CHANGES IN PERIPHYTON FATTY-ACID COMPOSITION IN CHLORINE-POLLUTED STREAMS

A manipulative experiment was conducted to evaluate a biochemical meth od for using periphyton in water quality assessment. Periphyton assemb lages that developed in situ on ceramic tiles placed in a reference si te in one stream were transferred into a reference site and a polluted site in each of three streams in eastern Tennessee. Samples of periph yton from each site were analyzed for chlorophyll a content, rate of p hotosynthesis (by ''C uptake), and fatty acid composition, 3, 17, and 35 days after being transferred to the sites. Chlorophyll a and photos ynthetic rates per unit of chlorophyll at polluted sites were generall y lower than at corresponding reference sites. More than 50 different fatty acids were separated and identified in the periphyton phospholip ids; 12 of the 50 accounted for more than 90% of the total fatty acids . Periphyton fatty-acid biomarkers revealed differences in the periphy ton taxonomic composition between reference and polluted sites. Fatty acid profiles indicated a shift from diatom to green alga-dominated as semblages in reference and chlorine contaminated sites respectively. I ndividual fatty-acid biomarkers specific for green algae (18:3omega3 o r alpha-linolenic acid) and diatoms (20:5omega3 or eicosapentaenoic ac id) proved particularly useful in quantifying the periphyton response to chlorine. The use of algal signature fatty acids may evolve into a quantitative automated method for measuring chlorine effect on stream periphyton.