National Water-Quality Assessment (NAWQA) Program
Nitrogen concentrations remained stable or increased in 84 percent of streams nationwide from 1993 to 2003, despite significant investments in urban strormwater controls, enhanced wastewater treatment, and agricultural conservation actions.
Nitrate concentrations have increased during low streamflows at the outlet of the Mississippi River since the mid 1990s-- indicating that nitrate concentrations in groundwater flowing into the river and its tributaries may be increasing and contributing to the increasing concentrations in the Mississippi River. The increasing nitrate groundwater contributions to some streams today may represent nitrogen inputs and management practices decades ago, thus the full effect of today’s management practices may not be measureable until many years in the future.
Concentrations of many pesticides declined from 1990s to 2008, corresponding to decreased applications, often from regulatory actions. Diazinon, an insecticide commonly used for home and garden uses, was phased out in late 2000. Widespread declines in diazinon levels in urban streams across the country were noted from 2000 to 2008.
As some pesticides are phased out, concentrations of new or alternative pesticides can increase in streams. As diazinon was phased out, there were widespread increases in concentrations of the insecticide fipronil in urban streams. Changes in pesticide use and the introduction of new pesticides require routine long-term stream monitoring for a wide arrary of pesticides to track how pesticide levels are changing over time.
Nitrate in the Mississippi River and its tributaries, 1980 to 2010: Are we making progress?
Nutrient Trends in Streams and Rivers of the U.S., 1993-2003
NOAA: Effects of Nutrient Enrichment in the Nationís Estuaries--A Deacde of Change
NAWQA Nutrient National Synthesis
Trends in Pesticide Concentrations in Urban Streams
Pesticide Levels Decline in Corn Belt Rivers
Maps Showing the National Distribution and Trends of Pesticide Use, 1992-2009
NAWQA Pesticide National Synthesis
Congressional Briefing April 11, 2014