October 10, 2011
Fertilizer is a vital component of both modern and ancient agriculture, its benefits ranging from increased soil health to increased agricultural productivity. Unfortunately because of its high nutrient content, which includes nitrogen and phosphorus, fertilizer can negatively affect water quality. Although nitrogen and phosphorous are both vital nutrient components of soil that promote soil health and plant growth, they can have drastic polluting effects when they are leached out of soil and carried off by water. The EPA cites agricultural runoff as the leading source of impairment to surveyed rivers and lakes. Because it is considered a nonpoint source (link to: http://water.epa.gov/polwaste/nps/whatis.cfm) of water pollution, managing agricultural runoff is one of the greatest challenges posed to water quality.
The effects of agricultural runoff on water quality varies from nitrate pollution in groundwater as it percolates down from soils, to eutrophication of freshwater and coastal ecosystems, which greatly threatens both biodiversity and ecosystem services. Eutrophication is rated by the EPA as “the most widespread water quality problem in the United States” (Plaster 339). Algal blooms resulting from nutrient abundance (of phosphorous in freshwater ecosystems and nitrogen in coastal ecosystems) can greatly affect the entire food web in a given ecosystem, as their decomposition consumes the dissolved oxygen in the water and creates a hypoxic zone. Once the water is hypoxic, there is not enough dissolved oxygen to sustain most forms of life. The ecosystem is further altered and biodiversity is further threatened as turbidity increases (due to the dead matter from the algal blooms clouding the water). Areas like this in the United States and around the world are known as dead zones.
A dramatic example of one such dead zone is the Gulf of Mexico hypoxic zone, which was caused in a large part by agricultural runoff is in the Mississippi River watershed. The USGS describes the Gulf of Mexico Dead Zone as “an area of approximately 6,000-7,000 square miles of water with oxygen levels below 2 parts per million.” Nutrient-enriched waters, resulting from runoff in the Mississippi River Delta, made their way into the Gulf of Mexico and caused the subsequent eutrophication which is responsible for the area’s current hypoxic state. Now these areas of the Gulf of Mexico support fewer organisms, which poses a threat to both biodiversity and local fisheries.
Though the challenges of managing pollution from agricultural runoff are numerous and complicated, by following a series of Best Management Practices individuals and the agriculture industry can limit their impact on the environment, while still maintaining healthy and productive soils (Plaster 342). Practices such as conservation tillage, efficient irrigation, proper management of livestock and their manure, and many other sustainable agricultural practices can help reduce agricultural runoff. Also, improving fertilization practices and applications can reduce excess fertilizer and thus nutrient pollution from agricultural runoff.
In addition to changing our agricultural practices, there are other methods that can stem fertilizer runoff into watersheds. For example, a recent study reported by Science Daily found that water quality increased after lawn fertilizers were banned. Furthermore, in an attempt to mitigate problems like the hypoxia in the Gulf of Mexico, the USGS is currently exploring how the restoration of wetlands and other natural ecosystems could help filter nutrients out of runoff before it reaches streams or coastal waters. Though many of these problems may seem daunting, awareness of the issues and education of the public in Best Management Practices can help reduce water pollution and maintain the vitality of both freshwater and costal ecosystems for future generations.
Cited: Plaster, Edward J. Soil Science and Management. 5th edition. New York: Delmar-Cengage, 2009.
About the authors: Vivian Breckenridge and Julia Mangione are working towards their bachelor degrees in the USC Dornsife College of Letters, Arts and Sciences.