BLOOMINGTON – Are nitrogen and phosphorus loads in the state’s rivers increasing or decreasing? An associate professor emeritus with the University of Illinois examined the findings during a recent nutrient loss meeting in Bloomington.
Dr. Gregory McIsaac gave an update on how loads have changed over time. McIsaac compared 1980-96 and 2013-2017. Water yield in inches per year was up 13 percent and nitrate loads were up 7 percent. Total phosphorus load was up 26 percent.
For point source discharges between 2011 and 2017, total nitrogen was down 14 percent with phosphorus down 22 percent.
“Southern Illinois has relatively low nitrate loads and the highest are from Chicago and Central Illinois where we have more tile drainage,” McIsaac explained.
There is a promising development in the Mackinaw River as the higher nitrate yields from 1996-2006 were followed by less nitrates from 2009-2017. McIsaac says there is a need to look more closely at what is causing these changes but he considers it good news.
Major changes were observed along the Illinois River because of changes in calculations.
“When we do see changes I think we need to quantify what are the causes of those changes,” added McIsaac.
Increases in phosphorus are somewhat common in the Midwest possibly because of more excessive rainfall events resulting in more runoff. So, why is the Mackinaw River seeing a different trend?
“It could be there is more efficient use of nitrogen and fertilizer in that watershed,” concluded McIsaac. “There is certainly some good work that could be done to try and figure that out.”