Low-Level Nitrogen Pollution More Harmful Than Previously Thought

February 15 - Nitrogen-rich fertilizers, widely used in agriculture, have been shown to reduce biodiversity in areas where they are applied, even in low amounts. It has long been acknowledged that areas of concentrated nitrogen pollution can cause drastic changes in ecosystems, but a recent study shows a marked drop in the biodiversity of areas that were subjected to low-level nitrogen deposition, such as fertilized agricultural lands.

The study, appearing in the journal Nature, examined the biodiversity of agricultural plots, some of which were subjected to slow fertilization with nitrogen, while others were left alone as a control. Over the 20 year study, the plots deposited with nitrogen showed a 17 percent drop in the number of plant species, compared with the control plots. Plots showed significant signs of recovery when nitrogen deposition was stopped midway through the study, suggesting that much of the damage can be undone if fertilizer use is reduced or halted.

Several things have disrupted Earth's natural nitrogen cycle, including the use of agricultural fertilizers, ammonia production, and the burning of fossil fuels. One ecological consequence in particular has been nutrient pollution caused by soil erosion and runoff from agricultural zones. For example, excess nitrogen in the Mississippi River system has led to the creation in the Gulf of Mexico of a dead zone, an oxygen-depleted area where most forms of marine life cannot survive.

The National Research Council report Water Implications of Biofuels Production in the United States says that increased national interest in biofuels will mean increased use of fertilizers and pesticides, which would impact the water quality of groundwater, rivers, and coastal and offshore waters. Corn -- today's biofuel crop of choice -- has higher application rates of both fertilizer and pesticides per acre than for soybeans and mixed-species grassland biomass. If farmers switch from growing other crops to corn, larger amounts of soluble nitrogen could run off and migrate to drinking water wells, rivers, and streams and impact human health. The report suggests ways to reduce these issues, such as using certain perennial crops or prairie polyculture that hold the soil and nutrients in place better than most row crops like corn.

Another Research Council report, Mississippi River Water Quality and the Clean Water Act: Progress, Challenges, and Opportunities, recommends that EPA and USDA strengthen their cooperative activities designed to reduce the impacts of agriculture on the water quality of the Mississippi River and the Northern Gulf of Mexico.

• Water Implications of Biofuels Production in the United States
• Mississippi River Water Quality and the Clean Water Act: Progress, Challenges, and Opportunities

• USDA
• EPA