What was done
The authors measured carbon (C) sequestration along two transects across submerging coastal landscapes (Hell Hook and Cedar Creek) of the Chesapeake Bay in Dorchester County, Maryland, USA, from which data they developed a model of C sequestration by coastal marshes.

What was learned
Hussein et al. determined that "coastal marsh soils are accreting vertically and migrating laterally over the [adjacent] low-lying forest soils to keep pace with sea-level rise," and that during the last 150 years, the rate of C sequestration by the marsh soils averaged 83.5 ± 23 g m^-2 yr^-1, whereas prior to that period it had averaged 29.2 ± 5.35 g m^-2 yr^-1.  These rates are much greater than those of either local forest or agricultural soils.  What is more, the three scientists report that "C sequestration in mineral soils of agro and upland forest ecosystems is generally of limited capacity and tends to reach [a] steady-state condition within relatively short time," but that "in coastal marsh soils, C sequestration will continue to occur with time by accumulation in the organic horizons, and with increasing storage capacity."

Based on a model they developed from their data, Hussein et al. project that, driven by sea-level rise, C sequestration by coastal marsh ecosystems over the next 100 years will average 400 ± 162 g m^-2 yr^-1.

What it means
Hussein et al. conclude that "coastal marsh ecosystems tend to sequester C continuously with increasing storage capacity as marsh age progresses," and that "C sequestration in coastal marsh ecosystems under positive accretionary balance acts as a negative feedback mechanism to global warming," much as we have suggested in the past [see our reviews of the studies of Choi et al. (2001) and Hussein and Rabenhorst (2002)].

References
Choi, Y., Wang, Y., Hsieh, Y.-P. and Robinson, L.  2001.  Vegetation succession and carbon sequestration in a coastal wetland in northwest Florida: Evidence from carbon isotopes.  Global Biogeochemical Cycles 15: 311-319.

Hussein, A.H. and Rabenhorst, M.C.  2002.  Modeling of nitrogen sequestration in coastal marsh soils.  Soil Science Society of America Journal 66: 324-330.