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New insights into phosphorus mobilisation from sulphur-rich sediments: time-dependent effects of salinisation.

van Diggelen JM, Lamers LP, van Dijk G, Schaafsma MJ, Roelofs JG, Smolders AJ - PLoS ONE (2014)

Bottom Line: Although several studies have addressed the effects of salinisation, interactions between salinity changes and nutrient cycling in freshwater systems are not fully understood.Although salinisation was shown to lower short-term P mobilisation as a result of increased calcium concentrations, it may increase long-term P mobilisation by the interactions between sulphate reduction and oxygen availability.Our study showed time-dependent responses of sediment P mobilisation in relation to salinity, suggesting that sulphur plays an important role in the release of P from FeSx-rich sediments, its biogeochemical effect depending on the availability of Fe(2+) and O2.

View Article: PubMed Central - PubMed

Affiliation: B-WARE Research Centre, Radboud University Nijmegen, Mercator 3, Nijmegen, The Netherlands; Institute for Water and Wetland Research, Department of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Nijmegen, The Netherlands.

ABSTRACT
Internal phosphorus (P) mobilisation from aquatic sediments is an important process adding to eutrophication problems in wetlands. Salinisation, a fast growing global problem, is thought to affect P behaviour. Although several studies have addressed the effects of salinisation, interactions between salinity changes and nutrient cycling in freshwater systems are not fully understood. To tackle eutrophication, a clear understanding of the interacting effects of sediment characteristics and surface water quality is vital. In the present study, P release from two eutrophic sediments, both characterized by high pore water P and very low pore water iron (Fe(2+)) concentrations, was studied in a long-term aquarium experiment, using three salinity levels. Sediment P release was expected to be mainly driven by diffusion, due to the eutrophic conditions and low iron availability. Unexpectedly, this only seemed to be the driving mechanism in the short term (0-10 weeks). In the long term (>80 weeks), P mobilisation was absent in most treatments. This can most likely be explained by the oxidation of the sediment-water interface where Fe(2+) immobilises P, even though it is commonly assumed that free Fe(2+) concentrations need to be higher for this. Therefore, a controlling mechanism is suggested in which the partial oxidation of iron-sulphides in the sediment plays a key role, releasing extra Fe(2+) at the sediment-water interface. Although salinisation was shown to lower short-term P mobilisation as a result of increased calcium concentrations, it may increase long-term P mobilisation by the interactions between sulphate reduction and oxygen availability. Our study showed time-dependent responses of sediment P mobilisation in relation to salinity, suggesting that sulphur plays an important role in the release of P from FeSx-rich sediments, its biogeochemical effect depending on the availability of Fe(2+) and O2.

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Sodium (Na+), calcium (Ca2+) and sulphur (S) pore water concentrations (µmol L−1) in both sediments (A: left, B: right).Significant differences between treatments are indicated with different letters.
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pone-0111106-g001: Sodium (Na+), calcium (Ca2+) and sulphur (S) pore water concentrations (µmol L−1) in both sediments (A: left, B: right).Significant differences between treatments are indicated with different letters.

Mentions: As expected, pore water chemistry was strongly affected by changes in surface water salinity (Fig. 1). Under brackish conditions, Na+ showed a highly significant (p<0.005) gradual increase in the pore water over time. For the low salinity and control treatment, no significant changes in pore water Na+ concentrations occurred in sediment A, while Na+ concentrations showed a significant decrease (p<0.05) over time at a low salinity in sediment B. An interaction between treatment and sediment type was found for both Na+ and S concentrations, which means that the treatments had a significant, but different, effect on the two sediments. Pore water S concentrations also showed a highly significant (p<0.005) gradual increase at the high salinity treatment in both sediments (Fig. 1). At a low salinity, S concentrations remained at a steady level while the control treatment showed a small, but not significant, increase. Moreover, no clear differences in sulphide concentrations were found between sediments or treatments (average values ranged between 0–50 µmol L−1 for sediment A, and between 0–500 µmol L−1 for sediment B; data not shown).


New insights into phosphorus mobilisation from sulphur-rich sediments: time-dependent effects of salinisation.

van Diggelen JM, Lamers LP, van Dijk G, Schaafsma MJ, Roelofs JG, Smolders AJ - PLoS ONE (2014)

Sodium (Na+), calcium (Ca2+) and sulphur (S) pore water concentrations (µmol L−1) in both sediments (A: left, B: right).Significant differences between treatments are indicated with different letters.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4219700&req=5

pone-0111106-g001: Sodium (Na+), calcium (Ca2+) and sulphur (S) pore water concentrations (µmol L−1) in both sediments (A: left, B: right).Significant differences between treatments are indicated with different letters.
Mentions: As expected, pore water chemistry was strongly affected by changes in surface water salinity (Fig. 1). Under brackish conditions, Na+ showed a highly significant (p<0.005) gradual increase in the pore water over time. For the low salinity and control treatment, no significant changes in pore water Na+ concentrations occurred in sediment A, while Na+ concentrations showed a significant decrease (p<0.05) over time at a low salinity in sediment B. An interaction between treatment and sediment type was found for both Na+ and S concentrations, which means that the treatments had a significant, but different, effect on the two sediments. Pore water S concentrations also showed a highly significant (p<0.005) gradual increase at the high salinity treatment in both sediments (Fig. 1). At a low salinity, S concentrations remained at a steady level while the control treatment showed a small, but not significant, increase. Moreover, no clear differences in sulphide concentrations were found between sediments or treatments (average values ranged between 0–50 µmol L−1 for sediment A, and between 0–500 µmol L−1 for sediment B; data not shown).

Bottom Line: Although several studies have addressed the effects of salinisation, interactions between salinity changes and nutrient cycling in freshwater systems are not fully understood.Although salinisation was shown to lower short-term P mobilisation as a result of increased calcium concentrations, it may increase long-term P mobilisation by the interactions between sulphate reduction and oxygen availability.Our study showed time-dependent responses of sediment P mobilisation in relation to salinity, suggesting that sulphur plays an important role in the release of P from FeSx-rich sediments, its biogeochemical effect depending on the availability of Fe(2+) and O2.

View Article: PubMed Central - PubMed

Affiliation: B-WARE Research Centre, Radboud University Nijmegen, Mercator 3, Nijmegen, The Netherlands; Institute for Water and Wetland Research, Department of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Nijmegen, The Netherlands.

ABSTRACT
Internal phosphorus (P) mobilisation from aquatic sediments is an important process adding to eutrophication problems in wetlands. Salinisation, a fast growing global problem, is thought to affect P behaviour. Although several studies have addressed the effects of salinisation, interactions between salinity changes and nutrient cycling in freshwater systems are not fully understood. To tackle eutrophication, a clear understanding of the interacting effects of sediment characteristics and surface water quality is vital. In the present study, P release from two eutrophic sediments, both characterized by high pore water P and very low pore water iron (Fe(2+)) concentrations, was studied in a long-term aquarium experiment, using three salinity levels. Sediment P release was expected to be mainly driven by diffusion, due to the eutrophic conditions and low iron availability. Unexpectedly, this only seemed to be the driving mechanism in the short term (0-10 weeks). In the long term (>80 weeks), P mobilisation was absent in most treatments. This can most likely be explained by the oxidation of the sediment-water interface where Fe(2+) immobilises P, even though it is commonly assumed that free Fe(2+) concentrations need to be higher for this. Therefore, a controlling mechanism is suggested in which the partial oxidation of iron-sulphides in the sediment plays a key role, releasing extra Fe(2+) at the sediment-water interface. Although salinisation was shown to lower short-term P mobilisation as a result of increased calcium concentrations, it may increase long-term P mobilisation by the interactions between sulphate reduction and oxygen availability. Our study showed time-dependent responses of sediment P mobilisation in relation to salinity, suggesting that sulphur plays an important role in the release of P from FeSx-rich sediments, its biogeochemical effect depending on the availability of Fe(2+) and O2.

Show MeSH
Related in: MedlinePlus