#          Selected Findings and Current Perspectives on Urban and Agricultural         Water Quality by the National Water-Quality Assessment Program      

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         Studies by the USGS National Water-Quality Assessment (NAWQA) program         in the last decade describe water-quality conditions in nearly 120         agricultural and 35 urban watersheds ("urban" primarily         refers to residential and commercial development over the last 50         years). The findings show that for both urban and agricultural areas, nonpoint chemical contamination is an issue. Much work still needs to be done in urban areas with point source contamination as well, including infrastructure improvements. Appreciable improvements in overall water quality, however, will depend upon effective management of point and nonpoint sources.  The findings show that nonpoint chemical contamination is an         agricultural and urban issue. Whereas a lot of work still needs to be         pursued with point source contamination and infrastructure         improvements in urban areas (such as related to combined and sanitary         sewer overflows), appreciable improvements in water quality also will         depend upon management of nonpoint sources. The NAWQA findings also         show that water-quality conditions and aquatic health reflect a         complex combination of land and chemical use, land-management         practices, population density and watershed development, and natural         features, such as soils, geology, hydrology, and climate. Contaminant         concentrations vary from season to season and from watershed to         watershed. Even among seemingly similar land uses and sources of         contamination, different areas can have very different degrees of         vulnerability and, therefore, have different rates at which improved         treatment or management can lead to water-quality improvements.      

##          Water Quality in Agricultural Watersheds      

-          Nitrogen and phosphorus in surface water commonly exceed levels that         contribute to excessive algae. For example, average annual         concentrations of phosphorus in nearly 80 percent of streams sampled         in agricultural areas were greater than the U. S. Environmental         Protection Agency (USEPA) desired goal for preventing nuisance plant         growth in streams. Excessive plant growth can lead to low dissolved         oxygen, which can be harmful to fish and other aquatic life.      
-          Nitrate is often elevated above background levels in shallow ground         water underlying farmland. Concentrations in about 20 percent of         shallow wells sampled in agricultural areas exceeded the USEPA         drinking water standard. This result is a concern in rural areas where         shallow ground water is used for domestic supply; these domestic wells         are not regulated and owners often do not know the quality of their         well water or whether their wells are vulnerable to contamination.         Nitrate is most often elevated in karst (carbonate) areas or where         soils and aquifers consist of sand and gravel. These natural features         enable rapid infiltration and downward movement of water and         chemicals. Some of the more vulnerable areas are the Central Valley of         California, and parts of the Pacific Northwest, the Great Plains, and         the Mid-Atlantic region. In contrast, ground-water contaminants         underlying farmland in parts of the upper Midwest are barely         detectable, despite similar high rates of chemical use. In these areas         ground-water contamination may be limited because of relatively         impermeable, poorly drained soils and glacial till that cover much of         the region, and because tile drains provide quick pathways for runoff         to streams.      
-          Pesticides are widespread. At least one pesticide was detected in more         than 95 percent of stream samples. Pesticides were detected in more         than 60 percent of shallow wells sampled in agricultural areas.      
-          Pesticides commonly occur in mixtures. Two-thirds of stream samples         collected in agricultural areas contained 5 or more pesticides, and         more than one-quarter of the samples contained 10 or more. Ground         water contained fewer pesticides; about 30 percent of the wells         sampled contained 2 or more.      
-          Concentrations of pesticides generally are low and below         drinking-water standards. However, the risk to humans and the         environment from present-day low levels of contaminant exposure         remains unclear. For example, current standards and guidelines do not         yet account for exposure to mixtures, and many pesticides and their         breakdown products do not have standards or guidelines.      
-          Herbicides—most commonly atrazine and its breakdown product         desethylatrazine, and metolachlor, cyanazine, and alachlor—occur         more frequently and usually at higher concentrations in agricultural         streams and ground water than in urban waters. Their occurrence is         linked to their use; they rank in the top five in national herbicide         use for agriculture.      
-          Insecticides that were used in the past still persist in agricultural         streams and sediment. DDT was the most commonly detected         organochlorine compound, followed by dieldrin and chlordane. Their         uses were restricted in the 1970s and 1980s and, yet, more than 20         years later, one or more sediment-quality guidelines were exceeded at         more than 20 percent of agricultural sites.      

##          Water Quality in Urban Watersheds      

-          Concentrations of fecal coliform bacteria commonly exceed recommended         standards for water-contact recreation.      
-          Concentrations of total phosphorus are generally as high in urban         streams as in agricultural streams. More than 70 percent of sampled         urban streams exceeded the USEPA desired goal for preventing nuisance         plant growth.      
-          Insecticides, such as diazinon, carbaryl, chlorpyrifos, and malathion,         occur more frequently, and usually at higher concentrations in urban         streams than in agricultural streams. Concentrations are low in urban         streams, rarely exceeding USEPA drinking-water standards. However,         effects on aquatic life may be more of a concern. Concentrations of         insecticides exceeded at least one guideline established to protect         aquatic life in every sampled urban stream.      
-          Herbicides are widespread in surface water (detected in 99 percent of         urban stream samples) and ground water (detected in more than 50         percent of sampled wells). Most common are those applied to lawns,         golf courses, and road right-of-ways, such as atrazine, simazine, and         prometon.      
-          Similar to agricultural areas, pesticides in urban waters commonly         occur in mixtures; nearly 80 percent of stream samples contained 5 or         more pesticides. Two of the most commonly detected insecticides in         mixtures were diazinon and chlorpyrifos; common herbicides detected         were simazine and prometon.      
-          Sediment in urban streams is associated with higher frequencies of         occurrence of DDT, chlordane, and dieldrin and higher concentrations         of chlordane and dieldrin than sediment in agricultural streams.         Sediment-quality guidelines for organochlorine pesticides were         exceeded at 36 percent of sampled urban sites.      
-          Volatile organic compounds, which are used in plastics, cleaning         solvents, gasoline, and industrial operations, occur widely in shallow         urban ground water. Some of the most frequently detected of the 60         analyzed compounds were the commercial and industrial solvents         trichloroethene (TCE), tetrachloroethene (PCE), and methylene         chloride; the gasoline additive methyl tert-butyl ether (MTBE); and         the solvent and disinfection by-product of water treatment,         trichloromethane (also known as chloroform).      
-          Concentrations of selected trace elements, such as cadmium, lead,         zinc, and mercury, are elevated above background levels in populated         urban settings, most likely caused by emissions from industrial and         municipal activities and motor vehicles. Sediment cores from         streambeds and reservoirs, which can be used to track changes over         long time periods, indicate that lead increased from 1940s to the         1970s, and began to decrease after it was removed from gasoline.         Concentrations are not yet down to background levels. Decreases also         are noted for DDT and chlordane.      
-          In contrast to lead, DDT, and chlordane, sediment cores indicate that         zinc and polycyclic aromatic hydrocarbons (PAHs, which result from         fossil fuel combustion) are increasing. These increases most likely         relate to increasing motor vehicle traffic in watersheds.         Sediment-quality guidelines for PAHs were exceeded at more than 40         percent of urban sites.      
-          Toxic compounds in streambed sediment in urban areas, such as DDT,         chlordane, dieldrin, and PCBs, also were found in fish tissue, often         at higher concentrations than in the sediment. One or more         organochlorine compounds were detected in 97 percent of whole fish samples         collected at urban sites, and PCBs were detected in more than 80         percent of whole fish samples. Concentrations of organochlorine compounds         exceeded guidelines to protect wildlife at more than 10 percent of         urban sites; wildlife guidelines for PCBs were exceeded at nearly 70         percent of urban sites. These findins have contributed to decisions by some states to issue fish-consumption advisories.      
-          Deteriorated water quality and sediment, as well as habitat         disturbances, contribute to degraded biological communities in urban         streams. The greatest effects are seen in areas with the highest human         population densities and watershed development. Pollution-tolerant         algae and aquatic invertebrates (such as worms and midges), as well as         omnivorous fish communities, prevail at the affected sites.      

###          Contacts for additional information or questions:      

         Tim Miller (703) 648-6868 (tlmiller@usgs.gov) Pixie Hamilton (804)         261-2602 (pahamilt@usgs.gov)      

###          For Internet access to NAWQA publications, data, and maps:      

http://water.usgs.gov/nawqa

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