Thursday, June 7, 2007 - 8:15 AM
356

Is Chlorophyll the Appropriate Indicator of Nutrient Enrichment in Illinois Streams?

Todd V. Royer1, Mark B. David2, Lowell E. Gentry2, Corey A. Mitchell2, Karen M. Starks2, and Matt R. Whiles3. (1) School of Public and Environmental Affairs, Indiana University, 1315 East Tenth Street, Bloomington, IN 47405, (2) Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, (3) Department of Zoology and Center for Ecology, Southern Illinois University, Life Science II, Carbondale, IL 62901

To comply with the Clean Water Act, states are developing nutrient standards to protect the ecological integrity of streams and rivers.  In the agriculturally-dominated landscape of Illinois, this has been problematic because nutrient enrichment is rarely the sole cause of poor integrity.  We used a combination of approaches to examine relationships among algal abundance (as chlorophyll-a), nutrients, and factors such as light, substrate conditions, discharge, and drainage area.  A state-wide survey of >100 stream sites found a median sestonic chl-a value of 5 mg/m3 during both low and high flow conditions.  Sestonic chl-a is a potential indicator for larger rivers, but the relationship with phosphorus was weak.  Periphyton occurred in <50% of the sites and had a median value of 15 mg/m2 during low flow.  We placed artificial substrata in 26 sites throughout Illinois to examine growth on a common substrate.  In neither case was periphytic chl-a related to any nutrient measure.  We conclude that chl-a is a poor indicator of nutrient enrichment in Illinois streams because suspended sediments and low substrate stability disrupt the expected algal response to increased nutrients.  Currently, physical habitat, rather than nutrients, appears to be the main constraint on ecological integrity of Illinois streams.

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