Developing Subaqueous Soil Interpretations: Shellfish and Dredged Material Placement.

Over the past decade considerable effort has been put forth to map the subaqueous soils in a number of shallow lagoons and embayments. With these resource data in hand our current goals are to develop use and management interpretations for these soil resources.  In particular, our focus is toward the development of soil-based interpretations regarding the effects of placing dredged material on the land surface, and to determine what soils are best suited for shellfish.  A potential problem in many subaqueous soils is the extreme acidity produced when sulfide-bearing dredged material is placed on land and the sulfides oxidize (acid sulfate conditions).  Using a mesocosm approach, we elucidated the environmental conditions that will develop when dredged material is placed on the land surface.  Dredged materials were collected from two coastal lagoons and two embayments. Materials were placed into 72 mesocosms, placed out of doors and exposed to rainfall.  Rainfall leachate is analyzed for pH, conductivity, and sulfate content.  Results suggest that soils dredged from cove and bottom landscapes have the highest potential, while deltas and washover fans have the lowest potential to develop acid sulfate conditions.  These data suggest we can easily identify and map soils that have the potential to create acid sulfate conditions.  To explore relationships between subaqueous soil and shellfish productivity, small scale aquaculture plots were established in two coastal lagoons in Rhode Island. Oyster (Crassostrea virginica) growth is monitored on five different soil landscapes.  After one growing season (14-16 weeks), initial results suggest that differences between growth rates of oysters occur on different subaqueous soil landscapes, slower growth was observed on cove and bottom landscapes.  These data suggest we may be able to map subaqueous soils that have the highest potential for shellfish growth.