科研之友
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摘要
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 (11.3 mu mol l(-1)) compared to low-deposition lakes (3.3 mu mol 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 mu mol N m(-2) h(-1) and 293 mu mol 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.
- 出版日期2012-4
