Shallow lakes under alternative states differ in the dominant greenhouse gas emission pathways

Abstract

Over the past decades, shallow lakes of the Pampean Plain, Argentina, have been shifting from clear vegetated to turbid phytoplanktonic states due to anthropic pressures. It is not clear, though, if this change in state also involves a change in the overall CO2 and CH4 balance of these lakes. Therefore, the main objective of this work was to assess potential differences in the C gas (CH4 and CO2) balance of shallow lakes under contrasting states—clear vegetated and turbid phytoplanktonic. We sampled two clear and two turbid shallow lakes in the Pampean region along an annual cycle and we measured all of the major C gas emission pathways: diffusive and ebullitive fluxes and also emissions from emergent vegetated habitats. CO2 and CH4 diffusive, ebullitive and vegetated habitat fluxes were comparable between states, but they differed in their relative contribution to the C gas balance because of differences in the coverage of the habitats associated to these pathways. Mean annual, area-weighted CO2 and CH4 fluxes of clear lakes were 41.9 ± 19.0 and 15.4 ± 18.5 mmol m−2 d−1, respectively, and 7.7 ± 7.3 and 17.9 ± 19.8 mmol m−2 d−1 for CO2 and CH4 fluxes, respectively, for turbid lakes. Despite major differences in the relative contribution of the emission pathways between states, there was a remarkable convergence between states in total greenhouse gas emissions when expressed in terms of mean annual CO2 equivalent greenhouse gas flux.