Quantifying gas ebullition with echosounder: the role of methane transport by bubbles in a medium‐sized lake

Full seasonal sets of chemical and isotope profiles from the pore water of Lake Kinneret (Sea of Galilee, Israel) were produced to study methanogenesis and methanotrophy processes and the couplings between methane (CH 4 ), sulfur, and iron. Sulfate is depleted within the upper 10 cm of the sediment mainly by traditional bacterial sulfate reduction by organic matter. Maximum sulfate reduction rates calculated from sulfate concentration profiles are found at the water-sediment interface (0-1 cm 2 1.4 3 10 212 6 0.2 3 10 212 mol cm 23 s 21 ). CH 4 concentrations and modeling of dissolved inorganic carbon (DIC) and its stable carbon isotope (d 13 C DIC ) suggest that maximum methanogenesis rates of 2.5 3 10 213 6 1.5 3 10 213 mol cm 23 s 21 occur at 5-12-cm depth in the sediments, and that it ends at 20 cm. Of the produced CH 4 , 50-75% is converted to gas bubbles of CH 4 before it reaches the bottom water. Model results suggest the occurrence of anaerobic oxidation of CH 4 (AOM) in the deep sediments of the lake below the zone of methanogenesis.

Section: Discussionsupporting

confidence: 46%

Quantifying rates of methanogenesis and methanotrophy in Lake Kinneret sediments (Israel) using pore‐water profiles

Adler

Eckert

Sivan

2011

“…Modeling of methane ebullition-We simulated methane ebullition using bubbles of 4 mm and 6 mm diameters, typical sizes found in natural aquatic environments (Ostrovsky et al 2008;Maeck et al 2013). Bubbles were released from 20 m, 40 m, and 70 m (Fig.…”

Section: Resultsmentioning

confidence: 99%

Paradox reconsidered: Methane oversaturation in well‐oxygenated lake waters

Tang

Mcginnis

Frindte

et al. 2014

123

144

The widely reported paradox of methane oversaturation in oxygenated water challenges the prevailing paradigm that microbial methanogenesis only occurs under anoxic conditions. Using a combination of field sampling, incubation experiments, and modeling, we show that the recurring mid-water methane peak in Lake Stechlin, northeast Germany, was not dependent on methane input from the littoral zone or bottom sediment or on the presence of known micro-anoxic zones. The methane peak repeatedly overlapped with oxygen oversaturation in the seasonal thermocline. Incubation experiments and isotope analysis indicated active methane production, which was likely linked to photosynthesis and/or nitrogen fixation within the oxygenated water, whereas lessening of methane oxidation by light allowed accumulation of methane in the oxygen-rich upper layer. Estimated methane efflux from the surface water was up to 5 mmol m 22 d 21 . Mid-water methane oversaturation was also observed in nine other lakes that collectively showed a strongly negative gradient of methane concentration within 0-20% dissolved oxygen (DO) in the bottom water, and a positive gradient within $ 20% DO in the upper water column. Further investigation into the responsible organisms and biochemical pathways will help improve our understanding of the global methane cycle.

“…This is mainly due to the relative paucity of data compiled for methane (,100 lakes) compared to that compiled for CO 2 (.5000 lakes), but this variation is also connected to methodological limitations in the measurement of CH 4 ebullition as well as plantmediated emissions from littoral vegetation. More field data and the emerging use of hydroacoustics to measure ebullition (Ostrovsky et al 2008) will help to better constrain global estimates of CH 4 emission from lakes.…”

Section: Current Role Of Lakes In the Global C Cyclementioning

confidence: 99%

Lakes and reservoirs as regulators of carbon cycling and climate

Tranvik

Downing

Cotner

et al. 2009

2,240

1,756

We explore the role of lakes in carbon cycling and global climate, examine the mechanisms influencing carbon pools and transformations in lakes, and discuss how the metabolism of carbon in the inland waters is likely to change in response to climate. Furthermore, we project changes as global climate change in the abundance and spatial distribution of lakes in the biosphere, and we revise the estimate for the global extent of carbon transformation in inland waters. This synthesis demonstrates that the global annual emissions of carbon dioxide from inland waters to the atmosphere are similar in magnitude to the carbon dioxide uptake by the oceans and that the global burial of organic carbon in inland water sediments exceeds organic carbon sequestration on the ocean floor. The role of inland waters in global carbon cycling and climate forcing may be changed by human activities, including construction of impoundments, which accumulate large amounts of carbon in sediments and emit large amounts of methane to the atmosphere. Methane emissions are also expected from lakes on melting permafrost. The synthesis presented here indicates that (1) inland waters constitute a significant component of the global carbon cycle, (2) their contribution to this cycle has significantly changed as a result of human activities, and (3) they will continue to change in response to future climate change causing decreased as well as increased abundance of lakes as well as increases in the number of aquatic impoundments.