21 



monitored more frequently, the resultant OSIs from both mounds are not significantly 

 different. 



Hurricane Gloria affected FVP more severely than MQR; however, FVP recovered 

 more quickly than MQR (Figure 4-2). By 1987, both were progressing towards normal 

 (reference) OSI levels. The June 1991 survey documented the radical shift of OSIs at MQR 

 stations. Finally, Hurricane Bob and the "Halloween" storm of 1991, both of which 

 occurred after the 1991 CLIS survey, did not prevent the recolonization documented in the 

 1992 survey. 



It is apparent that MQR has cycled through several stages of stress and recovery, and 

 that the recovery has been slower than at other CLIS mounds. The current state of MQR, 

 improved since 1991 but still below reference, is a result of the decrease of habitat quality 

 observed between the 1987 and 1991 REMOTS® surveys. A smaller scale decrease in OSI 

 values also occurred at CS-1 (from 11 to 7) during the same time interval (Figure 4-1). The 

 cause of the stress recorded at MQR during this time period is crucial to understanding 

 recolonization factors at MQR. 



4.3 Recolonization Factors at MQR 



Factors affecting habitat quality and postdisturbance recolonization are either chemical 

 or physical or both. Previous explanations of the slow benthic recolonization at MQR have 

 been chemical, including the presence of hypoxic water, a high organic content of MQR 

 sediments, and elevated levels of sediment contaminants (SAIC 1990a, Murray 1992). 

 Physical factors which may be responsible for benthic disturbance include both large-scale 

 and small-scale processes. Large-scale events include storms as in the obvious case of 

 Hurricane Gloria (SAIC 1989b); these events should affect all of the mounds at CLIS, as 

 well as the CLIS reference areas. Small-scale disturbances include biological (macrofauna) 

 and anthropogenic (trawling, etc.) sources. Both of these types of small-scale disturbances 

 could occur within individual mounds. 



It is clear that both the concentrations of contaminants and the content of organic 

 carbon in the sediments at MQR are higher than at other capped CLIS mounds. High 

 organic carbon would be expected to ameliorate contaminant effects, to some extent, by 

 "removing" or binding contaminants so that they are not as available to biota. Results from a 

 recent coring study at MQR indicated that the capping material at MQR does contain 

 relatively high levels of polyaromatic hydrocarbons (PAHs) (Murray 1992). The presence of 

 methane in REMOTS® pictures as recent as the present survey indicates that relatively high 

 concentrations of organic carbon remain in the MQR sediments. However, the pattern of 

 recolonization determined from the sequence of OSIs at MQR suggests that recolonization 

 does occur, despite the potential stress associated with contaminated sediments. 



Recolonization of the Mill-Quinnipiac River Disposal Mound (MQR): Results of a REMOTS® Survey, August 1992 



