Due to increasing nitrogen concentrations in surface waters (6) and eutrophication of coastal waters (14,26,51), the quantification of denitrification rates in sediments of lakes, rivers, and estuaries has gained importance. Different methods for measuring denitrification have been developed: the acetylene inhibition technique (41), measurement of nitrate disappearance (2), calculation of nitrate fluxes into the sediment from pore water profiles (20), the 15 N nitrate dilution method (16), direct measurement of N 2 production (40), the nitrogen massbalance approach (1), and the 15 N isotope pairing technique (IPT) (23). All of these methods have advantages but also potential problems and limitations (38,39).The acetylene inhibition technique is a very simple method. It is widely used, and its sensitivity has been improved by N 2 measurements based on N 2 /Ar ratios. However, many different studies have documented that the acetylene method systematically underestimates denitrification (20). Several causes may be responsible for artifacts: (i) inhibition of coupled nitrification-denitrification by acetylene (19), (ii) incomplete blockage of N 2 O reductase at low nitrate concentrations (3), (iii) incomplete blockage of N 2 O reductase when sulfide is present (3), (iv) diffusion of N 2 O toward deeper sediment layers and reduction to N 2 (39), and (v) catalytic oxidation of NO into NO 2 (4). The disappearance of nitrate can overestimate denitrification because nitrate may not only be denitrified but also reduced to ammonia (16,20) or assimilated (36). On the other hand, it may also underestimate denitrification because it does not consider coupled nitrification-denitrification. The calculation of nitrate fluxes into the sediment from pore water profiles has the same problems as described for the nitrate disappearance method. In addition, the resulting fluxes across the sediment-water interface and the diffusive boundary layer often underestimate denitrification, because of insufficient vertical resolution of the profiles and because only diffusive and not turbulent transport is considered when the fluxes are calculated (11, 21). The 15 N nitrate dilution method with subsequent measurement of 15 N nitrate disappearance and 15 N ammonia production quantifies denitrification and nitrification but still neglects coupled nitrification-denitrification and assimilation. Direct measurement of N 2 production has the advantage to include coupled nitrification-denitrification but requires a very sensitive analysis because of the small N 2 production compared to the N 2 background. The mass-balance approach on larger systems such as whole lakes may lead to considerable errors due to a combination of the errors of each term in the mass-balance.The 15 N IPT has the advantage that denitrification of both NO 3 Ϫ diffusing from the overlaying water and NO 3 Ϫ from nitrification within the sediment can be quantified.The purpose of this study is to briefly describe the principles of the 15 N IPT, to review the different applications ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.