Carbon outwelling across the shelf following a massive mangrove dieback in Australia: Insights from radium isotopes

Sippo, James Z.; Maher, Damien T.; Schulz, Kai G.; Sanders, Christian J.; McMahon, Ashly; Tucker, James P.; Santos, Isaac R.

doi:10.1016/j.gca.2019.03.003

Cited by 42 publications

(31 citation statements)

References 64 publications

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“…The higher values probably indicate lower respiratory inputs of CO2 from mangroves (Maher et al, 2013b). Our findings here are consistent with the finding of Sippo et al (2019) that changes to oceanic carbon outwelling rates following mangrove loss are likely associated with a gradual loss of sediment carbon; similar to our finding of increased sediment δ 13 C values in the impacted site, an isotope effect may have been due to loss of sediment mangrove C or replacement of mangrove peats with marine sediment.…”

Section: Sedimentsupporting

confidence: 91%

Stable isotopes track the ecological and biogeochemical legacy of mass mangrove forest dieback in the Gulf of Carpentaria, Australia

Harada¹,

Connolly²,

Fry³

et al. 2020

Preprint

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Abstract. A combination of elemental analysis and stable isotope analysis (SIA) was used to assess and monitor C, N and S cycling of a mangrove ecosystem that suffered mass dieback of trees in the Gulf of Carpentaria, Australia in 2015–16, attributed to an extreme drought event. Three field campaigns were conducted over a period from 2016 to 2018, at 8, 20 and 32 months after the event. Samples including invertebrates, mangroves, and sediment were analysed for CNS elemental and isotopic compositions including compound-specific stable isotope analysis (CSIA) of amino acid carbon. Samples collected from the impacted ecosystem were enriched in 13C, 15N and 34S relative to those from an adjacent unimpacted reference ecosystem, likely indicating lower mangrove carbon fixation, lower nitrogen fixation and lower sulfate reduction in the impacted ecosystem. For example, invertebrates representing the feeding types of grazing, leaf feeding, and algae feeding were more 13C enriched at the impacted site, by 1.7–4.1 ‰ and these differences did not change over the period from 2016 to 2018. The CSIA data indicated widespread 13C enrichment across five essential amino acids and all groups sampled (except filter feeders) within the impacted site. Mangrove seedling and sapling populations increased substantially from 2016 to 2018 in the impacted forest, suggesting recovery of the mangrove vegetation. Recovery of CNS cycling, however, was not evident even after 32 months, suggesting a biogeochemical legacy of the mortality event. Continued monitoring of the post-dieback forest would help to predict the long-term trajectory of ecosystem recovery. In such long-term monitoring programs, SIA that can track biogeochemical changes over time can help to detect underlying biological mechanisms that drive changes and recovery of the mangrove ecosystem. To gain further insight, our use of CSIA can help show feeding dependencies in mangrove food webs and their response to disturbances.

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Section: Sedimentsupporting

confidence: 91%

Stable isotopes track the ecological and biogeochemical legacy of mass mangrove forest dieback in the Gulf of Carpentaria, Australia

Harada¹,

Connolly²,

Fry³

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…The higher values probably indicate lower respiratory inputs of CO 2 from mangroves (Maher et al, 2013b). Our findings here are consistent with the finding of Sippo et al (2019) that changes to oceanic carbon outwelling rates following mangrove loss are likely associated with a gradual loss of sediment carbon; similar to our finding of increased sediment δ 13 C values in the impacted site, an isotope effect may have been due to loss of sediment mangrove C and/or replacement of mangrove peats with marine sediment.…”

Section: Sedimentsupporting

confidence: 91%

Stable isotopes track the ecological and biogeochemical legacy of mass mangrove forest dieback in the Gulf of Carpentaria, Australia

Harada¹,

Connolly²,

Fry³

et al. 2020

Biogeosciences

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Abstract. A combination of elemental analysis, bulk stable isotope analysis (bulk SIA) and compound-specific stable isotope analysis of amino acids (CSIA-AA) was used to assess and monitor carbon (C), nitrogen (N) and sulfur (S) cycling of a mangrove ecosystem that suffered mass dieback of trees in the Gulf of Carpentaria, Australia in 2015–2016, attributed to an extreme drought event. Three field campaigns were conducted 8, 20 and 32 months after the event over a period from 2016 to 2018 to obtain biological time-series data. Invertebrates and associated organic matter including mangroves and sediments from the impacted ecosystem showed enrichment in 13C, 15N and 34S relative to those from an adjacent unimpacted reference ecosystem, likely indicating lower mangrove carbon fixation, lower nitrogen fixation and lower sulfate reduction in the impacted ecosystem. For example, invertebrates representing the feeding types of grazing, leaf feeding and algae feeding were more 13C enriched at the impacted site, by 1.7 ‰–4.1 ‰, and these differences did not change over the period from 2016 to 2018. The CSIA-AA data indicated widespread 13C enrichment across five essential amino acids and all groups sampled (except filter feeders) within the impacted site. The seedling density increased from 0.2 m−2 in 2016 to 7.1 m−2 in 2018 in the impacted forest, suggesting recovery of the vegetation. Recovery of CNS cycling, however, was not evident even after 32 months, suggesting a biogeochemical legacy of the mortality event. Continued monitoring of the post-dieback forest is required to predict the long-term trajectory of ecosystem recovery. This study shows that time-series SIA can track biogeochemical changes over time and evaluate recovery of an impacted ecosystem from an extreme event.

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“…Of the combined total carbon mineralization (subsurface DIC production + CO 2 respiration at the soil surface), 25% is released at the forest floor surface in a separate process, and approximately all subsurface DIC production is exported to adjacent tidal waters in the form of DOC (∼30%), dissolved CH 4 (<0.2%) and DIC (∼70%). A considerable, but unquantified, amount of exported DIC, DOC, and CH 4 is derived from groundwater derived from adjacent upland [13,[74][75][76][94][95][96][97]101,103], so it is unclear exactly how much dissolved carbon exported from mangroves is derived from soil mineralization. The supersaturation of mangrove waters leads to significant CO2 (40 Tg C a −1 ) and CH4 (0.19 Tg C a −1 ) release to the atmosphere.…”

Section: Carbon Flow Through the World's Mangrove Ecosystems And Contmentioning

confidence: 99%

Carbon Cycling in the World’s Mangrove Ecosystems Revisited: Significance of Non-Steady State Diagenesis and Subsurface Linkages between the Forest Floor and the Coastal Ocean

Alongi

2020

Forests

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Carbon cycling within the deep mangrove forest floor is unique compared to other marine ecosystems with organic carbon input, mineralization, burial, and advective and groundwater export pathways being in non-steady-state, often oscillating in synchrony with tides, plant uptake, and release/uptake via roots and other edaphic factors in a highly dynamic and harsh environment. Rates of soil organic carbon (CORG) mineralization and belowground CORG stocks are high, with rapid diagenesis throughout the deep (>1 m) soil horizon. Pocketed with cracks, fissures, extensive roots, burrows, tubes, and drainage channels through which tidal waters percolate and drain, the forest floor sustains non-steady-state diagenesis of the soil CORG, in which decomposition processes at the soil surface are distinct from those in deeper soils. Aerobic respiration occurs within the upper 2 mm of the soil surface and within biogenic structures. On average, carbon respiration across the surface soil-air/water interface (104 mmol C m−2 d−1) equates to only 25% of the total carbon mineralized within the entire soil horizon, as nearly all respired carbon (569 mmol C m−2 d−1) is released in a dissolved form via advective porewater exchange and/or lateral transport and subsurface tidal pumping to adjacent tidal waters. A carbon budget for the world’s mangrove ecosystems indicates that subsurface respiration is the second-largest respiratory flux after canopy respiration. Dissolved carbon release is sufficient to oversaturate water-column pCO2, causing tropical coastal waters to be a source of CO2 to the atmosphere. Mangrove dissolved inorganic carbon (DIC) discharge contributes nearly 60% of DIC and 27% of dissolved organic carbon (DOC) discharge from the world’s low latitude rivers to the tropical coastal ocean. Mangroves inhabit only 0.3% of the global coastal ocean area but contribute 55% of air-sea exchange, 14% of CORG burial, 28% of DIC export, and 13% of DOC + particulate organic matter (POC) export from the world’s coastal wetlands and estuaries to the atmosphere and global coastal ocean.

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Carbon outwelling across the shelf following a massive mangrove dieback in Australia: Insights from radium isotopes

Cited by 42 publications

References 64 publications

Stable isotopes track the ecological and biogeochemical legacy of mass mangrove forest dieback in the Gulf of Carpentaria, Australia

Stable isotopes track the ecological and biogeochemical legacy of mass mangrove forest dieback in the Gulf of Carpentaria, Australia

Stable isotopes track the ecological and biogeochemical legacy of mass mangrove forest dieback in the Gulf of Carpentaria, Australia

Carbon Cycling in the World’s Mangrove Ecosystems Revisited: Significance of Non-Steady State Diagenesis and Subsurface Linkages between the Forest Floor and the Coastal Ocean

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