and seasonally. The results indicate small-scale spatial and 

 temporal variability not only in DO concentrations, but also in 

 the vertical distribution of salinity and temperature. In part, 

 this variability is the result of frequent tide or wind-induced 

 mixing of the water column. In addition, estuarine flow patterns 

 (i.e., the interaction of variable freshwater inputs from the 

 Connecticut and Thames Rivers with changing tidal regimes) move 

 parcels of water having very different temperature, salinity, and 

 DO characteristics through the area at different times. 



While some of the CTD/DO plots obtained on 27 and 29 

 July suggest that the water column was seasonally stratified, 

 others show a vertically mixed pattern at a variety of bottom 

 depths with no apparent correlation between depth or location. 

 Given the above considerations, the observed changes in 

 temperature, salinity, and density at depth more likely reflect 

 the passage of different parcels of water at the time of sampling 

 rather than a stable and persistent density gradient. The absence 

 of near-bottom oxygen depletion, and the uniform vertical 

 distribution of dissolved oxygen observed at nearly every station, 

 further suggest that the water column was well-mixed at the time 

 of the survey. Similar results were found at the Western Long 

 Island Sound (WLIS) Disposal Site and the Central Long Island 

 Sound (CLIS) Disposal Site in 1987. The WLIS survey was performed 

 in November 1987 and a well-mixed water column was seen (due to 

 the cooler water temperatures) . At CLIS, which was sampled in 

 late August and early September 1987, results were similar to 

 those found at NLON. An absence of near-bottom oxygen depletion 

 and a uniform vertical distribution of dissolved oxygen 

 concentrations suggested a mixed water column at the time of the 

 CLIS survey. 



In the absence of a strong and persistent pycnocline, 

 the development of hypoxia or anoxia in near-bottom waters at New 

 London would not be expected. The data support this conclusion 

 but also indicate a strong daily fluctuation in the DO regime. On 

 27 July, DO concentrations throughout the water column were well 

 above levels which have been defined as biologically "critical" 

 (Table 4-1) . Two days later, most of the DO values at the site 

 could still be considered aerobic but were noticeably lower, while 

 values at three nearby reference stations (W-Ref, 1500NW and 

 NE-Ref ) were in the "hypoxic" range (Table 4-1) . These results 

 might be attributable to either the in-situ consumption of oxygen 

 or an influx of low DO parcels of water. The sampling used in 

 the present survey did not allow accurate assessments of either 

 the spatial distribution of such water masses or the frequency and 

 duration of their passage. 



One of the objectives of the CTD/DO sampling at New 

 London was to assess near-bottom dissolved oxygen concentrations 

 relative to REMOTS benthic analyses at and near the disposal 

 site. While it is difficult to relate the instantaneous DO 

 measurements to potential biological effects, the CTD/DO results 

 generally show that while the potential for transient hypoxic 



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