Mangroves as a Source of Greenhouse Gases to the Atmosphere and Alkalinity and Dissolved Carbon to the Coastal Ocean: A Case Study From the Everglades National Park, Florida. Issue 12 (10th December 2020)

• Record Type: Journal Article
• Authors: Reithmaier, Gloria M. S.; Ho, David T.; Johnston, Scott G.; Maher, Damien T.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 12(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-10
• Subjects: blue carbon -- mangrove carbon budget -- estuarine mixing -- lateral carbon export -- organic alkalinity -- porewater input; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2020JG005812
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: 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 (N2 O) 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/m 2 /day), CH4 (56 μmol/m 2 /day), and N2 O (2 μmol/m 2 /day) to the atmosphere. Dissolved carbon export (DIC = 142 mmol/m 2 /day, DOC = 39 mmol/m 2 /day, normalized to mangrove area) was several‐fold higher than previously reported carbon burial rates in the study area (~28 mmol/m 2 /day). The majority of the DIC was exported as TAlk (97 mmol/m 2 /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