A previous article opened a discussion on the general challenges with regulating agriculture; this article continues that discussion along with the focus on water quality issues and nutrient losses. Both the farmer and the regulator stand in a similar position: the farmer prefers not to lose nutrients from the fields where they are intended to feed growing crops; the regulator prefers that those nutrients do not leave the field and become pollution in bodies of water. Each side’s goals, however, are substantially complicated by the unpredictable realities of weather, particularly precipitation.
Background
As discussed previously, crop farming is not directly regulated by the federal Environmental Protection Agency (EPA) under the Clean Water Act (CWA). By comparison, pollution from point sources is directly regulated. EPA uses the National Pollutant Discharge Elimination System (NPDES) to issue permits for point source pollution which limits discharges and requires compliance with specific technology-based, numeric standards. This is a very specific regulatory undertaking. Actual technology-based controls must be put in place to meet this numeric standard. Continued water quality challenges, however, are leading regulatory efforts towards use of the more comprehensive Water Quality Standards (WQS). States are required to establish these standards for each body of water in the state. They begin by designating the use for the water body (e.g., drinking water, swimming, etc.), then the state has to develop criteria for specific pollutants designed to protect that designated use for the water body. (More on the discussion in this paragraph can be found here.)
Nonpoint source pollution is not included in the specific NPDES regulatory effort and EPA does not have a direct method of regulation. Nonpoint source pollution can be indirectly regulated under state laws and regulations, as well as via the Total Maximum Daily Load (TMDL) provisions that work in conjunction with the WQS. The state is responsible for establishing a TMDL, which prescribes an amount of a particular pollutant that a specific body of water can handle and still meet the WQS for its designated use, and submitting it to EPA. The process for doing so is extremely complex and difficult. States must figure out how much of a pollutant a water body can handle and then allocate that amount among all sources of the pollutant, including nonpoint sources such as farming. Proper allocation, of course, requires a complete picture of all sources of the pollutant, which further complicates the effort and many states have struggled to implement TMDLs or have decided against doing so. This is especially true for setting a specific numeric criteria for the pollutant. Some notable recent water quality discussions have focused on TMDLs that assign allocations to agricultural nonpoint source pollution, with the most prominent example being the TMDL for the Chesapeake Bay watershed which is being challenged in federal court. In a similar legal matter, environmental groups have sued EPA to force them to impose federal numeric water quality standards and establish a TMDL for the Mississippi River Basin to address the Gulf of Mexico hypoxia issue. This matter is under appeal and will continue to be closely watched. (More on the discussion in this paragraph also can be found here and here.)
Discussion
That most natural of realities – the weather – increases the difficulty and complexity of establishing a TMDL. Weather, particularly precipitation, can have a substantial impact on nutrient loading in waterways. The main nutrients of concern are phosphorus and nitrogen, important for fertilizing crops.
In 2012, much of the country, including Illinois, was suffering under a major drought,. The drought peaked in May, June and July but not before it stressed and damaged crops. The drought is believed to have had a significant effect on nutrient loading in Illinois waterways both in 2012 and even more so in 2013. The drought stress on crops is thought to have limited the amount of nutrients the crops were able to take up and use during the growing season which likely left more nutrients in the ground to be exported during a wet 2013. Research and work to understand this is ongoing.
Chart 1 below is taken from the U.S. Geological Survey (USGS) National Water Information System website and it shows the nitrate concentration in a specific central Illinois body of water (Kickapoo Creek near Bloomington, IL) for the months of May and June 2012 during the height of the drought. The level of 10 milligrams per liter is the EPA standard for safe drinking water and is more of a benchmark for this discussion than any final determination of water quality, let alone drinking water. As the drought continued and worsened, the levels of nitrate fall noticeably in this waterway.
Chart 2 is also from the USGS website for the same location but for May and June of 2013. The first half of 2013 was the wettest spring on record for Illinois. The nitrate levels for the entire time are well above where they were in 2012, peaking in early June and then again at the end of the month. In this localized example, we see the substantial impact that weather can have on the outcome for nutrient loading in the same waterway. The substantial difference in nitrate levels for this waterway highlights a localized example of the impacts of weather – specifically a wet year following a drought – on nitrogen exports. These two charts leave many questions about how to address it.
Phosphorus and nitrogen tend to take different exits out of the field, with phosphorus generally as surface run-off and nitrogen through subsurface tile drainage. The two have in common the fact that exports of both are predominantly the product of large rain-producing storms. The amount of rain has been consistently found to be the most important variable in determining the amount of nutrients leaving fields. Three times the amount of nitrogen can be exported in wet years than dry years and drier years produce lower concentrations of nitrates in the water than wetter years. One of the factors is that with more water moving during large storms there are fewer opportunities for denitrification and natural or biological absorption in streams and stream banks. Similarly, most phosphorus exported from fields happens during large storms where water runs off of the fields – the larger the storm, the more runoff and the more phosphorus exported.
Time of the year is also important to the export of both nutrients. Spring, especially April to June, is when these nutrients are mostly likely to leave the fields. Much of this is due to moderate temperatures and bare soil without vegetative cover, allowing more water to move through the soil and take nutrients with it. By summer and early fall, growing crops and warmer temperatures means less storm water moves through the soil carrying nutrients to water bodies. In fact, a spring storm and summer storm with the same amount of rain will produce very different outcomes in terms nutrient export and as much as three times the amount of nitrogen can leave the field during spring storms. Complicating matters further is that while most of the nutrients are lost in the spring, the biggest water quality problems occur in late summer and early fall.
Finally, soil issues are also important. For example, phosphorus can build up in clay soils over a long time which also impacts how much of it is exported during storms. Even more important to nutrient loss, however, may be the large pores in the soil called macropores, through which water is quickly transported taking nutrients with it. Unfortunately, some farming practices that help with runoff may increase the challenges for tile drainage because improved soil organic matter and the creation off large pores in the soil by earthworms may actually increase the nitrogen moving into tiles. In other words, practices such as no-till farming might help reduce phosphorus loss from run-off while contributing to nitrogen loss through tiles.
The final chart below (data compiled from here, here and here) illustrates the complex relationship between nitrogen application, precipitation, and Gulf of Mexico hypoxia on a much larger scale. The blue line in the graph shows the size of the “dead zone” each year in 1985-2009, as measured in square miles on the left axis. The year-to-year variability in the amount of Gulf hypoxia is evident. The red line illustrates the quantity of nitrogen (N) fertilizer used in the Mississippi River Basin, as measured in thousands of tons on the left axis. In contrast to the Gulf hypoxia, year-to-year nitrogen fertilizer usage remains relatively flat. The conclusion is that the amount of hypoxia changes dramatically from year to year while nitrogen fertilizer usage does not. The answer most likely can be found in the green line on the graph, which represents the flow rate (amount of water) for the Mississippi River. Year-to-year variation in precipitation in the MRB leads to variation in the amount of water moving down the Mississippi River, carrying with it nutrients applied months if not years earlier. This graph highlights the impact of weather, particularly precipitation, and the challenges for addressing nonpoint source pollution.
Conclusion
Efforts to address water quality and nutrient loss likely needs to be grounded in the realities associated with farming, beginning with the unpredictable outcomes caused by the weather. Existing point source pollution regulatory tools cannot be expected to be effective if applied to farming nor can anyone expect a single, one-size-fits-all solution. Both farmers and regulators, however, have in common similar challenges from the weather and addressing water quality and nutrient loss from agriculture may well depend on this commonality. For example, can precision agricultural tools and risk management principles help guide the way forward? How can advances in technology, data management and equipment be best applied to conservation practices and water quality efforts? Do risk management principles have something to offer in terms of weather and production modeling? Moreover, will water quality and natural resource issues, including regulation, become a risk component needing management by farmers? Central to this discussion is the basic fact that losing nutrients to bodies of water is a loss to both the farmer and the natural resource base – lost nutrients do not feed growing plants in the field if they are in the water feeding algae.