by Art Hobson
PHOSPHORUS IN STREAMS: HOW MUCH IS SAFE?
As you probably know, Oklahoma’s limit on total phosphorus (TP) concentrations in streams crossing into their state has Arkansans concerned.
As in many public policy debates, the 2-year-old battle has turned on economic and regional interests, almost to the exclusion of scientific and environmental realities. The debate has not even inquired into the central point at issue: the particular limit chosen by Oklahoma. This limit is usually stated as 0.037 milligrams per liter, but I prefer 37 micrograms—millionths of a gram—per liter, because the numbers are then easier to follow.
Why 37? Why not, say, ten times larger, or ten times smaller? With the chicken industry, tourist industry, and water treatment plants at stake, one would think that this number would be carefully examined. Yet, in following the news on this issue, including two multi-page Arkansas Democrat-Gazette background articles, I have yet to find any significant examination of where this number comes from. It’s one more example of our collective science fright--our fear of thinking about science.
It took only a web search and a few emails to get the information needed to understand the reasoning behind Oklahoma’s limit. I’d like to share this information here. There are four relevant documents: The Oklahoma Water Resources Board (OWRB) report “Phosphorus in Oklahoma’s Scenic Rivers,” the U.S. Environmental Protection Agency (EPA) report “Ambient Water Quality Criteria Recommendations for Ecoregion 11,” a published scientific study titled “Nutrient Concentrations and Yields in Undeveloped Stream Basins” by Gregory Clark and others, and a report titled “Numerical Standard on Total Phosphorus for Scenic Rivers in Oklahoma” prepared by Riley Needham.
Phosphorus is a critical nutrient in fostering algae growth in waterways. Excessive algae inhibits the penetration of light into water, which cuts the production of oxygen by plants living in the water and turns the water a deep green. This suffocates fish and other life, turning waterways into putrid dead zones. This process is called “eutrophication.”
OWRB’s proposed TP limit of 37 is based on the Clark study and on standard EPA methodology. Clark gathered data from 85 relatively pristine streams, having little development within their basins, across the U.S. One of its many conclusions was that only 25% of these pristine streams had a worse (higher) TP level than 37. Standard EPA methodology is to choose this 25% cut-off as their standard. This is reasonable because this level, bordering the “worst 25% of the pristine streams,” is a lenient (i.e. favorable to business interests) estimate of the natural levels in which wildlife has evolved and thrived prior to human settlement. Ergo, Oklahoma’s TP limit.
In cases where it is impossible to obtain sufficient data for pristine streams in a region, EPA employs a second methodology: It gathers data for all streams, developed and pristine, and chooses the TP level that borders the 25% having the best or lowest TP (instead of the worst or highest TP). When both methods can be used and compared, it is found that they lead to roughly the same result—an outcome that justifies this second EPA methodology.
The Needham report throws a different light on all of this. Needham argues that the Clark study is not an appropriate basis for setting TP levels in Oklahoma, because it is based on a relatively small number of streams located all over the country that are not representative of Oklahoma streams, and especially because it includes a high fraction of western streams that have a history of high TP levels in their natural, pristine condition. Native Oklahoma organisms evolved under different conditions and might not be adapted to such high TP levels.
So Needham begins from the EPA report instead of from the Clark study. The EPA report covers a large number of developed and undeveloped streams, 437, all located within the Ozark mountains of Missouri, Oklahoma, and Arkansas. So it is more complete, and more regionally relevant, than the Clark study. One conclusion of the EPA study is that the best (least TP) 25% of these streams have a TP level below 10. So the second EPA methodology gives a recommended TP limit of 10, far lower than OWRB’s 37. Furthermore, the first EPA methodology, applied to a larger region that includes the Ozarks plus the Appalachian mountains, also gives a recommended TP limit of 10.
Needham also presents more direct data from projects that have attempted to restore formerly polluted streams by lowering TP levels. He cites many examples of successful restoration when high TP levels are lowered to between 10 and 20, and the important example of Lake Teneycomo in Missouri where TP has been lowered only to 40 but the water remains clogged with algae.
Partly in response to the Needham study, the Oklahoma Scenic Rivers Commission—a state agency—unanimously passed a resolution in December 2001 recommending to OWRB that a TP limit of 20 be established for Oklahoma’s rivers. But the OWRB raised this limit to 37, based on the Clark study. Oklahoma officially imposed this limit in July 2002, allowing 10 years for full compliance. [NOTE: I made a slight error here. The time-line is the other way around: OSRC reported first, and THEN the Needham study was done.]
TP levels on the Illinois river today run well over 100 and even as high as 426. Such levels exceed healthy levels many times over. In light of the evidence, Oklahoma’s TP limit of 37 is extremely lenient to business interests. The evidence shows that this level might not be low enough to prevent eutrophication, but that a level around 20 might be low enough. EPA methodology suggests that 10 is the appropriate level.
Environmentally and scientifically, the argument should not be over whether 37 is too low, but instead over whether it is too high.