Dynamics of dissolved methane and methane oxidation in dimictic Lake Nojiri during winter

Abstract

Changes in the vertical distribution of dissolved CH, were monitored during the autumnal lake overturn period in mesotrophic Lake Nojiri, Japan (4.4 km* in area and 9.4 X 10' m3 in vol). A survey in 1992 revealed that the surface CH, concentration was highest in December, when the lake overturned. During the following two winters (1993-1994 and 1994-1995) we carried out detailed sampling during the autumnal overturn period. As a result of lake overturn in mid-December, CH, that had accumulated in the hypolimnion during the stratification period mixed rapidly throughout the water column. Increased CH, in the epilimnion quickly disappeared after the overturn as a result of the rising of CH, oxidation activity throughout the water column. The in situ-specific CH, oxidation rate peaked at 0.274, 0.235, and 1.01 d-' at 0.5, 20, and 36 m, respectively, during the overturn, and then declined the following month. During this period, the diffusive flux of methane across the air-water interface increased but was not the dominant sink (avg rate of 4.5 kg lake-' d-l); instead, methane oxidation in the water column was the dominant CH, sink (avg rate of 67.8 kg lake-' d-l), removing -94% of the CH, during the overturn period. A significant methane flux from the bottom sediments throughout the overturn period was confirmed but decreased gradually as the overturn proceeded. The production of organic carbon as a result of CH, oxidation in the water column by methanotrophs was comparable in extent to that generated by primary production at that time.

Abundance, Activity, and Community Structure of Pelagic Methane-Oxidizing Bacteria in Temperate Lakes

“…Some other studies have also reported methane oxidation in lake water or sediments in the absence of O 2 , or at least at very low concentrations (1,35,42,54,62). Anaerobic oxidation of methane coupled to reduction of sulfate is well-known from various marine sediments (6,19,55) and saline lakes (29,31).…”

“…Aerobic methane-oxidizing bacteria (MOB) in the water columns of lakes consume a significant part of the methane produced in the sediment or in anaerobic layers of water (46,54). Besides metabolizing methane that would otherwise be emitted to the atmosphere, they represent a route for reentry of carbon back into the food-webs (2,26,30,46).…”

“…It can proceed both under aerobic and anaerobic conditions, but the latter seems to be extensive primarily in waters with high ionic strength, e.g., saline lakes and marine systems (29,31,55). Many strains capable of aerobic methane oxidation have been isolated and characterized, and phylogenetically all belong to either the ␥-proteobacteria (commonly referred to as "type I" methanotrophs) or the ␣-proteobacteria ("type II" methanotrophs) (10,12,24).Aerobic methane-oxidizing bacteria (MOB) in the water columns of lakes consume a significant part of the methane produced in the sediment or in anaerobic layers of water (46,54). Besides metabolizing methane that would otherwise be emitted to the atmosphere, they represent a route for reentry of carbon back into the food-webs (2,26,30,46).…”

Where Carbon Goes When Water Flows: Carbon Cycling across the Aquatic Continuum

“…For example, lakes emit roughly 8-48 Tg CH 4 year −1 , which is 6-16% of natural methane emissions and exceeds methane emissions from the ocean (Bastviken et al, 2004(Bastviken et al, , 2011Kirschke et al, 2013). In freshwater environments it has been estimated that anaerobic carbon mineralization contributes to 20-60% of total carbon mineralization rates (Boon and Mitchell, 1995;Hamilton et al, 1995;Utsumi et al, 1998), with methanogenesis making up 30-80% of this anaerobic activity (Kuivila et al, 1988;Bédard and Knowles, 1991). As such, it has been estimated that 20-59% of the OM delivered to sediments via suspended particles is converted to methane (Wetzel, 2001 and references therein).…”

Mangrove Methane Biogeochemistry in the Indian Sundarbans: A Proposed Budget

“…In fact, for stratified lakes, methanotrophs can consume up to 90% of the dissolved CH 4 (Utsumi et al, 1998;Kankaala et al, 2006). However, in well-mixed estuaries, the activity of methanotrophs has been shown to be significantly less, allowing for the possible escape of CH 4 to the atmospshere (Abril et al, 2007).…”