Development of Subaqueous Soil Interpretations: Eelgrass Restoration, Heavy Metal Accumulations and Carbon Storage.

Estuarine subaqueous soils are permanently flooded soils that occur immediately below the intertidal zone to water depths of generally <2.5 m in protected coves, bays, inlets, and coastal lagoons. Although mapping protocols for developing subaqueous soil surveys are well defined, the corresponding interpretations are lacking. The specific interpretations we are exploring include: the affect of soil type on the success of eelgrass restoration; the role of subaqueous soils in the storage and sequestration of carbon on a landscape and region-wide scale, and the relationships between heavy metal accumulation and subaqueous soil distribution. Ratings for the use and management of varying soil types for eelgrass restoration are being developed from eelgrass coverage assessments, experimental transplant survival, and eelgrass production measurements. Preliminary eelgrass coverage assessments of three Rhode Island coastal lagoons found that lagoon bottom and flood-tidal delta slope soil-landscape units have significantly higher average eelgrass cover than flood-tidal delta flat and washover-fan flat units. In order to explore carbon storage and sequestration in subaqueous soils, vibracore samples were collected from a range of soil landscape units from three Rhode Island coastal lagoons. Carbon pools (calculated on an area basis; Mg ha^-1) were compared to adjacent subaerial soils and among shallow subtidal landscape units, habitats, and estuaries. Our preliminary data found an average of 181 Mg ha^-1 of carbon stored in lower energy landscape units and 88 Mg ha^-1 in higher energy units. Subaqueous carbon pools were as large, or larger, than adjacent subaerial soils suggesting subaqueous soils may be an important carbon sink. Heavy metal accumulation is being assessed from XRF data per soil-landscape unit. We will continue to develop interpretations for subaqueous soil maps relative to carbon storage and sequestration, heavy metal accumulation, and eelgrass restoration.