McCrackin,M.L. and Elser,J.J.(2012): Denitrification kinetics and denitrifier abundances in sediments of lakes receiving atmospheric nitrogen deposition (Colorado, USA). Biogeochemistry, 108, 39-54.

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wAbstract
@The transport and deposition of anthropogenic nitrogen (N) to downwind ecosystems is significant and can be a dominant source of new N to many watersheds. Bacterially mediated denitrification in lake sediments may ameliorate the effects of N loading by permanently removing such inputs. We measured denitrification in sediments collected from lakes in the Colorado Rocky Mountains (USA) receiving elevated (5-8 kg N ha-1 y-1) or low (ƒ2 kg N ha-1 y-1) inputs of atmospheric N deposition. The nitrate (NO3-) concentration was significantly greater in high-deposition lakes (11.3ƒΚmol l-1) compared to low-deposition lakes (3.3ƒΚmol l-1). Background denitrification was positively related to NO3- concentrations and we estimate that the sampled lakes are capable of removing a significant portion of N inputs via sediment denitrification. We also conducted a dose-response experiment to determine whether chronic N loading has altered sediment denitrification capacity. Under Michaelis-Menten kinetics, the maximum denitrification rate and half-saturation NO3- concentration did not differ between deposition regions and were 765 ƒΚmol N m-2 h-1 and 293ƒΚmol l-1 NO3-, respectively, for all lakes. We enumerated the abundances of nitrate- and nitrite-reducing bacteria and found no difference between high- and low-deposition lakes. The abundance of these bacteria was related to available light and bulk sediment resources. Our findings support a growing body of evidence that lakes play an important role in n removal and, furthermore, suggest that current levels of N deposition have not altered the abundance of denitrifying bacteria or saturated the capacity for sediment denitrification.

Keywords: Atmospheric nitrogen deposition; Denitrification; Lake; denitrifier abundance; Sedimentx

Introduction
Methods
@Study site
@Field sampling and laboratory procedures
@Statistical analysis
Results
@Water and bulk sediment characteristics
@Denitrification assays
@Most probable number of denitrifiers
Discussion
@Factors influencing denitrification rates
@Factors influencing denitrifier abundance
@Estimated N removal in high-elevation lakes
Acknowledgments
References


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