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.