22 



The average small-scale surface boundary roughness for the reference area stations 

 (3.5 cm) was higher than that observed at the stations within the borrow pit (2.33 cm). The 

 reference stations are located in relatively shallow water, where the bottom may be affected 

 by the scouring action of waves and currents during high-wind events or by fishing (oyster 

 dredging) activity. The increased boundary roughness, presence of a surface shell lag 

 deposit, and shallow RPD depths observed at several of the reference stations may reflect 

 such periodic physical disturbance (Figure 3-5). However, it is notable that similar evidence 

 of physical disturbance was not observed at the borrow pit stations. 



3.2.2 Biological Conditions and Benthic Recolonization 



Three parameters can be used to assess the benthic recolonization rate and overall 

 health of the benthic environment within the borrow pit relative to the reference area: 

 apparent Redox Potential Discontinuity (RPD) depth, infaunal successional status, and the 

 Organism Sediment Index (OSI). 



The redox potential discontinuity (RPD) measured in each image provides an estimate 

 of the apparent depth of oxygen penetration into the surface sediment. The replicate- 

 averaged apparent RPD measurements for the borrow area stations ranged between relatively 

 high values of 6.33 cm and 4.55 cm at Stations 150S and 25NW, respectively, to a low value 

 of 0.90 cm at Station lOONW (Table 3-1 ; Figure 3-6). The overall average RPD value of 

 3.04 cm is considered indicative of relatively well-aerated surface sediments within the 

 borrow pit. None of the replicate images obtained within the borrow pit showed any 

 evidence of low dissolved oxygen conditions or visible redox rebounds. However, methane 

 gas bubbles were observed within the sediment column in the images obtained at Stations 

 lOONE, 25NW, and lOOSE (Table 3-1). The presence of methane suggests that the dredged 

 material at these stations contains a relatively high inventory of organic matter that is being 

 decomposed under anaerobic conditions at depth. It is notable, however, that the dredged 

 material at the sediment surface at these and other stations within the borrow pit appeared 

 well oxygenated. 



The overall average RPD value for the reference area stations (1.66 cm) was 

 considerably lower than the borrow pit station average of 3.04 cm (Table 3-2). Replicate 

 images at Stations REF5 and REF4 had extremely shallow RPD depths of 0.42 cm and 0.52 

 cm, respectively, possibly related to physical disturbance of the sediment surface (Figure 3- 

 5). There was no indication of low dissolved oxygen conditions, methane, or visible redox 

 rebounds at the reference area stations. 



As expected for a recent dredged material deposit, the successional stage 

 recolonization status of the Morris Cove borrow pit included principally Stage I pioneering 



Monitoring Cruise at the Morris Cove Borrow Pit 



