Modification of sediment redox potential by three contrasting macrophytes: implications for phosphorus adsorption/desorption

Abstract

Freshwater macrophytes may increase sediment redox potential and the affinity of sediments for phosphorus through radial oxygen loss from their below-ground biomass. This study demonstrated that the ability to alter sediment redox potential differs between macrophytes, according to their capacity to transport oxygen. Of the emergent macrophytes, Typha domingensis increased sediment redox potential (218 mV above bare sediment) to a greater extent than Bolboschoenus caldwellii (41 mV above bare sediment). However, the inhibition of convective flow in T. domingensis reduced its oxidizing ability by 78 mV. In contrast, Potamogeton crispus, a submerged macrophyte, had no influence on sediment redox potential. The presence of T. domingensis also increased phosphorus uptake from the water column by 0.88 mg P m⁻² day⁻¹, above that of bare sediments. In addition, inundation predictably decreased sediment redox potential from 175 mV to −176 mV over a 42-day period. Similarly, the addition of cellulose (10 mg L⁻¹) decreased sediment redox potential by 42 mV. Consequently, deposition of organic debris may counteract the oxidizing effects of macrophytes that have a limited capacity to transport oxygen, such as P. crispus. Results suggest that macrophytes play an important role in facilitating the restoration of freshwater systems.