Effect of copper on algal communities from oligotrophic calcareous streams

Two sets of experiments were done to quantify the effects of chronic copper exposure on natural periphyton in a nonpolluted calcareous river. The results of short-term (up to 6 h exposure) experiments corroborated the significance of pH on copper toxicity. Copper toxicity increased when pH was reduced from 8.6 to 7.7, and this was related to the effect of pH on copper speciation (free copper concentration increased from 0.2% to 2.3% of total copper). Longer term experiments demonstrated that periphyton communities exposed to copper under pH variation (8.2-8.6) were already affected at 10 mug.L-1 (20-80 ng.L-1 Cu2+) after 12 days of exposure. Copper exposure caused stronger effects on structural (algal biomass and community structure) than on functional (photosynthetic efficiency) parameters of periphyton. Changes in community composition included the enhancement of some taxa, (Gomphonema gracile), the inhibition of others (Fragilaria capucina and Phormidium sp.), and the appearance of filament malformations (Mougeotia sp.). The results of our study demonstrated that several weeks of exposure to copper (10-20 mug.L-1) were sufficient to cause chronic changes in the periphyton of oligotrophic calcareous rivers. This degree of copper pollution can be commonly found in the Mediterranean region as a result of agricultural practices and farming activities.