Abstract Small artificial waterbodies such as farm dams are recognized as important sources of anthropogenic emissions. Carbon dioxide (CO 2 ) fluxes from farm dams are highly variable across spatial scales, with sites acting as sources or sinks based on single daytime measurements. However, diel variations are an overlooked source of temporal variability in CO 2, complicating upscaling efforts. To provide a more accurate estimate of the CO 2 source‐sink status of farm dams, four irrigation dams were monitored for dissolved CO 2 at half‐hourly intervals over a five‐month period in 2021–2022. Carbon dioxide concentrations were undersaturated between 12% and 37% of the measurements, indicating a dominance of CO 2 production over consumption when considering diel cycles and seasonal patterns. Carbon dioxide was consistently lower during daytime and early night periods compared with late‐night and exhibited large diel shifts up to 57–99 μM. Diel CO 2 amplitude was driven primarily by metabolic controls, as revealed by strong correlations with dissolved oxygen and temperature, except for one irrigation dam which indicated CO 2 variation was driven by external inputs. Spatial variability based on previously acquired data (inter‐dam coefficient of variation (CV) 105%) was higher than diel (CV 34%–54%) and seasonal (CV 13%–29%) variability. However, if only daytime CO 2 measurements are considered, total CO 2 emissions over the study period would be underestimated by between 11% and 148%, demonstrating the consequence of not including diel variation. Future refinements of upscaled farm dam CO 2 emission estimates will require more geographically dispersed studies that feature diel measurements to constrain uncertainty in these highly variable systems.
Webb et al. (Sun,) studied this question.