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Abstract

Mangrove forests of the Sinu´ river delta in
Cispata´ bay, Colombia, show large differences in soil
carbon storage between fringe (oceanic) and basin
(estuarine) mangroves. We were interested in testing
whether these differences in soil carbon are associated
with sediment transport processes or whether most of
the carbon is produced in situ within the mangrove
system. Given past sedimentation dynamics of the
Sinu´ river, we hypothesized that a large portion of soil
carbon in basin mangroves is due to sedimentation.
We determined total organic carbon content (TOC) as
660.93 ± 259.18 MgC ha-1 for basin soils up to a
sampling depth of 1 m, and as 259 ± 42.61 MgC ha-1
for fringe soils up to 80 cm depth (maximum soil depth
for fringe soils). Using analyses of mineralogy (Aland
Fe-oxides, clay minerals) as well as isotopic
analyses of carbon (d13C), the origin of the sediments
and their carbon was determined. We found that basin
soils in Cispata´ bay show similar mineralogical
composition than those of fluvial sediments, but the
carbon concentration of river sediments was close to
zero. Given the large capacity of the Fe and Al oxides
in clay minerals to store dissolved carbon, and that the
isotopic composition of the carbon is mostly of plant
origin, we concluded contrary to our initial hypothesis
that the carbon stored in basin mangrove soils are
produced in situ. The deposited fluvial sediments do
play an important role for carbon storage, but mostly
in providing binding surfaces for the stabilization of
organic carbon.