『Abstract
Nitrate and sulfate are two major terminal electron acceptors
of anaerobic respiration in nearshore sediments. Potential nitrate
and sulfate reduction rates (NRR and SRR) were determined on surficial
sediments sampled at 14 sites representing a wide range of shallow-water
depositional environments. The rates were obtained by supplying
undisturbed slices of sediments with nitrate, sulfate or both
using a flow-through reactor technique. No external electron donor
was added to the sediments. The results indicate that all studied
sediments harbored viable and coexisting nitrate- and sulfate-reducing
communities, which were able to instantaneously consume the electron
acceptors supplied to the reactors. On average, NRR exceeded SRR
by about one order of magnitude (309±180 nmol NO3-
cm-3 h-1 versus 37±29 nmol SO42-
cm-3 h-1). The NRR:SRR molar ratio, however,
varied significantly from site to site, with values ranging from
1.7 to 59. Nitrate production, indicative of incomplete nitrate
reduction, was observed in all studied sediments and, on average,
accounted for 45% of NRR (range 3-80%). Production of sulfate
under nitrate-reducing conditions was observed in 10 out of 14
of the studied sediments, suggesting a common occurrence of sulfide
oxidation coupled to nitrate reduction. Oxidation of sulfide accounted
for 0 to 40% of NRR in the nitrate-only experiments. When both
electron acceptors were supplied simultaneously, net sulfate consumption
decreased on a average by 45%. The effect of nitrate on SRR was
highly variable, however, ranging from near complete inhibition
to a 25% enhancement of SRR. Overall, the results of this study
point to the need to critically reassess the model formulations
used to represent anaerobic respiration processes and their interactions
in early diagenetic models.』
1. Introduction
2. Materials and methods
2.1. Study sites
2.2. Flow through reactor (FTR) experiments
2.3. Reaction rate calculations
2.4. Analytical and statistical methods
3. Results
3.1. Site and sediment characteristics
3.2. Rates
3.2.1. Nitrate reduction rates (NRR) and nitrate production
rates (NiPR)
3.2.2. Sulfate reduction rates (SRR)
3.2.3. Ammonium production rates (APR)
3.2.4. Sulfate production rates (SPR)
3.3. Comparison of NRR and SRR
4. Discussion
4.1. Coexisting nitrate and sulfate reducers
4.2. Potential rates of nitrate and sulfate reduction
4.3. Incomplete denitrification and sulfide oxidation
4.4. Ammonium production
4.5. Nitrate reduction pathways
4.6. NRR:SRR: comparison with previous studies
4.7. Is sulfate reduction inhibited by nitrate?
5. Conclusions
Acknowledgements
References