Effects of copper on periphyton communities assessed in situ using chemical-diffusing substrates

Chemical-diffusing substrates were designed to allow delivery of toxicants to mature periphyton communities under natural conditions without contamina ting the surrounding environment. Artificial stream validation studies were conducted in which the effects of substrate-released copper (Cu) on periph yton communities were compared to those generated in a more conventional ma nner (via water column additions). Effects of copper on the following commu nity parameters were assessed: total community biomass (measured as ash-fre e dry mass), relative chlorophyll a (chl a) and adenosine triphosphate cont ents, and relative biomass of heterotrophic bacteria. Exposure of more labo ratory periphyton communities to substrate-released Cu generated dose-respo nse relationships and recovery models that were indistinguishable from thos e generated by the conventional route of exposure. The results of this stud y demonstrate the utility of chemical-diffusing substrates in field validat ions of laboratory toxicity tests and in investigations of the effects of s tress history on periphyton tolerance to toxicants.