CALIBRATION SETS FOR QUANTIFYING ECOLOGICAL CHARACTERISTICS OF RIVER ALGAE: HABITAT VARIABILITY AND SPATIAL SCALE.

D.F. Charles and M.G. Potapova. Patrick Center for Environmental Research, The Academy of Natural Sciences, 1900 Ben Franklin Parkway, Philadelphia, PA 19103

The usefulness of algae as environmental indicators depends largely on our ability to quantify the relevant ecological characteristics of the species found in our samples. One of the best approaches for obtaining these data is the development of calibration sets consisting of many specially-selected sites where both algal samples and environmental data are collected. Based on our analysis of USGS NAWQA program data on benthic algal samples collected from 750 sites throughout the USA, we make the following recommendations concerning selection of sites. Most important is that the values of environmental parameters of greatest interest are evenly distributed from highest to lowest; the range of values should be as large as feasible and represent that of rivers to which the ecological data will be applied. Minimize the range of values of environmental variables that have an important influence on algal assemblages, but are not of interest to the overall study. Include at least 30 sites; more are necessary if there is large variability in assemblage composition or site environmental characteristics. The geographic area represented should be as uniform as possible, but can be as large as several major watersheds or states, as long as specific sites meet the above criteria.