The advective transport of algal cells into the interstices of the hyporheic zone of the River Elbe was spatially and temporally heterogenous. Even deep sediment layers were reached by large phytoplankton species. Therefore, it is suggested that (i) the advective interstitial transport patterns vary between different algal sizes and morphotypes and (ii) sediment characteristics, expressed by the permeability coefficient k f of porous media, affect retention and retardation of surface water algae during subsurface transport. The transport behaviour of different green algae (Chlorella sp., Scenedesmus acuminatus, Desmodesmus communis, and Pediastrum duplex) and algal sized microspheres was tested in flowthrough column experiments with hyporheic sediments. The algal cell transport was directly related to the permeability of the column sediments.
IntroductionAlgal cells, both planktonic and benthic, have been found in many groundwater systems (WASMUD, 1989;KUEHN et al., 1992;COLWELL et al., 1994;BORNETTE et al., 1996) and hyporheic zones of streams (POULÍCKOVA, 1987; POULÍCKOVA et al., 1998). These empirical findings suggest an advective transport of algal cells in subsurface environments. However, little information is available about the subsurface transport behaviour of algal cells. Previous research on interstitial transport of particles has focused on disease-causing bacteria and viruses (BALES et al., 1997;PERSONNÉ et al., 1998;SIMONI et al., 1998; CHEN and STRE-VETT, 2001) and on bacteria used for bioremediation and degradation of groundwater contaminants (HARVEY and GARABEDIAN, 1991;CAMESANO and LOGAN, 1998;FULLER et al., 2000). The transport characteristics of groundwater protozoa in contaminated aquifer systems were described by few studies (SINCLAIR et al., 1993;HARVEY et al., 1995;HARVEY et al., 1997). For shallow sandy marine systems, the advective transport of suspended particles across the water-sediment interface using surrogates for algae defined as microspheres (HUETTEL et al., 1996;RUSCH and HUETTEL, 2000) and algal cells (PILDITCH, 1998;HUETTEL and RUSCH, 2000) depended on sediment permeability . Investigations of chemical factors controlling organic particulate transport through porous media have identified ionic strength, pH, organic carbon content, and physicochemical cell surface properties of bacteria as major variables (JEWETT et al., 1995;O'MELIA, 1995;MCCALAU and BALES, 1995;HUANG et al., 1999;SMETS et al., 1999). The import of algae into the hyporheic zone Internat. Rev. Hydrobiol.