EPA nutrient inventories
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The effects of excess nitrogen phosphorus on human health and the environment cannot be adequately evaluated until fluxes are quantified at regular intervals. Nitrogen and phosphorus inventories were compiled for 2002, 2007, and 2012 to assess changes in inputs and fluxes across the contiguous USA. Nitrogen and phosphorus inputs and fluxes changed little at the national level from 2002 to 2012, obscuring large regional shifts. Nitrogen and phosphorus inputs decreased and crop removal increased in the eastern USA; but synthetic fertilizer inputs increased throughout the Great Plains. These changes coincided with regulations that decreased nitrogen emissions and increased demand for domestic biofuels. This research highlights the capacity for society to alter the nitrogen cycle across the country through market and regulatory actions.