Atmospheric carbon dioxide (CO2) is fixed by mangrove vegetation and stored in its biomass and sediments. Part of the sediment carbon can be exported to coastal waters via tidally driven pore‐water ...exchange. Here, we quantify pore water‐derived dissolved CO2 export using in situ, high‐resolution observations of 222Rn and CO2 over a spring‐neap tidal cycle in a mangrove‐fringed estuary (Coffs Creek, Australia). 222Rn‐derived pore‐water exchange rates were 11.5–34.9 cm d−1 (23.0 ± 6.7) over 30 tidal cycles. Pore‐water exchange released CO2 from intertidal sediment at rates of 61–213 (136 ± 43) mmol m−2 d−1. This is equivalent to ~ 94% of the total CO2 input into the estuary and approximately two times of the water‐atmosphere CO2 emission. These observations reveal that tidal pumping is a major regulator of both mangrove pore‐water exchange and associated dissolved CO2 export to the ocean. Combining our estimates with literature data, a first‐order global pore water‐derived dissolved CO2 export from mangroves was estimated to be 83 ± 50 Tg C yr−1. This is higher than an earlier estimates of global mangrove CO2 emissions to the atmosphere (34.1 ± 5.4 Tg C yr−1) and carbon burial in sediments (18.4–34.4 Tg C yr−1), implying that pore water‐derived CO2 escapes to the atmosphere within and beyond mangrove waters. Overall, CO2‐rich pore water seems to be a widespread, important pathway of CO2 into mangrove‐dominated estuaries and should be considered in mangrove carbon assessments in the context of global climate change and blue carbon.
Blue carbon ecosystems, including mangroves, saltmarshes, and seagrasses, mitigate climate change by storing atmospheric carbon. Previous blue carbon research has focused on organic carbon stocks. ...However, recent studies suggest that lateral inorganic carbon export might be equally important. Lateral export is a long‐term carbon sink if carbon is exported as alkalinity (TAlk) produced via sulfate reduction coupled to pyrite formation. This study evaluates drivers of pyrite formation in blue carbon ecosystems, compares pyrite production to TAlk outwelling rates, and estimates global pyrite stocks in mangroves. We quantified pyrite stocks in mangroves, saltmarshes, and seagrasses along a latitudinal gradient on the Australian East Coast, including a mangrove dieback area, and in the Everglades (Florida, USA). Our results indicate that pyrite stocks were driven by a combination of biomass, tidal amplitude, sediment organic carbon, sediment accumulation rates, rainfall, latitude, temperature, and iron availability. Pyrite stocks were three‐times higher in mangroves (103 ± 61 Mg/ha) than in saltmarshes (30 ± 30 Mg/ha) and seagrasses (32 ± 1 Mg/ha). Mangrove pyrite stocks were linearly correlated to TAlk export at sites where sulfate reduction was the dominant TAlk producing process. However, pyrite generation could not explain all TAlk outwelling. We present the first global model estimating pyrite stocks in mangroves, giving a first‐order estimate of 197 Mg/ha (RMSE = 24 Mg/ha). In mangroves, estimated global TAlk production coupled to pyrite formation (∼3 mol/m2/y) is equal to ∼24% of their global carbon burial rate, highlighting the importance of including TAlk export in future blue carbon budgets.
Plain Language Summary
Mangroves, saltmarshes, and seagrasses (known as blue carbon ecosystems) have the potential to buffer climate change by taking up carbon dioxide. Scientists assess this potential by measuring the amount of carbon that is stored in the soils of these ecosystems. However, soil carbon is partly broken down by microorganisms and can be exported to the coastal ocean. Carbon export to the coastal ocean is also a carbon sink. The prerequisite, however, is that carbon breakdown is coupled to the formation of iron sulfide minerals (i.e., pyrite), which prevents reactions that would lead to carbon dioxide release. This study examined the driving factors and global importance of iron sulfide mineral formation and related carbon export in blue carbon ecosystems. We found that biological, climatic, and geological factors impact iron sulfide mineral formation. We used these findings to develop the first global model predicting iron sulfide mineral reserves in mangroves. Our results show that the dissolved carbon produced during sulfide mineral formation corresponds to a quarter of the carbon stored in mangrove soils. This study highlights the importance of considering dissolved carbon export when evaluating the potential of blue carbon ecosystems for mitigating climate change.
Key Points
Alkalinity export from blue carbon ecosystems is a long‐term carbon sink if alkalinity production is coupled to pyrite formation
We present the first global model for pyrite stocks in mangroves, estimating that mangrove pyrite stocks average around 197 Mg/ha
Globally, pyrite formation in mangroves produces 0.45–0.68 Tmol alkalinity per year, making the process a substantial carbon sink
Mangroves are one of the most carbon‐dense forests on the Earth and have been highlighted as key ecosystems for climate change mitigation and adaptation. Hundreds of studies have investigated how ...mangroves fix, transform, store, and export carbon. Here, we review and synthesize the previously known and emerging carbon pathways in mangroves, including gains (woody biomass accumulation, deadwood accumulation, soil carbon sequestration, root and litterfall production), transformations (food web transfer through herbivory, decomposition), and losses (respiration as CO2 and CH4, litterfall export, particulate and dissolved carbon export). We then review the technologies available to measure carbon fluxes in mangroves, their potential, and their limitations. We also synthesize and compare mangrove net ecosystem productivity (NEP) with terrestrial forests. Finally, we update global estimates of carbon fluxes with the most current values of fluxes and global mangrove area. We found that the contributions of recently investigated fluxes, such as soil respiration as CH4, are minor (<1 Tg C year−1), while the contributions of deadwood accumulation, herbivory, and lateral export are significant (>35 Tg C year−1). Dissolved inorganic carbon exports are an order of magnitude higher than the other processes investigated and were highly variable, highlighting the need for further studies. Gross primary productivity (GPP) and ecosystem respiration (ER) per area of mangroves were within the same order of magnitude as terrestrial forests. However, ER/GPP was lower in mangroves, explaining their higher carbon sequestration. We estimate the global mean mangrove NEP of 109.1 Tg C year−1 (7.4 Mg C ha−1 year−1) or through a budget balance, accounting for lateral losses, a global mean of 66.6 Tg C year−1 (4.5 Mg C ha−1 year−1). Overall, mangroves are highly productive, and despite losses due to respiration and tidal exchange, they are significant carbon sinks.
Most research evaluating the potential of mangroves as a sink for atmospheric carbon has focused on carbon burial in sediments. However, the few studies that have quantified lateral exchange of ...carbon and alkalinity indicate that the dissolved carbon and alkalinity export may be several‐fold more important than burial. This study aims to investigate rates and drivers of alkalinity, dissolved carbon, and greenhouse gas fluxes of the mangrove‐dominated Shark River estuary located in the Everglades National Park in Florida, USA. Spatial surveys and 29‐hr time series were conducted to assess total alkalinity (TAlk), organic alkalinity (OAlk), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) dynamics. Dissolved carbon and greenhouse gas concentrations were coupled to porewater input, which was examined using radon‐222. Shark River was a source of CO2 (92 mmol/m2/day), CH4 (56 μmol/m2/day), and N2O (2 μmol/m2/day) to the atmosphere. Dissolved carbon export (DIC = 142 mmol/m2/day, DOC = 39 mmol/m2/day, normalized to mangrove area) was several‐fold higher than previously reported carbon burial rates in the study area (~28 mmol/m2/day). The majority of the DIC was exported as TAlk (97 mmol/m2/day), which remains dissolved in the ocean for millennia and, therefore, represents a long‐term sink for atmospheric carbon. By integrating our results with previous studies, we argue that alkalinity, dissolved carbon, and greenhouse gas fluxes should be considered in future blue carbon budgets.
Plain Language Summary
Protecting mangroves can help us deal with one of the biggest challenges of our time: Climate change. Mangroves remove carbon dioxide – the gas that is making the world hotter – from the air around us and store it in their surrounding soils. Many scientists have studied how much carbon is trapped in mangrove soils, and the newest studies say that some of that trapped carbon is flushed out to the coastal ocean. We wanted to find out for ourselves so we went to Everglades National Park, which protects the biggest mangrove forest in North America. We cruised along the Shark River estuary and spent day and night on the boat to uncover this carbon mystery. We found that the estuary loses greenhouse gasses to the atmosphere, but much less compared to what it loses to the Gulf of Mexico. We could also confirm that the amount of carbon lost was much greater than what is trapped in soils. We encourage other researchers to investigate dissolved carbon export in other mangroves in order to find out how much mangroves can alleviate the impacts of climate change.
Key Points
Two spatial surveys and two 29‐hr time series were conducted to explore the biogeochemistry of the Shark River estuary
The mangrove‐dominated estuary was a source of dissolved carbon and greenhouse gases
Alkalinity, dissolved carbon and greenhouse gas fluxes should be integrated in future blue carbon budgets
Quantum optical circuits can be used to generate, manipulate, and exploit nonclassical states of light to push semiconductor based photonic information technologies to the quantum limit. Here, we ...report the on-chip generation of quantum light from individual, resonantly excited self-assembled InGaAs quantum dots, efficient routing over length scales ≥1 mm via GaAs ridge waveguides, and in situ detection using evanescently coupled integrated NbN superconducting single photon detectors fabricated on the same chip. By temporally filtering the time-resolved luminescence signal stemming from single quantum dots we use the quantum optical circuit to perform time-resolved excitation spectroscopy on single dots and demonstrate resonance fluorescence with a line-width of 10 ± 1 μeV; key elements needed for the use of single photons in prototypical quantum photonic circuits.
For 17 days in August and September 2002, the LIGO and GEO interferometer gravitational wave detectors were operated in coincidence to produce their first data for scientific analysis. Although the ...detectors were still far from their design sensitivity levels, the data can be used to place better upper limits on the flux of gravitational waves incident on the earth than previous direct measurements. This paper describes the instruments and the data in some detail, as a companion to analysis papers based on the first data.
•UNCD and DLC films were modified by UV/O3 treatments, O2 or NH3-containing plasmas.•Surface composition, wettability and surface energy change upon modifications.•Higher efficiency of UNCD ...modifications was observed.•Cell attachment and growth were influenced by the surface termination and roughness.
Diamond and diamond-like carbon (DLC) films possess a set of excellent physical and chemical properties which together with a high biocompatibility make them attractive candidates for a number of medical and biotechnological applications. In the current work thin ultrananocrystalline diamond (UNCD) and DLC films were comparatively investigated with respect to cell attachment and proliferation after different surface modifications. The UNCD films were prepared by microwave plasma enhanced chemical vapor deposition, the DLC films by pulsed laser deposition (PLD). The films were comprehensively characterized with respect to their basic properties, e.g. crystallinity, morphology, chemical bonding nature, etc. Afterwards the UNCD and DLC films were modified applying O2 or NH3/N2 plasmas and UV/O3 treatments to alter their surface termination. The surface composition of as-grown and modified samples was studied by X-ray photoelectron spectroscopy (XPS). Furthermore the films were characterized by contact angle measurements with water, formamide, 1-decanol and diiodomethane; from the results obtained the surface energy with its dispersive and polar components was calculated. The adhesion and proliferation of MG63 osteosarcoma cells on the different UNCD and DLC samples were assessed by measurement of the cell attachment efficiency and MTT assays. The determined cell densities were compared and correlated with the surface properties of as-deposited and modified UNCD and DLC films.
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