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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Hyporheic Processes
INFLUENCES OF PERIPHYTON BIOMASS DYNAMICS ON BIOLOGICAL COLMATION PROCESSES OF THE HYPORHEIC ZONE.
R.B. Ibisch and D. Borchardt. Institute of Aquatic Resources Research and Management, University of Kassel, Germany
Essential functions of the hyporheic zone in river ecosystems are controlled by river bed permeability. As a superimposed regulative factor the intrusion of suspended solids into the stable gravel bed of rivers strongly influences bed permeability and sediment porosity. These processes, known as colmation, lower the exchange between the surface and the hyporheic water thereby affecting habitat quality for fish and aquatic invertebrates. Temporal clogging patterns have been studied in the eutrophicated River Lahn, a 5th order stream in Germany by a series of experiments. A set of relevant variables was monitored during a three year study: seasonal biomass dynamics of stone-surface periphyton, discharge and concentration of suspended particles. A gravel-filled flow-through column was designed in order to differentiate between internal and external clogging processes including the dynamic patterns. Daily temperature curves were measured in vertical profiles in the river bed and permitted the estimation of vertical infiltration velocities and their variations through the year. The experiments indicate that in particular during low flow conditions the vertical infiltration rates are reduced despite elevated hydraulic gradients. A major factor is the development of high periphyton biomass which contributes significantly to the sealing of hyporheic interstices.
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