Original paper

Ökologische Untersuchungen an den Aufwuchsalgen der obersten Donau und ihrer Quellflüsse

[Ecological Studies on the Periphyton in the Upper Danube and her Headwaters]

Backhaus, Dietrich


A yearlong study was made of the periphyton biomass growing on thin polyethylene foils, monthly exposed in the upper Danube and her headwaters. In the unpolluted sections of the rivers the highest values of ashfree dry weight appear in the springtime. With increasing eutrophication or pollution the annual variations of biomass production become more and more indifferent (Tab. 1). Foils exposed for 2-3 months don't produce higher periphyton quantities than those with an exposure time of 30 days only. Stream courses with a relatively low current velocity mostly develop a higher production of dry matter than the faster flowing ones. In the little nutritive clean river source of the Breg the algal biomass per surface unit may arise as high as in the eutrophicated or polluted parts of the streams investigated in this series. Therefore, the standing crop per se cannot be used as a resource to estimate the water quality. Net and drawing samples from the whole river length in different times of the year showed a little contribution of the attached algal species to the organismic drift (Tab. 2, 3). The dominant free-floating forms are respresented by little motil or nonmotil cells (zoospores, gametes, exospores, akinetes, Chlorella spp., little and very little Flagellatae), further by several epipelic diatoms and fungi. The whole number of drift components (especially the filamentous bacteria) can be considered to a certain degree as a measure for the extent of pollution.