Assessment of methane and carbon dioxide emissions in two sub‐basins of a small acidic bog lake artificially divided 30 years ago

Abstract

Although lakes are important sources of methane (CH4) and carbon dioxide (CO2) to the atmosphere contributing to global warming, their CH4 and CO2 emissions are rarely assessed. In particular, increasing inputs of terrestrial dissolved organic carbon (DOC) may affect gas dynamics and alter seasonal changes in gas production. Here, we analysed variations in CH4 and CO2 dynamics in sub‐basins of an acidic bog lake, which was artificially divided into four quarters three decades ago, leading to divergence in water chemistry and biology. In the divided lake, only the south‐west basin (SW) received DOC inputs from an adjacent peat bog, while the north‐east basin (NE) was hydrologically disconnected. A year‐long determination of CH4 and CO2 production and emission patterns in the two contrasting basins exposed the indirect mechanisms by which DOC supply exercised control on greenhouse gas dynamics in this shallow lake. In both basins, dissolved CH4 was negatively correlated with dissolved oxygen (O2) through the water column, suggesting that aerobic methanotrophy is an important regulator of CH4 emissions in this lake. In contrast, the amount of CO2 stored in oxic and anoxic layers was not significantly different between the basins, suggesting that O2 is not the most important driver of dissolved CO2. Estimated total CH4 and CO2 emissions were 2.1 and 1.7 times lower in the NE basin than in the SW basin, with major CH4 and CO2 emissions occurring during the fall turnover. The differences in CH4 and CO2 emissions suggest that the hydro‐physical properties, namely seasonal temperature, the duration of stratification and O2 availability, are the main drivers of CH4 and CO2 emissions to the atmosphere from small shallow lakes under the influence of DOC inputs under global warming pressure.

Methane emissions from contrasting urban freshwaters: Rates, drivers, and a whole‐city footprint

“…Ebullition events were recognized by sudden steep concentration increases, which were occasionally followed by a decline. Only concentration increases with an r 2 > .7 were taken into account to compute diffusive fluxes (Martinez‐Cruz et al, ; Sepulveda‐Jauregui, Martinez‐Cruz, Lau, & Casper, ). Ebullition flux was calculated as the difference between the total and diffusive flux.…”

Sub-oxycline methane oxidation can fully uptake CH4 produced in sediments: case study of a lake in Siberia

“…However, despite segregation between the epilimnion and the hypolimnion, bubbles formed in the sediments might transfer CH 4 to the epilimnion during their migration to the surface of the lake. Nevertheless, at each sampling and monitoring station, CH 4 and CO 2 fluxes were determined in triplicate with a dynamic closed chamber coupled to a greenhouse gas analyzer (UGGA 30 P, Los Gatos Research, CA, USA; data acquisition frequency of 1 s −1 and CH 4 sensitivity of 30 ppb) 17 . During a total of 54 flux measurements over a total time of 4.5 h, no evidence of bubbling was found; i.e., peak increase of CH 4 concentration within the chamber 17 .…”

“…Nevertheless, at each sampling and monitoring station, CH 4 and CO 2 fluxes were determined in triplicate with a dynamic closed chamber coupled to a greenhouse gas analyzer (UGGA 30 P, Los Gatos Research, CA, USA; data acquisition frequency of 1 s −1 and CH 4 sensitivity of 30 ppb) 17 . During a total of 54 flux measurements over a total time of 4.5 h, no evidence of bubbling was found; i.e., peak increase of CH 4 concentration within the chamber 17 . Bubbles were only occasionally visually observed in the littoral region at the western section of the lake.…”

“…From the bottom to the surface, the profile showed a sharp decrease of the CH 4 concentration below the detection limit of our method (5 nmol L −1 ) in the benthic zone of the water column, well below the oxycline and the photic zone, and showed an increase in CH 4 concentration in the aerobic epilimnion. This profile was created using a high resolution, high sensitivity method 16,17 which allowed the net methane production and oxidation rates to be determined using a diffusion-reaction model, showing a short distance transition between both processes in the hypolimnion. This CH 4 concentration profile was correlated to methanotroph and methanogenic archaea abundances determined by pmoA and mcrA gene qPCR, respectively.…”

Long-Read Amplicon Sequencing of Nitric Oxide Dismutase (nod) Genes Reveal Diverse Oxygenic Denitrifiers in Agricultural Soils and Lake Sediments

“…To demonstrate the wide applicability of this approach, several sediment samples from lakes with different trophic status were also queried ( Table 1). Soil from the top layer (0-10 cm) of several agricultural fields with and without long-term fertilizations in Ning-Xiang, China [13], and sediments from a meso-oligotrophic, an eutrophic and a dystrophic lake in Germany [11,12,14], were sampled ( Table 1). The abundance of nod genes and bacterial 16S rRNA was quantified by qPCR, representing respective measure of putative oxygenic denitrifiers and total bacteria in these samples.…”