shelf and oceanic experiments (Fig. 6). These observations 

 suggest that there is a causal link between the phosphate pool 

 and bacterial activity. However, it is not known whether this 

 effect is brought about directly by the bacteria or perhaps by 

 reduced bacterial grazing by microtlagellates. 



Also, the fact that the response of the shelf community was 

 opposite to that of the oceanic communities in terms of both 

 bacterial activity per cell and net phosphate change may be an 

 effect of the known biological differences between the 

 communities. The oceanic community has a greater diversity 

 of bacterial populations as well as a more highly developed 

 microbial loop than shelf waters (Azam ct al.. 1983). Thus 

 oceanic waters harborbacterial populations that can metabolize 

 HCH and its metabolites, and in an active microbial loop, these 

 populations would quickly exert dominance. In shelf waters, 

 the rise in bacterial numbers in the treated containers (Fig. 3) 

 may simply reflect diminished grazing pressure because the 

 cell-specific activity for bacteria decreased here (Fig. 1 1 ). 



Wheeler and Kirchman (1986) suggested that bacterial 

 uptake is an important sink for seawater ammonium. In the 

 oceanic experiment the changes in cell-specific activity for 

 bacteria and ammonium uptake rates are similar and, therefore, 

 enhanced bacterial activity is one possible explanation for the 

 elevated ammonium uptake rates. However, in the shelf 

 experiment, cell-specific activity decreased in the same 

 containers that ammonium uptake rates increased and, therefore, 

 a similar cause and effect is less plausible here. 



The results of the HCH analysis on the wall washings 

 (Fig. 1) indicate that little HCH was lost to wall adhesion 

 andthat the HCH decreases observed over the experiments 

 were due to chemical or biochemical breakdown. Therefore, 

 the greater per-cell bacterial activity in the oceanic area may 

 also be responsible for the slightly greater disappearance of 

 HCH from the oceanic containers (around 35%) than from the 

 shelf container (around 31%), particularly in the case of oceanic 

 replicate #2, that exhibited the greatest net loss of HCH (Fig. 1 ); 

 bacterial activity (Fig. 4); ammonium change (Fig. 9); 

 ammonium uptake rate (Fig. 10); and bacterial activity per cell 

 (Fig. 11). However, certain freshwater phytoplankton also 

 have been shown to metabolize HCH (Sodergran, 1971; Singh, 

 1973) and hydrophobic pollutants are accumulated to varying 

 degrees by marine phytoplankton (Rice & Sikka, 1973). Thus, 

 neither the organisms nor the mechanisms responsible for the 

 observed decrease in HCH can be identified in our experiments. 



This work was supported by NSF grant #DPP86 13769. This 

 project was part of the Third Joint US-USSR Bering & Chukchi Seas 

 Expedition aboard the Soviet research vessel Akademik Korolev. We 

 express appreciation to the US Fish and Wildlife Service, USA, and 

 the State Committee for Hydrometeorology, USSR, who made our 

 participation possible. In addition, we would like to thank Dr. Richard 

 Dugdale for analyzing the 13N samples and Dr. Clifford Rice for his 

 helpful comments on pesticide effects. Last, but not least, we would 

 like to thank the captain and crew of the R/V Akademik Korolev for 

 their many contributions to our work at .sea. 



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