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Biogeosciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/bg-2016-533
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
09 Jan 2017
Review status
A revision of this discussion paper was accepted for the journal Biogeosciences (BG) and is expected to appear here in due course.
Sediment phosphorus speciation and mobility under dynamic redox conditions
Chris T. Parsons1, Fereidoun Rezanezhad1, David W. O'Connell1,2, and Philippe Van Cappellen1 1Ecohydrology Research Group and The Water Institute, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada
2Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, College Green, Museum Building, Dublin 2, Ireland
Abstract. Anthropogenic nutrient enrichment has caused phosphorus (P) accumulation in many freshwater sediments, raising concerns that internal loading from legacy P may delay the recovery of aquatic ecosystems suffering from eutrophication. Benthic recycling of P strongly depends on the redox regime at the sediment-water interface (SWI) that, in many shallow environments, tends to be highly dynamic as a result of, among others, bioturbation by macrofauna, root activity, sediment resuspension and seasonal variations in bottom water oxygen (O2) concentrations. To gain insight into the mobility and biogeochemistry of P under fluctuating redox conditions, a suspension of sediment from a hyper-eutrophic freshwater marsh was exposed to alternating 7-day periods of purging with air and nitrogen gas (N2), for a total duration of 74 days. At the start of each anoxic period, algal necromass was added to simulate the deposition of fresh autochtonous organic matter. Phosphatase activities up to 2.4 mmol h−1 kg−1 indicated the potential for rapid mineralization of added organic-P (Po), in particular during the periods of aeration when the activity of phosphomonoesterases was up to 37 % higher than under N2 sparging. Aqueous phosphate concentrations remained low (~2.5 µM) under oxic conditions, due to sorption to Fe/Mn-oxides. During anoxic periods, once nitrate was depleted, the reductive dissolution of Fe/Mn-oxides released P. However, only 4.5 % of the released P accumulated in solution while the rest was redistributed among the particulate phases, including the humic fraction. Thus, under the relatively short-term redox fluctuations imposed in the experiments, P remobilization to the aqueous phase remained relatively limited and poly-phosphate did not accumulate. The results also emphasize the important control bottom water nitrate concentrations may exert on internal P loading in eutrophic environments.

Citation: Parsons, C. T., Rezanezhad, F., O'Connell, D. W., and Van Cappellen, P.: Sediment phosphorus speciation and mobility under dynamic redox conditions, Biogeosciences Discuss., https://doi.org/10.5194/bg-2016-533, in review, 2017.
Chris T. Parsons et al.
Chris T. Parsons et al.

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