Morphologies and Properties of Subaqueous Soils Supporting Seagrasses.
Larry Ellis, Kelly Fischler, and Mary Collins. Univ of Florida, Soil & Water Science Dept, 2169 McCarty Hall A, PO Box 110290, Gainesville, FL 32611
In a subaqueous environment, submerged aquatic vegetation (SAV) act as ecosystem engineers, thus amplifying the role of biota as a soil forming factor. Presented here is a summary of SAV/soil relationship concepts from sediment-based literature along with the initial conclusions of pedologists who have recently begun studying these “sediments” from a soils-based perspective. Typically, SAV is thought to reduce current velocities and therefore enhance the settling of suspended particles. Additionally, some particles are directly trapped by SAV blades and re-suspension of particles is muted. In environments supporting seagrasses, suspended particles are often silt-sized or smaller and can contain considerable organic fractions. Thus seagrasses increase the concentration of fine particles and organic matter (OM) in the soil. While many seagrass leaves are exported from the system, some are deposited to the soil surface. Thus seagrasses add OM to the soil surface. Additionally seagrasses add organic matter to the soil by the decay of roots and the exudation of organic matter. Seagrass beds support large numbers of burrowing invertebrates that facilitate the mixing of sedimentary and root-based organic matter. Finally, seagrasses are also known to oxidize the soil in the rhizosphere thus restricting sulfate reduction and facilitating the oxidation of soil organic matter. There is still much debate concerning the relative contributions of the various OM sources (e.g. from adjacent ecosystems, rivers, and the grassbed). Understanding these contributions is important for pedology because it allows for the refinement of subaqueous soil formation models.