WASHINGTON, Aug. 10 (UPI) -- The U.S. Geological Survey in a study of nitrate levels in the Mississippi River basin found no consistent declines at eight of its survey sites from 1980-2008.
"While conservation practices may have decreased nitrate levels in some portions of the basin, we aren't seeing widespread effects at larger scales," Lori Sprague, USGS hydrologist and lead investigator, said in a statement.
High levels of nutrients like nitrates lead to decreased levels of oxygen in water, causing a condition known as hypoxia, or dead zones, in the Gulf of Mexico. The National Wildlife Federation found that this year's dead zone is one of the largest on record because heavy rains and snowmelt washed agricultural fertilizers into the river.
USGS scientists found overall nitrate transport into the Gulf of Mexico was 10 percent higher in 2008 than in 1980.
USGS scientists found that most of the nitrates in the Gulf of Mexico came from increases in levels upstream from Iowa. The study added that slow nitrate movement through groundwater suggests problems in rivers may develop over several years.
"When we analyze long-term nutrient trends for the Mississippi River or other rivers, it's important that we consider flow variations, because water quality can change greatly from year to year due to precipitation and runoff," USGS hydrologist Robert Hirsch said.
