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Benthic Habitat Mapping
Summary
Dredging and the aquatic disposal of marine sediments have direct impacts on the environment, primarily the seafloor and benthic habitats. Material dredged from harbors and navigation channels is often placed in underwater disposal sites by ports and the U.S. Army Corps of Engineers (USACE). These groups, as well as resource agencies and the public, are concerned about the fate of that material, the benthic communities impacted by the disposal, and the fish and crustaceans that feed upon those benthos.
Various seafloor characterization and benthic habitat mapping techniques are used to select disposal sites, to characterize sediments to be dredged, to monitor disposal sites, and to evaluate environmental impacts of open-water disposal of dredged sediments. Two main environmental concerns surrounding the disposal of dredged material at open-water sites are 1) whether the material remains in its predicted location and 2) whether there are impacts to biological resources. During the past decade in both the U.S. and overseas, a significant effort has been made to investigate how benthic mapping techniques can be used to determine the physical impacts of dredging operations. This investigative effort has resulted in two recent guidance documents developed by the Centre for Environment, Fisheries, and Aquaculture Science (CEFAS) in Scotland and the U.S. Minerals Management Service (MMS). These guides advocate the use of a variety of benthic mapping techniques to monitor environmental impacts of dredging. They place primary emphasis on the use of traditional grab sampling and subsequent taxonomic analyses to evaluate impacts of dredging on benthic communities. CEFAS also concludes that underwater still and video photography are effective when assessing seabed habitat over hard or consolidated bottoms where grab or core sampling is not as efficient. What laws govern dredging activities?
In the U.S., regulation of dredged material disposal in inland and ocean waters is a shared responsibility of the U.S. Environmental Protection Agency (EPA) and the USACE. These agencies have published guidance documents on recommended monitoring approaches and techniques for evaluating the environmental impacts of disposal. Disposal site monitoring may use a variety of survey methods, many of which involve seafloor or benthic habitat mapping. Under the Disposal Area Monitoring System (DAMOS) program, developed and managed by the USACE New England District, environmental monitoring surveys using precision bathymetry, side-scan sonar, and sediment profile imaging (SPI) are conducted regularly (every one to five years) at each of eleven open-water disposal sites along the coast of New England. Benthic habitat mapping techniques help document the entire area of the seafloor where physical changes (i.e., changes in sediment type, depth, and topography) may have resulted from disposal and the impacts of such changes to resident benthic communities.
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