The kinetics of denitrification in permeable sediments
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Permeable sediments comprise the majority of shelf sediments, yet the rates of denitrification remain highly uncertain in these environments. Computational models are increasingly being used to understand the dynamics of denitrification in permeable sediments, which are complex environments to study experimentally. The realistic implementation of such models requires reliable experimentally derived data on the kinetics of denitrification. Here we undertook measurements of denitrification kinetics as a function of nitrate concentration in carefully controlled flow through reactor experiments on sediments taken from six shallow coastal sites in Port Phillip Bay, Victoria, Australia. The results showed that denitrification commenced rapidly (within 30 min) after the onset of anoxia and the kinetics could be well described by Michaelis–Menten kinetics with half saturation constants (apparent Km) ranging between 1.5 and 19.8 μM, and maximum denitrification rate (Vmax) were in the range of 0.9–7.5 nmol mL−1 h−1. The production of N2 through anaerobic ammonium oxidation (anammox) was generally found to be less than 10 % of denitrification. Vmax were in the same range as previously reported in cohesive sediments despite organic carbon contents one order of magnitude lower for the sediments studied here. The ratio of sediment O2 consumption to Vmax was in the range of 0.02–0.09, and was on average much lower than the theoretical ratio of 0.8. As a consequence, models implemented with the theoretical ratio of 0.8 are likely to overestimate denitrification by a factor of ~3. The most likely explanation for this is that the microbial community is not able to instantaneously shift or optimally use a particular electron acceptor in the highly dynamic redox environment experienced in permeable sediments. In contrast to previous studies, we did not observe any significant rates of oxic denitrification.
KeywordsPermeable sediment Denitrification Anammox Michaelis–Menten Kinetics Oxic denitrification
This work was supported by the Australian Research Council (DP0985790 to PLMC and RNG). Glud was additionally supported by the commission for Scientific Research in Greenland; KVUG; GCRC6507 and ERC-2010-AdG_20100224. We are grateful to the editor Maren Voss and two anonymous reviewers for their constructive feedback that helped improve this manuscript.
- Boudreau BP, Huettel M, Forster S, Jahnke RA, McLachlan A, Middelburg JJ, Nielsen P, Sansone F, Taghon GL, van Raaphorst W, Webster IT, Weslawski JM, Wiberg P, Sundby B (2001) Permeable marine sediments: overturning an old paradigm. EOS Trans Am Geophys Union 82:133–136Google Scholar
- Burdige DJ (2006) Geochemistry of marine sediments. Princeton University Press, PrincetonGoogle Scholar
- Canfield DE, Thamdrup B, Kristensen E (2005) Aquatic geomicrobiology. Elsevier, AmsterdamGoogle Scholar
- Cook PLM, Wenzhöfer F, Rysgaard S, Galaktionov OS, Meysman FJR, Eyre BD, Cornwell JC, Huettel M, Glud RN (2006) Quantification of denitrification in permeable sediments: insights from a two dimensional simulation analysis and experimental data. Limnol Oceanogr Methods 4:294–307CrossRefGoogle Scholar
- Emery KO (1968) Relict sediments on continental shelves of the world. Am Assoc Pet Geol Bull 52:445–464Google Scholar
- Huettel M, Webster IT (2001) Porewater flow in permeable sediments. In: Boudreau BP, Jørgensen BB (eds) The benthic boundary layer. Oxford University Press, Oxford, pp 144–179Google Scholar
- Reynolds WD (2008) Saturated hydraulic properties: laboratory methods. In: Carter MR, Gregorich EG (eds) Soil sampling and method of analysis. CRC Press, Boca Raton, pp 1013–1024Google Scholar