Seasonal patterns in stream periphyton fatty acids and community benthic algal composition in six high-quality headwater streams

Abstract

Fatty acids are integral components of periphyton and differ among algal taxa. We examined seasonal patterns in periphyton fatty acids in six minimally disturbed headwater streams in Pennsylva- nia's Appalachian Mountains, USA. Environmental data and periphyton were collected across four seasons for fatty acid and algal taxa content. Non-metric multidimensional scaling ordination suggested signif- icant seasonal differences in fatty acids; an ordination on algal composition revealed similar seasonal pat- terns, but with slightly weaker separation of summer and fall. Summer and fall fatty acid profiles were driven by temperature, overstory cover, and conduc- tivity and winter profiles by measures of stream size. Ordination on algal composition suggested that sum- mer and fall communities were driven by overstory and temperature, whereas winter communities were driven by velocity. The physiologically important fatty acid 18:3x6 was highest in summer and fall. Winter samples had the highest 20:3x3. Six saturated fatty acids differed among the seasons. Periphyton fatty acids profiles appeared to reflect benthic algal species composition. This suggests that periphyton fatty acid composition can be useful in characterizing basal food resources and stream water quality.