The U.S. Geological Survey (USGS) released a new study on October 30 showing a decrease in nitrate levels in the Illinois River between 2000 and 2010, marking the first significant decline observed in the Mississippi River Basin since 1980.
While the Illinois River has exhibited a decrease in nitrate levels, the Missouri and Mississippi Rivers have not shown similar indications of progress, according to USGS.
As part of the USGC National Water-Quality Assessment program, nitrate concentration and flux from 1980 through 2009 were estimated at eight sites in the Mississippi River Basin, which included the Iowa, Illinois, Ohio and Missouri Rivers.
USGS researchers used the “weighted regressions on time, discharge and season” method – a fairly new statistical tool, introduced in 2010, that evaluates trends in long-term water quality studies based on instantaneous measurements and daily data records or river discharge and provides time histories without the influence of year to year variations in discharge.
As stated in the report, the data collected revealed a reduction in nitrate concentration for both the Illinois and Iowa Rivers. The Illinois River level declined by 21 percent, while the Iowa River decrease was a much lower 10 percent.
The lowest nitrate level of the eight sites was found in the Ohio River, which has remained relatively stable over the past 30 years.
“These results show that solving the problem of the dead zone will not be easy or quick. We will need to work together with our federal and state partners to develop strategies to address nitrate concentrations in both groundwater and surface water,” said Lori Caramanian, U.S. Department of the Interior deputy assistant secretary for water and science.