Spatial and temporal variability of the periphyton biomass in a prealpine river (Necker, Switzerland) msacc: 1991-07-07

Abstract

In a prealpine river with an unpredictable discharge regime chlorophyll and ash free dry mass (AFDM) were monitored as a measure of the periphyton biomass in a gravel/boulder reach from February 1989 to March 1990. During this period five major floods occurred which moved the stream bed sediment and thus eliminated most of the periphyton. Apart from flood events themselves, time since the last flood proved to be the most important factor controlling the temporal distribution of chlorophyll and AFDM. Hence, maximum periphyton biomass (945 mg chl m^-2 and 189 g AFDM m^-2) was observed at the end of May about five months after the last stream bed moving flood. Some data indicate that the resistance of the periphyton community to severe floods was dependent on the substratum size. Stone size and biomass per area were generally positively correlated. Spatial variability of both biomass parameters was high.