. T. Driscoll, A. T. Herlihy, J. H. Kellogg, P. S. Murdoch, J. R. Webb, and K. E. Webster. 2003. Response of surface water chemistry to the Clean Air Act Amendments of 1990. EPA/620/R-03/001, U.S. Environmental Protection Agency, Washington, DC.