Subaqueous Soils, Water Quality, and Estuary Health.
Margot K. Payne and Mark H. Stolt. Univ of Rhode Island, 105 Coastal Institute Kingston, 1 Greenhouse Road, Kingston, RI 02881
Recent soil survey efforts along the Atlantic Coast (US states of Delaware, Florida, Maine, Maryland, Rhode Island) have begun to include the mapping of subtidal environments in shallow estuaries. The mapping of these “subaqueous soils” is being driven by a recognized need for an inventory of the shallow subtidal resources. Many of these estuarine resources are being severely degraded by pollution as a result of urbanization of coastal areas. Recent demographic studies suggest that in the next 50 years 70% of the US population will live within 50 miles of the coast. Thus, continued development of coastal areas will result in increased runoff and nutrient inputs into estuaries resulting in environmental problems such as eutrophication, algal blooms, hypoxia, and fin and shellfish kills. Because soil properties and characteristics develop in response to the environment, subaqueous soils have been suggested as a possible indicator of the degree that these ecosystems have become degraded. The objective of this study is to begin to develop a soil-based approach to evaluate the quality and health of a shallow estuary. Such an indicator would allow estuary management teams to target particular estuaries for conservation, protection, and restoration of resources based on soil survey information. Three estuaries are being examined in this study: Greenwich Bay, Little Narragansett Bay, and Wickford Harbor (1200, 990, and 160 ha, respectively). Bathymetric maps were created for the study areas using a fathometer and pressure sensor tide gauges to correct depths to NAVD88. On average, 13 depth soundings per hectare were recorded. Between 40 and 45 individual soil-landscape units were identified and delineated in each estuary based on slope, depth, surficial geology, and geographic location. Predominant landscape units within the bays include bay bottom, depositional shoreline platform, mainland cove, fluviomarine bottom, and submerged beach units. Anthropogenic marina units, dredged channels, and dredge deposit shoals were also recognized. Soil cores were collected in 7 landscape units typically found in each estuary using a Macaulay peat sampler or vibracore for descriptive purposes and to characterize the soils in regard to total nitrogen, organic carbon, potential acidity, salinity, bulk density, and particle size distribution. Each month throughout the field season, redox potential is measured at 2 cm intervals within the top 15 cm of the soil at two stations within each unit. In addition, dissolved oxygen, chlorophyll a, and total suspended solids are measured monthly at each station to assist in determining the influence of water quality on the subaqueous soils. This research will aid in understanding the relationships between subaqueous soils and the landforms and water quality of the environment in which they exist. These relationships are critical to developing pedologic models that can be used to predict soil types and map subaqueous soils in shallow coastal waters.