Diel Variability of CO₂ Emissions From Northern Lakes

Abstract

This is of the same order of magnitude as the CO 2 emissions from land use change, or the carbon transport from continents to the ocean (Ciais et al., 2013), making CO 2 emissions from lakes important in the global carbon cycle. Lakes are concentrated in boreal regions, which contain roughly 30% of global lakes (Downing et al., 2006;Verpoorter et al., 2014), and together with the arctic region contribute 17% of global lake CO 2 emissions (Aufdenkampe et al., 2011). Potential climate change effects in boreal lakes, including increased runoff (Larsen et al., 2011;Weyhenmeyer et al., 2015) and increased carbon mineralization rates (Bergström Abstract Lakes are generally supersaturated in carbon dioxide (CO 2 ) and emitters of CO 2 to the atmosphere. However, estimates of CO 2 flux ( CO 2 E F ) from lakes are seldom based on direct flux measurements and usually do not account for nighttime emissions, yielding risk of biased assessments.Here, we present direct CO 2 E F measurements from automated floating chambers collected every 2-3 hr and spanning 115 24 hr periods in three boreal lakes during summer stratification and before and after autumn mixing in the most eutrophic lake of these. We observed 40%-67% higher mean CO 2 E F in daytime during periods of surface water CO 2 supersaturation in all lakes. Day-night differences in wind speed were correlated with the day-night CO 2 E F differences in the two larger lakes, but in the smallest and most wind-sheltered lake peaks of CO 2 E F coincided with low-winds at night. During stratification in the eutrophic lake, CO 2 was near equilibrium and diel variability of CO 2 E F insignificant, but after autumn mixing CO 2 E F was high with distinct diel variability making this lake a net CO 2 source on an annual basis.We found that extrapolating daytime measurements to 24 hr periods overestimated CO 2 E F by up to 30%, whereas extrapolating measurements from the stratified period to annual rates in the eutrophic lake underestimated CO 2 E F by 86%. This shows the importance of accounting for diel and seasonal variability in lake CO 2 emission estimates.Plain Language Summary Considerable carbon cycling occurs within lakes, and carbon inputs from the catchment can be processed internally, stored in sediment and biomass or transported downstream. Additionally, carbon is exchanged with the atmosphere, resulting in lake uptake or atmospheric emission of carbon dioxide. Carbon dioxide exchanges from lakes have globally significant implications, but may be highly variable in time in ways that are not yet accounted for in emission estimates. Here, we estimated carbon dioxide exchange during multiple days and nights in three lakes with different nutrient levels during summer and autumn. For the most nutrient rich lake we also covered the period of water column mixing in autumn, which constitutes a critical time for carbon exchange. When carbon dioxide emission exceeded uptake, we found 40%-67% higher average exchange rates during daytime than nighttime. In contrast, the most nutrient...

Differential Controls of Greenhouse Gas (CO2, CH4, and N2O) Concentrations in Natural and Constructed Agricultural Waterbodies on the Northern Great Plains

“…For example, CH 4 can exhibit midday maxima in concentration (Kim et al., 2015; Xing et al., 2004), while CO 2 levels often peak at night (Raymond et al., 2013; Wiik et al., 2018), and N 2 O has been observed to increase (Rosamond et al., 2011; Wu et al., 2018), decrease (Molina et al., 2021), and exhibit no change overnight (Baulch et al., 2012). These patterns are further complicated by potential diel variability in wind speed overnight (MacIntyre et al., 2021; Rudberg et al., 2021). Here, we chose to calculate CO 2 ‐eq flux using observed daytime values and extrapolating over the full 24‐hr period, because an earlier investigation of these regional ponds did not reveal any evidence of consistent diel variability of GHG fluxes (Jensen et al., 2022).…”

Greenhouse gas emissions hotspots and drivers of urban freshwater bodies in areas of the Yangtze River delta, China

“…As previous reported the GHG emissions from freshwater bodies may have strong variation over a day (Rudberg et al, 2021; Sieczko et al, 2020), thus a selected sampling site was employed for a 24‐h observations for GHG fluxes. Figure 4 shows a clear pattern that the variation of CH 4 emissions were consistent with temperature changes over 24‐h observations.…”

Carbon dioxide reduction by photosynthesis undetectable even during phytoplankton blooms in two lakes

“…It is possible that wind suppresses the phytoplankton signal on lake pCO 2 , because CO 2 at the lake surface, where phytoplankton are photosynthesizing and, thus, consuming CO 2 , is mixed with CO 2 from waters from below. Wind exposure may also explain why lake pCO 2 does not increase in autumn after mixing starts in this lake, even though this is typically observed in eutrophic lakes when deep-water, CO 2 water mixes with surface oxygen-rich water [30].…”

“…During migration, it easy to underestimate G. semen densities by sampling too early or too late during the day. It is also known that the carbon ux has high diel and seasonal variability [30,34], with diel variations being especially pronounced during mixing events [30]. Thus, it is likely that the pCO 2 measurements at the surface of the lakes caused an under-or overestimation of pCO 2 for our sampling dates due to the time of sampling.…”