Acetylene inhibition technique

Sprensen, J. (1978) Denitrification rates in a marine sediment measured by the acetylene inhibition technique. Appl. Environ. Microbiol. 36 139-143. 

Loshe, L. H., Kloosterhuis, H. T., van Raaphorst, W., and Helter, W. (1996). Denitrification rates as measured by the isotope paring method and by acetylene inhibition technique in continental shelf sediments of the North Sea. Mar. Ecol. Prog. Ser. 132, 169—179. 

MEVIS/IPM, membrane inlet mass spectrometry/isotope pairing method TCD, gas chromatography-thermal conductivity detector AIT, acetylene inhibition technique IPM, isotope pairing method with isotope ratio mass spectrometry MIMS, membrane inlet mass spectrometry Stoichiometery, benthic flux DICiDIN stoichiometry MIMS + N03, membrane inlet mass with N03 amendment 15N2 production, 15N03 or 15NH4 conversion to 15N2. 

In the acetylene inhibition technique, acetylene is added to a water sample, which inhibits the reduction of N2O to N2 (Sorensen, 1978). The accumulation of N2O is then measured using gas chromatography and an electron capture detector and the denitrification rate is taken to be equal to the total N2O flux. One potential problem is incomplete inhibition of N2O reduction to N2, particularly in the presence of hydrogen sulfide, a compound commonly found under anaerobic conditions. Another potential problem with the technique is that acetylene also inhibits nitrification, a process that often supplies the NOs and N02 substrates for denitrification. To inhibit nitrification is to inhibit denitrification if it is at aU substrate limited (Hynes and Knowles, 1978). 

A wide range of techniques are used to determine catabolic nitrate reduction rates. These include mass balance methods using input-outputs, acetylene inhibition techniques, dinitrogen production rates, nitrate consumption rates, nitrate pore water profiles, and stable isotope tracer techniques. The limitations and advantages of these methods are discussed by Seitzinger (1988) and Herbert (1999). 

Hutchins, S. R. (1992). Inhibition of alkylbenzene biodegradation under denitrifying conditions by using the acetylene block technique. Applied and Environmental Microbiology, 58(10), 3395-8. 

Denitrification is the reduction of N03 N02 NO N2O —> N2 gas that is mediated by bacteria under anaerobic conditions, most generally in microbial mats and sediments. There are a number of methods to measure denitrification acetylene inhibition, isotope pairing, changes in N2 fluxes, and changes in the N2 to argon (Ar) ratio. Each of the techniques has their pros and cons and none is clearly superior under all conditions (see reviews by Cornwell et al, 1999 Chapter 6 by Devol, this volume). 

The most important methods of measuring denitrification are (1) the detection of totally produced gas by incubation, (2) isotope-labeling methods with and N, and (3) the acetylene (C Hj) inhibition technique. 

At last, the inhibition technique takes advantage of the property of acetylene to block the reduction of N O to N after it is injected into the sediment. The total amount of N O produced is then the measure for the denitrification rate as it is easy to determine by gas chromatography (Andersen et al. 1984) or by microsensors (Christensen et al. 1989). The advantage of this method is that analyses can be carried out rapidly and sensitively. Problems are (a) N O reduction is sometimes incomplete, (b) a homogenous distribution of in the pore water is difficult to maintain, (c) inhibits nitrification in the sediment meaning that the coupled system (nitrification / denitrification) might be seriously affected due to the applied method, and... 

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