In the boreal lakes the CO 2:O 2 ratio was mainly related to DOC concentration, in contrast to the sub-Arctic and high-Arctic localities, where conductivity was the major statistical determinant. Regardless of location, the majority of the lakes were CO 2 supersaturated. The boreal lakes were generally undersaturated with O 2, while the sub-Arctic and high-Arctic lakes ranged from O 2 saturated to oversaturated. Across all regions, CO 2 saturation levels varied more (6–1374%) than O 2 saturation levels (85–148%) and hence CO 2 saturation governed the CO 2:O 2 ratio. We assessed water chemistry and concentrations of dissolved O 2 and CO 2, as well as the CO 2:O 2 ratio in three groups of lakes separated by steps of approximately 10 degrees latitude in South-Eastern Norway (near 60° N), sub-Arctic lakes in the northernmost part of the Norwegian mainland (near 70° N) and high-Arctic lakes on Svalbard (near 80° N). Our aim here is to provide a better understanding of net heterotrophy and gas balance at the catchment scale in a set of boreal, sub-Arctic and high-Arctic lakes. However, the differences in environmental drivers of CO 2 concentrations are not well constrained along latitudinal and thus climate gradients. Lakes are significant players for the global climate since they sequester terrestrially derived dissolved organic carbon (DOC), and emit greenhouse gases like CO 2 to the atmosphere.
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