CHOICE OF SUBSTRATE TYPE FOR WATER QUALITY ASSESSMENT USING BENTHIC ALGAE.

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

Effectiveness of monitoring programs that use benthic algae as water quality indicators depends greatly on sampling design, and in particular, on the choice of substrate from which the algae are sampled. We used USGS NAWQA data from rivers throughout the U.S. to compare the value of quantitative algal samples collected from hard (e.g. rock, wood) and soft sediment substrates. We calculated various algal indices and metrics for assessing water quality, and developed nutrient inference models. There was no consistent difference in the performance of inference models and other metrics based on samples taken from hard and soft substrates. However, models developed for one substrate had low predictive power when used for estimations based on samples collected from another substrate. We therefore conclude that the most cost-effective water quality monitoring program would be one based on samples taken from the single substrate that is most common in rivers of an area for which a metric or inference model is being developed. Water quality estimates could be improved more by sampling additional sites than by sampling additional substrates.