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 (2
kg N ha-1 y-1) inputs of atmospheric N deposition.
The nitrate (NO3-) concentration
was significantly greater in high-deposition lakes (11.3Κmol l-1)
compared to low-deposition lakes (3.3Κmol 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 Κmol N
m-2 h-1 and 293Κmol 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; Sedimentx
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