Sediment phosphorus speciation and mobility under dynamic redox conditions
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 with...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-07-01
|
| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/3585/2017/bg-14-3585-2017.pdf |
| _version_ | 1819072231604486144 |
|---|---|
| author | C. T. Parsons F. Rezanezhad D. W. O'Connell D. W. O'Connell P. Van Cappellen |
| author_facet | C. T. Parsons F. Rezanezhad D. W. O'Connell D. W. O'Connell P. Van Cappellen |
| author_sort | C. T. Parsons |
| collection | DOAJ |
| description | 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 within surficial sediment. In many shallow environments, redox
conditions tend to be highly dynamic as a result of, among others,
bioturbation by macrofauna, root activity, sediment resuspension and seasonal
variations in bottom-water oxygen (O<sub>2</sub>) concentrations. To gain insight
into the mobility and biogeochemistry of P under fluctuating redox
conditions, a suspension of sediment from a hypereutrophic freshwater marsh
was exposed to alternating 7-day periods of purging with air and nitrogen gas
(N<sub>2</sub>), for a total duration of 74 days, in a bioreactor system. We present
comprehensive data time series of bulk aqueous- and solid-phase chemistry,
solid-phase phosphorus speciation and hydrolytic enzyme activities
demonstrating the mass balanced redistribution of P in sediment during redox
cycling. Aqueous phosphate concentrations remained low
( ∼ 2.5 µM) under oxic conditions due to sorption to
iron(III) oxyhydroxides. During anoxic periods, once nitrate was depleted,
the reductive dissolution of iron(III) oxyhydroxides released P. However,
only 4.5 % of the released P accumulated in solution while the rest was
redistributed between the MgCl<sub>2</sub> and NaHCO<sub>3</sub> extractable fractions of
the solid phase. Thus, under the short redox fluctuations imposed in the
experiments, P remobilization to the aqueous phase remained relatively
limited. Orthophosphate predominated at all times during the experiment in
both the solid and aqueous phase. Combined P monoesters and diesters
accounted for between 9 and 16 % of sediment particulate P. Phosphatase
activities up to 2.4 mmol h<sup>−1</sup> kg<sup>−1</sup> indicated the potential for
rapid mineralization of organic P (P<sub>o</sub>), in particular during
periods of aeration when the activity of phosphomonoesterases was 37 %
higher than under N<sub>2</sub> sparging. The results emphasize that the magnitude
and timing of internal P loading during periods of anoxia are dependent on
both P redistribution within sediments and bottom-water nitrate
concentrations. |
| first_indexed | 2024-12-21T17:34:26Z |
| format | Article |
| id | doaj.art-a3a29c71476c4b1da079bd19b4d4eb8d |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-21T17:34:26Z |
| publishDate | 2017-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-a3a29c71476c4b1da079bd19b4d4eb8d2022-12-21T18:55:49ZengCopernicus PublicationsBiogeosciences1726-41701726-41892017-07-01143585360210.5194/bg-14-3585-2017Sediment phosphorus speciation and mobility under dynamic redox conditionsC. T. Parsons0F. Rezanezhad1D. W. O'Connell2D. W. O'Connell3P. Van Cappellen4Ecohydrology Research Group and The Water Institute, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, CanadaEcohydrology Research Group and The Water Institute, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, CanadaEcohydrology Research Group and The Water Institute, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, CanadaDepartment of Civil, Structural and Environmental Engineering, Trinity College Dublin, College Green, Museum Building, Dublin, IrelandEcohydrology Research Group and The Water Institute, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, CanadaAnthropogenic 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 within surficial sediment. In many shallow environments, redox conditions tend to be highly dynamic as a result of, among others, bioturbation by macrofauna, root activity, sediment resuspension and seasonal variations in bottom-water oxygen (O<sub>2</sub>) concentrations. To gain insight into the mobility and biogeochemistry of P under fluctuating redox conditions, a suspension of sediment from a hypereutrophic freshwater marsh was exposed to alternating 7-day periods of purging with air and nitrogen gas (N<sub>2</sub>), for a total duration of 74 days, in a bioreactor system. We present comprehensive data time series of bulk aqueous- and solid-phase chemistry, solid-phase phosphorus speciation and hydrolytic enzyme activities demonstrating the mass balanced redistribution of P in sediment during redox cycling. Aqueous phosphate concentrations remained low ( ∼ 2.5 µM) under oxic conditions due to sorption to iron(III) oxyhydroxides. During anoxic periods, once nitrate was depleted, the reductive dissolution of iron(III) oxyhydroxides released P. However, only 4.5 % of the released P accumulated in solution while the rest was redistributed between the MgCl<sub>2</sub> and NaHCO<sub>3</sub> extractable fractions of the solid phase. Thus, under the short redox fluctuations imposed in the experiments, P remobilization to the aqueous phase remained relatively limited. Orthophosphate predominated at all times during the experiment in both the solid and aqueous phase. Combined P monoesters and diesters accounted for between 9 and 16 % of sediment particulate P. Phosphatase activities up to 2.4 mmol h<sup>−1</sup> kg<sup>−1</sup> indicated the potential for rapid mineralization of organic P (P<sub>o</sub>), in particular during periods of aeration when the activity of phosphomonoesterases was 37 % higher than under N<sub>2</sub> sparging. The results emphasize that the magnitude and timing of internal P loading during periods of anoxia are dependent on both P redistribution within sediments and bottom-water nitrate concentrations.https://www.biogeosciences.net/14/3585/2017/bg-14-3585-2017.pdf |
| spellingShingle | C. T. Parsons F. Rezanezhad D. W. O'Connell D. W. O'Connell P. Van Cappellen Sediment phosphorus speciation and mobility under dynamic redox conditions Biogeosciences |
| title | Sediment phosphorus speciation and mobility under dynamic redox conditions |
| title_full | Sediment phosphorus speciation and mobility under dynamic redox conditions |
| title_fullStr | Sediment phosphorus speciation and mobility under dynamic redox conditions |
| title_full_unstemmed | Sediment phosphorus speciation and mobility under dynamic redox conditions |
| title_short | Sediment phosphorus speciation and mobility under dynamic redox conditions |
| title_sort | sediment phosphorus speciation and mobility under dynamic redox conditions |
| url | https://www.biogeosciences.net/14/3585/2017/bg-14-3585-2017.pdf |
| work_keys_str_mv | AT ctparsons sedimentphosphorusspeciationandmobilityunderdynamicredoxconditions AT frezanezhad sedimentphosphorusspeciationandmobilityunderdynamicredoxconditions AT dwoconnell sedimentphosphorusspeciationandmobilityunderdynamicredoxconditions AT dwoconnell sedimentphosphorusspeciationandmobilityunderdynamicredoxconditions AT pvancappellen sedimentphosphorusspeciationandmobilityunderdynamicredoxconditions |