USGS science fora changing world

Monitoring the Water Quality of the Nation's Large Rivers NASQAN Program

The U.S. Geological Survey (USGS) has monitored the water quality in the Rio Grande Basin as part of the redesigned National Stream Quality Accounting Network (NASQAN) since 1995 (Hooper and others, 1997). The NASQAN program was designed to characterize the concentra­ tions and transport of sediment and selected chemical constituents found in the Nation's large rivers including the Mississippi, , and Columbia in addition to the Rio Grande. In these four basins, the USGS currently (1998) operates a network of 40 NASQAN sites, with an emphasis on quantifying the mass flux for each constituent (the amount of material moving past the site, expressed in tons per day). By applying a consistent flux-based approach in the Rio Grande Basin, the NASQAN pro­ gram is generating the information needed to identify regional sources for a variety of constit­ uents, including agricultural chemicals and trace elements, in the basin. The effect of the large reservoirs on the Rio Grande can be observed as constituent fluxes are routed downstream. The analysis of constituent fluxes on a basin-wide scale will provide the means to assess the influence of human activity on water-quality conditions in the Rio Grande.

Environmental Setting Irrigation withdrawals from the Rio Grande site at El Paso is 125 river miles (in the lower Rio Grande Valley, which downstream of Elephant Butte The Rio Grande originates in the San comprises Cameron, Hildalgo, Starr, and Reservoir in New and 1 .7 miles Juan Mountains of southern Colorado and Willacy Counties) accounted for about 44 upstream of the American at El follows a 1,885-mile course before it percent of the surface-water irrigation Paso. Streamflow in the Rio Grande at flows into the (fig. 1). withdrawals in during 1994 (Texas El Paso is controlled largely by releases Along the way, the river and its tributaries Water Development Board, 1996). from Elephant Butte Reservoir. At drain a land area of 182,200 square miles. , much of the flow in the This drainage encompasses a widely Site Selection Rio Grande is diverted for irrigation and varied landscape in the and municipal uses to the American Canal Mexico, including mountains, forests, and Eight NASQAN sampling sites in Texas and the Acequia Madre Canal deserts. The basin is home to diverse (fig. 1, table 1) were selected in the Rio in Mexico. Downstream of El Paso/ native plants and wildlife as well as some Grande Basin to monitor the fluxes from Ciudad Juarez, the Rio Grande has little 10 million people 8 million in Mexico subbasins. Sites were located specifically or no flow until the waters of the Rio alone. For approximately two-thirds of its to measure inflow and outflow of material Conchos, which originates in the Sierra course, the river also serves as the from the two main-stem reservoirs Madre Occidental in Mexico, join the boundary between the United States (Amistad International and Falcon river near Presidio/Ojinaga. and Mexico. International) that strongly affect the flux Rio Grande at Foster Ranch In this mostly arid to semiarid region, of chemical constituents and sediment in near Langtry (2) is approximately the absence of flow in the river as well as the the Rio Grande. Land use in the subbasins 600 miles downstream of El Paso and presence of flow determines the basin's is dominated by rangeland, with forest, 300 miles downstream of the character. Many of the river tributaries are agricultural, and urban areas constituting confluence of the Rio Grande and Rio intermittent streams. Much of the flow is the remainder (Texas Natural Resource Conchos. Because much of the water controlled by numerous reservoirs in the Conservation Commission, 1994, fig. reaching El Paso is diverted, basin. Throughout the basin, an extensive 1.2). In descriptions of each site below, Streamflow at Foster Ranch is largely system of water structures captures and the numbers in parentheses correspond to from the . This site, in controls the flow of water in the subbasins site numbers in figure 1 and table 1. conjunction with the site, to meet regional needs for , Rio Grande at El Paso (1) reflects provides data to describe the flux of power generation, and storage for domestic, drainage of the entire Rio Grande main constituents and sediment into agricultural, and industrial purposes. stem in Colorado and . The Amistad International Reservoir.

U.S. Geological Survey USGS Fact Sheet FS-083-98 U.S. Department of the Interior Table 1. Description of NASQAN sampling sites in the Rio Grande Basin [ . not applicable] Incremental ^itp Drainage Incremental Mean increase/ one increase in streamflow decrease in no. Name area (fig- 1) (square drainage area (cubic feet streamflow \ w / miles) (square miles) per second) (cubic feet per second) 1 Rio Grande at El Paso, Tex. 29,267 0 640 640

f 2 Rio Grande at Foster Ranch nearrf., »_ -.Langtry, 0 J ^ Tex. . -,r- ._ __ .. 80,742 51,475 1,946 -T«-'- -Ct_1,306 ' 3 Pecos River near Langtry, Tex. 35,179 0 262 262 4 Rio Grande below near Del Rio, Tex. 123,143 42,401 2,510 302 5 Rio Grande below Laredo, Tex. 132,578 9,435 3,433 923 6 Rio Grande below , Tex. 159,270 26.692 3,223 -210 " 7 Arroyo Colorado at Harlingen, Tex. 182 -- 247 ~"M^K 8 Rio Grande near Brownsville, Tex. 176,333 1 7,063 2,226 -997

Pecos River near Langtry (3) is on and biological processes to alter the quality data on the outflow from the reservoir, the Pecos River approximately 15 miles of the inflowing water. These processes which can be compared to data on the upstream of its confluence with the Rio include deposition of sediment, evaporative inflow to assess the effect of retention Grande. The Pecos River is the major concentration of solutes, and biological and transformation of material within tributary to the Rio Grande within the removal of nutrients. This site provides the reservoir. United States. The Pecos River originates in the mountains of northern ior New Mexico, flows southward through EXPLANATION eastern New Mexico, and empties into Red Bluff Reservoir at the Texas-New SUBBASIN-ddentified by the location Mexico border. The flow of the Pecos of the most downstream point of the River at Langtry has been regulated by subbasin. except for closed basins) this reservoir since 1937. The Pecos | | Rio Grande at El Paso River joins the Rio Grande at the %f~] Rio Grande at Foster Ranch upstream end of Amistad International | | Pecos River near Langtry Reservoir. 35 Rio Grande below Amistad Dam I"*1 ' | Rio Grande below Amistad Dam near Del Rio (4). Water in Amistad | ,./ ] Rio Grande below Laredo 34° International Reservoir has a mean I | Rio Grande Below Falcon Dam residence time of about 1.6 years, which ELEPHANT RUT" [*'' | Rio Grande near Brownsville allows for numerous chemical, physical, RESERVOIR | | Closed basin NASQAN sampling site (number refers to table 1)

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Laredo \ United States 99° '~ FALCON INTERNATIONAL RESERVOIR LACUNA MWRI .6 r~Nv Mission Willacy N« /'" ^ ville Cameron Hidalgo

Figure 1. Rio Grande Basin showing subbasins and NASQAN sampling sites. Rio Grande below Laredo (5). lead, and zinc, many common water- attributed to natural saline springs, About 37 percent of the water that soluble pesticides such as atrazine and irrigation return flows, and evaporation discharges from the Rio Grande Basin metalochlor, and suspended sediment. during the summer months. enters the river between the Amistad Frequency of sampling ranges from 6 to Metals also could be present in International Reservoir and Laredo. This 10 times per year depending on local site the Rio Grande because of extensive reach also has large centers of population characteristics. In the upper Rio Grande mining in New Mexico and in the Rio and industry that could affect water Basin, flow generally peaks in the early Conchos Basin in Mexico. The rapid quality. This site provides data to account summer. In the middle and lower regions development of maquiladoras for the inflow of chemical constituents of the basin, flow is controlled primarily (assembly plants in Mexico) also could and sediment from this major subbasin to by releases from Amistad International contribute to trace element the Rio Grande and to describe the and Falcon International Reservoirs. concentrations in the lower Rio Grande quality of inflow to Falcon International Because these reservoir releases are Basin (Texas Natural Resource Reservoir. dictated largely by irrigation needs, Conservation Commission, 1994). Rio Grande below Falcon Dam sti eamflow in the middle and lower basin Historical data for riverbed sediments (6) is 2.5 miles downstream of Falcon tends to be more e e.ily distributed than in the Rio Grande indicate increasing Dam. The Rio Salado in Mexico, which that in the upper basin and peak flows temporal trends in more trace elements joins the Rio Grande at the upstream end typically occur in the late summer and in the reaches of the river near El Paso of Falcon International Reservoir, is the early fall. The sampling strategy is to and Laredo than in other reaches, major tributary to this reach. This site assess water-quality conditions throughout which could be related to human provides data on the retention and the range of flows, with an emphasis on activities within the subbasins transformation of materials transported high flows. The strategy will be adjusted upstream of El Paso and Laredo (Lee into Falcon International Reservoir. as the program progresses in an iterative and Wilson, 1997). Arroyo Colorado at Harlingen (7) process as more is learned about patterns Numerous pesticides could be and Rio Grande near Brownsville (8) of concentrations and fluxes throughout present in the waters of the lower Rio reflect the total outflow of the Rio Grande the basin. Grande Basin. The presence of to the Laguna Madre and the Gulf of pesticides would be a likely Mexico. These sites reflect runoff from the Water-Quality Issues consequence of the large variety of crops grown year-round in the basin principal agricultural area in the Rio Until recently, few studies had Grande Basin. At Anzalduas Dam near and the fact that irrigation water examined the water quality of the entire commonly returns to the streams. Mission, Tex., much of the flow in the Rio Rio Grande Basin in detail. In general, the Grande is diverted into the Anzalduas water is of good quality in the upper parts Questions NASQAN Data Canal for irrigation. On the U.S. side of the of the basin, but the quality decreases as Might Answer basin downstream of Anzalduas Dam, the water moves downstream.The decrease Specific questions regarding the almost all the water withdrawn from the in downstream quality of water generally Arroyo Colorado or the Rio Grande for Rio Grande Basin that NASQAN is associated with large quantities of data might answer include: irrigation and municipal purposes is agricultural return flow, a lack of effective returned to the Arroyo Colorado. The What are the sources for the high wastewater treatment, and extensive year- salinity in the Rio Grande Basin? Are Arroyo Colorado drains into the Laguna round agriculture in the lower basin. Madre, which effectively becomes an Salinity has long been recognized as the salinity-control programs estuary for the Rio Grande during a major water-quality problem throughout developed by the Texas Natural and summer irrigation seasons. the Rio Grande Basin. In some places, the Resource Conservation Commission Sampling Strategy water is not suitable for drinking or for (TNRCC) and Pecos River irrigation. A common measure of salinity Commission (Texas Natural Constituents measured as a part of is the concentration of dissolved solids, Resource Conservation Commission, the NASQAN program include major which is large (generally greater than 1994) helping to decrease the nutrients and carbon, suspended and 1,000 milligrams per liter) below El Paso. dissolved solids concentrations in the dissolved trace elements such as copper, These large concentrations can be Pecos River?

Irrigation in the Lower Rio Grande Valley Elephant Butte Reservoir on the Rio Grande, New Mexico (TNRCC photo) What pesticides are present in the waters The USGS has included the Rio Hooper, R.P., Goolsby, D.A., Rickert, D.A., Grande Basin as one of the study areas for and McKenzie, S.W., 1997, NASQAN of the Rio Grande Basin? What are the A program to monitor the water quality of major source areas for the pesticides? the Biomonitoring of Environmental Status the Nation's large rivers: U.S. Geological Do observed concentrations exceed or and Trends (BEST) program (Tim Bartish, Survey Fact Sheet FS-055-97, 6 p. approach health advisories or U.S. Geological Survey, written commun., 1997). Fish tissues and fluid were collected International Boundary and Water maximum contaminant levels Commission, United States and Mexico, during fall 1997 at all eight Rio Grande established by the U.S. Environmental 1994, Flow of the Rio Grande and related NASQAN sites for biomarker assessment. data: Water Bulletin 64, 131 p. Protection Agency? Biomarkers are physiological changes in an What associations can be observed ____1994, Binational study regarding the organism that indicate exposure to a presence of toxic substances in the Rio between mining and industrial chemical. The information from the BEST Grande/Rio Bravo and its tributaries activities in the Rio Grande Basin and program will indicate how fish are affected along the boundary portion between the concentrations of trace elements within by water quality in various reaches of the United States and Mexico Final report, September 1994: 246 p. the river system? basin (Tim Bartish, U.S. Geological Survey, written commun., 1997). Kelly, V.J., in press, Columbia River Basin Relation to other USGS In 1995, the USGS, in cooperation NASQAN Program Monitoring the with various State and local agencies, water quality of the Nation's large rivers: Water-Quality Programs U.S. Geological Survey Fact Sheet collected bottom-sediment cores from FS-004-98. Elephant Butte, Amistad International, and The NASQAN program and the Falcon International Reservoirs as part of a Lee, R.W, and Wilson, J.T., 1997, Trace USGS NAWQA (National Water-Quality study to assess historical changes in elements and organic compounds Assessment) program, which involves associated with riverbed sediments in the surface-water quality in the Rio Grande intensive water-quality studies in smaller Rio Grande/Rio Bravo Basin, Mexico and Basin (Van Metre and others, 1997). areas called study units, are Texas: U.S. Geological Survey Fact Sheet Concentrations of trace elements and some FS-098-97, 6 p. complementary (Hooper and others, persistent pesticides and organic 1997). Comparable data are collected in Levings, G.W., Healy, D.F., Richey, S.F., and compounds in bottom sediments, in many both programs. A central feature of the Carter, L.F., 1998, Water quality in the cases, can provide a partial historical record NAWQA program is an examination of Rio Grande Valley, Colorado, New of water quality. Mexico, and Texas, 1995-95: U.S. the effect of land use on water quality. Geological Survey Circular 1162, 39 p. The USGS recently has completed a Products of the NASQAN high-intensity sampling phase for the Texas Natural Resource Conservation Program Commission, 1994, Regional assessment NAWQA in the upper Rio Grande Basin of water quality in the Rio Grande Basin: (upstream of El Paso) (Levings and Data from the Rio Grande NASQAN Austin, Tex., Watershed Management others, 1998). The Upper Rio Grande are published annually in the USGS water Division, Texas Natural Resource NAWQA, with its study of cause-and- Conservation Commission Publication resources data for Texas reports (for AS-34, 377 p. effect relations between land use and example, Gandara and others, 1997). water quality within a part of the larger Additionally, NASQAN data from the Rio Texas Water Development Board, 1996, Surveys of irrigation in Texas 1958,1964, regional NASQAN setting, exemplifies Grande Basin (and the Mississippi, the complementary nature of the 1969, 1974, 1979, 1984, 1989, and 1994: Colorado, and Columbia Basins) are being Austin, Tex., 59 p. NASQAN and NAWQA programs. released electronically on the World Wide Findings from NAWQA studies might be Web at http://water.usgs.gov/public/ Van Metre, PC., Mahler, B.J., and Calender, used to develop regional models that Edward, 1997, Water-quality trends in the nasqan. Rio Grande/Rio Bravo Basin using address the influence of land use on After the initial 3 to 5 years of data sediment cores from reservoirs: U.S. water quality in NASQAN basins. collection have been completed and Geological Survey Fact Sheet Work is being done by the USGS in baseline concentrations have been FS-221-96, 8 p. cooperation with the TNRCC Clean established for the measured constituents in Any use of trade, product, or firm names Rivers Program to study the occurrence the basin, the Rio Grande NASQAN and distribution of dissolved is for descriptive purposes only and does program might be altered to more closely not imply endorsement by the U.S. hydrophobic organic compounds such as examine specific water-quality issues. organochlorine pesticide s and Government. polychlorinated biphenyls (PCBs) within Selected References For additional copies of this the Rio Grande Basin (J.B. Moring, U.S. Geological Survey, written commun., Anderholm, S.K., Radell, M.J., and Richey, S.F., report or more information 1995, Water-quality assessment of the Rio 1998). A new method, the semi- Grande Valley study unit, Colorado, New about the Rio Grande permeable membrane device (SPMD), is Mexico, and Texas Analysis of selected NASQAN program, please being used to assess the occurrence of nutrient, suspended-sediment and pesticide contact selected organic compounds in streams. data: U.S. Geological Survey Water-Resources SPMDs simulate the exposure to and Investigations Report 94-4061, 203 p. passive uptake of highly lipid-soluble Ellis, S.R., 1991, National Water-Quality NASQAN Rio Grande Basin organic compounds by biological Assessment Program The Rio Grande Coordinator membranes and concentrate such Valley: U.S. Geological Survey Open-File 8011 Cameron Rd. compounds above ambient Report 91-160, 2 p. Austin, TX 78754-3898 concentrations in water. The small Gandara, S.C., Gibbons, W.J., Andrews, F.L., (512)873-3071 concentrations of the compounds in Jones, R.E., and Barbie, D.L., 1997, Water streams might not be detected by resources data, Texas, water year 1996: U.S. Geological Survey Water-Data Report TX- traditional sampling methods. ByD.L. Lurry, D.C. Reutter. and 96-3, 347 p. F.C. Wells