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Water Air Soil Pollut (2007) 183:129–142 DOI 10.1007/s11270-007-9362-8

Phosphorus Entrainment Due to Resuspension in a Lowland River, Spree, NE Germany – A Laboratory Microcosm Study
Andreas Kleeberg & Michael Hupfer & Giselher Gust

Received: 11 August 2006 / Accepted: 4 February 2007 / Published online: 21 February 2007 # Springer Science + Business Media B.V. 2007

AbstractResuspension 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, 15.47 106 cells ml−1) than those (4.3 g m−2 h−1, 2.1 mg P m−2 h−1, 3.06 106 cells ml−1) of coarser sandy FRB sediment. The microcosm used so far in marine research is suited to compare riverine resuspension suggesting thelower 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 waterimplies a temporarily enhanced P bioavailability, turnover and subsequent P transformations. Keywords bacteria . erosion chamber . hydrodynamics . particles . sediment . shear velocity

A. Kleeberg (*) : M. Hupfer Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, Germany e-mail: kleeberg@igb-berlin.de G. Gust Ocean Engineering 1, Hamburg University ofScience and Technology, Schwarzenbergstr. 95, 21073 Hamburg, Germany

Abbreviations C0 drag coefficient 1 m above bottom FRB Freienbrink (sampling station at River Spree, mineral sediment) KOB Kossenblatt (sampling station at River Spree, organic sediment) P phosphorus ρ [rho] density of the fluid SPM suspended particulate matter SRP soluble reactive phosphorus t [tau] bottom shear stress TPtotal phosphorus TPSPM total phosphorus content of suspended particulate matter u0 flow velocity 1 m above bottom umean mean flow velocity u* shear (friction) velocity

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Water Air Soil Pollut (2007) 183:129–142

1 Introduction The amount, composition and temporal variation of suspended particulate matter (SPM) and fluxes of phosphorus (P) within rivers are strongly regulated by retentionand release processes (e.g., Haggard, Ekka, Matlock, & Chaubey, 2004). This is an important mechanism to understand as the transport of sediment-associated P in lowland rivers often constitutes a high percentage (23–61%) of the total annual P flux (e.g., Svendsen, Kronvang, Kristensen, & Graesbol, 1995). Moreover, entrainment of P from the sediments and its subsequent dislocation may stimulateriverine, lacustrine as well as marine phytoplankton production (e.g., House, 2003; Reddy, Kadlec, Flaig, & Gale, 1999) contributing this way to a displacement of eutrophication potential. Sorption and desorption of P in riverine sediments have been well investigated, particularly due to their importance in regulating the P concentration in stream water (e.g., Haggard et al., 2004; House, 2003; Schulz& Herzog, 2004). In contrast, much less is known about P fluxes due to resuspension events associated with changing flow conditions (e.g., Sharpley, Krogstad, McDowell, & Kleinman, 2003). Consequently, the impact of ‘in-stream’ hydrologic conditions on the extent of benthic P entrainment for river systems is poorly documented both in magnitude and source strength from pore water and sediment....