62 



promoting rapid benthic recolonization. The availability of oxygen in the bottom waters of 

 western Long Island Soimd is always a major concern during the smnmer months. In 

 comparison to other Long Island Sound disposal sites (CLIS, NLDS) bendiic 

 recolonization at WLIS tends to be slower, due to the profound effects of seasonal 

 hypoxia. 



Hypoxia is a condition of reduced DO concentrations in the water column, generally 

 occurring within the western and central regions of Long Island Sound in mid to late 

 August. The complications associated with seasonal hypoxia and benthic recolonization at 

 WLIS has been documented by DAMOS monitoring efforts since 1985 (SAIC 1987). This 

 annual decrease in DO is the direct result of eutrophication, the influx of primary nutrients 

 from terrestrial sources into the protected waters of western and central Long Island 

 Soimd. Although the cause of hypoxia is clearly defined, its onset and severity are directly 

 dependent on many other environmental factors (i.e., nutrient mput, frequency of storms, 

 fresh water input, water temperature, etc.). 



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 mg 1'. However, the appearance of hypoxic conditions in the bottom 

 waters and surficial sediment layers has been documented with DO concentrations as high 

 as 5.0 mg r' (LISS 1990). Furthermore, bottom water DO concentrations in the East 

 River and extreme western Long Island Sound have been known to fall to anoxic levels 

 (0.0 mg-r') during the month of August, decimating the entire infaunal population. 



During prior monitoring efforts at WLIS, a CTD probe equipped with a DO sensor 

 was used to monitor oxygen concentrations at the disposal site and reference areas 

 (Williams 1995; EUer and Williams 1996). In recent field operations, this practice has 

 been discontinued due to the shortcomings associated with the instantaneous measurement 

 of DO. The collection of DO profiles of the water colimin during the relatively short 

 survey period did not provide the data necessary to discern the possible influences of 

 dredged material deposition from the seasonal effects within the region. 



In order to track the development of hypoxic conditions in Long Island Sound, a 

 comprehensive DO data set for stations located throughout the region was obtained from 

 the Connecticut Department of Environmental Protection (CTDEP), Bureau of Water 

 Management. The data was collected as part of the CTDEP Long Island Sound Summer 

 Hypoxia Monitoring Program and consisted of surface and bottom water DO values for 

 eighteen primary stations monitored throughout 1996, as well as a number of secondary 

 summer stations (Jime through September). Seasonal monitoring stations 5,8, and 9, and 

 annual monitoring stations C2 and D3 were chosen due to their location relative to WLIS 

 (Figure 4-6). 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1996 



