34 



will remove any larval set, so the 

 mound apex is usually slower to 

 recruit than the rest of the deposit. 

 Secondly, the armored surface will be 

 faunally distinct from the rest of the 

 deposit because of the coarse grain 

 size. Attached epifauna (e.g., hydroids) 

 and other sedentary or attached 

 organisms may form a distinct species 

 assemblage that is different from the 

 rest of the disposal mound and the 

 reference stations. The unstated null 

 hypothesis being tested is: 



H : The sediment grain-size major 

 mode on the disposal mound is 

 not different from the ambient 

 seafloor. 



Sediment grain-size (major mode) can 

 be confirmed either through 

 examination of the REMOTS® 

 photographs (rapid data return) or 

 from grab samples and conventional 

 laboratory grain-size analyses. 

 Rejection of the null hypothesis would 

 lead you back to Box 2.3; acceptance of 

 the null hypothesis would lead to the 

 next tier now that a change in physical 

 attributes has been eliminated as a 

 possible explanation for the anomalous 

 colonization pattern. 



Another physical factor is the mass 

 or geotechnical properties of disposed 

 sediments. Sediments which have 

 very high water content (non- 

 Newtonian muds) may not provide 

 settling larvae with adequate support 

 to keep them at or near the sediment- 

 water interface until adequate 

 consolidation has occurred. 

 Conversely, disposed sediments 

 representing over-consolidated "fossil" 

 clays from deep excavation of channel 



bottoms may be too cohesive for 

 penetration by infauna, or the 

 concentration of detrital (labile) food 

 may be too low in concentration in 

 these relict clays to support growth. 

 These same factors may affect (directly 

 and negatively) larval choices for 

 settlement. 



Many of the above physical factors 

 can be recognized from REMOTS® 

 sediment-profile images. For example, 

 changes in the physical attributes of 

 the mound apex can be documented 

 through sequential surveys. Difference 

 in geotechnical properties between the 

 mound and ambient bottom are 

 detectable from the amount of prism 

 penetration and the appearance of the 

 sedimentary fabric. If evidence for 

 adverse physical factors are present, it 

 is accepted as the most parsimonious 

 explanation for the anomalous nature 

 of colonization documented. 

 Monitoring then is continued back in 

 Tier I, and the colonization status of 

 the mound is rechecked after 6-12 

 months. 



Underlying Assumptions : The 

 management decision not to 

 implement any further action and to 

 continue to monitor colonization is 

 based on the assumption that, over 

 time, the physical properties of the 

 sediments will come into some kind of 

 "steady state" condition that will allow 

 successful, albeit slower, colonization. 

 For example, scour of the mound apex 

 will be limited by the armoring effect, 

 sediments will consolidate to 

 accommodate recruitment, or "tight" 

 sediments will be disaggregated 

 gradually and mixed with ambient 

 sediments to permit colonization. 



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



