STARDUST II - Spatial and Temporal Assessment
of high Resolution Depth profiles Using novel Sampling Technologies The fate of pollutants in fluvial and marine sediments in cross-border zones
1 Macrophytes are important in the biogeochemistry of flowing rivers, although most information so far has relied on measurements of nutrients in plant tissues. This yields only indirect information on the nutrient uptake fluxes by roots and shoots and about nutrient translocation between roots and shoots. Here, we studied nitrogen uptake through experiments with enriched 15N stable isotopes.2 Two macrophytes (Potamogeton natans and Ranunculus fluitans) were grown in a closed race track-shaped flume, allowing us to control the hydraulic conditions in and around the plants. Overall ammonium uptake rates (µmol g-1 dry mass h-1) were higher for R. fluitans than P. natans.3 In addition to differences between the species, the spatial position of individuals within the plant patch and water flow were also important in explaining ammonium uptake. Thus, ammonium uptake was high at the leading edge of the patch and increased with velocity. Plant characteristic, such as the angle at which the plants bent in the flow, was also correlated with ammonium uptake. Differences in nutrient uptake associated with hydrodynamic parameters raised the question of how the two are related. For both species, uptake was not correlated with Reynolds stress, indicating the poor effect of turbulent mixing in determining ammonium uptake.
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STARDUST II is a project funded by the INTERREG III A programme (France/Walloon Region/Flanders
French-Flemish subprogramme) of the European Community's Regional Development Fund.
Hosted by the Flanders Marine Institute (VLIZ)
