Carbon Distribution In Subaqueous Soils.

Recent studies suggest that subaqueous soils may potentially be important carbon sinks that had previously been unaccounted for in the global carbon budget. In his study, we tested whether soil mapping units could
be useful predictors of carbon pools in subaqueous environments.  Cove, Drowned Channel, Fluviomarine Bottom, and Bayfloor landscape units had the highest amount of carbon stored in the upper meter of soil, averaging 181 Mg/ha (p<0.05;). Sandier landscapes including Shoal, Spit, and Mainland Shoreface had much lower carbon pools with an average of only 57 Mg/ha. On landscape units in which multiple samples were analyzed for a single estuary, very little standard error was observed within most landscape units. Despite having the lowest average bulk density in soil horizons, Little Narragansett Bay had the highest carbon pools of the bays in the four soft-bottom landscape units. The higher carbon content in Little Narragansett Bay could be due to the large amount of organic matter brought in from the Pawcatuck River that accumulates in the soils in calm parts of the bay. Carbon pools in these subaqueous soils are very similar to those reported for forested mineral subaerial soils in New England. Soil organic carbon concentrations ranged from 20-87 g/kg for marine-deposited soils in low energy landscape units. This falls within the range of A horizons of subaerial soils in New England. The soil organic carbon content for high-energy sites was similar to terrestrial B horizons and ranged from 0.9-10 g/kg. The rapid rate of deposition in subaqueous environments suggests that greater amounts of carbon are sequestered yearly in these subaqueous soils than in subaerial soils with similar carbon contents.