Agricultural Pollution

Agricultural pollution occurs when a farmer saturates their watershed with excessive nutrient run off.  Agricultural runoff typically comes from either livestock waste or fertilizers.  Both of these materials contain nutrients that help plants and microbes grow, especially phosphorus and nitrogen.  When applied to growing crops, nutrient loading can increase yields and profit.  However, when they are deposited in marine and aquatic environments they cause eutrophication.  Eutrophication results in blooms of nuisance populations, especially algae, followed by crashes.  Eutrophication causes murky green water that is actually congested with photosynthetic life and hypoxic zones beneath the light penetration zone.  Animals that are subjected to the hypoxic zone die and oxygen is further depleted as decomposers respire while breaking down their bodies.

Citizens in North Carolina were outraged when the hog industry invaded their homes and marshes.  In 1992, North Carolina was home to 2 million hogs.  Within 6 years, the state became home to 10 million (North Carolina in the Global Economy).  Facilities called concentrated animal feeding operations, or CAFOs, are machine-like complexes that pack animals together as tightly as possible without harming their profit. Sows are stored in sow stalls so small that the animals cannot even turn around.  In North Carolina, hog CAFOs require lagoons, which are basically cesspools of hog excrement.  When Hurricane Floyd struck the coast of North Carolina, the content of the lagoons contaminated the water supply.  One operation leaked 20 million gallons of hog excrement into the New River in 1995 (North Carolina in the Global Economy).  “CAFOs house them as tightly as possible where they never see grass or sunlight. If you can envision one thousand chickens in your bathroom, in cages stacked to the ceiling, you're honestly getting the picture. (Actually a six-foot by eight room could house 1,152)” (Kingsolver).  Feeding operations like these have no use for the animal waste, so they either store it indefinitely or allow it to seep into the water table either through leaks or during storms.  Uncontrollable animal waste is dangerous for people in the community because it pollutes the water source.  It also threatens the environments that ultimately absorb the chemicals contained in the waste.

 

Traditionally, farms grew both livestock and crops.  When both animals and plants coexisted on the same properties, manure composting was more common than it is today.  Composting is a microbial process that breaks down dead plants and animal waste, thereby releasing organic nutrients.  Once composted, the nutrients can be taken by plant roots.  Farm waste was once produced, composted, and applied to plants as fertilizer at the same facility.  Now most farms either grow crops or livestock but not both.  Furthermore, many plant-growing farms grow monocultures of just one crop, and many CAFOs house one type of animal.  When food production is segregated by species, farms produce massive quantities of useless waste.  Since they cannot use it, they have to store it in manure lagoons, which are unreliable at preventing the waste from entering the water table.

Corn, the primary crop grown in the United States, is a plant with a tremendous appetite for fertilizer.  According to Michael Pollan, traditional methods of growing food were less expensive for farmers but took longer to grow a smaller harvest.  Therefore, farmers treat their plants with synthetic fertilizers that typically include nitrogen and phosphorus.  Vegetable farmers squeeze every ounce of profit that they can from their land by saturating their soil with fertilizers.  Nitrogen is among the most limiting nutrients for plant growth, so fertilizers add it to fields in shocking numbers.  “Worldwide, humans create about 160 million metric tons of nitrogen each year, compared to natural rates of terrestrial biological nitrogen fixation, which are between 90 and 120 million metric tons annually” (Dybas).  American farmers now feel pressure to grow crops using methods that they themselves do not trust for their own health.  Peggy Naylor, wife of a corn farmer close to the Des Moines River, does not drink water from her own well without filtering it through a special reverse-osmosis faucet to remove the excess nitrates from fertilizers on the farm (Pollan).  Sadly, the fertilizers impact the healthfulness of her own resources, but they also flow down the Des Moines River which eventually joins the Mississippi River.  The Mississippi River carries fertilizers accumulated from, “31 states and 40 percent of the contiguous United States” (Dybas). The Mississippi River delta marshes cannot sufficiently filter the quantity of agricultural pollution it is subjected to.  Fertilizer companies recommend using a hundred pounds of fertilizer per acre, but farmers like Peggy Naylor’s husband exceed the recommended use by an additional 80 percent to ensure a lucrative harvest (Pollan).  This may be the quickest way for Naylor to turn a profit, but it’s a short term method.  Ultimately, it is harmful to the environment because it causes eutrophication.  Eutrophication occurs when microbial life grows faster than their habitat can sustain.  It causes nuisance blooms which rapidly deplete oxygen.

Eutrophication can cause nuisance blooms and hypoxic zones on a small scale, but it also causes massive lifeless zones in the oceans.  The Gulf dead zone is a hypoxic zone in the Gulf of Mexico that experiences progressively lower levels of oxygen every summer.  Dead zones destroy and displace marine life.  Either animals flee the hypoxic zones, or they are trapped and suffocate.    Dan Leonard, a clam farmer interviewed by Cheryl Lyn Dybas, sees the impact of farm runoff on his business every year.  Fertilizer runoff is heaviest following spring fertilization, when most farmers have applied it to seedlings and young crops to nourish them for the rest of the growing season.  Populations bloom following the runoff, and the hypoxic zones are most depraved of oxygen by the summer.  Leonard says that, “’Every summer, the dead zone grows, snuffing out more fish, crabs, and other animals.  And we’re the perpetrators of the crime, with our excess fertilizer and untreated sewage and other waste flowing into the gulf’” (Dybas).  Sadly, the Gulf of Mexico is only one of 146 dead zones reported by Cheryl Dybas.  Even more sadly, this figure doubles every decade.  Furthermore, 43 of 146 reported dead zones occur in United States waters (Dybas).  These figures illustrate that popular farming methods in the United States, which transmit untreated livestock waste and fertilizer runoff to the water table, deposit gluttonous quantities of agricultural pollution into oceans and salt marshes.

In addition to causing dead zones, agricultural pollution erodes soil.  R. Eugene Turner describes the effects of nutrient inundation, “One way is that the belowground biomass may be inversely related to the nutrient loading.  Root and rhizome biomass declines with increased nutrient loading in many freshwater, brackish, and saltwater coastal wetlands.”  Because nitrogen and phosphorus are abundant in polluted soils, plants expend less energy developing root structures to seek nutrients.  Instead, they focus their energy on growing aboveground biomass.  Although the aboveground vegetation seems healthy, the soil and sediment disintegrate without the root mats to hold them together.

Farms that keep openly pastured livestock are less likely to accumulate hazardous amounts of waste than CAFO’s because the waste is less concentrated and can break down more rapidly.  A more sustainable approach to farming would incorporate livestock and vegetable growing at the same facility so that livestock waste could be composted on site for vegetable fertilizer.  A system like this does not rely on synthetic fertilizers because the plants get all of the nutrients they need from the compost.  Plants that use industrial fertilizers only absorb about 20 percent of the amount applied to the soil (Pollan).  Livestock waste runs off from both CAFOs and sustainably managed livestock-vegetable farms.  However, more waste runs off from CAFOs because they house far more animals in far smaller spaces and there is typically no need for them to compost the waste and apply it to plants.  Furthermore, farms that rely on compost for fertilizer do not transmit additional nutrients to the water basin, whereas 80 percent of commercial fertilizers, on top of CAFO livestock waste, flows through salt marshes.

Sustainable farming is not only possible but pragmatic.  “According to the USDA records from the 1990s, farms less than four acres in size had an average net income of $1,400 per acre.  The per-acre profit declines steadily as farm size grows, to less than $40 per acre for farms above a thousand acres” (Kingsolver).  Small scale farms do not need to rely on fertilizers in order to make a profit because of three factors.  First, they grow diverse products, instead of monocultures which are susceptible to disease and parasites.  They also use their space more efficiently and carefully, without trashing areas that seem unimportant.  Lastly, they sell more directly to customers than major corporations who have nation-wide distribution through supermarkets. 

Sources

Alvarez-Rogel, J., F.J. Jiminez-Carceles, and C. Egea Nicolas.  “Phosphorus and Nitrogen Content in the Water of a Coastal Wetland in the Mar Menor Lagoon (Se Spain):  Relationships with Effluents from Urban and Agricultural Areas.”  Water, Air, and Soil Pollution, Volume 173 (2006): 21-38.

Butler, Carol A., & Weis, Judith S.  Salt Marshes: A Natural and Unnatural History.  New Brunswick: Rutgers University Press.  2009.

Callaway, John C. “The Challenge of Restoring Functioning Salt Marsh Ecosystems.”  Journal of Coastal Research, Special Issue 40 (2005): 24-35.

Corman, Sarah S., Charles T. Roman, John W. King, and Peter G. Appleby.  “Salt Marsh Mosquito-Control Ditches:  Sedimentation, Landscape Change, and Restoration Implications.”  Journal of Coastal Research, 28.4 (2012): 874-880.

Dybas, Cheryl Lyn.  “Dead Zones Spreading in World Oceans.”  BioScience 55.7 (2005): 552-557.

Kingsolver, Barbara.  Animal, Vegetable, Miracle.  New York: Harper Perennial.  2007.

Nelson, Joanna L. and Erika S. Zavaleta.  “Salt Marsh as a Coastal Filter for the Oceans:  Changes in Function with Experimental Increases in Nitrogen Loading and Sea-Level Rise.”  PLoS ONE, 7.8 (2012): 1-14.

“Overview.”  North Carolina in the Global Economy.  Duke University Center on Globalization, Competitiveness & Governance, 2011.  Web 18 April 2013.  <http://www.soc.duke.edu/NC_GlobalEconomy/hog/overview.shtml>.

Pollan, Michael.  The Omnivore’s Dilemma.  New York: Penguin Books.  2006.

Stagg, Camille L. and Irving A Mendelssohn.  “Restoring Ecological Function to a Submerged Salt Marsh.”  Restoration Ecology, 18.S1 (2010): 10-17.

Turner, R. Eugene.  “Beneath the Salt Marsh Canopy:  Loss of Soil Strength with Increasing Nutrient Loads.”  Estuaries and Coasts, Volume 34 (2011): 1084-1093.