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generated by bag impact on the bottom would be smothered. Deposits of material greater than 

 several millimeters depth would probably bury many invertebrates, which have adapted to 

 extremely low sedimentation rates characteristic of the abyssal seafloor. Analogies with benthic 

 recovery rates from abyssal turbidites suggest that it may take hundreds to thousands of years to 

 return to an equilibrium community of animals following episodic disposal of waste materials 

 greater than several centimeters over large areas of the abyssal seafloor. Given this very 

 long-duration response of the abyssal community to disturbances on the large scale of turbidity 

 flows, it would be preferable to limit the size and number of waste placement sites to minimize 

 overall environmental impact. 



Direct transport of contaminants to surface waters by abyssal animals via bioaccumulation 

 processes would not occur because they do not venture out of abyssal depths. There does exist 

 one potential pathway, however, via transport in the yolks of eggs of certain fishes and 

 invertebrates. These eggs are known to rise to shallow depths in the ocean and develop into 

 larvae which, in turn, mature into juveniles, and the juveniles then return to the abyssal depths. 

 While the eggs, larvae, and/or juveniles are at the shallow water depths, they could be consumed 

 by other species closer to food chains utilized by man. 



Ten-year numerical simulations of a simplified abyssal food chain were run to simulate impact of 

 a one-year duration placement of sewage sludge and/or organic-rich dredged material on the 

 abyssal seafloor. One model simulation predicts a significant perturbation of the reproductive 

 and growth cycle, with the natural 1-year cycle altered to a 6-year cycle for the megafauna 

 (fishes and large invertebrates); we note that the timing of these cycles may be an artifact of 

 oversimplifications in the modeled food chain - or this timing may ttim out to be real - at this 

 point too little is known about the origin of this mathematical result to make any informed 

 judgements about its origin (see Figure 4). To better understand the significance for eggs of 

 megafauna as potential pathways for contaminant export from the abyssal seafloor, the export of 

 polycyclic aromatic hydrocarbons (PAHs) via this pathway was estimated using data from the 

 1 06-mile site: the annual transport of PAHs from a 1-year placement of sewage sludge and/or 

 dredged material (assuming 1x10* m') is estimated to be 1 .7 grams, truly minuscule (Valent and 

 Young 1995). 



Geochemical Processes - Placement of million-plus cubic meters of sewage sludge and/or 

 dredged material on the abyssal seafloor would significantly alter the local oxic/anoxic balance 

 affecting geochemical processes at the seafloor surface and in the subseafloor (see Figure 5). We 

 have conducted numerical model simulations of the impact of placement and remineralization of 

 combined sewage sludge and dredged material on the abyssal subseafloor, predicting the impact 

 of organic matter oxidation reactions on profiles of oxygen, nitrate, sulfate, sulfide, ammonium, 

 total inorganic carbon, alkalinity, and particulate organic carbon. The model results show that 

 the available oxygen in the water overlying and downcurrent of the isolation site would not be 

 depleted to a level injurious to abyssal animals. However, to attain geochemical equilibrium 

 (referenced to conditions prior to waste placement) would take thousands to tens-of-thousands of 

 years. This result is not surprising because turbidite deposits at abyssal depths which occurred 



