Evaluation of Exposure Times for Periphyton Biomass Estimate using Artificial Substrata in Headwater Streams

During the spring and fall of 1994 and winter of 1995, the exposure time of periphyton biomass on terval. In the streams with low periphyton biomass (chi. a: 2-4 mg/) in natural rocks, biomass of arttificial substrata (unglazed tile: ) exceeded that of the natural rocks after 28 days, while sites with high biomass (chi. a: 20-60 mg/) in natural rocks showed slower biomass accumulation after 40 days. Due to the high licht input and temperature in a Partially shaded mountain stream, development of periphyton biomass in spring occurred faster than that of winter. In general, development of periphyton biomass placed on artificial substrata took 4-5 weeks in spring and at least 6 weeks In winter to reach the natural level.