Illinois River Standards "Unrealistic," Researcher Says

FAYETTEVILLE, Ark. —As the controversy surrounding the Illinois River water quality heads into court, University of Arkansas researchers have determined that, although some improvements can be made, the phosphorus levels set by Oklahoma are unrealistic within the next decade.

"We wanted to look at the science and address the information gap between what we know and what we don’t know," explained Marc Nelson, assistant director of the Arkansas Water Resources Center.

Nelson and Thomas Soerens, associate professor of civil engineering, and biological and agricultural engineering graduate student Kati studied phosphorus sampling results. Nelson will present their analysis on Tuesday, April 23, at the Arkansas Water Resources Conference in Fayetteville, Ark.

"Mass balance analysis is common in engineering and has often been used in watershed studies," said Nelson. "But when I started looking for the data for the Illinois River, I found that no one had ever done a mass balance for this system."

Nelson and Soerens have been sampling the Illinois River water regularly at the Highway 59 bridge since 1997. Nelson used the five years of sampling data to perform a mass balance analysis of the Illinois River watershed. The analysis included point-source data from the sewage treatment facilities in Rogers, Springdale, Prairie Grove and Fayetteville, Arkansas, and non-point-source data from the Illinois River watershed.

"One idea critical to this approach is that once phosphorus enters the stream, it eventually all flows down the stream," explained Nelson. "It can be delayed in a process known as nutrient cycling where sediments adsorb the phosphorus and then are washed down stream in storm events or biomass such as algae use the nutrient for growth but then release it when they die."

A mass balance analysis is similar to balancing a checkbook. In a checkbook all deposits and withdrawals are recorded to track how much money is in the account. In a mass balance analysis, the inflow and outflow in a system are monitored. In a watershed analysis, it will determine if the watershed is accumulating nutrients or whether it is passing them downstream via its rivers.

The researchers found that although point-source discharge is only 3 percent of the total input, it accounts for 43 percent of the phosphorus in the Illinois River, while non-point sources account for only 57 percent of the total. At present discharge from the Fayetteville sewage treatment plant and the Rogers treatment plant are below 1 mg/l. Together Fayetteville and Rogers account for only 16 percent of the point-source phosphorus discharge into the Illinois River.

"This is very different from previous assumptions," said Nelson. "Past analyses have always assumed that since point sources represent 3 percent of the input, they also represent 3 percent of the output. But we found that is not the case at all. This means that a great deal of the non-point source phosphorus is remaining in the watershed."

According to Nelson, total phosphorus inputs to the watershed are very high and increasing at 5 percent per year. However, the percent of watershed phosphorus reaching the river each year is low, implying phosphorus is accumulating in the watershed at a rate of around 15 pound per acre of pasture per year.

"Current recommendations are to limit total soil-test phosphorus content to 300 pounds per acre," Nelson explained. "At an accumulation rate of 15 pounds per acre per year and land application reaching back 20 years, the entire watershed is nearing these limits. The phosphorus accumulation in the watershed is going to have a long-term impact on water quality."

Nelson calculated the rate change in phosphorus levels in the Illinois River and determined that if the level of phosphorus continues to rise at present rates, in 10 years total phosphorus content it will have doubled from present levels.

"Application rates are increasing and the phosphorus levels are continuing to rise because of this huge reserve in the watershed," said Nelson. "Although total phosphorus levels could be dropped by one-third by limiting point-source discharges to 1 mg/l, meeting Oklahoma’s arbitrary 0.037 mg/l requirement is not a realistic goal within the next decade, and possibly for some time after that."

Noting that Fayetteville and Rogers are already below the proposed 1 mg/l limit, Nelson points to a lack of regulation for some of the problems. Arkansas currently has no discharge limits for its waterways because it sets no numerical in-stream phosphorus limits. Arkansas is not alone in this, Nelson added. Oklahoma does not set phosphorus limits in its rivers either, except for those designated as scenic rivers.

"It is a matter of politics, which if far beyond my understanding as a scientist," said Nelson. "But if the states don’t do something voluntarily, the Environmental Protection Agency is going to step in with mandated limits, just as it has with the new storm water runoff requirements for construction sites, cities and industries."

The Arkansas Water Resources Conference will be held at the University of Arkansas Center for Continuing Education and the Radisson Hotel in downtown Fayetteville. It will begin at 8:00 a.m. on April 23 and end at noon on April 24. Registration information and a detailed conference agenda can be obtained from the Arkansas Water Resources Center website at: http://www.uark.edu/depts/awrc or by calling (479) 575-5867.