A synthesis of methane emissions from shallow vegetated coastal ecosystems. (16th March 2020)

• Record Type: Journal Article
• Authors: Al‐Haj, Alia N.; Fulweiler, Robinson W.
• Is Part Of: Global change biology. Volume 26:Number 5(2020)
• Page Start: 2988
• Page End: 3005
• Publication Date: 2020-03-16
• Subjects: global carbon budget -- mangrove -- methanogenesis -- methanotrophy -- salt marsh -- seagrass -- synthesis; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.15046
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: Vegetated coastal ecosystems (VCEs; i.e., mangroves, salt marshes, and seagrasses) play a critical role in global carbon (C) cycling, storing 10× more C than temperate forests. Methane (CH4 ), a potent greenhouse gas, can form in the sediments of these ecosystems. Currently, CH4 emissions are a missing component of VCE C budgets. This review summarizes 97 studies describing CH4 fluxes from mangrove, salt marsh, and seagrass ecosystems and discusses factors controlling CH4 flux in these systems. CH4 fluxes from these ecosystems were highly variable yet they all act as net methane sources (median, range; mangrove: 279.17, −67.33 to 72, 867.83; salt marsh: 224.44, −92.60 to 94, 129.68; seagrass: 64.80, 1.25–401.50 µmol CH4 m −2 day −1 ). Together CH4 emissions from mangrove, salt marsh, and seagrass ecosystems are about 0.33–0.39 Tmol CH4 ‐C/year—an addition that increases the current global marine CH4 budget by more than 60%. The majority (~45%) of this increase is driven by mangrove CH4 fluxes. While organic matter content and quality were commonly reported in individual studies as the most important environmental factors driving CH4 flux, they were not significant predictors of CH4 flux when data were combined across studies. Salinity was negatively correlated with CH4 emissions from salt marshes, but not seagrasses and mangroves. Thus the available data suggest that other environmental drivers are important for predicting CH4 emissions in vegetated coastal systems. Finally, we examine stressor effects on CH4 emissions from VCEs and we hypothesize that future changes in temperature and other anthropogenic activites (e.g., nitrogen loading) will likely increase CH4 emissions from these ecosystems. Overall, this review highlights the current and growing importance of VCEs in the global marine CH4 budget. Abstract : Vegetated coastal ecosystems (VCEs; mangroves, salt marshes, and seagrasses) are well‐known for their carbon storage capacity. However, most studies on the carbon cycle in VCEs overlook a potentially important mechanism of carbon loss—methane emissions. Remarkably, methane emissions from VCEs are not currently included in global marine methane budget estimates. Here we show that VCEs are net methane emitters and that carbon loss through methane emissions is relatively small when compared to carbon stored. Furthermore, we demonstrate that accounting for their methane emissions leads to a 60%–70% increase in the global marine methane budget. See Letter to the Editor on this article by Rosentreter and Williamson, 26, 5351–5352 .See also Response to Letter to the Editor on this article by Al‐Haj and Fulweiler, 26, e10–e11 .