Overall spatiotemporal dynamics of greenhouse gasses and oxygen in two subtropical reservoirs with contrasting trophic states

•Two subtropical reservoirs with contrasting trophic states were characterized.•Methane, oxygen, and carbon dioxide were measured with high resolution methods.•Several parameters related to carbon cycling were determined over three seasons.•These parameters were regrouped in a single graphical representation.•Eutrophication caused a complete redistribution of the major bioprocesses involved. The impact of cultural eutrophication on carbon cycling in subtropical reservoirs was assessed using high-resolution measurements of dissolved gas concentration, atmospheric exchange, and uptake/production rates of methane, carbon dioxide, and oxygen. Seasonal measurements were performed in two reservoirs that pertain to the same hydrological basin but are drastically different in terms of allochthonous carbon input. These results were used to feed a mass balance model, from which a large number of overall parameters were determined to explicitly describe the dynamics and spatial attributes of the carbon cycle in the reservoirs. A single graphical representation of each reservoir was created to facilitate an overall appraisal of the carbon cycle. The impact of cultural eutrophication was profound and resulted in a complete redistribution of how the various bioprocesses participated in the methane, carbon dioxide, and oxygen cycles. Among several identified impacts of eutrophication, it was observed that while eutrophication triggered increased methane production, this effect was followed by a similar increase in methane emissions and methanotrophic rates, while gross primary production was depleted. [Display omitted]