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Assessment of Chlorophyll-a as a Criterion for Establishing Nutrient Standards in the Streams and Rivers of Illinois

^a School of Public & Environmental Affairs, Indiana Univ., Bloomington, IN 47405
^b Dep. of Natural Resources and Environmental Sciences, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801
^c current address: Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824
^d Dep. of Zoology and Center for Ecology, Southern Illinois Univ., Carbondale, IL 62901

View larger version (43K): [in this window] [in a new window]   Fig. 1. Map of Illinois showing the major river networks and the distribution of the 138 sites used for the study.

View larger version (22K): [in this window] [in a new window]   Fig. 2. Distribution of sestonic chlorophyll-a (chl-a) concentrations across the state of Illinois during the 2004 high-discharge (high-Q) and low-Q surveys (see text for explanation). See Appendix A for the list of sites used in each survey.

View larger version (21K): [in this window] [in a new window]   Fig. 3. Relationship between watershed area and sestonic chlorophyll-a (chl-a) concentrations across the state of Illinois during the 2004 surveys (see text for explanation) and during 2005. Samples for 2005 were collected in July (open symbols, n = 35) and 5 wk later in August or September (filled symbols, n = 35). See Appendix A for the list of sites used in each survey.

View larger version (17K): [in this window] [in a new window]   Fig. 4. Relationship between total P and sestonic chlorophyll-a (chl-a) concentrations during the 2004 low-discharge survey using all sites (upper panel), and only sites with an open canopy (<25%) and total P concentrations of <0.2 mg L–1 (lower panel; n = 38). The dashed vertical line indicates an apparent threshold value of 0.07 mg L–1 total P.

View larger version (13K): [in this window] [in a new window]   Fig. 5. Box-and-whisker plots of benthic chlorophyll-a (chl-a) density during the 2004 high- discharge (high-Q) and low-Q surveys (see text for explanation). Horizontal lines indicate the 25th, 50th, and 75th percentiles; whiskers indicate the 10th and 90th percentiles. Circles represent sites outside the 10th or 90th percentiles.

View larger version (22K): [in this window] [in a new window]   Fig. 6. Factors that influence the biotic integrity of Illinois streams. Land use, channel alterations, and pollution inputs can directly and indirectly decouple the expected cause-and-effect relationship between nutrient loading, algal biomass, O2 deficit, and biotic integrity. Not all factors and interactions are shown.