A method for the spectrophotometric measurement of chlorophyll a and pheophytin a in benthic microalgae

A method is described that allows the measurement of river periphyton chlorophyll a and pheophytin a both on rocks and in soft sediments. The method involves successive extractions directly from frozen samples with boiling methanol. Pigments are estimated by optical density measurements before and after acidification. Methanol is superior to acetone for the distinction of chlorophyll a and pheophytin a by this means. Estimating the mean abundance of river periphyton poses considerable problems. Because of the patchy distribution of substrates and the variability of periphyton abundance even on a single type of substrate, many samples must be examined for a good estimate of biomass. Extraction and measurement of chlorophyll are more convenient than cell counting and possibly 1 The work on which this publication is based allow a direct estimation of photosynthetic was supported in part by funds provided by the United States Department of the Interior as authopotential. While artificial substrates have rized under the Water Resources Research Act of often been used for both cell counts (see 1964, as amended. Hynes 1970; Sl&deZekovh 1962) and chloro-