XVI International Botanical Congess

The variation in distributions of diatoms over broad regional scales has implications for their use in metrics and for other water quality indicator approaches. Analysis of diatom and water chemistry data collected by The Academy of Natural Sciences from 116 sites on 47 rivers throughout the eastern USA identified four main groups of sites, described equally well by geographic region (e.g., Southeast Coastal Plain) and by major geochemistry characteristics (e.g., pH, salinity). Ecological indicators of major geochemical water chemistry characteristics tended to perform best when developed using data from one or more of the regions. Indicators designed to identify anthropogenically polluted sites were most effectively calibrated using data from smaller scales and sites with narrower ranges of major geochemical characteristics.