SEASONAL-VARIATION OF EPILITHIC EXTRACELLULAR ENZYME-ACTIVITY IN 3 DIVERSE HEADSTREAMS

Extracellular enzyme activity of intact epilithon was assayed over 15 months on small stones from a calcareous headstream, and also from an intermittently-acid and a permanently-acid headstream on millstone-gri t. Glycosidase activity (beta-D-glucosidase, beta-D-galactosidase, bet a-D-xylosidase) was greater in the calcareous stream. Phosphatase acti vity, however, was highest in the permanently-acid stream and intermed iate in the calcareous stream. The activity of epilithic enzymes relat ive to each other was the same in all three streams; i.e. phosphatase > beta-D-glucosidase > beta-D-galactosidase > beta-D-xylosidase > sulp hatase. There was no general seasonal pattern to epilithic enzyme acti vity; summer maxima found in the calcareous stream were less obvious o r absent in the millstone-grit streams. Correlation coefficients and m ultiple-regression analysis suggested that epilithic enzyme activity w as potentially controlled by variables indicative of water quality (pH , temperature, conductivity, A320, Al concentration, main-river flow) and by epilithic microbial variables (bacterial activity and abundance , chlorophyll-a) but not by variables which described stone character and location (water velocity and depth, stone size). This conclusion a greed with results of an earlier summer-only survey of 15 calcareous a nd millstone-grit headstreams.