Shrinking Number of Long-term Monitoring Sites Could Hamper Scientists’ Ability to Measure Recovery of Impaired Streams

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Consistent, national-scale and long-term water-quality monitoring of the Nation's rivers and streams has declined, in some cases, by more than half over time

The number of long-term stream-quality monitoring sites operated at the national scale by Federal agencies declined from 1985 to 2014 compared to the number that were sampled from 1975 to 1984, following passage of the 1972 Clean Water Act. Reductions in stream-quality monitoring have the effect of limiting the ability of scientists to assess long-term water-quality trends. Natural resource managers and policy makers rely on scientific assessments of trends to develop effective water-quality improvement programs.

From 1975 to 1984, the number of long-term stream-quality monitoring sites operated by Federal agencies expanded to track trends and to evaluate the effectiveness of national investments in water-pollution control. From 1985 to 2014, however, the number of long-term stream-quality monitoring sites declined due to increased monitoring costs and an emphasis placed on short-term surveys designed to address the immediate needs of water-pollution control investigations. As a result of program reductions and eliminations, the USGS National Water Quality Network is the only long-term, national-scale network that routinely monitors the quality of rivers and streams and reports on trends and changes that address high priority water-quality issues. The USGS also monitors water quality at other long-term sites in cooperation with selected states.

These are among the findings of U.S. Geological Survey (USGS) authors in a chapter, “Progress and Lessons Learned from Water-Quality Monitoring Networks” of a recently published book, Chemistry and Water: The Science Behind the World’s Most Crucial Resource. “This chapter examines the important role of long-term monitoring networks in trend detection in order to determine if water quality is getting better or worse, and why” said Donna Myers, USGS Chief of the Office of Water Quality and lead author of the chapter.

Long-term monitoring networks are characterized by repeated sampling at sets of related river and stream sites at regular intervals over multi-decadal periods of time. Monitoring of this type is critical for the detection of long-term trends and changes in water quality.  This type of monitoring has declined in many of the Nation’s most important rivers and streams such as the Colorado, Columbia, and Rio Grande Rivers and in the Mississippi River and its major tributaries, as well as in smaller streams in urban and agricultural areas. These vital waterways are sources of public, industrial, and agricultural water supplies; they provide water for recreation; and they support valued populations of fish and wildlife.

Map of current USGS National Water Quality Network sites in the United States
The USGS National Water Quality Network monitors the status and trends of the Nation’s surface-water quality at more than 100 sites across the United States.(Credit: Jeff Deacon, U.S. Geological Survey. Public domain.)

Data from these long-term sites are used to track progress toward meeting water-quality goals set by the Federal government in conjunction with states and other partners. Long-term monitoring sites have been important for demonstrating improvements in stream chemistry in places like New York State and the Northeastern United States, generally. “These monitoring networks have provided accountability for emission reductions resulting from New York State and Federal policies.  Stream chemistry has improved as a result of a 70 percent reduction in sulfur dioxide emissions since passage of the Clean Air Act amendments of 1990. The improvements in stream chemistry are a result of improvements in the chemistry of precipitation falling on streams and their watersheds,” said Gregory Lampman, Senior Project Manager, Environmental Research at the New York State Energy Research and Development Authority.

Long-term stream monitoring sites are used to track long-term trends in nitrogen and phosphorus levels entering coastal waters of the northern Gulf of Mexico from the Mississippi River, entering the Chesapeake Bay from the Susquehanna, Potomac, and Patuxent Rivers, and entering western Lake Erie from the Maumee River.  Excessive levels of nitrogen and phosphorus from river inputs to coastal and Great Lakes waters can cause algae to bloom and to produce algal toxins. Algal toxins can be harmful to human health and recreation. Algal blooms eventually die-off and decompose, creating deficits in dissolved oxygen levels required to support recreational and commercial fisheries.

The number of long-term sites sampled over time since enactment of the 1972 Clean Water Act is relatively small, making these sites rare and highly valuable for the detection of long-term trends. Only 217 USGS sites have been sampled long enough to assess 40-year trends in any of the six commonly-reported water-quality measures investigated for the chapter. The majority of 36,000 sites sampled by USGS over this time period were done so as part of short-term surveys to address other types of monitoring needs.

The numbers of USGS monitoring sites sampled through 2014 for six measures—atrazine, chloride, nitrate, sulfate, suspended sediment, and total phosphorus—declined by 26 percent to as much as 58 percent compared to the number of sites sampled during the decade after passage of the Clean Water Act. These types of monitoring sites address national-scale issues like pesticide contamination, increased salinity and acidity of freshwaters, nutrient enrichment, and excessive soil erosion.

“Water-quality monitoring is a costly activity and difficult tradeoffs are necessary so that the need for short-term monitoring to assess current conditions is balanced against the need for long-term monitoring to detect multi-decadal trends” said Myers.

Sustaining consistent and long-term monitoring networks is important because these sites have information crucial to the description of water-quality trends over long periods of time. “These data are irreplaceable because once the opportunity to collect samples has passed, it is not possible go back and collect the data required to establish a baseline against which to evaluate current and future trends” said Gary Rowe, Chief Scientist, National Water Quality Assessment Project.

Chemistry and Water: The Science Behind the World’s Most Crucial Resource is available online or in print from Elsevier.