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Cutting to the CoreContributors: Mark Stolt, URI Natural Resources Science; Michael Bradley, URI Environmental Data Center (EDC); James Turenne and Maggie Payne, USDA Natural Resources Conservation Service (NRCS); John King, GSO It is not exactly like drilling for oil and hoping for a gusher, but there is much to be revealed by digging down and taking core samples from the shallow seafloor to help guide how we manage our coastal ecosystems. Taking core samples is labor intensive, and analyzing them requires even more time and attention to detail. The information hidden in the cores, however, is essential to marine and soil scientists in understanding the history of a site and the composition of benthic habitats. While a SPI image (see page 6) provides a detailed look at the water column-soil interface, it provides little information regarding the deeper soil and sediment. To investigate the deeper materials, cores are collected. A core is a cylindrical sample of soil and sediment that can be many meters long. The top part of a core sample contains material that was recently deposited. As you go down the core, the material is older and older. Cores provide a detailed history, sometimes over thousands of years, of a specific site. They can show evidence of extreme climatic events, changes in the hydrology of an area, changes in the ecology of a specific location, and they can even document when areas were first covered by marine waters. The SPI camera is rapid and is helpful for covering larger areas, but coring delivers much greater detail of information than does SPI. MapCoast coring is done from a pontoon boat. A vibra-core is inserted through a “moon pool” (or hole) in the deck of the boat and into the soils and sediments at the bottom of the estuary. A vibra-core, as the name implies, uses vibration as the force to drive an aluminum or PVC core barrel into the lagoon or Bay bottom. The weight of the device along with the high-speed vibration allows soil, sediment, and small rock fragments less than 8 centimeters (cm) (3 inches) to enter the core. Once the vibra-core reaches the desired depth (typically 2 meters), the core is pulled out using a winch or chain-fall. Numerous cores are collected for an area and examined. The sampling locations are recorded with a GPS. Cores are labeled on the boat and taken back to the University of Rhode Island (URI) where they are stored in a refrigerator until being described and sampled. Prior to this analysis, cores are cut in half in a laboratory and photographed using a high-resolution digital camera. One half of the core is measured every 1.3 cm (0.5 inch) for physical properties (e.g., density) and archived in a repository for future use. The other half of the core is studied by horizon (soil layers having the same properties). The scientist records such properties as color; amount of sand, silt, and clay; rock and shell fragments; presence of hydrogen sulfide; pH; and numerous other properties that allow MapCoast researchers to accurately characterize, classify, and map the shallow-water landscape. These data are stored in a database program designed for soil surveys. Samples of each of the layers are placed in bags and sent to the soil lab at URI or to the National Soil Survey Laboratory (the largest soil lab in the world) in Lincoln, Neb., where a full analysis of the chemistry and physical properties is completed. The physical, chemical, and morphologic information is used to create a database of the soil types that occur in shallow-water estuarine environments. This information allows scientists to develop soil map units and build use and management interpretations for the various soil types that occur within an estuary. |
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