Despite increases in human population and agricultural production, new national data show meaningful progress in reducing nutrient pollution sources across the United States.
By the USGS Water Resources Mission Area
A new study led by the U.S. Environmental Protection Agency (EPA), in collaboration with USGS, presents the next generation of the National Nutrient Inventory (NNI). The NNI is a comprehensive source of nutrient data for the entire lower 48 United States from 1987 to 2017. USGS-developed methods and datasets were key inputs to the inventory.
Nitrogen (N) and phosphorus (P) are natural elements in air, land and water, and are also critical to feeding and powering the world our world. Farmers apply these important nutrients as fertilizer on crops, pasture, and orchards to ensure a fruitful harvest–providing food on our dinner tables and sustaining our livestock. However, when nutrients are applied in excess to cropland or released through wastewater, industrial activities, or air emissions, they can pose potential risks to human and ecosystem health.
For example, excessive nutrients entering waterbodies can contribute to harmful algal blooms, which threaten drinking water supplies, aquatic ecosystems, recreation, and local economies. Certain N compounds when lost to the atmosphere can lead to poor air quality and pose a threat to vulnerable groups—especially those with respiratory conditions.
The NNI provides insight into how nutrients from agricultural, urban, and industrial sources vary across space and time. Spanning 30 years at a fine spatial resolution, the inventory provides critical information for decision makers to better understand nutrient dynamics and support efforts to protect land, air, water resources, and human health.
The NNI highlights progress in reducing nutrient pollution
Despite the expansion of nutrient-producing activities, the NNI data show progress in reducing the average impacts of nutrient pollution nationwide.
Over the years, U.S. farmers have become more efficient in how they use nutrients, which has helped produce more crops while minimizing losses to the environment. This improvement has kept stability in our agricultural surplus, which is the amount of excess nutrients left on fields after harvest, while demonstrating that increased food production does not have to come at the expense of water quality.
Urban areas across the U.S. have seen relatively large increases in population growth over the past several decades. Yet NNI data show that N and P inputs from urban sources have not increased substantially, likely due to advances in wastewater treatment and the phaseout of P-containing detergents.
Industry, transportation, and agriculture all produce N emissions. While agricultural N emissions have increased, total N emissions have declined by 22% due to substantial reductions from industry and transportation.
A collaborative science effort
The NNI is the product of a partnership between the USGS and the EPA. USGS researchers provided key expertise and nutrient datasets, such as N and P from fertilizer and manure, and implications of how these data have changed over time. The EPA integrated these datasets and led the study as part of their broader nutrient portfolio research initiative looking to support federal, state, Tribal, and local partners in their efforts to assess and improve water quality to benefit aquatic and human health.
By improving understanding of the magnitude and spatial distribution of nutrient sources across the landscape, the NNI helps to inform nutrient management strategies for agricultural, atmospheric, and urban pollution.
