Mississippi River Water Quality and the Clean Water Act Progress, Challenges, and Opportunities (2008) / Chapter Skim
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2 Characteristics of the Mississippi River System
2 Characteristics of the Mississippi River System
Pages 21-64
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From page 21... ...
The Mississippi River basin supports a high diversity and abundance of wildlife with their concomitant economic and social benefits. The Mississippi River valley is as an important international migration corridor for waterfowl and the site of the Upper Mississippi River National Wildlife and Fish Refuge, which is the longest river refuge in the continental United States.
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From page 22... ...
22 0.6 % 58% 18% 21% [w & w w 2.4 %] 500 km km land uses, and FIGURE 2-1 Mississippi River drainage basin, major tributaries,FIGURE 2-1 the Gulf of Mexico hypoxic area (as of 1999)
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From page 23... ...
As this chapter explains, the quality of water in the Mississippi River basin reflects both natural processes and human influences across varying scales of time and space. The chapter is divided into four sections: Mississippi River physiography and population; historic alterations of the Mississippi River system and its river basin; Mississippi River water quality; and water quality impacts on the northern Gulf of Mexico.
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From page 24... ...
The upper and lower Mississippi River basins comprise about 15 and 7 percent, respectively, of the surface land area that can affect Mississippi River water quality.
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From page 25... ...
. FIGURE 2-3 Landforms and landscape features affect runoff rates and the ability of the land to absorb water before it runs into waterways, both of which can affect water quality.
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From page 26... ...
Approximately 60 percent of the river basin consists of agricultural land (Figure 2-1) , and the central portion of the basin, extending from Iowa to Ohio and from the Ohio and Missouri Rivers northward almost to the Canadian border, supports extensive croplands.
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From page 27... ...
. Although the Missouri River watershed is roughly 2.5 times larger than the next largest of the Mississippi River's six major tributary watersheds Midwestern states listed in this category include Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.
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From page 28... ...
In comparison, the upper Mississippi River contributes 19 percent of the total of Mississippi River discharge into the Gulf of Mexico, followed by the Missouri River and the lower Mississippi River (13 percent each) , the Arkansas River, and the Red River.
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From page 29... ...
HISTORIC ALTERATIONS OF THE MISSISSIPPI RIVER SYSTEM Over the past two centuries, land use changes across the Mississippi River watershed and hydrologic changes along the length of its riverfloodplain ecosystem have had significant impacts on water quality in both the Mississippi River and the Gulf of Mexico. One important land use change across the watershed has been substantial applications of nitrogen- and phosphorus-based fertilizers in the last half century, primarily to increase production of row crops.
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From page 30... ...
Land Uses and Wetlands The conversion of vast areas of Mississippi River basin prairies and forests to cropland and other agricultural land following European settlement has had tremendous implications for Mississippi River water quality. Large areas of virgin forests across the basin had been cleared in the 1850s, and by 1920 they were reduced largely to remnant forests (Greeley,
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From page 31... ...
Wetland ecosystems, once ubiquitous in the Mississippi River basin, serve important functions in regulating runoff and in reducing runoff of pollutants. Large losses of wetland areas, many of which were drained for conversion to agricultural land along the Mississippi River, have eliminated most of the natural buffering systems that could help reduce runoff of pollutants, toxic substances, and nutrients into the Mississippi River tributaries and mainstem (Table 2-2)
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From page 32... ...
Navigation Improvements on the Upper Mississippi River On the upper Mississippi River, most changes to river hydrology and ecosystems have been driven by Congress and the efforts of the U.S. Army Corps of Engineers to improve river navigation.
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From page 33... ...
. FIGURE 2-6 Levee Construction Along the Lower Mississippi River Large and extensive levees are the primary structures that affect flow and volume along the lower Mississippi River.
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From page 34... ...
Army Corps of Engineers began an extensive flood control program of channelization and levee construction along the lower Mississippi, along with the establishment of floodways in Missouri and Louisiana. Levee construction has reduced considerably the natural floodplain of the Mississippi River basin and the natural aquatic ecosystems along its course (Table 2-3)
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From page 35... ...
As a result, the spatial and temporal distributions of water velocities, bottom substrate, and water depths differ markedly from conditions that existed prior to the twentieth century. MISSISSIPPI RIVER WATER QUALITY Many Mississippi River water quality issues of today resemble the issues of the early 1970s, when the Clean Water Act was being drafted, but their relative importance has shifted in the past 35 years.
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From page 36... ...
Today, some parts of the river -- mainly near large municipalities -- still experience fecal bacteria counts that exceed water quality standards. Fecal bacteria and new inputs of toxic substances can be controlled through existing mechanisms in the Clean Water Act.
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From page 37... ...
Excess phosphorus has caused notable water quality problems in freshwater systems, such as noxious and toxic algal blooms, decreased water clarity, and low dissolved oxygen conditions. Likewise, excess nitrogen and sometimes phosphorus have led to algal blooms in estuarine and coastal marine systems with the same results.
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From page 38... ...
. Similar changes are seen throughout the Mississippi River basin (Figure 2-7)
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From page 39... ...
that can be regulated only marginally by dams on the Mississippi River mainstem and its tributaries, because the mainstem upper Mississippi River dams do not create reservoirs, but navigation pools. Thus, nitrate loadings to the Mississippi River can be controlled effectively only through control of nitrate concentrations.
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From page 40... ...
Nitrogen can be converted from atmospheric gas to ammonia and nitrate by bacteria on the roots of leguminous plants. Nutrients in the Mississippi River basin originate from the same multiple sources, but mostly from diffuse nonpoint sources (Figure 2-9)
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From page 41... ...
are about equally divided among the combined upper and middle Mississippi, lower Mississippi, Ohio, and Missouri watersheds and are relatively high. The majority of the nitrogen and phosphorus flux -- for example, 56 percent of the nitrate -- is from above the confluence of the Ohio River with the Mississippi River, and it derives mainly from nonpoint agricultural sources (Goolsby et al., 1999; Turner and Rabalais, 2004)
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From page 42... ...
A coordinated effort to manage the nutrient content of the Mississippi River needs to account for the multiple sources of nutrients that affect water quality and the activities that generate them. Nutrient Uptake and Transformation The proximity of sources to large streams and rivers is an important determinant of nitrogen delivery to coastal waters receiving Mississippi River discharge.
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From page 43... ...
FIGURE 2-11 + – FIGURE 2-11 Wet deposition of NH4 and NO3 averaged for 1990-1996 data from the National Atmospheric Deposition Program in each of the 133 accounting units that make up the Mississippi River basin. NOTE: Blue circles indicate where NADP and CASTNet (Clean Air Status and Trends Network)
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From page 44... ...
The human-modified landscape and hydrology of the Mississippi River system over centuries, coupled with population growth, agriculture, industrialization, urbanization, increased combustion of fossil fuel, and increased use of fertilizers in the post-World War II era, all have reduced the capacity to remove contaminants naturally across the entire watershed. Today's significant water quality problems in the Mississippi River basin and its offshore coastal waters are related to these landscape developments, coupled with increased nutrient loads derived primarily from agricultural fertilizers and activities.
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From page 45... ...
Elevated nitrate levels have been a problem in some areas of the Mississippi River basin. For example, in the Ohio River watershed, water quality advisories are issued every spring in Columbus, Ohio, for excess nitrate levels in local waters (Mitsch et al., 2001)
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From page 46... ...
sediment deprivation in the Mississippi River deltaic plain, where combined natural and human-caused factors are leading to loss of coastal wetlands and barrier islands. Sediment-related problems along the Mississippi River thus range from too much to not enough sediment in different sections along the length of the Mississippi River corridor and can result in impairments to ecosystems and water quality.
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From page 47... ...
The figure shows a steadily declining trend of suspended sediments in the river. It should be noted that estimates of suspended sediment yields and loads from the Mississippi River watershed vary among investigators because of variability in water discharge; length and completeness of the period of record; effects of variations of velocities with depth; logistical issues related to working in a large river; and sampling frequency (Meade, 1995; Turner and Rabalais, 2004)
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From page 48... ...
The effects of sediments and sedimentation on water quality and habitat are important issues along the upper Mississippi River and provide examples of excess sediment as a pollutant. The Minnesota River, for example, contributes a large amount of sediment to the Mississippi just below Minneapolis-St.
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From page 49... ...
. Other Pollutants In addition to concerns about nutrients and sediments, there are many other Mississippi River water quality problems.
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From page 50... ...
Fecal bacteria also are an important water quality concern in areas of the mainstem Mississippi River. The distribution of all of these contaminants along the river depends on the nature and location of the source, their stability, their dilution by receiving waters, and their adsorption by sediments and the movement of these sediments.
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From page 51... ...
Along the Mississippi River, they are typically most highly concentrated in suspended sediments near Minneapolis and St. Louis.
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From page 52... ...
. PCBs are legacy contaminants that are stored in bed sediments in the navigation pools of the upper Mississippi River.
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From page 53... ...
Most of the 10 states along the mainstem Mississippi River list some reach as being of impaired water quality, and most of these impair ments are based on fish tissues that contain unacceptable concentrations of toxic substances. For example, Illinois, Minnesota, Missouri, Tennessee, and Wisconsin list the entire river for PCBs; Tennessee lists dioxin and chlordane; and Minnesota and Wisconsin list mercury, all on the basis of high concentrations in fish.
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From page 54... ...
As a result of these improvements, Minnesota now lists only 36 miles of the Mississippi River as having impaired water quality because of fecal coliforms in the vicinity of the Twin Cities, all upstream of the main wastewater treatment plant. Further downstream in Illinois, several areas along the Mississippi River have fecal coliform counts with annual averages lower than the standard, but Illinois lists the entire river along its border as being of impaired quality due to fecal coliforms because of high counts during storm runoff.
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From page 55... ...
Geological Survey WATSTORE database; Illinois River Watch; specific samples from the 1991-1992 USGS study)
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From page 56... ...
For many emerging contaminants, little is known about potential effects on humans and aquatic ecosystems, especially for long-term, lowlevel exposure, which is the typical scenario. WATER QUALITY IMPACTS IN THE GULF OF MEXICO The Mississippi River and its freshwater discharge, sediment delivery, and nutrient loads have strongly influenced the physical and biological processes in the adjacent Gulf of Mexico over geologic time and past centuries, and even more strongly during the last half of the twentieth century.
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From page 57... ...
Figure 2-17 FIGURE 2-17 Similar size and expanse of bottom-water hypoxia in mid-July 2002 (shaded area) and in mid-July 2001 (outlined 57 with dashed line)
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From page 58... ...
. The size and persistence of hypoxia on the Louisiana-Texas shelf, however, along with its connection to changes in Mississippi River nutrient delivery, make the Gulf of Mexico hypoxic zone a notable example.
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From page 59... ...
. Nutrients delivered from the Mississippi River basin support phytoplankton growth in the immediate vicinity of the river discharges, as well as across the broader Louisiana and upper Texas coasts.
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From page 60... ...
Specific indicators demonstrate increased accumulation of phytoplankton biomass -- stable carbon isotopes, silica, remains of diatoms, the abundance of a specific diatom that can generate harmful toxic substances, and specific phytoplankton pigments. These trends show that while there are signs of increased production and oxygen depletion earlier in the twentieth century, the most dramatic changes have occurred since the 1960s, when the nitrate concentration and load from the Mississippi River began to increase.
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From page 61... ...
The action plan calls for a long-term adaptive management strategy that couples management actions with enhanced monitoring, modeling, and research. Implementation will depend on a series of voluntary and incentive-based activities, designed within a series of subbasin strategies, including best management practices on agricultural lands, wetland restoration and creation, river hydrology remediation and riparian buffer strips, and stormwater and wastewater nutrient removal (Mitsch et al., 2001)
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From page 62... ...
For example, many portions of the upper Mississippi River contain islands and large backwater areas important to recreational activities such as boating, fishing, and trapping, and they share the river, its channel, and its numerous navigation pools with commercial navigation. By contrast, the lower Mississippi River below Cairo, Illinois, contains fewer islands and is leveed off from most of its previous floodplain areas.
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From page 63... ...
Excess nutrient input to the Mississippi River, in various forms of dissolved and particulate nitrogen and phosphorus, causes significant water quality problems both within the Mississippi River itself and in the coastal waters of the northern Gulf of Mexico. These latter problems manifest themselves as Gulf of Mexico hypoxia, one of the nation's prominent regional-scale water quality problems.
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From page 64... ...
, water quality in the lower Mississippi River is determined largely by inputs in the upper Mississippi River basin, with different portions of the upper river basin having a dominant influence for particular constituents. For example, sediment loads are determined largely by the Missouri River contributions, and nutrient contributions are primarily from the upper Mississippi River.
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