Nitrate in the Mississippi River Basin

Last updated September 23, 2023

The increase in pollution of the Mississippi River has greatly affected the species that live in the water, as well as those who rely on the river for food and recreational purposes. One of the main types of pollution is an excess of nitrate (NO−3) caused by chemical wastes from power plants and agricultural runoffs. The watershed covers about 40% of the lower 48 states, with 7 of the 10 top agricultural producing states being within this watershed.^[1]

Nitrogen cycle

Nitrogen undergoes the nitrogen cycle, where it is converted into different forms (i.e nitrogen ( $N_{2}$ ), nitrate( $NO_{3}^{-}$ ), and ammonia ( $NH_{3}$ )) through various processes, such as fixation, ammonification, nitrification, and denitrification.

Nitrogen’s impact on the environment is not solely determined on its form within the nitrogen cycle, but the overall concentration of each form. Negative effects on the environment can be observed when these different forms of nitrogen are in excess. The Environmental Protection Agency has set a maximum of 10 mg/L nitrate concentration in drinking and surface waters.^[3] When nitrogen in the form of nitrate is in excess, it can lead to a dead zone. A dead zone is a body of water that has a depleted oxygen concentration that is low and can lead to the suffocation of animals.^[4] An example of this is the dead zone located off the coast of the Mississippi River. According to NOAA, the 2016 predicted size of this dead zone is going to be approximately 5,898 square miles with a nitrate concentration of 146,000 metric tons of nitrate flowing down the Mississippi and Atchafalaya River into the Gulf of Mexico.^[5] Nitrate concentrations have increased significantly (by factors of 2 to greater than 5) since the early 1900s.^[6] This is due to the agricultural runoff from the farming states that are released into the Mississippi River. More than half (52%) of the nitrogen concentration comes from soybeans and corn.^[7]

Concentration of nitrate

Proper investigation of nitrite concentration changes and effects requires accurate quantification of nitrite levels The Weighted Regressions on Time, Discharge, and Season (WRTDS) method is used to estimate the concentration. The following equation provides the estimate:

$\ln(c)=\beta _{0}+\beta _{1}t+\beta _{2}ln(Q)+\beta _{3}sin(2\pi t)+\beta _{4}cos(2\pi t)+\varepsilon$ (1)

where $c$ is the nitrate concentration, $\beta _{0}$ , $\beta _{1}$ . $\beta _{2}$ , $\beta _{3}$ , and $\beta _{4}$ are fitted coefficients, $t$ is time, $Q$ is mean daily streamflow, and $\varepsilon$ is the unexpected variability from other sources.^[8] This calibration curve is generated every day and compared to the one for the previous day. An issue found with this is that the discharge changes day by day. This variation of discharge can increase the concentration one day, and the next day, there could be a decrease in it. This can make it problematic to observe the trends in the concentrations.^[8]

Trends

Land use practices in the Mississippi River Basin have significantly decreased the amount of available nitrogen in the soil.^[9] This nitrogen is usually in the form of nitrate.^[9] The nitrate seeps through the soil and gets into the ground water through agricultural practices such as tile drainage, which eventually makes its way into the surface waters.^[10] Nitrate concentration can be dangerous passed a certain level. The water in the Des Moines River is near the maximum legal level of nitrate concentrations for drinking water, and the EPA has declared much of the fish in the river unsafe to eat.^[9]

Nitrate concentration estimations were made from 1980 to 2010 at a site of the Mississippi River above the Old River Outflow Channel, which is also known as the Old River Control Structure. Its purpose is to flow the water from the Mississippi River into the Atchafalaya Basin in order to prevent the Mississippi River from changing course. This study shows that from 1980 to 2010, the nitrate concentrations remained constant; however, there was a 12% increase in the concentration from 2000 to 2010. The sources of this nitrogen are unknown and the reasons as to why nitrate is increasing in some areas of the Mississippi River Basin while decreasing in others is still a mystery.^[11] However, nitrate concentrations were higher during the fall and winter months as opposed to the spring and summer months. This general increasing trend is what leads scientists to believe the dead zone in the Gulf of Mexico at the mouth of the Mississippi River is growing.^[8]

Drainage from crop fields has caused nitrate to leach into groundwater, which has adversely affected some drinking water sources in the Mississippi River Basin.^[9] In surface waters, high nitrate levels have led to instances of eutrophication, which have caused dissolved oxygen levels to significantly decrease in affected water bodies including the coastal waters of the Gulf of Mexico.^[9] Furthermore, altered nitrate to silicate ratios have caused coastal marine ecosystems to move away from a diatom based system to a less productive system.^[12]

Remediation

A possible way to lower the concentrations of nitrate is to rebuild landscapes. Grass and catch crop buffers and forest buffers are successful at preventing a buildup of excess nitrate. Any increase in vegetation leads to a decrease in the nitrate concentration, due to its uptake into the plant. The wetlands are the natural barrier to this, but they are being rapidly destroyed. The best way to prevent the dead zone is to remediate and rebuild the wetlands off the coast of Louisiana.^[13] In order for at least 40% of nitrate concentrations to be removed, 22,000 square kilometers of wetlands have to be rebuilt. This proves to be difficult because that would require 65 times the amount of wetland restorations that has happened over the past 10 years.^[14]

Changing agricultural practices could help solve the nitrate problem as well. Strip-till farming and the use of Winter Cover crops have the effect of minimizing nitrate leaching.^[15]

Related Research Articles

In a chemical reaction, chemical equilibrium is the state in which both the reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system. This state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but they are equal. Thus, there are no net changes in the concentrations of the reactants and products. Such a state is known as dynamic equilibrium.

<span class="mw-page-title-main">Nitrate</span> Polyatomic ion (NO₃, charge –1) found in explosives and fertilisers

Nitrate is a polyatomic ion with the chemical formula NO⁻
₃. Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insoluble nitrate is bismuth oxynitrate.

A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Many sources of fertilizer exist, both natural and industrially produced. For most modern agricultural practices, fertilization focuses on three main macro nutrients: nitrogen (N), phosphorus (P), and potassium (K) with occasional addition of supplements like rock flour for micronutrients. Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid application processes, using large agricultural equipment or hand-tool methods.

Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplankton productivity". Water bodies with very low nutrient levels are termed oligotrophic and those with moderate nutrient levels are termed mesotrophic. Advanced eutrophication may also be referred to as dystrophic and hypertrophic conditions. Eutrophication can affect freshwater or salt water systems. In freshwater ecosystems it is almost always caused by excess phosphorus. In coastal waters on the other hand, the main contributing nutrient is more likely to be nitrogen, or nitrogen and phosphorus together. This depends on the location and other factors.

The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen, making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems.

A fen is a type of peat-accumulating wetland fed by mineral-rich ground or surface water. It is one of the main types of wetlands along with marshes, swamps, and bogs. Bogs and fens, both peat-forming ecosystems, are also known as mires. The unique water chemistry of fens is a result of the ground or surface water input. Typically, this input results in higher mineral concentrations and a more basic pH than found in bogs. As peat accumulates in a fen, groundwater input can be reduced or cut off, making the fen ombrotrophic rather than minerotrophic. In this way, fens can become more acidic and transition to bogs over time.

In probability theory and statistics, the beta distribution is a family of continuous probability distributions defined on the interval [0, 1] or in terms of two positive parameters, denoted by alpha (α) and beta (β), that appear as exponents of the variable and its complement to 1, respectively, and control the shape of the distribution.

Nitrification is the biological oxidation of ammonia to nitrate via the intermediary nitrite. Nitrification is an important step in the nitrogen cycle in soil. The process of complete nitrification may occur through separate organisms or entirely within one organism, as in comammox bacteria. The transformation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an aerobic process performed by small groups of autotrophic bacteria and archaea.

Denitrification is a microbially facilitated process where nitrate (NO₃⁻) is reduced and ultimately produces molecular nitrogen (N₂) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitrification as a type of respiration that reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter. The preferred nitrogen electron acceptors in order of most to least thermodynamically favorable include nitrate (NO₃⁻), nitrite (NO₂⁻), nitric oxide (NO), nitrous oxide (N₂O) finally resulting in the production of dinitrogen (N₂) completing the nitrogen cycle. Denitrifying microbes require a very low oxygen concentration of less than 10%, as well as organic C for energy. Since denitrification can remove NO₃⁻, reducing its leaching to groundwater, it can be strategically used to treat sewage or animal residues of high nitrogen content. Denitrification can leak N₂O, which is an ozone-depleting substance and a greenhouse gas that can have a considerable influence on global warming.

Dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes. Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 mg of O₂/liter. When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels. Once DO declines below 0.5 ml O₂/liter in a body of water, mass mortality occurs. With such a low concentration of DO, these bodies of water fail to support the aquatic life living there. Historically, many of these sites were naturally occurring. However, in the 1970s, oceanographers began noting increased instances and expanses of dead zones. These occur near inhabited coastlines, where aquatic life is most concentrated.

The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency towards further change. For a given set of reaction conditions, the equilibrium constant is independent of the initial analytical concentrations of the reactant and product species in the mixture. Thus, given the initial composition of a system, known equilibrium constant values can be used to determine the composition of the system at equilibrium. However, reaction parameters like temperature, solvent, and ionic strength may all influence the value of the equilibrium constant.

Denitrifying bacteria are a diverse group of bacteria that encompass many different phyla. This group of bacteria, together with denitrifying fungi and archaea, is capable of performing denitrification as part of the nitrogen cycle. Denitrification is performed by a variety of denitrifying bacteria that are widely distributed in soils and sediments and that use oxidized nitrogen compounds in absence of oxygen as a terminal electron acceptor. They metabolise nitrogenous compounds using various enzymes, turning nitrogen oxides back to nitrogen gas or nitrous oxide.

The Gibbs adsorption isotherm for multicomponent systems is an equation used to relate the changes in concentration of a component in contact with a surface with changes in the surface tension, which results in a corresponding change in surface energy. For a binary system, the Gibbs adsorption equation in terms of surface excess is:

Human impact on the nitrogen cycle is diverse. Agricultural and industrial nitrogen (N) inputs to the environment currently exceed inputs from natural N fixation. As a consequence of anthropogenic inputs, the global nitrogen cycle (Fig. 1) has been significantly altered over the past century. Global atmospheric nitrous oxide (N₂O) mole fractions have increased from a pre-industrial value of ~270 nmol/mol to ~319 nmol/mol in 2005. Human activities account for over one-third of N₂O emissions, most of which are due to the agricultural sector. This article is intended to give a brief review of the history of anthropogenic N inputs, and reported impacts of nitrogen inputs on selected terrestrial and aquatic ecosystems.

In agriculture, leaching is the loss of water-soluble plant nutrients from the soil, due to rain and irrigation. Soil structure, crop planting, type and application rates of fertilizers, and other factors are taken into account to avoid excessive nutrient loss. Leaching may also refer to the practice of applying a small amount of excess irrigation where the water has a high salt content to avoid salts from building up in the soil. Where this is practiced, drainage must also usually be employed, to carry away the excess water.

Agricultural pollution refers to biotic and abiotic byproducts of farming practices that result in contamination or degradation of the environment and surrounding ecosystems, and/or cause injury to humans and their economic interests. The pollution may come from a variety of sources, ranging from point source water pollution to more diffuse, landscape-level causes, also known as non-point source pollution and air pollution. Once in the environment these pollutants can have both direct effects in surrounding ecosystems, i.e. killing local wildlife or contaminating drinking water, and downstream effects such as dead zones caused by agricultural runoff is concentrated in large water bodies.

Conservation programs for the Mississippi River watershed have been designed to protect and preserve it by implementing practices that decrease the harmful effects of development on habitats and to overlook monitoring that helps future planning and management. A main focus is nutrient pollution from agricultural runoff of the nation's soybean, corn and food animal production, and problems relating to sediment and toxins. Conservation programs work with local farmers and producers to decrease excess nutrients because they cause major water quality problems along with hypoxia and loss of habitat. Organizations such as the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force and USDA programs such as the Upper Mississippi River Forestry Partnership and the Mississippi River Basin Healthy Watersheds Initiative contribute to conserving what is left of the Mississippi River watershed.

Equilibrium chemistry is concerned with systems in chemical equilibrium. The unifying principle is that the free energy of a system at equilibrium is the minimum possible, so that the slope of the free energy with respect to the reaction coordinate is zero. This principle, applied to mixtures at equilibrium provides a definition of an equilibrium constant. Applications include acid–base, host–guest, metal–complex, solubility, partition, chromatography and redox equilibria.

Urine patches in cattle pastures generate large concentrations of the greenhouse gas nitrous oxide through nitrification and denitrification processes in urine-contaminated soils. Over the past few decades, the cattle population has increased more rapidly than the human population. Between the years 2000 and 2050, the cattle population is expected to increase from 1.5 billion to 2.6 billion. When large populations of cattle are packed into pastures, excessive amounts of urine soak into soils. This increases the rate at which nitrification and denitrification occur and produce nitrous oxide. Currently, nitrous oxide is one of the single most important ozone-depleting emissions and is expected to remain the largest throughout the 21st century.

Ammonia pollution is pollution by the chemical ammonia (NH₃) – a compound of nitrogen and hydrogen which is a byproduct of agriculture and industry. Common forms include air pollution by the ammonia gas emitted by rotting agricultural slurry and fertilizer factories while natural sources include the burning coal mines of Jharia, the caustic Lake Natron and the guano of seabird colonies. Gaseous ammonia reacts with other pollutants in the air to form fine particles of ammonium salts, which affect human breathing. Ammonia gas can also affect the chemistry of the soil on which it settles and will, for example, degrade the conditions required by the sphagnum moss and heathers of peatland.

References

↑ "Mississippi River Facts - Mississippi National River & Recreation Area (U.S. National Park Service)". www.nps.gov. Retrieved October 8, 2016.
↑ Ibanez, Jorge G.; Hernandez-Esparza, Margarita; Doria-Serrano, Carmen; Fregoso-Infante, Arturo; Singh, Mono Mohan (2007). Environmental Chemistry Fundamentals. New York City, New York: Springer Science+Business Media, LLC. pp. 152–154. ISBN 978-0-387-26061-7.
↑ PG, Mr. Brian Oram. "Nitrate Nitrite Nitrogen in Surfacewater and Drinking Water". www.water-research.net. Retrieved October 9, 2016.
↑ "What is a dead zone?". National Oceanic and Atmospheric Administration NOAA. National Ocean Service Department of Commerce. September 3, 2014. Retrieved November 20, 2016.
↑ "Average 'dead zone' for Gulf of Mexico predicted | National Oceanic and Atmospheric Administration". www.noaa.gov. Retrieved October 8, 2016.
↑ Goolsby, Donald A.; Battaglin, William A; Aulenbach, Brent T.; Hooper, Richard P. (2000). "Nitrogen Flux and Sources in the Mississippi River Basin". The Science of the Total Environment. 248 (2–3): 75–86. Bibcode:2000ScTEn.248...75G. CiteSeerX 10.1.1.531.6264 . doi:10.1016/s0048-9697(99)00532-x. PMID 10805229.
↑ Alexander, Richard B.; Smith, Richard A.; Schwarz, Gregory E.; Boyer, Elizabeth W.; Nolan, Jacqueline V.; Brakebill, John W. (2008). "Differences in Phosphorus and Nitrogen Delivery to the Gulf of Mexico from the Mississippi River Basin". Environmental Science & Technology. 42 (3): 822–830. Bibcode:2008EnST...42..822A. doi: 10.1021/es0716103 . PMID 18323108.
1 2 3 Murphy, J.C.; Hirsch, R.M.; Sprague, L.A. (2013). "Nitrate in the Mississippi River and Its Tributaries, 1980-2010: An Update". U.S. Geological Survey Scientific Investigations Report 2013-5169.
1 2 3 4 5 Turner, R. Eugene; Rabalais, Nancy N. (2003). "Linking Landscape and Water Quality in the Mississippi River Basin for 200 Years". BioScience. 53 (6): 563. doi: 10.1641/0006-3568(2003)053[0563:llawqi]2.0.co;2 .
↑ Halberg, G.R. (1989). "Nitrate in ground water in the United States". Nitrogen management and ground water protection. pp. 35–74. doi:10.1016/B978-0-444-87393-4.50009-5. ISBN 9780444873934.{{cite book}}: |journal= ignored (help)
↑ Sprague, Jennifer C. Murphy, Robert M. Hirsch, and Lori A. "Nitrate in the Mississippi River and Its Tributaries, 1980–2010: An Update". pubs.usgs.gov. Retrieved May 6, 2017.{{cite web}}: CS1 maint: multiple names: authors list (link)
↑ Turner, R. E. (August 1, 2002). "Element ratios and aquatic food webs". Estuaries. 25 (4): 694–703. doi:10.1007/BF02804900. ISSN 0160-8347. S2CID 54936605.
↑ Hornbeck, J. Hope (1999). "Biological Remediation of Nitrate Pollution at the Land/Water Interface". Student On-Line Journal. 5.
↑ Mitsch, William J.; Day, John W.; Zhang, Li; Lane, Robert R. (2005). "Nitrate-nitrogen retention in the wetlands in the Mississippi River Basin". Ecological Engineering. 24 (4): 267–278. doi:10.1016/j.ecoleng.2005.02.005.
↑ Kladivko, E. J.; Kaspar, T. C.; Jaynes, D. B.; Malone, R. W.; Singer, J.; Morin, X. K.; Searchinger, T. (July 1, 2014). "Cover crops in the upper midwestern United States: Potential adoption and reduction of nitrate leaching in the Mississippi River Basin" (PDF). Journal of Soil and Water Conservation. 69 (4): 279–291. doi: 10.2489/jswc.69.4.279 . ISSN 0022-4561.

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[1] "Mississippi River Facts - Mississippi National River & Recreation Area (U.S. National Park Service)". www.nps.gov. Retrieved October 8, 2016.

[2] Ibanez, Jorge G.; Hernandez-Esparza, Margarita; Doria-Serrano, Carmen; Fregoso-Infante, Arturo; Singh, Mono Mohan (2007). Environmental Chemistry Fundamentals. New York City, New York: Springer Science+Business Media, LLC. pp. 152–154. ISBN 978-0-387-26061-7.

[3] PG, Mr. Brian Oram. "Nitrate Nitrite Nitrogen in Surfacewater and Drinking Water". www.water-research.net. Retrieved October 9, 2016.

[4] "What is a dead zone?". National Oceanic and Atmospheric Administration NOAA. National Ocean Service Department of Commerce. September 3, 2014. Retrieved November 20, 2016.

[5] "Average 'dead zone' for Gulf of Mexico predicted | National Oceanic and Atmospheric Administration". www.noaa.gov. Retrieved October 8, 2016.

[6] Goolsby, Donald A.; Battaglin, William A; Aulenbach, Brent T.; Hooper, Richard P. (2000). "Nitrogen Flux and Sources in the Mississippi River Basin". The Science of the Total Environment. 248 (2–3): 75–86. Bibcode:2000ScTEn.248...75G. CiteSeerX 10.1.1.531.6264 . doi:10.1016/s0048-9697(99)00532-x. PMID 10805229.

[7] Alexander, Richard B.; Smith, Richard A.; Schwarz, Gregory E.; Boyer, Elizabeth W.; Nolan, Jacqueline V.; Brakebill, John W. (2008). "Differences in Phosphorus and Nitrogen Delivery to the Gulf of Mexico from the Mississippi River Basin". Environmental Science & Technology. 42 (3): 822–830. Bibcode:2008EnST...42..822A. doi: 10.1021/es0716103 . PMID 18323108.

[:0-8] 1 2 3 Murphy, J.C.; Hirsch, R.M.; Sprague, L.A. (2013). "Nitrate in the Mississippi River and Its Tributaries, 1980-2010: An Update". U.S. Geological Survey Scientific Investigations Report 2013-5169.

[linking-9] 1 2 3 4 5 Turner, R. Eugene; Rabalais, Nancy N. (2003). "Linking Landscape and Water Quality in the Mississippi River Basin for 200 Years". BioScience. 53 (6): 563. doi: 10.1641/0006-3568(2003)053[0563:llawqi]2.0.co;2 .

[10] Halberg, G.R. (1989). "Nitrate in ground water in the United States". Nitrogen management and ground water protection. pp. 35–74. doi:10.1016/B978-0-444-87393-4.50009-5. ISBN 9780444873934.{{cite book}}: |journal= ignored (help)

[11] Sprague, Jennifer C. Murphy, Robert M. Hirsch, and Lori A. "Nitrate in the Mississippi River and Its Tributaries, 1980–2010: An Update". pubs.usgs.gov. Retrieved May 6, 2017.{{cite web}}: CS1 maint: multiple names: authors list (link)

[12] Turner, R. E. (August 1, 2002). "Element ratios and aquatic food webs". Estuaries. 25 (4): 694–703. doi:10.1007/BF02804900. ISSN 0160-8347. S2CID 54936605.

[13] Hornbeck, J. Hope (1999). "Biological Remediation of Nitrate Pollution at the Land/Water Interface". Student On-Line Journal. 5.

[14] Mitsch, William J.; Day, John W.; Zhang, Li; Lane, Robert R. (2005). "Nitrate-nitrogen retention in the wetlands in the Mississippi River Basin". Ecological Engineering. 24 (4): 267–278. doi:10.1016/j.ecoleng.2005.02.005.

[15] Kladivko, E. J.; Kaspar, T. C.; Jaynes, D. B.; Malone, R. W.; Singer, J.; Morin, X. K.; Searchinger, T. (July 1, 2014). "Cover crops in the upper midwestern United States: Potential adoption and reduction of nitrate leaching in the Mississippi River Basin" (PDF). Journal of Soil and Water Conservation. 69 (4): 279–291. doi: 10.2489/jswc.69.4.279 . ISSN 0022-4561.

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