‘Unfortunately, there is no widespread evidence of improving conditions …’
Massive efforts to improve water quality haven’t been effective in many large U.S. rivers, where nitrate levels remain at high levels after surging in the second half of the 20th century.
Between 1945 and 1980, nitrate levels in large U.S. rivers increased up to fivefold as chemical fertilizer use increased dramatically in the Midwest. In some urbanized areas along the East and West coasts during the same period, river nitrate levels doubled.
In recent decades, nitrate changes have been smaller but nitrate levels have remained high in most of the rivers examined in a new U.S. Geological Survey study.
“Long-term monitoring of 22 large U.S. rivers provides a rare glimpse into how water quality conditions have changed over the last 65 years,” said Edward Stets, lead author of the study. “Although the greatest increases in nitrate concentrations occurred prior to 1980, levels have since remained high in most rivers. Unfortunately, there is no widespread evidence of improving conditions.”
High nitrate levels can lead to the formation of zones of low oxygen in coastal waters, which harms fisheries, recreational use, and ecological habitat, causing major economic impacts. High nitrate levels also pose a threat to drinking-water supplies, sometimes resulting in high water treatment costs, and can harm aquatic life.
The USGS study, reported in the Journal of the American Water Resources Association, includes rivers flowing into the Great Lakes and coastal waters such as Long Island Sound, Delaware River estuary, Chesapeake Bay, San Francisco Bay, and the Gulf of Mexico.