Soil-Landform Relationships in Shallow Estuarine Ecosystems of Downeast Maine.
Christopher T. Flannagan, Wetland Studies and Solutions, Inc., 5300 Wellington Branch Drive, Suite 100, Gainesville, VA 20155 and Laurie J. Osher, Univ of Maine, 105 Deering Hall, Orono, ME 04469.
Estuaries occupy the boundaries between terrestrial and marine systems. In recognition of their importance to the health of coastal habitats, US soil scientists have begun to investigate the genesis and morphology of the soils in estuaries and near shore coastal environments. Like upland soils, the soils of estuaries support plant growth, are susceptible to erosion and degradation of soil quality, and provide the physical and chemical resources needed for ecosystem growth and sustainability. Taunton Bay is a small, shallow estuary that is representative of nearly 50% of Maine's 4800 km coastline. Like upland soils, we observed that soil properties vary across the subaqueous landscape in predictable patterns. Landforms in the estuary were delineated by percent slope, slope shape, and water depth, as well as position relative to proximity to the estuary edge, tributary streams and estuary channels. The dominant parent material for the alluvial deposited sediments in the estuary are silts being eroded from coastal bluffs and silty clays being removed from a glaciomarine silty clay deposit blanketing the landscape beneath the present estuary. The major landforms in the Taunton Bay estuary are, in order of percent cover: Bay Bottom, Channel Shoulder, Estuary Channel, Terrestrial/Estuary Edge, Coastal Cove, Submerged & Filled Fluvial Channel, Mussel Shoal. Soils in the Bay Bottom have the finest textures and the most uniform properties. Soils on the estuary's channel shoulders have the greatest slopes, and the higher bulk density and range in soil characteristics than the soils of the Bay Bottom. Channels in the Taunton Bay estuary are approximately 23 m deep. This is too deep to support plant growth in this location, and as such, the sediments at the base and sides of the channel were not characterized. Coastal Cove soils tend to be coarser textured than the soils of the Bay Bottom and have shallower slopes. Mussel Shoal landforms appear as individual colonies growing from the Bay Bottom. The surface of the Mussel Shoal soils is approximately one meter closer to the water surface than the surface of the soils of the Bay Bottom landscape. While the Mussel Shoals appear to be living on the Bay Bottom, soil morphology to a depth of 300 cm illustrates that these locations have been host to mussel communities for hundreds of years. The Terrestrial/Estuary Edge and Submerged & Filled Fluvial Channel landforms are closest to non-submerged soils at the estuary edge. The soils of these landforms have bisequal morphology caused by sea level rise and subsequent inundation and burial of upland soils. As with all landscapes inhabited by people, there are smaller landforms in the estuary with morphology indicative of human alteration, including sandy deltas formed from mine tailings and finer textured zones the received dredged materials from an adjacent man-made channel.