30 



and recruitment of shellfish beds 

 located in harbors near navigation 

 channels. Dredging operations are 

 terminated in the late spring, during 

 the period of intensive recruitment. 

 Experience has shown that disposal 

 mounds are well-populated by 

 pioneering polychaetes within 1-2 

 weeks following cessation of disposal 

 operations. Because it is unrealistic to 

 assume that monitoring cruises always 

 can be scheduled contractually to 

 occur immediately after disposal stops, 

 a 4 to 12 week period was chosen to 

 allow sufficient time to schedule field 

 operations while still insuring that any 

 enhanced recruitment phase can be 

 detected. 



Box 2.2 "Is Stage I Population Density 



Greater Than Reference?" 



Because newly constructed disposal 

 mounds represent competition-free 

 space and the sediment usually is 

 organically enriched over the ambient 

 bottom, disposal mounds experience a 

 dense, generally uniform recruitment 

 of pioneering polychaetes over the 

 entire surface. The only noted 

 exception to this general "rule of 

 thumb" is the mound apex, which may 

 experience localized scour and erosion 

 (see boxes 2.5 - 2.6 with accompanying 

 discussion). The unstated null 

 hypothesis being tested is: 



H : The population density of 



opportunistic polychaetes on the 

 disposal mound as detected in 

 REMOTS® photographs is not 

 significantly less than that on 

 the ambient seafloor outside the 

 disposal site boundaries. 



If no further disposal takes place, 

 the population of pioneering 

 polychaetes may converge with the 

 ambient bottom after a period of two 

 years or more. Therefore this 

 hypothesis states a prediction that is 

 valid for only active disposal sites. 



The high rate of colonization is 

 documented from REMOTS® images by 

 counting the number of tubes per 

 linear centimeter along the sediment- 

 water interface. These densities are 

 compared with mean densities from 

 appropriate reference stations located 

 outside the designated boundaries of 

 the disposal site. At present, three 

 reference stations are sampled at each 

 site. The selection of "appropriate" 

 reference stations will include the 

 following factors: 



1. More than one reference location 

 outside the disposal site is needed 

 to characterize the ambient bottom 

 adequately (Hurlbert, 1984). 



2. The reference stations should have 

 had the same community structure 

 as the (pre)disposal mound area 

 (determined by a baseline survey). 



3. The reference stations should have 

 a similar sediment type as the 

 (pre)disposal mound location. The 

 reference station should show no 

 physical or chemical evidence of 

 historical disposal. 



4. The reference stations and disposal 

 mound should be located within 

 comparable water depths and as 

 near to one another as possible 

 without subjecting the reference 

 stations to the possibility of 



An Integrated, Tiered Approach to Monitoring and Management of Dredged Material Disposal Sites 



