53 



benthic environment (Figure 4-3C). However, the consistency between the three replicate 

 photographs collected in July 1996 suggests otherwise. 



Studies pertaining to seasonal cycles throughout Long Island Sound have 

 documented higher SOD within both deposited sediments and ambient material in late 

 spring (May- June; Rhoads et al. 1975). Eutrophication of the water column via waste 

 water input and terrestrial run-off promotes the development of a winter-spring plankton 

 bloom. Phytoplankton populations quickly grow and exploit the abundance of primary 

 nutrients in solution. As nutrient concentrations in the water column return to normal 

 levels, much of the phytoplankton dies, accumulates at the sediment-water interface, and 

 decays. Aerobic microbes exploit the organic detritus as a food source, producing carbon 

 dioxide (CO2) and recycling many of the nutrients. Microbial respiration begins to 

 consume a significant percentage of the available molecular oxygen in the bottom waters. 

 As bottom water temperatures increase during the spring months, microbial activity at the 

 sediment-water interface and total SOD also increase, as the supply of organic material at 

 the sediment- water interface is slowly exhausted. 



Both aerobic and anaerobic processes continue below the sediment-water interface 

 as complex organic molecules are broken down by bacterial action as well as chemical 

 oxidation. Biomrbation by the resident benthic infauna population also continues, as 

 molecular oxygen is incorporated v/ithin the surficial sediment layers through pore water 

 exchange. The relatively high DO concentrations (6 to 8 mg-l"^ ) within the water column 

 in late spring tend to support the greater oxygen demand associated with the annual 

 phytoplankton extinction without impacting the infaunal communities residing in most 

 dredged material deposits (CLIS 95, CLIS 94, etc.) or ambient Long Island Sound 

 sediments (CLIS Reference Areas). 



However, the REMOTS® data obtained over Station 200N in July 1994 and July 

 1996 suggest the impacts of this seasonal introduction of organic material (phytoplankton) 

 may be of a greater magnimde, due to the pre-existing organic load and SOD within the 

 highly enriched CDM. Therefore, the surficial sediment layers at Station 200N appear to 

 be more susceptible to namrally occurring shifts in the oxygen budget, in comparison to 

 other stations over the NHAV 93 mound. During environmental monitoring surveys 

 conducted in September of 1995 and 1997, Station 200N displayed moderate to deep RPD 

 depths. Stage III activity, and correspondingly high OSI values (Morris 1997 and Cole 

 1998). The results of the September REMOTS® surveys suggest the benthic conditions 

 present at 200N promote rapid recolonization upon the reduction of organic material input, 

 stabilization of SOD, and remrn of adequate DO concentrations (Figure 4-3 D). 



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



