Sun-baked fields and bone-dry streambeds set the scene in 2012 as a severe drought gripped much of the Midwest. If farmers in the Corn Belt were hoping for moisture on their parched crops, they sure got it when torrential rains hit the region in 2013. Not only did the 2013 rains wet crops and fill waterways, but they also brought some of the highest nitrate pollution levels ever recorded in streams in parts of Iowa, Minnesota and Illinois.
As the world heats up from climate change, a shift in the water cycle is at the forefront of the changes. Or as one business leader aptly explained, "[i]f climate change is the shark, then water is its teeth."
Details of the high nitrate concentrations came from a recently released joint USGS-EPA study that tested untreated water from 100 streams across 11 Midwestern states. Many water quality and habitat characteristics were reviewed including fish, invertebrates and algae, with the nitrate assessments comparing the findings to others from over 1,000 regional streams during the past 20 years.
Nitrate is a type of nitrogen that is also a common contaminant in lakes, rivers, streams and groundwater. Excessive nitrates in water can hurt ecosystems and spawn harmful algal blooms that suck up the oxygen in the water to form "dead zones" that extinguish or force out aquatic life. Water with excessive nitrate levels that is drunk by infants also has the potential to cause the dangerous "blue baby syndrome." In general, and as confirmed by the USGS here, agricultural areas are susceptible to pollution from nitrates and other types of nitrogen because of heavy application of synthetic nitrogen fertilizer and manure to farm fields - in this case mainly for corn production.
The study is unique in that it linked changing precipitation patterns of drought followed by deluge to the spike in pollution. As Peter Van Metre, a USGS hydrologist and the study's lead author, explained:
The highest nitrate concentrations in 2013 were in streams in Iowa, closely followed by southern Minnesota and central Illinois. Drought conditions in 2012 allowed excess nitrogen to build up in the soils until spring rains in 2013 flushed the nitrate into streams, leading to unusually high levels.
In effect, precipitation patterns over many years can determine the amount of nitrate and other pollutants that run into local waters.
Drought, Deluge and Rural Waters
While the Midwest's one-two drought and deluge combo in 2012-13 could seem anomalous, it might be getting more likely. As the world heats up from climate change, a shift in the water cycle is at the forefront of the changes. Or as one business leader aptly explained, "[i]f climate change is the shark, then water is its teeth."
As scientists from the Intergovernmental Panel on Climate Change (IPCC) have determined, the probability for more intense droughts and precipitation events is increasing. This is due to warmer air in the atmosphere which can lead to extensive dry spells interspersed with brief but heavy precipitation and flooding because the warmer air can hold more water. (Of course, there are many factors that contribute to situations like droughts and floods, not the least geography.)
In the Midwest the expectation is that rainstorms will dump more water over the coming years, punctuated by droughts that are more scorching. It's not hard to foresee the implications from what the USGS study found: Water quality will likely suffer as torrential rains carry more contaminant-laden runoff from farm fields into local streams, rivers and groundwater. Often the runoff will be filled with nitrogen from fertilizers, along with other soil-additive nutrients like phosphorus, all of which have the potential to overwhelm the environment's ability for absorption. The EPA already considers nonpoint source pollution, where many sources contribute, as the greatest threat to US water resources, one that is especially problematic for agricultural areas.
Water pollution from runoff doesn't stop at local boundaries. The Des Moines Water Works lawsuit against three rural Iowa counties for nitrate-heavy pollution as a result of runoff is a case in point. On a much grander scale, the giant perennial Gulf of Mexico dead zone is another, and one produced largely by nutrient-contaminated water that drains farm fields and then runs off into streams and eventually into the Mississippi River and empties in the Gulf.
Ultimately, farmers and those in rural communities have a tremendous role to play in building resilience into the landscape as we face a climate that is more extreme and less predictable. This resilience means a future of agriculture that can reduce water pollution through steps like precision fertilizer application, more cover-cropping and restoration of buffer strips and wetlands. Since we know the ravages of climate change are upon us, it's in everyone's best interest to recognize the importance of the upstream-downstream connection and the need for cooperative preparation.