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4.0 DISCUSSION 



During the September 1995 REMOTS® sediment-profile photography surveys over 

 NHAV 93, CLIS 94, FVP, and the CLIS reference areas, a trend of lower than expected 

 RPDs and indications of low dissolved oxygen (DO) concentrations was observed. 

 Seasonal hypoxia, due to eutrophication in the protected waters of the central and western 

 Long Island Sound causing the degradation of water quality, had apparently affected both 

 the benthic and near-bottom pelagic habitats. The Long Island Sound Study (LISS), a US 

 Environmental Protection Agency (EPA) monitoring program, officially recognizes the 

 onset of hypoxia at a DO concentration of 3.0 mgT . However, the appearance of hypoxic 

 conditions in the bottom waters and surface sediments has been documented with DO 

 concentrations as high as 5.0 mgT 1 (LISS 1990). For the past several years DAMOS 

 monitoring activity has not included water sampling for DO or other water quality 

 parameters as part of its field operations because the instantaneous measure during the 

 relatively short survey period was not sufficient to determine seasonal events. However, 

 further investigation was required to determine whether the decline in the RPD and OSI 

 values at CLIS and the reference stations was related to disposal activity or a regional 

 hypoxia event. 



A comprehensive DO data set for stations throughout the Long Island Sound was 

 obtained from the Connecticut Department of Environmental Protection, Water 

 Management Division (DEP). The data was collected as part of the DEP Long Island 

 Sound Summer Hypoxia Monitoring Program and consisted of surface and bottom DO 

 values for 18 primary stations that were monitored throughout the year as well as a number 

 of secondary summer stations (June to September). Seasonal monitoring stations 23, 26, 

 and 27 and annual monitoring stations H2 and H4 were chosen due to their location 

 relative to CLIS (Figure 4-1). 



Although the data for seasonal stations 23, 26, and 27 does not continue through the 

 September 1995 field effort, a decrease in DO concentrations (4.5 mgT 1 ) was observed at 

 stations 23 and 27 in mid-August (Julian Day 226) suggesting a seasonal DO event within 

 the central Long Island Sound region (Figure 4-1). Stations 23 and 27 are situated in close 

 proximity to the disposal site in similar water depths and bottom current patterns. Both 

 stations show a downward progression in DO values for the summer of 1995. Station 26, 

 approximately 7 km north of CLIS, is located in shallower water and tends to be 

 influenced by the drainage of the Quinnipiac River and New Haven Harbor. The data at 

 Station 26 show a drastic reduction in bottom water DO, decreasing from 8.2 mgT to 

 3.4 mgT 1 over the first forty days of the monitoring program. Oxygen levels then show 

 significant rebound to 6.4 mgT 1 on Julian Day 226, displaying higher concentrations of DO 

 data, relative to the deeper stations. 



Monitoring Cruise at the Central Long Island Sound Disposal Site, September 1995 



