The kinetics of denitrification in permeable sediments Victor Evrard • Ronnie N. Glud • Perran L. M. Cook Received: 13 May 2012 / Accepted: 28 August 2012 / Published online: 9 September 2012 Ó Springer Science+Business Media B.V. 2012 Abstract Permeable sediments comprise the major- ity of shelf sediments, yet the rates of denitrification remain highly uncertain in these environments. Com- putational models are increasingly being used to understand the dynamics of denitrification in perme- able 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 con- trolled flow through reactor experiments on sediments taken from six shallow coastal sites in Port Phillip Bay, Victoria, Australia. The results showed that denitrifi- cation 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 K m ) ranging between 1.5 and 19.8 lM, and maximum denitrification rate (V max ) were in the range of 0.9–7.5 nmol mL -1 h -1 . The production of N 2 through anaerobic ammonium oxi- dation (anammox) was generally found to be less than 10 % of denitrification. V max 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 O 2 consumption to V max 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 overesti- mate 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. Keywords Permeable sediment  Denitrification  Anammox  Michaelis–Menten  Kinetics  Oxic denitrification Introduction Humans have massively increased the rate at which fixed nitrogen (N) enters the marine environment V. Evrard (&)  P. L. M. Cook Water Studies Centre, School of Chemistry, Monash University, Wellington Road, Clayton, VIC 3800, Australia e-mail: victor.evrard@monash.edu R. N. Glud Institute of Biology and Nordic Center for Earth Evolution (NordCEE), University of Southern Denmark, Odense M, Denmark R. N. Glud Scottish Marine Institute, Scottish Association for Marine Science, Oban, Scotland R. N. Glud Greenland Climate Research Centre (CO Greenland Institute of National Resources), Nuuk, Greenland 123 Biogeochemistry (2013) 113:563–572 DOI 10.1007/s10533-012-9789-x