Salinity Influence on Methane Emissions from Tidal Marshes

Abstract

The relationship between methane emissions and salinity is not well understood in tidal marshes, leading to uncertainty about the net effect of marsh conservation and restoration on greenhouse gas balance. We used published and unpublished field data to investigate the relationships between tidal marsh methane emissions, salinity, and porewater concentrations of methane and sulfate, then used these relationships to consider the balance between methane emissions and soil carbon sequestration. Polyhaline tidal marshes (salinity >18) had significantly lower methane emissions (mean ± sd=1±2 gm −2 yr −1) than other marshes, and can be expected to decrease radiative forcing when created or restored. There was no significant difference in methane emissions from fresh (salinity=0-0.5) and mesohaline (5-18) marshes (42±76 and 16±11 gm −2 yr −1, respectively), while oligohaline (0.5-5) marshes had the highest and most variable methane emissions (150±221 gm −2 yr −1). Annual methane emissions were modeled using a linear fit of salinity against log-transformed methane flux ( logðCH 4 Þ ¼ À0:056 Â salinity þ 1:38; r 2 = 0 . 5 2 ; p < 0.0001). Managers interested in using marshes as greenhouse gas sinks can assume negligible methane emissions in polyhaline systems, but need to estimate or monitor methane emissions in lower-salinity marshes.

Relationships Between Salinity and Short-Term Soil Carbon Accumulation Rates from Marsh Types Across a Landscape in the Mississippi River Delta

“…Furthermore, if these marshes transition to more saline marshes due to climate change, or towards fresh marshes due to large scale restoration actions, the short-term global carbon pool may change. Balancing the greenhouse gas emissions from each of these four marsh types with the short-term carbon accumulation rates may provide a comprehensive understanding of the role of these marshes in overall carbon sequestration (Poffenbarger et al 2011;Holm et al 2016;Krauss et al 2016). For example, fresh marshes may accumulate a large amount of carbon, but they produce methane gas during anaeraboic metabolism, which has a global warming potential that is 25 times greater than carbon dioxide (Whiting and Chanton 2001).…”

Increased Methane Emissions by an Introduced Phragmites australis Lineage under Global Change

“…Based on this experiment and previous work showing that introduced Phragmites has traits that support relatively high productivity in field settings (Mozdzer and Zieman 2010;Mozdzer and Megonigal 2012;Tulbure et al 2012), we suggest that the spread of introduced Phragmites will increase CH 4 emissions from North American wetlands, and that methane emissions will increase as atmospheric CO 2 concentration continues to rise. These changes in CH 4 emissions will cause radiative forcing unless there is an equivalent increase in carbon sequestration (Poffenbarger et al 2011).…”

“…However, these systems are also capable of emitting enough CH 4 to completely offset the radiative benefits of carbon sequestration, especially in low salinity systems (Poffenbarger et al 2011). Thus, there is a need to understand how interacting global change factors such as elevated CO 2 , anthropogenic N pollution, and plant invasion will alter CH 4 emissions and the radiative balance of tidal wetlands.…”

The significance and vulnerability of Australian saltmarshes: implications for management in a changing climate

“…This efficiency occurs because methane emissions are dramatically reduced in environments where methanogenic bacteria are inhibited by salt (Poffenbarger et al 2011), and because the biogeochemical conditions in tidal wetlands are conducive to long-term carbon retention (DeLaune et al 1990;Choi and Wang 2004). A review by Duarte et al (2005a) reported a mean organic carbon burial rate of 1.51 Mg ha yr -1 for saltmarsh (maximum 17.2 Mg ha yr -1 ) exceeding the maximum burial rate of undisturbed Amazonian forest (1.02 Mg ha yr -1 ) (Grace et al 1993;Nellemann et al 2009).…”

“…Rates of accumulation of carbon and loss will vary within estuaries (Alongi 2012), as will rates of gaseous flux (Poffenbarger et al 2011), with some mangroves and saltmarshes being net exporters or emitters of carbon. The success of mangrove and saltmarsh restoration programs under REDD+ and PES frameworks will be linked to long-term stability of the site and the soil carbon stores being accumulated (Alongi 2011).…”