Phosphorus Entrainment Due to Resuspension in a Lowland River, Spree, NE Germany - A Laboratory Microcosm Study

摘要

Resuspension of benthic phosphorus (P) often constitutes a high percentage of the annual P flux in lowland rivers. To study P entrainment at controlled shear velocity (u~*) sediment from lowland River Spree of slower flowing (0.1-0.3 m s~(-1)) stretch Kossenblatt (KOB) and of faster flowing (0.5-0.7 m s~(-1)) stretch Freienbrink (FRB) was incubated in a microcosm at incrementally enhanced u~* (0.34-1.9 cm s~(-1)). Particle and P entrainment rates as well as the number of particle-associated bacteria of fine-grained mud-like KOB sediment were much higher (16.7 g m~(-2) h~(-1), 104.9 mg P m~(-2) h~(-1), 15.47 10~6 cells ml~(-1)) than those (4.3 g m~(-2) h~(-1), 2.1 mg P m~(-2)h~(-1), 3.06 10~6 cells ml~(-1)) of coarser sandy FRB sediment. The microcosm used so far in marine research is suited to compare riverine resuspension suggesting the lower u~* the more particles are deposited and the more P can be retained (KOB FRB). Conversely, correspondingly more and easier particu- late P and bacteria can again be remobilised (KOB FRB) if u~* increases. The general relationship found for u~* and the entrainment of particulate P and bacteria as well as their decelerated and selective deposition where bacteria may stay longer in the water implies a temporarily enhanced P bioavailability, turnover and subsequent P transformations.