U.S. river quality: not all signs are good.

U.S. river quality: Not all signs are good

The first major long-term study ofwater quality in the nation's rivers shows some diverging trends. Though it reports that between 1974 and 1981 there were widespread decreases in contamination from fecal bacteria and inorganic lead, it also reports widespread increases in nitrate levels, river salinity and concentrations of the toxic metals arsenic and cadmium. What will make these increases especially difficult to manage, the water researchers say, is that they are largely linked to diffuse sources of pollution --ones not addressed by the Environmental Protection Agency's massive program for upgrading water quality through better sewage treatment.

The new study, reported in the March27 SCIENCE, quantifies trends for 24 different measures of water quality. It is based on data collected over seven and a half years by two nationwide sampling networks, which together surveyed more than 300 major U.S. river sites.

"Perhaps the foremost surprise,' sayshydrologist Richard A. Smith of the U.S. Geological Survey in Reston, Va., one of the study's authors, is the nitrate trend. Over the sampling period, there was about a 50 percent increase in nitrate concentrations at 116 sampling sites, he points out. The main factors contributing to this increase were fertilizer runoff and acid rain.

Nitrates contribute to the oxygen depletion--and eventual oxygen starvation --of coastal estuaries, Smith says; at levels higher than those measured in this study, they can be a human health hazard as well. And there is growing concern that nitrates might develop into carcinogens. For example, Smith says, "It's possible that nitrates in drinking water could get converted into [carcinogenic] nitrosamines by the body.' Studies are under way to explore this at the University of Nebraska in Omaha.

Another surprising finding was that thegrowing levels of cadmium and arsenic found polluting many rivers come not from direct discharge into the waters by industry, but rather from atmospheric deposition of air pollutants--especially coal-combustion emissions. As for the increased salinity found in more than a third of the sampling sites, the researchers were able to correlate much of it to the use of road suit.

Finally, while their analysis confirmsthe benefits of sewage treatment plants in lowering fecal bacteria levels in river water, it raises questions about the plants' overall significance in limiting biologically serious oxygen depletion. Limiting oxygen depletion by removing oxygen-demanding wastes has been a primary justification for investing in better plants --at a national cost of more than $100 billion over the past 15 years. But, says Smith, though previous studies had suggested that as much as 13 percent of U.S. streams (as measured in miles) might be benefiting from better sewage treatment, this more comprehensive analysis now suggests the benefit is closer to 1 or 2 percent.