New insights into diel to interannual variation in carbon dioxide emissions from lakes and reservoirs

Abstract

Accounting for temporal changes in carbon dioxide (CO 2 ) emissions from freshwaters remains a challenge for global and regional carbon budgets. Here, we synthesize 171 site-months of eddy covariance flux measurements of CO 2 from 13 lakes and reservoirs in the Northern Hemisphere (NH) and quantify the magnitude and dynamics at multiple temporal scales. We found pronounced diel and sub-monthly oscillatory variations in CO 2 flux at all sites. Diel variation converted sites to daily net sinks of CO 2 in only 11% of site-months. Upscaled annual emissions had an average of 25% (range 3-58%) interannual variation. Given temporal variation remains under-represented in inventories of CO 2 emissions from lakes and reservoirs, revisions in CO 2 flux are needed using a better representation of sub-daily to interannual variability. Constraining short-and long-term variability is necessary to improve detection of temporal changes of CO 2 fluxes in response to natural and anthropogenic drivers.

Eddy covariance data reveal that a small freshwater reservoir emits a substantial amount of carbon dioxide and methane

“…Eddy covariance (EC) systems are increasingly being deployed on lakes and reservoirs to constrain sub-daily GHG fluxes over large spatial footprints, enabling the quantification of whole-ecosystem GHG fluxes at multiple temporal scales (e.g., A.K. Baldocchi et al 2020;Golub et al 2021;Eugster et al 2011;Vesala et al 2011;Waldo et al 2021). EC systems are used to determine the net exchange of carbon dioxide (CO2), methane (CH4), and/or other gases at sub-hourly time scales via micrometeorology and in situ atmospheric trace gas concentrations measured using infrared gas analyzers (A.K.…”

“…EC systems are used to determine the net exchange of carbon dioxide (CO2), methane (CH4), and/or other gases at sub-hourly time scales via micrometeorology and in situ atmospheric trace gas concentrations measured using infrared gas analyzers (A.K. Baldocchi et al 2020;Golub et al 2021;Vesala et al 2011). By collecting near-continuous, high frequency data (typically measured at 10-20 Hz and reported as 30-minute means), EC systems allow GHG fluxes to be estimated at sub-daily to annual timescales, improving our understanding of GHG flux temporal variability beyond traditional discrete measurements (Golub et al 2021;Reed et al 2018;Vesala et al 2011).…”

“…Baldocchi et al 2020;Golub et al 2021;Vesala et al 2011). By collecting near-continuous, high frequency data (typically measured at 10-20 Hz and reported as 30-minute means), EC systems allow GHG fluxes to be estimated at sub-daily to annual timescales, improving our understanding of GHG flux temporal variability beyond traditional discrete measurements (Golub et al 2021;Reed et al 2018;Vesala et al 2011).…”

“…Additionally, EC systems often capture a larger spatial footprint compared to traditional discrete measurements, as measured fluxes represent the average flux from the atmospherically-mixed area upwind of the deployed EC system (Golub et al 2021, Waldo et al 2021. Thus, EC systems can greatly increase the temporal resolution and spatial extent of measured fluxes in lakes and reservoirs, with the caveat that important considerations and data filtering are needed for EC systems in small waterbodies (Scholz et al 2021).…”

“…While the majority of reported freshwater EC studies have been conducted on short timescales (days to months; e.g., Erkkiliä et al 2018;Gorsky et al 2021;Jammet et al 2015;Podgrajsek et al 2014Podgrajsek et al , 2015Vesala et al 2006Vesala et al , 2011, longer-term studies measuring CO2 or CH4 fluxes in lakes and reservoirs on annual timescales are becoming more common (e.g., A.K. Baldocchi et al 2020;Golub et al 2021;Huotari et al 2011;Jammet et al 2017;Liu et al 2016;Reed et al 2018;Shao et al 2015;Scholz et al 2021;Taoka et al 2020;Waldo et al 2021). An annual study conducted in Lake Erie, USA found this highly-eutrophic system was a small sink of CO2 during the summer productive season yet ultimately a CO2 source on annual timescales (Shao et al 2015).…”