Differences in iron, manganese, and phosphorus binding in freshwater sediment vegetated withLittorella uniflora and benthic microalgae

Abstract

Undisturbed sediment cores from an oligotrophic lake were percolated with artificial porewater to examine the effects of isoetid macrophytes, Littorella uniflora, and benthic microalgae on daily dynamics of sediment retention of phosphorus (P) by either iron (Fe) or manganese (Mn). Retention of Fe and Mn was observed due to oxidation processes mediated by oxygen release from L. uniflora roots and benthic microalgae. Therefore increased retention of P was observed because of P precipitation with oxidized Fe- and Mn-compounds. During light periods, the ratio between Fe and P precipitation in the sediment was positively correlated with the P uptake by L. uniflora (p < 0.001, r2 = 0.984). The atomic precipitation ratio between Fe and P was between 1 and 2. The ratio between oxidized Fe-compounds and Fe-bound phosphate in the sediment was positively correlated with the root density of L. uniflora (p < 0.001, r2 = 0.995). The ratio between Mn and P precipitation was higher (≥6) than the ratio between Fe and P. The role of benthic primary producers on P retention in freshwater littoral sediments is discussed.