Connecting the drops between farm fields and mounting water risks

The heavy spring rains in the Midwest that have flooded farm fields, disrupted shipping and triggered numerous evacuations are also driving two disturbing projections for this summer: another large algal bloom in Lake Erie and a dead zone in the Gulf of Mexico the size of Massachusetts.

Each spring, heavy loads of nitrogen and phosphorus from chemical fertilizers flow off farm fields into rivers and streams. In years of extreme precipitation, which the latest National Climate Assessment predicts will occur more often, those loads greatly increase.

When they reach lakes and coastal zones, the nutrients feed the growth of algae, often turning water a sickly pea-soup green. The cyanobacteria that comprise algal blooms can also release neurotoxins that have killed dogs and pose risks to human health.

While no government agency tracks the number of algal blooms nationally, the Washington, D.C.-based Environmental Working Group found cases of almost 300 blooms in rivers, lakes and bays in 48 states and the Gulf of Mexico since 2010. In August 2014, a toxic algal bloom in Lake Erie sat over Toledo, Ohio’s drinking water intake, forcing the city to warn residents not to use their tap water for drinking, cooking, or filling their pets’ water bowls. Two years later, a huge toxic bloom along Florida’s Atlantic Coast led the state to declare emergencies in two counties. 

Last week, NOAA scientists forecast that this summer’s Gulf of Mexico dead zone — an area of low to no oxygen that can kill fish and other marine life — will cover 7,829 square miles, close to the record set in 2017 and four times the government’s target size. The dead zone forms in mid-summer when excessive amounts of decomposing algae consume most of the water’s available oxygen, threatening lucrative shrimp, crab and fish harvests off the coasts of Louisiana and Texas, along with the jobs that depend on them.

Some 80 percent of the nitrogen and more than 60 percent of the phosphorus that fuels algal growth in the Gulf comes from farmland in the greater Mississippi Basin.

Meanwhile, a peer-reviewed study published last week in the journal Environmental Research finds that nitrate contamination of U.S. drinking water, most of it originating from fertilizer, may cause as many as 12,500 cancer cases per year.

Clearly, greater efforts are needed to reduce nitrogen and phosphorus in the nation’s waters. While septic systems, concentrated livestock operations, and lawn and golf course fertilizers also contribute to these nutrient loads, farmland runoff dominates in most regions.

The good news is that incentivizing farmers to adopt nutrient-conserving cropland practices can simultaneously reduce risks to clean water, fisheries, local economies and human health, while often lifting farmers’ net profits. 

For example, the planting of noncash crops during the off-season protects otherwise barren soils from wind and water erosion. Cover crops also suppress weeds, aerate the soil, boost soil fertility and expand its water-holding capacity. Clover, hairy vetch and other cover crops that add nitrogen to the soil can substantially reduce the need for chemical fertilizer, as well.

The greater societal benefits from cover-cropped fields — safer drinking water, fewer toxic algal blooms, smaller dead zones, increased carbon sequestration and greater resilience to droughts and floods — warrant greater public investment to bring this practice to scale. 

Maryland, which is working collaboratively with neighboring states to clean up the Chesapeake Bay, is leading the way. Cover crops get planted on 29 percent of its agricultural land — the highest of any state, according to USDA’s 2017 Agricultural Census. This year Maryland has earmarked $22.5 million to help offset farmers’ costs for seed, labor and equipment to plant fall cover crops.

Nationwide, cover cropping expanded about 50 percent between 2012 and 2017, to more than 15 million acres. That’s good progress, aided substantially by USDA’s soil health campaign, but with the practice deployed on only about 6 percent of U.S. cropland, there’s a long way to go.

The construction of wetland buffers between farms and streams can also keep pollutants out of waterways, while slowing floods and restoring habitat for birds and wildlife. Iowa’s Conservation Reserve Enhancement Program, a federal, state and local partnership, has shown that strategically placed wetlands remove 30 to 70 percent of nitrogen loads from farm drainage. Wetland restoration could be funded through a tax on chemical fertilizer, which would also spur more judicious use.

As agricultural communities grapple with the aftermath of record spring floods, and another summer of algal blooms and dead zones approaches, it’s time to connect the drops and scale up solutions that can reduce our water-related health and economic risks.

Sandra Postel is the director of the Global Water Policy Project and author of “Replenish: The Virtuous Cycle of Water and Prosperity.”