n 



Mud clasts were observed at ten stations, and ripples were noted at six stations. 

 Biological processes accounted for relief measured at only two stations. The majority of 

 replicate photographs, however, demonstrated low surface relief, pointing to the absence of 

 recent disposal activity. 



3.2.3 Apparent Redox Potential Discontinuity Depth 



The Apparent Redox Potential Discontinuity (RPD) depth is the depth of the upper 

 oxygenated sediment layer. This depth is related to the rate of supply of molecular oxygen 

 into the bottom and the consumption of that oxygen by the sediment and associated 

 microfauna. The boundary between high-reflectance, aerobic sediment and underlying gray to 

 black sediment is termed the apparent RPD. 



Mean apparent RPD values ranged from 1.26 to 3. 13 cm and were evenly distributed 

 above and below 2.0 cm. There was no obvious spatial pattern in the distribution of RPD 

 values among stations. Shallow RPD depths have been documented under the DAMOS 

 Program in areas affected by past dredged material disposal (e.g., SAIC 1984). RPD values 

 measured at the Mill-Quinnipiac River (MQR) disposal mound located in the Central Long 

 Island Sound Disposal Site ranged from 0.54 to 2.00 cm in August of 1992. Although 

 disposal operations at the MQR mound ceased in 1983, recolonization of the mound by 

 ambient benthos has been relatively slow compared to other disposal mounds within CLIS. 

 The wide range of RPD values measured among stations showing dredged material at the 

 Bridgeport Disposal Site suggests that bioturbation in the area surveyed may have been 

 disrupted by surface disturbance (i.e., trawling). 



In addition, the reflectance contrasts across the RPD boundary were typically not 

 distinct and were similar for both ambient sediments and relic dredged material. Low RPD 

 contrasts indicate the lack of relatively high inputs of organic-rich material, such as recently 

 deposited dredged material. 



3.2.4 Infaunal Successional Stage 



Infaunal successional stages refer to the sequential appearances of benthic infauna 

 assemblages following seafloor disturbances, such as dredged material disposal or a major 

 storm event (Rhoads and Germano 1982, Revelas et al. 1987). The sequence proceeds from 

 the colonization of disturbed areas by Stage I pioneering assemblages (i.e., near-surface, tube- 

 dwelling polychaetes). Stage I organisms are eventually replaced by Stage II infaunal deposit 

 feeders (i.e., shallow-dwelling bivalves or tubicolous amphipods), followed by Stage III head- 

 down deposit feeders. The recolonization sequence generally proceeds to Stage III 

 assemblages as long as the bottom is not redisturbed. 



Reconnaissance Survey of the Historical Bridgeport Disposal Site, August 1992 



