Seston sedimentation in a lowland river (River Spree,Germany): their spatial and temporal variations and controlling factors

Sedimentation of organic particles plays a decisive role in streams in relation to pelagic loss as well as retention of nutrients and other substances. The plate sediment trap allows for the direct measurement of these net fluxes. Biweekly measurements were undertaken in the eutrophic lowland River Spree (MQ 14 m³ s^–1) 10 km upstream of Berlin in 1999 and 2000. Trapping rates between 0.5 and 25 g DW m^–2 day^–1 were found near the bank. The variance of seston sedimentation is controlled by the seston concentration, the settling velocity of the particles and the flow velocity. The sinking velocity exhibits significant seasonal fluctuations with highest values in summer. It is shown that the critical flow velocity for sedimentation is another important parameter. This controls the distribution of sedimentation over the width of the river and thus the effective average sedimentation rate for the entire river segment. This average rate ranged between 0.9 and 6.6 g DW m^–2 day^–1.