INFLUENCE OF AQUATIC MACROPHYTES ON PHOSPHORUS AND SEDIMENT POREWATER CHEMISTRY IN A FRESH-WATER WETLAND

The influence of the emergent aquatic macrophyte, Menyanthes trifoliata L. on sediment interstitial porewater chemistry, particularly on the distribution of soluble reactive phosphorus (SRP), was investigated at Silver Lake in southwestern Washington (Cowlitz County). Menyanthes trifoliata and many other wetland species create an oxygenated rhizosphere by translocation of oxygen to the roots. Close interval diffusion sampling showed that SRP, total soluble phosphorus (TSP), and concentrations of other redox-sensitive species such as T-Fe, Fe2+, and T-Mn were reduced in interstitial waters when macrophytes were present. Total alkalinity and pH also were lower and oxidation-reduction potentials were higher in sediments with plants than those in which the plants were removed. Rhizosphere oxidation appears to provide wetland species with a mechanism for sequestering phosphorus and for creating favorable concentration gradients within the root zone.