Role of Active Floodplains for Nutrient Retention in the River Rhine
- H. Olde Venterink *ac,
- F. Wiegmana,
- G. E. M. Van der Leeb and
- J. E. Vermaatad
- a IHE, Wetland Ecosystems, PO Box 3015, 2601 DA Delft, the Netherlands
c Utrecht University, Environmental Sciences, PO Box 80115, 3508 TC Utrecht, the Netherlands
b WL Delft Hydraulics, Rotterdamseweg 185, 2600 MH Delft, the Netherlands
d Vrije Universiteit, Institute for Environmental Studies, De Boelelaan 1087, 1081 HV Amsterdam, the Netherlands
We evaluated the importance of floodplains for nutrient retention in two distributaries of the river Rhine (Waal and IJssel) by monitoring N and P retention in a body of water during downstream transport. We hypothesized that (i) retention of P is much larger than retention of N and (ii) nutrient retention increases with an increasing amount of the discharge flowing through floodplains (Q F). The second hypothesis was tested by comparing retention between the rivers Waal (low Q F) and IJssel (high Q F), as well as at different discharges. Total nitrogen (TN) did not decrease significantly during downstream transport in both rivers, whereas 20 to 45% of total phosphorus (TP) disappeared during transport in the river IJssel. This difference between N and P retention—supporting the first hypothesis—was probably caused by differences in sedimentation through a much lower proportion of N adsorbed to particles than of P (2–3% of N vs. 50–70% of P). Phosphorus retention was only observed in the IJssel and not in the Waal, and absolute P retention (g P s−1 km−1) in the IJssel increased with increasing Q F The second hypothesis was, nevertheless, not fully supported, because the percentage P retention (% of P load) decreased (instead of increased) with increasing Q F. The percentage P retention increased with decreasing river depth and flow velocity; it seemed related to the efficiency of sediment trapping.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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