Anthropogenic nitrogen (N) inputs have been found to influence emissions of greenhouse gases from a variety of ecosystems, however, the effects of N loading on greenhouse gas dynamics in lakes are not well documented. We measured concentrations of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) in 26 alpine and subalpine lakes in the Colorado Rocky Mountains (USA) receiving elevated (>6 kg N ha^-1 yr^-1) or low (<2 kg N ha^-1 y^-1) rates of atmospheric N deposition.

Results/Conclusions

Mean concentrations of CO₂ were 26.9 μmol L^-1 and did not differ between N deposition regions. The concentration of CH₄ was greater in low deposition lakes (167 nmol L^-1) compared to high deposition lakes (48 nmol L^-1), while the opposite was true for N2O. The concentration of N2O averaged 29 nmol L^-1 in high deposition lakes compared to 22 nmol L^-1 in low deposition lakes and was positively correlated with water concentrations of nitrate. Our data suggest that, regardless of N inputs, CO₂ is the dominant greenhouse gas in the sampled lakes. Nitrous oxide is of particular interest, however, because it is nearly 300 times more potent than CO₂ as a greenhouse gas and because of its role in the destruction of stratospheric ozone. To understand the potential magnitude of lake N₂O production related to atmospheric N deposition, the greenhouse gas inventory methodology of Intergovernmental Panel on Climate Change was applied to available datasets. We estimate global N₂O emissions from lakes resulting from atmospheric deposition to be 7 – 371 Gg N y^-1 for 1993, increasing to 11 – 705 Gg N y^-1 in 2050. The 1993 estimates represent 0.5 – 25% of emissions from rivers and estuaries, suggesting that further research is required to better quantify emission rates from lentic ecosystems.