Greenhouse gas production in low-latitude lake sediments responds strongly to warming

Abstract

Inland water sediments receive large quantities of terrestrial organic matter [1][2][3][4][5] and are globally important sites for organic carbon preservation [5][6] . Sediment organic matter mineralization is positively related with temperature across a wide range of high-latitude ecosystems [6][7][8][9][10] , but the situation in the tropics remains unclear. Here we assessed temperature effects on the biological production of CO 2 and CH 4 in anaerobic sediments of tropical lakes in the Amazon and boreal lakes in Sweden. Based on conservative regional warming projections until 2100 11 , we estimate that sediment CO 2 and CH 4 production will increase 9-61 % above present rates. Combining the CO 2 and CH 4 as CO 2 equivalents (CO 2eq ) 11 , the predicted increase is 2.4 -4.5 times higher in tropical than boreal sediments. Although the estimated lake area in low latitudes is 3.2 times smaller than that of the boreal zone, we estimate that the increase in gas production from tropical lake sediments would be on an average 2.4 times higher for CO 2 and 2.8 times higher for CH 4 . The exponential temperature response of organic matter mineralization, coupled with higher increases in the proportion of CH 4 relative to CO 2 upon warming, suggests that the production of GHGs in tropical sediments will increase substantially. This represents a potential large-scale positive feedback to climate change. 2 Main textTropical and boreal biomes harbour approximately 50 % of the lakes on Earth 12 . These inland waters emit substantial amounts of carbon dioxide (CO 2 ; in the order of 0.5 Pg yr -1 ) 1,4,13,14 and methane (CH 4 ; 70 Tg yr -1 ) 15 . Organic matter escapes mineralization via burial in lake sediments, representing a global carbon (C) sink [13][14][15] . Cold conditions are favouring organic carbon (OC) preservation in lakes at northern latitudes [8][9][10]16 , whereas warm inland waters show intense organic degradation supporting high C emissions to the atmosphere 4,5,17,18 .Temperature and OC mineralization were recently shown to be strongly positively related in boreal lake sediments overlain by oxic water 9 . However, the majority of freshwater sediments below the uppermost layer (typically a few mm) are anoxic 19 , where the anaerobic biological degradation of OC releases not only CO 2 but also significant amounts of CH 4 15 . Although higher temperatures are also expected to increase metabolic responses 20 , the effects of changing temperatures on OC mineralization can depend on several factors including organic matter characteristics (e.g. the Carbon-QualityTemperature hypothesis) 21 . Thus, the temperature sensitivity of OC stocks at high latitudes previously reported [6][7][8]16 , may not be valid in the tropics where temperature sensitivity data is much more scarce 22 . We compared the anaerobic OC mineralization to CO 2 and CH 4 in tropical and boreal lake sediments along a temperature gradient. We simultaneously sampled a wide range of lake sediments from both tropical and boreal zones (see Suppl...

Effects of alternative electron acceptors on the activity and community structure of methane-producing and consuming microbes in the sediments of two shallow boreal lakes

“…In contrast to the potential CH 4 oxidation, the potential net CH 4 production rates (0.6-82.5 nmol g -1 DW d -1 ; 0.1-11.7 nmol cm -3 d -1 ) in the anaerobic incubations of the sediment slurries from the study lakes fell well within the range of reported CH 4 production rates in previous lake sediment studies: ~0-312 nmol g -1 DW d -1 (Schulz, Matsuyama and Conrad 1997;Marotta et al 2014;Karvinen, Lehtinen and Kankaala 2015) and ~1-23 nmol cm -3 d -1 (Sivan et al 2011;á Norði, Thamdrup and Schubert 2013). The potential net CH 4 production rates also well represent the magnitude and variation of the estimated potential gross CH 4 production rates, since anaerobic CH 4 oxidation was always a minor fraction of the potential net CH 4 production ( Table 2).…”

Freshwater methane and carbon dioxide fluxes : Spatio-temporal variability and an integrated assessment of lake and stream emissions in a catchment

“…Increased CH4 production in response to increased temperature has been shown in many laboratory studies (Duc et al, 2010;Segers, 1998;Zeikus & Winfrey, 1976) and some field studies Wik et al, 2014;Yvon-Durocher et al, 2014). The production of CO2 in sediments has also been shown to increase with temperature (Gudasz et al, 2010;Marotta et al, 2014). More than twofold differences in diel CH4 and CO2 have been demonstrated, highlighting the importance of including diel variability in flux measurements Natchimuthu et al, 2014;Podgrajsek et al, 2014).…”

Plant-mediated methane and nitrous oxide fluxes from a carex meadow in Poyang Lake during drawdown periods

“…However, most of these studies were concentrated in boreal or cold regions Juutinen et al 2003aJuutinen et al , 2003bChen et al 2009Chen et al , 2011. Although lake areas in low latitudes are much smaller than in high latitudes, the estimated sediment GHG productions from low latitude lakes were substantially higher than boreal lakes (Marotta et al 2014). Consequently, the knowledge of CH 4 and N 2 O emissions from various littoral wetlands, especially in largely unexplored tropical and subtropical lakes, will help reduce the uncertainty in global wetland CH 4 and N 2 O estimation.…”