In each experiment, the water was subdivided into three 

 7.5-1 containers a control that was not modified in any way; an 

 experimental container to which the HCH in an acetone solvent 

 was added; and a solvent control that was treated only with the 

 same amount of acetone that was used as the carrier for the 

 HCH. In the oceanic experiment, the HCH treatment was 

 replicated. At 0, 24, and 48 h after the experiments were 

 started, samples were withdrawn for each of the following 

 measurements: 



/. The concentration of HCH was routinely measured in 

 each container by withdrawing 1 ml samples. In the oceanic 

 experiment, the amount of HCH that adhered to the container 

 walls was also measured by washing down the container walls 

 with solvent at the end of the experiment. The specific amounts 

 of HCH and HCH already present in the ambient water, as well 

 as that added to the experimental containers, is shown in 

 Fig. 1. 



2. The concentration of nutrients, including nitrate and 

 nitrite ( N+N ), ammonium ( NH4), phosphate ( PO4 ), and silicate 

 (SKOHlj), were measured on an autoanalyzer using 

 conventional autoanalyzer techniques on 50-ml samples 

 (WhMedgc etal., 1981). 



3. The concentration of chlorophyll a was measured by 

 the extracted fluorescence method on 50-ml samples (Parsons 

 eial.. 1984). 



4. The rates of ammonium uptake were measured by the 

 "N tracer method on 1 1 samples (Sambrotto et al., 1986). 



5. Bacterial counts were obtained from staining and 

 direct microscopy, and bacterial activity was measured by the 

 'H thymidine technique on 1 50-ml samples (Fuhrman & 

 Azam, 1982). 



6. Microzooplankton abundance and was estimated from 

 ciliate counts. These were done immediately on board by 

 microscopic counting of unstained 100-ml samples. 



7. Additional volume was withdrawn from the 

 experimental containers for other measurements that are not 

 discussed here. The combined volume requirements of all 

 samples were accommodated within the experimental design 

 and the limitations imposed by the 7.5-1 containers. 



Results 



The amount of HCH added to the experimental containers 

 at the beginning of each experiment was composed of equal 

 parts of the a and y isomers (Fig. la). In all experimental 

 containers, the concentration of HCH decreased over the 48-h 

 period. The net loss of total HCH in the shelf and oceanic 

 replicate #1 were similar, although the net loss in oceanic 

 replicate #2 was almost 50% greater (Fig. Ic). In the oceanic 

 replicates, the net loss of a HCH was slightly greater than that 

 for Y -HCH. 



Functionally, the remaining measurements fall into one of 

 three groups. Group 1 measurements are those that reflect only 

 the biomass of the organisms in the containers and include 

 chl a. bacterial counts, and ciliate counts. Group 2 measurements 



a) 



CD 



d 



X 



b) 





X 



o 



100 

 80 

 60 

 40 

 20 

 



100 

 80 

 60 

 40 

 20 







.— ^ 



ft 



■ 



30 , 



JJl 



1 



t 



u — -L 



c 



E 

 nj 



DC a: 



I i 



o 00 



DC 



C\J 

 IT 



c\j 

 DC 



CM 

 DC 



« 



ffl E - « 



g I ^ g 



C) 



Shelf expt. 



Oceanic R.#f Oceanic R.#2 



Fig. I . The concentrations of a and y isomers of HCH in the experimental 

 (HCH) containers at the beginning and end of the shelf (Fig. la) and 

 oceanic (Fig. lb) experiments. Also shown are the total HCH 

 concentrations in the ambient water when it was first collected and the 

 concentrations recovered from the walls of the containers at the end 

 of the oceanic experiment. Each value is the result of two analyses. 

 Fig. 1 c summarizes the net changes in each isomer in the experimental 

 containers over the 48 h periods. 



are those that reflect both biomass and specific activity and 

 include bacterial activity and net changes in ambient nutrients. 

 Group 3 measurements reflect only the specific uptake rates of 



365 



