Over the last century, it has become commonplace for farmers to apply nitrogen and phosphorus fertilizers to increase crop yields and feed a growing world population. The environmental effects of these fertilizers, however, have been severe, with high nitrate levels in groundwater threatening human health, and increased nutrient loading in lakes, streams and coastal waters leading to overgrowths of algae and disruption of aquatic ecosystems.
Kim Van Meter has found that even though we have tried for decades to reduce nutrient loading to streams and groundwater, with billions of dollars spent, we are not seeing the expected decreases in stream nutrient loads. Her work shows that improvements in water quality have been slow to come due to large amounts of nitrogen and phosphorus that have accumulated in soil and groundwater – legacy nutrients – that may continue to pollute our rivers even after farmers have reduced fertilizer use or improved management.
“We hypothesize that it may take decades to achieve the desired improvements in water quality,” she says. “These time lags caused by legacy nutrients must be taken into account when setting policy goals and when considering the long-term cost-benefits of implementing conservation measures.”