Contrasting organic matter composition in pristine and eutrophicated mangroves revealed by fatty acids and stable isotopes (Rio de Janeiro, Brazil)

Chynel, Mathias; Rockomanovic, Sofia; Abril, Gwénaël; Barroso, Glenda Camila; Marotta, Humberto; Machado, Wilson; Sanders, Christian J.; Thiney, Najet; Méziane, Tarik

doi:10.1016/j.ecss.2022.108061

Cited by 10 publications

(2 citation statements)

References 88 publications

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“…Average monthly temperature and precipitation oscillate around 23 ± 3 °C (18 -28 °C) and 130 ± 108 mm (0 -501 mm), respectively. The creek catchment area (9,572 m 2 ) is in a pristine reserve with negligible anthropogenic impact (Chynel et al 2022). The tidal creek catchment is part of a broader mangrove forest area of 260,112 m 2 .…”

Section: Study Sitesmentioning

confidence: 99%

“…Higher urbanization and eutrophic settings surrounding the microtidal mangrove ) compared to the pristine, mesotidal creek (Chynel et al 2022) also contribute to organic enrichment and increase pCO2 in the microtidal creek. Previous studies found that sediment-atmosphere CO2 fluxes were 3 times lower in the mesotidal creek (~120 mmol m -2 d -1 ) when compared to a nearby eutrophic mangrove (Barroso et al 2022), confirming that pristine mangroves emit less CO2 into the atmosphere than impacted/eutrophic systems.…”

Section: Porewater-derived Versus Water-atmosphere Co2 Fluxesmentioning

confidence: 99%

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Tidally driven porewater exchange and diel cycles control CO2 fluxes in mangroves

Cabral,

Yau,

Reithmaier

et al. 2024

Preprint

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Mangrove soils are highly enriched in organic carbon. Tidal pumping drives seawater and oxygen into mangrove sediments during flood tide and releases carbon-rich porewater during ebb tides. Here, we resolve semi-diurnal (flood/ebb tides), diel (day/night) and weekly (neap/spring tides) drivers of porewater-derived CO2 fluxes in two mangroves and update global estimates of CO2 emissions. Tidal pumping controlled pCO2 variability within the mangrove creeks. The highest values of pCO2 (2,585-6,856 µatm) and 222Rn (2,315-6,159 dpm m-3) and lowest values of pH (6.8-7.1) and dissolved oxygen (1.7-3.7 mg L-1) at low tides were due to enhanced porewater export. 222Rn and pCO2 in mangrove porewater were respectively 4-15 and 38-41 times greater than surface waters. pCO2 increased by 50±30% from high to low tide, 9±22% from day to night and 57±5% from neap to spring tide with clear changes on hourly, diel, and weekly time scales. Both porewater-derived CO2 and water-air outgassing increased with tidal amplitudes (r2 = 0.34, p < 0.05). Combining our new estimates with literature data, global porewater-derived (16 sites) and water-atmosphere (52 sites) CO2 fluxes in mangroves would be upscale to 45±12 and 41±10 Tg C y-1, respectively. These fluxes account for 25% of net primary production and 238% of sediment carbon burial rates in global mangroves. Overall, our local observations and global compilation suggest that porewater-derived CO2 exchange is a major but often unaccounted source of CO2 in mangroves – which can be emitted to the atmosphere or laterally exported to the ocean – and should be included in carbon budgets to solve global imbalances.

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Section: Study Sitesmentioning

confidence: 99%

Section: Porewater-derived Versus Water-atmosphere Co2 Fluxesmentioning

confidence: 99%

Tidally driven porewater exchange and diel cycles control CO2 fluxes in mangroves

Cabral,

Yau,

Reithmaier

et al. 2024

Preprint

View full text Add to dashboard Cite

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Efficient oxidation attenuates porewater‐derived methane fluxes in mangrove waters

Yau,

Cabral,

Reithmaier

et al. 2024

Limnology & Oceanography

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Mangroves store significant amounts of carbon in both sediment and water. Methane (CH4) is often produced in anoxic, organic‐rich sediments during carbon degradation and released to overlying waters via porewater exchange. Yet, a portion of CH4 can be oxidized to CO2 before emission. Here, we investigate whether CH4 oxidation impacts its emissions using high‐temporal resolution CH4 concentration and stable isotope (δ13C‐CH4) observations collected over 14 tidal cycles in 2 Brazilian mangrove creeks with no river inputs. We found higher CH4 concentrations (~ 150 nM) more depleted in 13C (−75‰) during low tide than high tide at both creeks. Similar δ13C‐CH4 values between low tide surface waters and porewaters further suggest tidally driven porewater exchange as the main source of CH4. More 13C‐enriched CH4 in surface waters and surface sediments than deep sediments indicate partial CH4 oxidation prior to exchange with the atmosphere. A stable isotope mass balance revealed that 17–58% of CH4 was oxidized at rates of 3–25 μmol m−2 d−1 in the water column of tidal creeks. A larger portion of deep porewater CH4 (45–61%) was oxidized in sediments prior to porewater exchange with surface creek waters. The two mangrove creeks had average water–air CH4 fluxes of 51–109 μmol m−2 d−1 over spring‐neap tidal cycles. These aquatic CH4 emissions offset only < 3% of the mangroves' soil carbon sequestration. Overall, CH4 oxidation in both surface water and sediment attenuated CH4 emissions to the atmosphere.

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Sargassum beaching on mangrove sediments shifts microbial and crab metabolisms and enhances blue carbon storage

Chynel,

Abril,

Narayaninsamy

et al. 2024

Limnology & Oceanography

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Benthic metabolism and net carbon accumulation in mangroves sediments strongly depend on the quantity and quality of organic matter (OM) supplied, including material brought by coastal waters such as the macroalgae Sargassum spp. Mesocosms were used to assess the effect of eutrophication by Sargassum on mangrove sediments. The concentration of fatty acids (FAs), organic carbon and its carbon isotopic signature, and the sediments–air CO2 fluxes were used to follow the evolution of sedimentary OM in surface and subsurface sediments for 60 d. Sargassum beaching shifted microbial and crab metabolism, leading to a preferential degradation of the labile fraction of OM from both Sargassum (δ13C = −17.7‰ and high concentration of essential FAs) and mangrove leaves (δ13C: −28.9‰ and high concentrations of 18:2ω6 and 18:3ω3). Fatty acids composition of crabs hepatopancreas revealed they preferentially fed on Sargassum and these invertebrates also increased the particulate OM tidal export. In addition, microbial activity at the sediment surface was enhanced, as revealed by strong production of branched FAs and higher CO2 fluxes in mesocosms containing Sargassum. However, Sargassum beaching also increased the transfer and preservation of more refractory OM from mangrove leaves found in higher quantity in subsurface sediments (6–8 cm) after 60 d. Inputs of macroalgae induced a negative priming effect and enhanced the preservation of blue carbon in the sediments. This negative priming effect was enhanced by crab activities. These biotic interactions that include microbial communities apparently make mangrove efficient in storing carbon in a context of growing eutrophication of the tropical ocean.

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Contrasting organic matter composition in pristine and eutrophicated mangroves revealed by fatty acids and stable isotopes (Rio de Janeiro, Brazil)

Cited by 10 publications

References 88 publications

Tidally driven porewater exchange and diel cycles control CO2 fluxes in mangroves

Tidally driven porewater exchange and diel cycles control CO2 fluxes in mangroves

Efficient oxidation attenuates porewater‐derived methane fluxes in mangrove waters

Sargassum beaching on mangrove sediments shifts microbial and crab metabolisms and enhances blue carbon storage

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