Notes on Diatoms V. : Epilithic Diatom Biomass in the Des Moines River

Luxuriant epilithic growths of the diatom, Gomphonema olivaceum (Lyngbye) Kutz., were observed to be growing throughout a 320 km section of the Des Moines River. Flat rocks covered with the diatom growth were collected and the live weight of the diatom biomass per square centimeter was determined to be 0.7 gm. This included 0.021 gm dry weight of organic matter. Using these values, the standing epilithic diatom biomass in one 6 km section of the river was estimated to be 1260 metric tons (live weight) containing 37.6 metric tons dry weight of organic matter. The bulk of the growth consisted of polysaccharide material secreted as tubular stalks by G. olivaceum. Extensive growths were usually limited to rocky shoals and riffle areas, composed of either cobbles and boulders of glacial origin, or of rock rubble of local origin