Sidescan Sonar Image, Surficial Geologic Interpretation, and Bathymetry of the Long Island Sound Sea Floor off Hammonasset Beach State Park, Connecticut

Ongoing research by the U.S. Geological Survey (USGS) in Long Island Sound, a major East Coast estuary surrounded by the most densely populated region of the United States, is building upon cooperative research with the State of Connecticut that was initiated in 1982. During the initial phase of this cooperative program, geologic framework studies in Long Island Sound were completed and results published (Lewis and Needell, 1987; Needell and others, 1987; Lewis and Stone, 1991). Emphasis of the present program in Long Island Sound is shifting from framework studies toward studies of the sediment distribution, processes that control this sediment distribution, nearshore environmental concerns, and the relation of benthic community structures to the sea-floor geology. Because of the enormous surrounding population, large inputs of anthropogenic wastes (e.g., fertilizer and sewage) and toxic chemicals have produced stresses on the environment of the Sound, causing degradation and potential loss of benthic habitats (Long Island Sound Study, 1994). To examine this problem, we are constructing sidescan sonar mosaics (complete-coverage acoustic images) of the sea floor within areas of special interest, such as in areas affected by seasonal hypoxia like the Norwalk survey or near major coastal resources like the Hammonasset Beach survey (fig.1). The mosaic that we have constructed off Hammonasset Beach State Park and which is presented herein allows insight into the geological variability of the sea floor, which is one of the primary controls of benthic habitat diversity. It also provides a detailed framework for future research, monitoring, and management activities, and it improves our understanding of the complex processes that control the distribution of bottom sediments, benthic habitats, and associated infaunal community structures off one of the most significant coastal recreational facilities within the State of Connecticut. Because precise information on environmental setting is important to the selection of sampling sites and to the accurate interpretation of point measurements, the sidescan sonar mosaics also act as base maps for subsequent sedimentological, geochemical, and infaunal sampling and bottom photography