Holy Crop! How Chemical Fertilizers Endanger Fish and Pose Challenges to Engineers
By: Sonja Brankovic
When many of us hear the phrase “water pollution,” we may imagine a large factory pipe spewing sewage into a hapless lake. The crisis in Flint, Michigan comes to mind, where the city routed corrosive Flint River water into aging pipes – officials failed to test the water, and lead leached out of the pipes poisoning thousands of the people.
However, the most common way water is contaminated is through the presence of fertilizers, pesticides, and animal manure. In order to successfully grow crops for consumption, farmers need to apply nutrients (fertilizers and manure) that contain nitrogen (N) and phosphorous (P) to their fields. But when plants don’t fully utilize these compounds, they’re washed away into waterways by rain or leach into groundwater through the soil. The nitrogen and phosphorous nutrients then enrich the water in a process called eutrophication.
These nutrients cause an increase in the production of phytoplankton and algae, deoxygenate water when algal blooms collapse, kill and/or replace local fish populations, and can reduce the availability of recreational water areas because of slime and foul odors from decaying algae.
As you might expect, fertilizers, pesticides, and manure are commonly produced and used in the agricultural sector. In fact, nutrient pollution from agriculture is the top source of contamination in rivers and streams in the US, accounting for the impairment of over 130,000 miles of rivers and 1 million acres of lakes/reservoirs. According to the Food and Agriculture Organization (FAO) of the United Nations, agriculture is the leading cause of global water degradation.
What can farmers do to prevent nutrient loss?
Farmers aware of these water problems have a few potential courses of action to reduce eutrophication. Nutrient management – where N and P are applied in specified amounts, land placement, and time of year – can reduce runoff. The planting of cover crops is also helpful; using this method, farmers plant perennial crops that protect N- and P-enriched bare fields from rain events and erosion. No-till farming is another practice that has been a subculture in the rural farming community, with farmers recognizing that tilling exposes bare soil to erosion from wind and water, as well as kills helpful microbes and insects within the field. Although these conservation practices are not required, farmers who practice them voluntarily are eligible for conservation funding from the USDA’s Farm Service Agency (FSA). The FSA aims to protect the nation’s drinking water, reduce soil erosion, and preserve wildlife habitats through its conservation assistance.
Engineers can actively mitigate eutrophication
Although upstream prevention by farmers is important to reduce water pollution, clean-up methods are also needed. Geoengineers and lake managers handle wastewater contamination through coagulation and flocculation, followed by filtration. Coagulants are added to the affected water site to destabilize the charge of the unwanted particles, which allow the particles to stick together. Flocculants are then introduced to the destabilized particles to increase their size. These larger particles can then be filtered from the water, which has now been “treated”. However, the chemical coagulants used in this process are often prohibitively expensive and involve adding even more chemicals to an already polluted water source. Future engineers need to address these problems from the onset of nutrient pollution on the farming side to the controlled handling of wastewater and eutrophication events.