Diatom-based indicators were developed to assess environmental conditions in the Missouri, Ohio, and Upper Mississippi rivers. Disturbance gradients, comprising the first two principal components derived from a suite of stressor variables, included a trophic gradient (Trophic) and a gradient reflecting agriculture and other development activities (Ag/Dev). Diatom-based indicators were developed by creating models using weighted average calibration and regression-based transfer functions to relate planktonic and periphytic diatom species assemblages to each disturbance gradient. The most predictive disturbance models combined phytoplankton and periphyton assemblages into a single bioindicator model (observed versus inferred: Trophic r 2 root = 0.56; Ag/Dev r 2 root = 0. 70). The geographic applicability of bioindicators was assessed by limiting sample geographical range during model calibrations. Geographic scale was limited by creating bioindicators using samples from: (a) each river, and (b) combined Mississippi/Missouri samples excluding Ohio River sites which were chemically unique. Indicator performance decreased with geographically restrictive models, therefore river basin-wide models, developed across all three rivers, is recommended. The most effective diatom-based disturbance bioindicators for this great river ecosystem could be applied using phytoplankton, periphyton, or combined assemblages to infer both trophic and agriculture/development disturbances.
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Acknowledgments Special thanks to Adam Heathcote and Steve Juggins for statistical support and suggestions. We would like to thank all of our EMAP-GRE colleagues for their contributions including: field crews for sample collection and field measures, the EPA Mid-Continent Ecology Division lab in Duluth, Minnesota for chemical analyses, and K. Kennedy and L. Allinger for slide preparations. This study was supported by a grant to E. Reavie from the US Environmental Protection Agency under cooperative agreement CR-83272401. This document has not been subjected to the Agency’s required peer and policy review and therefore does not necessarily reflect the view of the Agency, and no official endorsements should be inferred. This is contribution number 534 of the Center for Water and the Environment, Natural Resources Research Institute, University of Minnesota Duluth.
- Great rivers
- Transfer functions