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USGS Open-File Report 2005-1162, Sidescan-Sonar Imagery and Surficial Geologic Interpretation of the Sea Floor off Bridgeport, Connecticut


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Figure 1. Map showing location of the Bridgeport, Connecticut study area (red polygon).
Figure 1. Map showing location of the Bridgeport, Connecticut, study area. Click on figure for larger image.

The U.S. Geological Survey (USGS), in cooperation with the National Oceanic and Atmospheric Administration (NOAA) and the Connecticut Department of Environmental Protection (CT DEP), has produced detailed geologic maps of the sea floor in Long Island Sound, a major East Coast estuary surrounded by the most densely populated region of the United States (fig. 1). These studies have built upon cooperative research between the USGS and the State of Connecticut that was initiated in 1982. The current phase of this research program is directed toward studies of sea-floor sediment distribution, processes that control sediment distribution, nearshore environmental concerns, and the relation of benthic community structures to the sea-floor geology.

Figure 2. Sidescan-sonar mosaic of the sea floor off Bridgeport, Connecticut (NOAA survey H11045).
Figure 2. Sidescan-sonar mosaic of the sea floor off Bridgeport, Connecticut, (NOAA survey H11045).

Anthropogenic wastes, toxic chemicals, and changes in land-use patterns resulting from residential, commercial, and recreational development have stressed the environment of the Sound, causing degradation and potential loss of benthic habitats (Koppelman and others, 1976; Long Island Sound Study, 1994). Detailed maps of the sea floor are needed to help evaluate the extent of adverse impacts and to help wisely manage resources in the future. Therefore, in a continuing effort to better understand Long Island Sound, we are constructing and interpreting sidescan-sonar mosaics (complete-coverage acoustic images of the sea floor) within specific areas of special interest (Poppe and Polloni, 1998). The mosaic presented herein, which was produced during survey H11045 by NOAA's Atlantic Hydrographic Branch, covers approximately 190.3 km² of the sea floor in west-central Long Island Sound off Bridgeport, Connecticut (fig. 2).

The mosaic and its interpretation serve many purposes, including:

  1. defining the geological variability of the sea floor, one of the primary controls of benthic habitat diversity;
  2. improving our understanding of the processes that control the distribution and transport of bottom sediments and the distribution of benthic habitats and associated infaunal community structures;
  3. providing a detailed framework for future research, monitoring, and management activities.

The sidescan-sonar mosaic also contributes to subsequent sedimentological, geochemical, and biological observations, because precise information on environmental setting is important for selection of sampling sites and for appropriate interpretation of point measurements.

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