Are methane emissions from mangrove stems a cryptic carbon loss pathway? Insights from a catastrophic forest mortality

Jeffrey, Luke C.; Reithmaier, Gloria Maria Susanne; Sippo, James Z.; Johnston, Scott G; Tait, Douglas R.; Harada, Yota; Maher, Damien T.

doi:10.1111/nph.15995

Cited by 84 publications

(57 citation statements)

References 48 publications

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“…However, due to the variability in efflux from individual chamber measurements, no statistical difference was observed between efflux from living and dead forest areas (ANOVA, p = 0.16). This builds on recent work at the same study site revealing no difference in sediment CH 4 effluxes 32 months postforest dieback and an eightfold greater CH 4 efflux from dead mangrove tree stems, compared to living mangrove tree stems (Jeffrey et al 2019).…”

Section: Ch 4 Effluxsupporting

confidence: 70%

Coastal carbon cycle changes following mangrove loss

Sippo

Sanders

Santos

et al. 2020

Limnology & Oceanography

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Global mangrove loss is occurring from deforestation and extreme climatic events, but changes to the coastal carbon cycle following mangrove mortality and/or loss are not well understood. In 2015/2016, a massive climate-driven mangrove dieback event occurred over~1000 km of Australian coastline. To assess carbon loss following mortality, carbon fluxes in adjacent living and dead forest areas were compared 8 and 20 months postforest dieback. Dead areas experienced an increase in soil CO 2 efflux by~189%, and a decrease in oceanic dissolved inorganic carbon (DIC) outwelling of~50% relative to living areas. DIC outwelling (predominantly carbonate alkalinity) and soil CO 2 efflux accounted for 81% and 16% of losses from the living forest, in comparison to 51% and 47%, respectively, from the dead forest. The dieback drove a shift from a dominance of oceanic carbon outwelling to increased atmospheric CO 2 emissions and decreased alkalinity exports. This shift was likely driven by increased oxygen sediment permeation and the loss of mangrove net primary productivity. Combining our new observations with literature data, we found a logarithmic relationship between soil carbon loss and time since mangrove loss. Using this relationship, we estimate ongoing global carbon losses from historical mangrove deforestation and dieback could be 13.7 AE 9.4 Tg C yr −1 , which is eightfold higher than previous estimates and offsets global mangrove carbon burial by~60%. Even if no future deforestation occurred, we estimate ongoing carbon losses to the atmosphere and ocean from current global mangrove losses of 27 Tg C over the next 30 yr.

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Section: Ch 4 Effluxsupporting

confidence: 70%

Coastal carbon cycle changes following mangrove loss

Sippo

Sanders

Santos

et al. 2020

Limnology & Oceanography

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“…Firstly, our understanding of the biogeochemical processes of CH 4 production, consumption and transport in mangrove ecosystems is still nascent. While all these processes should be taken into account for a reliable estimate of net CH 4 efflux, the relative contributions of mangrove stems (Jeffrey et al, 2019), canopies (Keppler, Hamilton, Brass, & Röckmann, 2006), and coarse woody debris (Warner, Villarreal, McWilliams, Inamdar, & Vargas, 2017) as CH 4 sources are still highly uncertain. Secondly, Rosentreter et al (2018) assumed that mangroves were inundated by water for 50% of the time, which might not be representative of the tidal regimes in all mangrove environments.…”

Section: Reduced Emissions From Deforestation and Degradation And Globalmentioning

confidence: 99%

“…Tree-mediated emissions have recently been identified as an important component of CH 4 balance in wetlands, floodplains, and upland forests (Covey & Megonigal, 2019). Jeffrey et al (2019) showed that mangrove stem emission was a novel pathway of CH 4 release, with dead trees being more significant emitters of CH 4 than living trees that accounted for ~26% of the net ecosystem F CH4 . These findings suggested that the passive diffusion of CH 4 from soil to stem might be more important than the active transpiration of CH 4 in sustaining stem emissions, which would account for the weak link between LE and F CH4 observed in this study.…”

Section: Biophysical Drivers Of F Ch4mentioning

confidence: 99%

Methane emissions reduce the radiative cooling effect of a subtropical estuarine mangrove wetland by half

Liu

Zhou

Valach

et al. 2020

Global Change Biology

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The role of coastal mangrove wetlands in sequestering atmospheric carbon dioxide (CO 2) and mitigating climate change has received increasing attention in recent years. While recent studies have shown that methane (CH 4) emissions can potentially offset the carbon burial rates in low-salinity coastal wetlands, there is hitherto a paucity of direct and year-round measurements of ecosystem-scale CH 4 flux (F CH4) from mangrove ecosystems. In this study, we examined the temporal variations and biophysical drivers of ecosystem-scale F CH4 in a subtropical estuarine mangrove wetland based on 3 years of eddy covariance measurements. Our results showed that daily mangrove F CH4 reached a peak of over 0.1 g CH 4-C m −2 day −1 during the summertime owing to a combination of high temperature and low salinity, while the wintertime F CH4 was negligible. In this mangrove, the mean annual CH 4 emission was 11.7 ± 0.4 g CH 4-C m-2 year −1 while the annual net ecosystem CO 2 exchange ranged between −891 and −690 g CO 2-C m −2 year −1 , indicating a net cooling effect on climate over decadal to centurial timescales. Meanwhile, we showed that mangrove F CH4 could offset the negative radiative forcing caused by CO 2 uptake by 52% and 24% over a time horizon of 20 and 100 years, respectively, based on the corresponding sustained-flux global warming potentials. Moreover, we found that 87% and 69% of the total variance of daily F CH4 could be explained by the random forest machine learning algorithm and traditional linear regression model, respectively, with soil temperature and salinity being the most dominant controls. This study was the first of its kind to characterize ecosystem-scale F CH4 in a mangrove wetland with longterm eddy covariance measurements. Our findings implied that future environmental changes such as climate warming and increasing river discharge might increase CH 4 emissions and hence reduce the net radiative cooling effect of estuarine mangrove forests.

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“…Tree density (tree m −2 ) is taken from Jeffrey et al () (their table 1). The value reported here is an average of three intertidal zones (upper, middle, and lower).…”

Section: Resultsmentioning

confidence: 99%

Stable isotopes indicate ecosystem restructuring following climate‐driven mangrove dieback

Harada

Fry

Lee

et al. 2019

Limnology & Oceanography

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Extreme climatic events can trigger sudden but often long‐lasting impacts in ecosystems by causing near to complete mortality of foundation (habitat‐forming) species. The magnitude and frequency of such events are expected to rise due to anthropogenic climate change, but the impacts that such events have on many foundation species and the ecosystems that they support remains poorly understood. In many cases, manipulative experimentation is extremely challenging and rarely feasible at a large scale. In late 2015 to early 2016, an extensive area of mangrove forest along ∼ 1000 km of coastline in the Gulf of Carpentaria, Australia, experienced severe dieback, an event associated with climatic extremes. To assess the effect this dieback event had on the mangrove ecosystem, we assessed benthic faunal assemblages and food web structure using stable carbon and nitrogen isotopes in a comparative experiment of impacted forest and adjacent unimpacted forest. Eighteen months after the dieback, the forest that suffered dieback contained significantly fewer crabs that rely on mangrove litter food source but more crabs that rely on microphytobenthos food source than the unimpacted forest. However, the infaunal biomass was largely unaffected by the mortality effect. This is most likely because microphytobenthos was largely unaffected and consequently, this buffered the food web responses. However, overall, the habitat value for mangrove ecosystem services most likely decreased due to lower physical habitat complexity following tree mortality. Longer‐term monitoring could lead to better understanding of biological effects of this extreme event and underlying biological mechanisms that drive changes and recovery.

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Are methane emissions from mangrove stems a cryptic carbon loss pathway? Insights from a catastrophic forest mortality

Cited by 84 publications

References 48 publications

Coastal carbon cycle changes following mangrove loss

Coastal carbon cycle changes following mangrove loss

Methane emissions reduce the radiative cooling effect of a subtropical estuarine mangrove wetland by half

Stable isotopes indicate ecosystem restructuring following climate‐driven mangrove dieback

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