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

A manipulative experiment was conducted to evaluate a biochemical method for using periphyton in water quality assessment. Periphyton assemblages that developed in situ on ceramic tiles placed in a reference site in one stream were transferred into a reference site and a polluted site in each of three streams in eastern Tennessee. Samples of periphyton from each site were analyzed for chlorophyll a content, rate of photosynthesis (by ''C uptake), and fatty acid composition, 3, 17, and 35 days after being transferred to the sites. Chlorophyll a and photosynthetic rates per unit of chlorophyll at polluted sites were generally lower than at corresponding reference sites. More than 50 different fatty acids were separated and identified in the periphyton phospholipids; 12 of the 50 accounted for more than 90% of the total fatty acids. Periphyton fatty-acid biomarkers revealed differences in the periphyton taxonomic composition between reference and polluted sites. Fatty acid profiles indicated a shift from diatom to green alga-dominated assemblages in reference and chlorine contaminated sites respectively. Individual fatty-acid biomarkers specific for green algae (18:3omega3 or alpha-linolenic acid) and diatoms (20:5omega3 or eicosapentaenoic acid) 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.