50 



As PAHs enter seawater from various sources, they quickly become adsorbed onto 

 organic and inorganic particulate matter, and the majority are then deposited in bottom 

 sediments. Once in bottom sediments, PAHs may undergo biotransformation and 

 biodegradation by benthic organisms. The principal degradative processes for PAHs in the 

 marine environment are photoxidation, chemical oxidation, and biological transformation by 

 microbes and aquatic animals (Keimish 1992). 



Normalized and non-normalized PAH concentrations were highest at 2000S. The 

 simis of LMW and HMW non-normalized PAH concentrations at 2000S were approximately 

 the same as at WLI, and concentrations at the other two reference stations were lower than at 

 WLI. After normalizing to fme-grained percentages, 2000S data were higher than at WLI 

 and were close to concentrations measured at the two higher NS&T stations (Sheffield Island 

 and Throgs Neck). Fine-grained normalized data at 2000W and WLIS-REF were still lower 

 than at WLI. 



Normalizing data to TOC serves to increase the relative PAH concentrations at the 

 WLIS reference stations. The sum of TOC-normalized PAH concentrations at 2000S was 

 higher than at all of the other stations for both LMW and HMW PAHs. Summed 

 concentrations of PAHs at 2000W and WLIS-REF were also higher when normalized, and 

 were higher than at WLI except for total LMW PAHs at 2000W. The apparent increases in 

 TOC-normalized data are due to the fact that TOC values at the WLIS reference stations are 

 lower overall than the NS&T data. 



4.4 Bottom Water Dissolved Oxygen 



The objective of the dissolved oxygen (DO) sampling was to assess near-bottom DO 

 concentrations relative to benthic habitat conditions within the reference areas and at the 

 active disposal point. Bottom waters DO concentrations, ranging from 5.6 to 5.9 mg-l'*, 

 were within the aerobic range (Table 4-3) and were slightly greater than the 4.1 to 



4.5 mg-r' range observed in 1990 (Germano et al. 1993). This increase in DO is expected 

 due to the cooler water temperamres during the June 1991 survey compared to temperamres 

 during the July 1990 survey. Near- surface DO concentrations, ranging from 9.0 to 



11.0 mg-r', were significantly greater than near-bottom values; however, this difference is 

 most likely attributable to thermal stratification which was apparent in the CTD profiles. 



Low DO levels do not appear to affect the behavior of benthic organisms or structure 

 of benthic assemblages until the concentration decreases to the dysaerobic threshold of 

 ~ 3 ppm (Table 4-4 and Tyson and Pearson 1991). Given the similarity of bottom water DO 

 concentrations at the disposal site and reference stations, this parameter has apparently not 

 been affected by disposal operations. Dissolved oxygen concentrations are usually not 

 dependent on localized phenomenon; DO levels in Long Island Sound have been linked to 

 broader oceanographic events, including seasonal temperamre shifts and nutrient inputs. 



Monitoring Cruise at the Western Long Island Sound Disposal Site, June 1991 



