# Monitoring the Water Quality of the Nation's Large Rivers

## Mississippi River Basin NASQAN Program

##  The U.S. Geological      Survey (USGS) has monitored water quality in the Mississippi      River Basin as part of the National Stream Quality Accounting      Network (NASQAN) since 1995, applying a basinwide perspective      to understanding water quality on a regional scale (Hooper and      others, 1997). The objectives of the Mississippi River Basin      NASQAN Program are to provide an ongoing characterization of      the concentrations and mass fluxes of sediment and chemicals      at key locations in the basin, to determine regional source areas      for these materials, and to assess the effect of human influences      on observed concentrations and fluxes. NASQAN complements the      ongoing USGS National Water-Quality Assessment (NAWQA) Program,      which is performing a detailed assessment in 23 subbasins within      the Mississippi River Basin (Hirsch and others, 1988). NASQAN      monitors the large rivers in the Mississippi River Basin, downstream      of NAWQA study units. NASQAN, in conjunction with NAWQA, can      provide the data and information needed by other USGS programs,      Federal and State agencies, other segments of the scientific      community, and by the public to address the present and future      status of water quality in the Mississippi River Basin.

 

### EnvironmentalSetting

The Mississippi RiverBasin, which drains about 41 percent of the conterminous UnitedStates, is the largest river basin in North America (fig.1). Itis the third largest river basin in the world, smaller than onlythe Amazon River Basin in South America and the Congo River Basinin Africa. More than 72 million people reside in the MississippiRiver Basin. In addition, the Mississippi River Basin containsone of the most productive farming regions in the world whichproduces the majority of the corn, soybeans, wheat, cattle, andhogs, as well as a significant amount of the cotton and rice grownin the United States. Furthermore, the majority of all pesticidesand fertilizers used in the United States are applied to croplandin the Mississippi River Basin. As a result of rainfall runoffand ground-water discharge, streams in the Mississippi River Basincarry suspended sediment, naturally occurring chemicals weatheredfrom the soil, and contaminants from human activities. These streams,and much of the dissolved and suspended material in them, eventuallyflow into the Mississippi River and ultimately are dischargedto the Gulf of Mexico. The water quality of the Mississippi Riverand its tributaries is an important regional and national issue.The land use and cultural changes that have occurred in the MississippiRiver Basin in the 1900's have had measurable effects on the qualityof water in the Mississippi River Basin. Because changes in landuse and water quality likely will continue to occur in the MississippiRiver Basin as agriculture production increases in response tothe growing worldwide demand for food and fiber, it is importantthat a long-term program of monitoring, data analysis, interpretation,and reporting be implemented for the Mississippi River Basin.

**Sampling in the Mississippi River Basin**
 

Bridge sampling on Platte River near Louisville, Nebraska.      (R.H. Coupe, photo)    
 

Cableway sampling on Missouri River near Pierre, South Dakota.      (R.H. Coupe, photo)    
 

Boat sampling on Missouri River near Omaha, Nebraska. (R.H.      Coupe, photo)    
MeasuringMass Flux
The choice of measuringmass flux (the amount of material that passes a set point) as theprimary objective in the NASQAN program requires a relatively highsampling frequency. Additionally, the emphasis on flux characterizationdictates that more samples must be collected during periods ofhigher streamflow. 

  The flux-based approachallows for the treatment of a river network as an integrated system.This approach provides data to describe and compare yields of non-pointsource contaminants across large regional basins, calculate loadsto receiving waters, including off-continent flux, and test regionalmodels of the influence of land use on water quality. 

 

Figure 1. The Mississippi River Basin and the location of      NAWQA study units.    
 

Figure 2.  Subbasins defined by NASQAN stations    
StationSelection
Eighteen NASQAN samplingstations (fig. 2, table 1) were selected at critical junctureswithin the Mississippi River Basin to provide the essential frameworkfor understanding fluxes of materials within the basin and tothe Gulf of Mexico. An important consideration for station selectionwas the influence of varying land use, the presence of major reservoirs,and input from major tributaries. Generally, stations were selectedwhere significant changes in mass flux were expected, such asat confluences of major tributaries or at the downstream end ofmajor reservoirs.

Table 1: Description of NASQAN sampling stations in the MississippiRiver Basin[Mean discharge: From 1980 to 1996, mi2, square miles; ft3/s,cubic feet per second]
Map      no.	
Sampling station	
Drainage      area      (mi2) 	
Mean discharge       (ft3/s) 		
Incremental increase in drainage area       (mi2)
 Incremental       increase in streamflow      (ft3/s) 
*Mississippi River Basin above Missouri River*1Mississippi R. at Clinton, IA85,60056,30085,60056,3002Mississippi River at Grafton, IL		 171,300	 130,200	85,700 73,900
 *Missouri River Basin*3Yellowstone River near Sydney, MT	 69,100 11,090 69,100 11,0904Missouri River near Culbertson, MT 91,600 9,500 91,600 9,5005Missouri River below Garrison Dam, ND 181,400 19,600 20,700 -9906Missouri River at Pierre, SD 243,500 23,700 62,100 4,1007Missouri River at Omaha, NE 322,800	35,80079,30012,1008Platte River at Louisville, NE 85,800 8,800 85,800 8,8009Missouri River at Hermann, MO 524,200 98,100 115,600 53,500
*Mississippi River Basin below the Missouri      River and the        Mississippi  River at Grafton* 10Mississippi River at Thebes, IL 713,200 243,400 17,700 15,100
*Ohio River Basin*11Ohio River at Greenup, KY 62,000 88,600 62,000 88,60012Ohio River at Cannelton Dam, KY 97,000 127,800 35,000 39,20013Wabash River at New Harmony, IN 29,200 31,300* 29,200 31,30014Tennessee River at Paducah, KY 40,300 60,400 40,300 60,40015Ohio River at Grand Chain, IL203,000	  295,900 37,100 76,400
*Lower Mississippi River*16Arkansas River at David Terry Dam, below Little      Rock, AR 158,300 51,100 158,300 51,10017Atchafalaya River at Melville, LA 93,300# 233,000& 93,300 varies18Mississippi River near       St. Francisville, LA 1,125,300 543,400 50,800 varies*Discharge from the Wabash at Mt. Carmel, IN      # Excludes contribution from Mississippi River Basin      &Includes Mississippi River Diversion.
SamplingStrategy
The chemical constituents measured in the NASQAN Program (table 2) include 47water-soluble pesticides, suspended and dissolved trace elements,major ions, nutrients, carbon, and suspended sediment. Samplesare collected from 6 to 15 times per year. The number of samplescollected at each station reflects the overall importance of thatstation to the flux or the predicated variability in water quality.For example, those stations downstream of major reservoirs arenot sampled as often as others because the long residence timesin the reservoirs result in the water being thoroughly mixed,thus dampening any seasonal effects.

Table 2: Constituents measured in the NASQAN programMeasurement Class  ExamplesSuspended sedimentConcentration of fine and coarse sediment particlesPesticidesCommon water-soluble pesticides, including atrazine and metalochlorSuspended and dissolved trace elementsLead, cadmium, copper, and zincCarbonDissolved and suspended organic carbon; dissolved inorganic      carbonNutrientsTotal and dissolved nitrogen and phosphorusMajor IonsCalcium, sulfate, and chlorideSupport VariablesStream discharge, temperature, pH, dissolved oxygen, conductivity
WaterQuality Issues
The climate, landuse, soils, physiography, and population vary widely across theMississippi River Basin. The annual runoff ranges from less than2 inches per year in the western part of the basin to more than50 inches per year in the southeastern part. Most of the fertilizerand pesticides used in the United States are applied to croplandin a 10-state area known as the corn belt (all or part of Illinois,Indiana, Iowa, Kansas, Minnesota, Missouri, Nebraska, Ohio, SouthDakota, and Wisconsin).This area is used primarily for croplandand produces most of the corn, soybeans, wheat, and sorghum grownin the United States. In some drainage basins, particularly inIowa, Illinois, and Indiana, more than 50 percent of all landis used for growing crops. Large numbers of livestock and poultryalso are produced in the central part of the basin (Battaglinand Goolsby, 1995). Furthermore, most of the basin's populationof 72 million people reside in the eastern half of the basin.Contaminants, including sediment, nitrogen, phosphorus, pesticides,trace elements, industrial organic compounds, and sewage, originatefrom these many different uses of land and can have substantialeffects on water quality in the Mississippi River Basin and theGulf of Mexico (Goolsby and others, 1997; Meade, 1995).

**Floods in the Mississippi River Basin**
 

Mississippi  River at St. Louis on July 30, 1993. Lighter      brown colors indicate areas of higher suspended sediment. (Strenco      Photography, used with permission)    
 

Wabash River flooding in the spring of 1997. (G.K. McCombs,      photo)    
 

Overflow of the Missouri River in 1997 on  Route 19 near Hermann,      Missouri. (R.R. Holmes, photo)    
Examplesof questions to be addressed by NASQAN
Specific questionsthat can be answered by NASQAN data in the Mississippi River Basininclude the following:
-  What is the  annual transport of nitrogen and phosphorus from the Mississippi  River Basin to the Gulf of Mexico? Which are the predominant  subbasins that produce these nutrients and what is the relation  between the yields of these nutrients and human influences such  as type and intensity of agriculture and urbanization?   What currently-used  herbicides and insecticides are present in runoff from the major  subbasins within the Mississippi River system? What are the concentrations  of these chemicals and how are the concentrations and fluxes  distributed in time and among subbasins?  How do long-term  increases in population, large-scale changes in land use and  agricultural practices, and changes in the use of agricultural  chemicals affect the concentrations and flux of nitrate and pesticides  within the Mississippi River Basin and to the Gulf of Mexico?  
-  What are  the dominant forms (organic or inorganic) and dominant chemical  species in which carbon, nitrogen, and phosphorus are transported  in the Mississippi River Basin? What is the predominant phase  (dissolved or particulate) in which each of these elements is  transported at key locations within the basin and into the Gulf  of Mexico? Are significant in-stream transformations occurring  among the forms of carbon and nitrogen as these elements are  transported through the Mississippi River Basin to the Gulf of  Mexico?   How do long-term  climatic cycles such as long dry periods (droughts) or long wet  periods affect the annual flux of nutrients (carbon, nitrogen,  phosphorus, silica) and other solutes?  What is the  yield of dissolved and suspended trace elements from major subbasins  within the Mississippi River Basin? How do ratios of the fluxes  of dissolved to suspended trace elements vary among subbasins,  and do the flux ratios or trace element concentrations indicate  enrichment attributable to human activities? Which major subbasins  most indicate trace-element enrichment, which trace elements  are enriched, and what are potential sources or causes of the  enrichment?  
-  What are  the annual fluxes of dissolved material and suspended sediment  from major subbasins within the Mississippi River Basin and what  are the annual fluxes of these materials to the Gulf of Mexico?  What fraction of the total mass of material transported from  the major subbasins is in the dissolved phase? How much is in  the suspended phase?    The Missouri River nearCulbertson, Montana. (R.H. Coupe, photo)  PreliminaryResults  Fluxes of total nitrogenand total phosphorus for 1995 and 1996 from the Mississippi RiverBasin into the Gulf of Mexico show a distinct seasonality (fig.3), corresponding with spring rains in the basin and the annualapplication of fertilizers to agricultural lands. The fluxes oftotal nitrogen and total phosphorus are similar in distribution,although the total nitrogen peaks are sharper, and are controlledby flow. Disproportionately large quantities of total nitrogenand total phosphorus discharging into the Gulf of Mexico originatein the Upper Mississippi and the Ohio River Basins. The two subbasinscontribute approximately 75 percent of the annual total nitrogenflux and 61 percent of the annual total phosphorus flux to theGulf of Mexico (fig. 4). Yet these two basins together only represent32 percent of the drainage area in the Mississippi River Basinand 52 percent of the annual flow of the Mississippi River intothe Gulf of Mexico. Further subdivision would be possible usingdata from all 18 NASQAN stations and would further identify sourceareas for these constituents.    **Figure 3.**Total nitrogen (A), total phosphorus(B), and flow (C), discharged to the Gulf of Mexico from the Mississippiand Atchafalaya Rivers in 1995 and 1996.    **Figure 4.** Percent flux of total nitrogenand total phosphorus into the Gulf of Mexico from the Mississippiand Atchafalaya Rivers by subbasin, 1995­96  NationalNASQAN Program  The Mississippi RiverBasin NASQAN Program is part of a national program that was redesignedin 1995 to focus on monitoring water quality in four of the Nation'slargest rivers-the Mississippi (including the Missouri and Ohio),the Colorado, the Columbia, and the Rio Grande. In these fourbasins, the USGS currently operates a network of 40 NASQAN stations,and applies a consistent flux-based approach to characterize thetransport of selected chemicals through the river systems.  Productsof the NASQAN Program  Data from the NASQANProgram are published annually in USGS data reports issued byeach State in the network. Additionally, NASQAN data are beingreleased electronically on the World Wide Web (http://water.usgs.gov/nasqan),and flux estimates for selected constituents at NASQAN stationswill be published periodically.  SelectedReferences  Battaglin,W.A., and Goolsby, D.A., 1995, Spatial data in geographic informationsystem format on agricultural chemical use, land use, and croppingpractices in the United States: U.S. Geological Survey Open-FileReport 94-4176, 87 p.  Goolsby,D.A., Battaglin, W.A., and Hooper, R.P., 1997, Sources and transportof nitrogen in the Mississippi River Basin: online at: http://wwwrcolka.cr.usgs.gov/midconherb/st.louis.hypoxia.html.  Hirsch,R.M., Alley, W.M., and Wilber, W.G., 1988, Concepts for a nationalwater-quality assessment program: U.S. Geological Survey Circular1021, 42 p.  Hooper,R.P., Goolsby, D.A., Rickert, D.A., and McKenzie, S.W., 1997,NASQAN-A program to monitor the water quality of the Nation'slarge Rivers: U.S.Geological Survey Factsheet FS-055-97, 6 p.  Meade, R.H.,1995, Contaminants in the Mississippi River: U.S. Geological SurveyCircular 1133, 140 p.  For AdditionalInformation, contact:  Chief, Office of Water Quality,U.S. Geological Survey National Center,12201 Sunrise Valley Drive, MS 412Reston, VA 20192  *by Richard H. Coupe Jr., and Donald A. Goolsby.Layout by Mark V. Bonito*    URL for this page is http://water.usgs.gov/nasqan/missfact/msfact.html  Last modified June 7, 1999. Page maintainedby rphooper