Monitoring and Assessing our Nation's Water Quality

By Timothy L. Miller, Pixie A. Hamilton, and Donna N. Myers

All of life depends on water, and all of us are citizens of a watershed. Our activities and the ways we use our water resources and the land adjacent to the water affect the quality of our drinking water, our recreational opportunities, and the health and diversity of aquatic plants and animals.

The quality of our water--from the nearby stream to the large river system--can be protected and enhanced by collecting timely and relevant information about water-quality conditions and by responding to that information. The USGS has monitored and assessed our Nation's streams and ground water since the late 19^th century. Today, USGS provides information on many water-quality issues, such as the suitability of water used for drinking and irrigation and the health of our aquatic ecosystems.

USGS describes the general health of water resources, as well as current and emerging water issues and priorities, all of which contribute to practical and effective water-resource management and strategies that protect and restore water quality. The findings are used by decision makers at all levels--including, for example, managers and planners in localities, States, Tribes, and Federal agencies, such as the National Park Service, Fish and Wildlife Service, Bureau of Reclamation, and U.S. Environmental Protection Agency; policy makers in Congress and non-governmental organizations; researchers in industry, academia, and consulting; and the general public.

Major water-quality programs (listed below, along with corresponding Web sites) touch many parts of the Nation, from Alaska and Hawaii to the coasts of Florida and Maine. For example, in partnership with the National Park Service since 1998, USGS has addressed water-quality issues in 64 national parks in 33 States--helping to ensure safer swimming beaches and drinking water, healthy stream habitats and aquatic life, adequate baseline monitoring, and assessment of contaminants in natural areas, such as in snow-packs and high-altitude lakes.

Through its National Stream Quality Accounting Network (NASQAN), USGS operates 32 stations to measure amounts of sediment and chemicals in five of the Nation's largest rivers (Mississippi, Columbia, Colorado, Rio Grande, and Yukon). Data from the stations aid in managing, using, and protecting these major, heavily regulated rivers that flow across interstate and international boundaries.

USGS also monitors 36 relatively small streams draining natural basins that have been minimally altered by human activities (referred to as the Hydrologic Benchmark Network). These data also are used to track subtle effects from atmospheric deposition and climate change.

At the other end of the spectrum, the USGS Toxic Substances Hydrology Program focuses on widespread contamination that poses significant risk to human health and the environment, including effects of mercury on aquatic ecosystems and the recent discovery of everyday chemicals, such as pharmaceuticals, personal care products, and hormones, in our waters. Identification of these additional chemicals in the environment also leads to improved understanding of how water systems function.

USGS hydrologists sample for mercury in a wetland.

As part of the National Water-Quality Assessment (NAWQA) Program, begun in 1991, USGS assesses water quality in 51 major river basins and aquifers across the Nation. Collectively, the studies advance our understanding of the quality of the Nation's waters and enables us to determine whether it is getting better or worse over time.

Overall, USGS water-quality monitoring, assessments, and research indicate that the Nation's waters generally are suitable for irrigation, drinking water supply, and other home and recreational use. Major challenges remain, however, in protecting water resources and aquatic ecosystems from nonpoint sources of pesticides, nutrients, metals, petroleum-based compounds, industrial and household solvents, and naturally occurring pollutants that continue to enter our aquifers and waterways in every basin.

A primary objective in USGS water-quality studies is to identify natural and human-related factors that affect water-quality conditions and transport of contaminants to ground water and over the land. For example, no longer is it appropriate to think that nonpoint-source contamination is exclusively associated with agriculture. Nonpoint sources in urban areas ("urban" primarily refers to residential and commercial development over the last 50 years), which cover less than 5 percent of land in the continental United States, have not typically been considered to be important contaminant sources compared to agricultural areas, which cover more than 50 percent of the United States. The studies, however, have documented elevated trace elements, as well as nutrients, pesticides, and volatile organic compounds commonly used around homes, gardens, and in commercial and public areas in urban streams and ground water. Improvements in water quality therefore will depend upon effective management of nonpoint sources in our urban centers along with agricultural areas, in addition to continued control of our "point" discharges of sewage and industrial wastes.

USGS studies also show that water-quality conditions are highly variable, differing from season to season and from watershed to watershed. Pollution levels and degradation of ecosystems vary because of differences in chemical use, land-management practices, watershed development, population, and natural features, such as soils, geology, hydrology, and climate. Even among seemingly similar land uses and sources of contamination, streams and ground water in different geographic areas show different vulnerability to contamination. This information allows decision makers to design more effective strategies for improving water quality in specific geographic areas.

Examples of USGS findings on water quality across the Nation include the following:

What's Used Is What's Found

• Contaminants found in urban and agricultural waters are closely associated with the chemicals that are used. For example, nitrogen and frequently-used herbicides (such as atrazine, metolachlor, alachlor, and cyanazine) generally were detected more often and at higher concentrations in streams and shallow ground water in agricultural areas, whereas phosphorus and insecticides used today (such as diazinon, carbaryl, and malathion) and those used historically (such as DDT, dieldrin, and chlordane) were detected more frequently and usually at higher concentrations in urban streams. Diazinon, commonly used by homeowners on lawns and gardens, was detected in 100 percent of samples from an urban stream draining suburbs of Sacramento, CA, always exceeding guidelines for protecting aquatic life.
• New pesticides and other synthetic chemicals are introduced into the marketplace every day and offer improvements in industry, agriculture, medical treatment, and common household conveniences, but these compounds ultimately enter our waterways. USGS laboratory techniques have led to the recent "discovery" in our waters of microbes, pharmaceuticals, and hormones. Nationally, 1 or more of 95 "organic wastewater compounds" (including antibiotics and other human and veterinary drugs, hormones, detergents, disinfectants, plasticizers, fire retardants, insecticides, and antioxidants) were detected in 80 percent of 139 streams sampled, and 82 of the 95 compounds were detected at least once. Steroids, non-prescription drugs, and insect repellents were the most commonly detected compounds.

Lay of the Land Matters--Transport of chemicals and vulnerability depends on natural features and land-use practices

• Natural features, such as geology, hydrology, and soils, can greatly control the movement of contaminants to ground water and over land. For example, in parts of the Upper Midwest, ground water underlying intensive agriculture is minimally contaminated where it is protected by relatively impermeable soils and glacial till. There are local hotspots of contamination where ancient glacial streams deposited sand and gravel, which enable rapid infiltration and downward movement of water and chemicals. In the Southeast, streams and ground water contain relatively low concentrations of nitrogen, partly because soils and hydrology favor its conversion to nitrogen gas. In contrast, nitrogen concentrations are relatively high in streams and shallow ground water in the Central Valley of California and parts of the Northwest, Great Plains, and Mid-Atlantic regions, because natural characteristics favor transport of nitrogen.
• Elevated concentrations of some toxins are naturally occurring. For example, arsenic, a mineral in certain rocks and soils, is naturally elevated in certain ground-water systems, generally highest in the West and parts of the Midwest and Northeast.
• Land-management practices can make a difference. For example, conversion from rill (or "furrow") irrigation to sprinkler or drip irrigation in many parts of the Yakima River Basin in Washington since the early 1990s has reduced runoff from farm fields, which has resulted in decreased suspended sediment, total phosphorus, and DDT in streams. USGS data collected from 1996 to 1998 showed that total DDT concentrations in large-scale suckers, smallmouth bass, and carp from the lower Yakima River had decreased by about half from the late 1980s, but still exceeded guidelines for the protection of fish-eating wildlife.

Concentrations of DDT, chlordane, dieldrin, mercury, and PCBs are analyzed for in fish tissue, such as carp, rock bass, and northern hog suckers in the Lake Erie- Lake St.-Clair Drainages.

The Big Picture--Interactions among water, air, and aquatic life

• Atmospheric deposition is the major source of mercury to many ecosystems, largely due to activities related to coal combustion and waste incineration. USGS studies show that concentrations of methylmercury (the most toxic form of mercury) strongly relate to the amount of wetlands in a watershed, and are enhanced by chemical and environmental variables, such as the presence of sulfur, carbon, organic matter, and dissolved oxygen. Nationwide, basins with the highest percentage of total mercury as methylmercury are along the East Coast, such as in the Santee River Basin in South Carolina and in basins in southern Florida.
• Fish, invertebrate, and algal communities are strongly influenced by aquatic conditions. Degraded water quality and stream habitat commonly result in increased numbers and types of pollution-tolerant and non-native species, such as worms, midges and omnivorous fish communities. Effects are most pronounced in urbanizing areas with watershed development and dense human populations, and ecosystems begin to degrade early in the urbanization process. For example, in the Anchorage, AK, area, biological degradation is evident when watersheds reach about 5 percent impervious area, which in Anchorage correlates with a population density as low as 125 to 250 people per square mile.
• Fish and other aquatic life in many basins have higher concentrations of toxic compounds than the contaminated sediment. For example, in the Lake Erie and Lake Saint-Clair watershed in Michigan and Ohio, concentrations of certain organochlorine insecticides, such as DDT and chlordane, were 10 to 100 times higher in fish than in the sediment.

Looking Down the Road at Trends

• USGS analyses of sediment cores (vertical tubes of mud) from reservoir and lake bottoms help to obtain a quick snapshot of water quality over time. Lead, PCBs, and DDT generally are decreasing over time in reservoir sediments sampled in 20 major urban centers since use of these compounds were restricted in the 1970s. But zinc and PAHs (polycyclic aromatic hydrocarbons, which result from the burning of hydrocarbons and other organic material) are increasing up to the present in urbanizing watersheds with increasing motor vehicle traffic, such as in Austin, Dallas, Chicago, Denver, Seattle, Anchorage, Los Angeles, Washington, DC, and Atlanta.
• Acidity has decreased in many streams draining coal regions--such as in the Allegheny and Monongahela River Basins in Pennsylvania and West Virginia and the Kanawha River Basin in West Virginia and Virginia--since the Surface Mining Control and Reclamation Act of 1977.

USGS water-quality data are readily available. The large USGS database on water-quality conditions is publicly available and can be readily accessed via the Internet (http://water.usgs.gov/nwis). It includes chemical data from rivers, streams, lakes, springs, and ground water from more than 335,000 sites. Selected field measurements, such as pH, temperature, and specific conductance, are available in real-time (updated at intervals of 4 hours or less) at more than 800 USGS sites.

Access online maps, data, and reports on USGS water-quality programs:
National Park Service Partnership: http://water.usgs.gov/nps_partnership/
National Water-Quality Assessment: http://water.usgs.gov/nawqa
Toxic Substances Hydrology: http://toxics.usgs.gov
Hydrologic Benchmark Network (HBN): http://water.usgs.gov/hbn
National Stream Quality Accounting Network: http://water.usgs.gov/nasqan
National Trends Network (NTN): http://bqs.usgs.gov/acidrain
Cooperative Water Program: http://water.usgs.gov/coop