51_ 



Data collected over the NHAV 93 mound provided mixed results, in comparison to 

 the September 1995 survey (Morris 1997). Station CTR showed dramatic improvement 

 with a 6-point increase in OSI values within a ten-month time period. Stations 200E and 

 200W also displayed solid improvement in benthic conditions with 2- and 1 -point increases 

 in OSI values, respectively. However, a significant decline in benthic conditions was 

 noted in the July 1996 versus September 1995 comparison of results for 200N. The 1996 

 median OSI value fell 4 points relative to 1995, due to the lack of Stage III activity and 

 shallower RPD depths. 



Station 200N was one of three areas of concern (200N, CTR, and 400S) discovered 

 during the July 1994 REMOTS® survey over the NHAV 93 mound due to the appearance 

 of dark sulphidic sediments and diffusional RPDs (Figure 4-3A; Morris and Tufts 1997). 

 As part of the DAMOS tiered monitoring protocol, sediment toxicity testing was 

 performed to verify the quality of the CDM at the sediment- water interface. Ampelisca 

 abdita bioassay testing found no significant difference in toxicity between the NHAV 93 

 CDM and sediments obtained from the historic Southern Reference Area (Morris and Tufts 

 1997). The benthic conditions observed in July 1994 were attributed to high labile organic 

 content within the CDM. 



Newly deposited sediments often support higher population densities of foraging 

 invertebrates by providing a concentrated food source within a competition-free space, 

 relative to ambient material (Germano et al. 1994). Fresh dredged material often possesses 

 a higher inorganic nutrient (N, P, Si, Fe, etc.) and organic material (bio-available Carbon) 

 content, in comparison to the depleted ambient sediments surrounding the disposal site 

 (Rhoads and Germano 1986). Disposal mounds composed of sediments that yield small to 

 moderate increases in nutrients and organic detritus tend to promote a healthy benthic 

 environment through faster recolonization and increased bioturbation (CLIS 95, CLIS 94, 

 etc.). Dredged material mounds with higher levels of organic material tend to recover at a 

 slower rate due to the increased sediment oxygen demand (SOD) caused by oxidation of 

 the labile organics (NHAV 93). 



During the September 1995 REMOTS® survey, Station 200N, as well as CTR and 

 400S, displayed significant improvement with deep RPDs and Stage III activity in the 

 subsurface sediment layers, despite the passage of a hypoxic event in the region two weeks 

 prior to monitoring activity (Figure 4-3B; Morris 1997). Apparently, a sufficient amount 

 of organic material was consumed within the dredged material deposit eighteen months 

 after the completion of the project, decreasing the SOD and allowing the development of a 

 stable benthic infaunal population. The degradation of conditions observed at Station 200N 

 during the July 1996 survey may be attributable to variability in SOD within a patchy 



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



