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Carbon outwelling and outgassing vs. burial in an estuarine tidal creek surrounded by mangrove and saltmarsh wetlands
Author(s) -
Santos Isaac R.,
Maher Damien T.,
Larkin Reece,
Webb Jackie R.,
Sanders Christian J.
Publication year - 2019
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.1002/lno.11090
Subject(s) - dissolved organic carbon , alkalinity , soil water , total organic carbon , environmental chemistry , environmental science , carbon dioxide , salt marsh , methane , surface water , total inorganic carbon , carbon fibers , hydrology (agriculture) , estuary , wetland , carbon sequestration , soil carbon , carbon cycle , chemistry , oceanography , soil science , geology , ecosystem , environmental engineering , ecology , materials science , geotechnical engineering , organic chemistry , composite number , composite material , biology
Mangrove‐ and saltmarsh‐dominated estuaries have high rates of organic carbon burial. Here, we estimate soil, pore water, and surface‐water carbon fluxes in an Australian estuarine tidal creek to assess whether (1) advective pore water exchange releases some of the soil carbon, (2) outwelling (lateral exports) represents a major carbon sequestration mechanism, and (3) methane emissions offset soil carbon sequestration. A radon ( 222 Rn) mass balance implied tidally driven pore‐water exchange rates ranging from 5.5 ± 3.6 to 15.6 ± 8.1 cm d −1 . Pore water exchange explained most of the dissolved organic carbon (DOC) and methane surface‐water fluxes but not dissolved inorganic carbon (DIC) and alkalinity. Organic carbon burial in soils derived from 239 + 240 Pu dating was 11–63 g C m −2 yr −1 . Methane and carbon dioxide emissions at the water–air interface were 0.27 ± 0.03 and 63 ± 166 mmol m −2 d −1 , respectively. When calculated as CO 2 ‐equivalents, aquatic CH 4 emissions converted to 19–94 g C‐CO 2 m −2 yr −1 . Upscaling methane and soil carbon fluxes to representative areas revealed that CH 4 emissions could offset < 5% of soil carbon burial. DIC outwelling (12 ± 6 mmol m −2 catchment d −1 ) was less than five‐fold greater than DOC and particulate organic carbon (POC) outwelling and four‐fold greater than catchment‐wide carbon burial. Because much of this DIC remains in the ocean after air–water equilibration, lateral DIC exports may represent an important long‐term carbon sink. Recent research has focused on quantifying carbon burial rates in blue carbon habitats such as saltmarshes and mangroves. We suggest that DIC outwelling and methane outgassing should also be considered when assessing the carbon sequestration capacity of these coastal vegetated habitats.