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occurs in the microaerobic siiiTicial microLi\er of the sediment tliioiigh nhich NH.. derived 

 front rcminerahzation of the relativeh' small ponion of paniculate nitrogen that acnialK 

 reaches the sediments, is fluxed. As the NH. diffuses through the surface microla\er on its 

 \\ay to the ^^•ater column, a fraction is oxidized to NOj (nitritlcation). a portion of \\hich is 

 subsequenlh' re-reduced to N- u here it escapes from the s>'slem. The combined effect is to 

 fa\or plnsical mechanisms of nitrogen remo\al from relaliA'ely ^^■ell tlushed systems such as 

 Boston Harbor. Hence, transport of large amounts of additional nitrogen to Massachusetts 

 Ba>- will likeh' not occur \'ia input from the proposed outfall. Secondly, the modeled zone 

 around the proposed outfall an here nutrient enrichment abo\e ambient is predicted to be 

 significant (e.g.. 200:1 dilution zone) is remarkabh' small, w'nh migration of effluent plume 

 tending toward the \\est. The eastern boundan of the dilution gradient is quite sharp, 

 according to this modef and onh' 5-8 km closer to Stellwagen Bank than that predicted for 

 the present outlall. It appears to this re\'ie\N'er tliat mixing is sufficiently intense at the outer 

 site that some degree of uncertainty' regarding the details of the model can be tolerated 

 without altering the o\'erall conclusion that nutrient input into Massachusetts Ba\' \\\\\ likely 

 not be much different. It would seem that a substantial modeling oversight would be required 

 to alter these conclusions, such as unforeseen lateral transport of a coherent plume for 

 substantial distances. 



With respect to potential effects of outfall-relaied nutrient ennchmeni upon 

 plnioplankton populations the preparers liaNe used a reasonable \\ eight of e\idciice approach 

 to conclude that the proposed outfall \\ lii not lead to large changes m plmopiankton 

 populations. An additional approach regarding this ma\- be to look at the zone of significant 

 nutrient enrichment and predict the Topical length of time a ph>toplankter would be rvpicalh' 

 be exposed to these enriched conditions. For example, giA^en proposed outfall discharge rates 

 (about 200.000 m'hr'') and a \olumetric estimation of the 200:1 dilution zone (about 216.000 

 nv) an estimated dilution rate of approximateh' 0.93 hr'' is obtained. Assuming rapid 

 homogeneous mixing NMthin this zone the 95° o clearance time is approximateh 5 hr. This is. 

 of course, not an entireh correct approach to be emplo>'ed and \Nill >ield an underestimate tor 

 this term, but when modeled propeii\' liie clearance time still might be rather short. Gi\en 

 N'arious nutrient-stimulated ph>ioplanktcn groNNlh rates it should be possible to proxide a 

 NAorst case estimation of the zone of ph>"toplankton population enrichment. The quasi-steady 

 state zone of biomass increase \\ould be the result of the race between the abilit\' of the 

 ph>ioplankton to rapidh- respond to transient nutrient enrichment and being dispersed to 

 population levels that are indistinguishable from that of the iecei\ing waters. It also iiiaN' be 

 possible to predict nutrient effects on ph>TOplankton b>' comparison of predicted dilution 

 properties of the outer outfall site with similar measures obtained for Boston Harbor where. 



