Climate models indicate that Midwestern US will likely experience warmer and more volatile weather in the future, with more intense rainfall and more frequent and severe droughts. Trends in this direction are already evident. The severe drought of 2012 was followed by an unusually wet spring in 2013. This exaggerated some extant problems and may provide a preview of some unexpected consequences of future climate if current agricultural practices continue.
Rainfall in Illinois during May, June, and July 2012 was the third lowest since 1895, when systematic measurements are available statewide. In 2013, April, May, June rainfall was the second wettest on record. The immediate and obvious impacts of the drought and floods were the subject of local news coverage. A less obvious impact is the unusually large quantity of nitrate in streams, rivers and lakes of the flat, tile drained regions of Illinois and other Corn Belt states in 2013.
Much of this nitrate derives from nitrogen fertilizer that many Corn Belt farmers applied to fields late 2011 and early 2012 in preparation for growing corn. They did not know, and could not have known at the time, that a severe drought would stunt their crop, so they fertilized as usual, expecting high yields. Unfortunately, the drought of 2012 limited crop growth, leaving much of the fertilizer in the soil as highly soluble and mobile nitrate. The abundant rainfall in spring 2013 washed much of the nitrate out of the soil profile, sending millions of dollars of fertilizer value into drain tiles, to ditches, streams and rivers.
Moreover, nitrate concentrations in public water supplies, like Lake Decatur, were above the drinking water standard for nearly four months. The city of Decatur spent approximately $100,000 to reduce the concentration to acceptable levels. Danville, Des Moines and other municipalities dependent on surface water in the region faced similar costs.
In addition to contaminating local water supplies, this nitrate flowed down the Mississippi River to the Gulf of Mexico where it stimulates the growth of algae in coastal waters and contributes to seasonal depletion of oxygen (hypoxia) in bottom waters. Most aquatic organisms depend on oxygen dissolved in the water to survive, so fish and other mobile species will try to escape oxygen depleted waters. But less mobile species are more likely to suffocate from the lack of oxygen. To date, the economic cost of these “dead zones” has been difficult to quantify because fish and shrimp catch is influenced by many other factors that are difficult to measure.
While the extreme weather of 2012-13 greatly increased the loss of nitrate from farm fields, since about 1980 nitrate losses have been large enough to cause drinking water concerns and contribute to depleted oxygen in coastal waters without extreme weather. Nitrate contamination of Lake Decatur has been discussed, researched, and debated for decades. In 2002, Decatur spent several million dollars to install a nitrate removal system in its water treatment plant.
A variety of conservation practices can reduce the loss of fertilizer as well as flooding. Winter cover crops, perennial crops, and wetland protection and restoration provide such advantages. Winter cover crops, such as rye and oats sown in the late summer or early fall, have the potential to sequester and recycle unused fertilizer nitrogen in farmers’ fields. Perennial crops, such as switchgrass, alfalfa or clover, typically require less fertilizer, but are often less profitable than corn and soybeans. Wetlands that intercept tile lines can remove nitrate before it enters streams.
But these practices are rarely used in the Corn Belt because they are costly to farmers and all or most of the benefits of these practices are enjoyed by people who live downstream. Federal, state, and local funds have been and are available to subsidize some of these conservation practices, but conservation funding has been dwarfed by the profits and public subsidies available for producing high corn yields.
The public has a choice to either keep business as usual, shift incentives from corn production toward conservation practices, or to regulate farming practices to reduce flooding and nutrient losses. Quantifying the costs and benefits of public policies in this context is complex because the costs and benefits are influenced by the dynamic and uncertain influences of weather and markets.
Under circumstances of volatility and uncertainty, it is considered prudent to diversify investments and conduct research to reduce uncertainty. Diversification may include investing in land uses that better retain water and nutrients. Investments in research can quantify the impact of land uses and weather events on water and nutrient losses, and assist in developing practices that utilize water and nutrients more efficiently than the current business as usual.
Gregory McIsaac is an associate professor emeritus with the Department of Natural Resources and Environmental Sciences at the University of Illinois at Urbana-Champaign.