the plankton and include the NHj uptake rates as well as the 

 bacterial activity on a per-cell basis. To further organize the 

 experimental results, the data are presented as the net changes 

 observed during the 48 h of the experiments (i.e., the 

 measurement at the time of observation minus the initial 

 [Otime] measurement). 



Chlorophyll a levels increased dramatically in all of the 

 containers in the shelf experiment (Fig. 2). The increase was 

 less in the incubations exposed to acetone (the acetone control 

 and the HCH containers). The observed increases in chl a 

 levels in the oceanic experiment were much less than those on 

 the shelf. Unfortunately, the untreated control in the oceanic 

 experiment ran out of sample volume before the final chl a 

 sample could be taken. 



The 48-h increase in bacterial numbers was the same for 

 both the acetone control and HCH experimentals in both shelf 

 and oceanic experiments (Fig. 3). However, the changes in 

 bacterial numbers relative to the untreated control were very 



control 



acetone HCH rep.#1 HCH rep.#2 



Fig. 2. Net 48 h changes in chl <; concentration in the untreated control, 

 acetone control and HCH experimental containers. Initial values for 

 each expenment are given in Table 1. 



control 



HCH rep,#1 HCH rep. #2 



Fig. 3. Net 4X h change in bacterial numbers in the untreated control, acetone 

 control and HCH experimental containers. (Note that untreated shelf 

 control did not change). Initial values tor each experiment are given 

 in Table 1. 



different between the shelf and oceanic areas. In the shelf 

 experiment, bacterial numbers in the acetone and HCH 

 containers increased more than the untreated control (which 

 did not change). In the oceanic experiment, the opposite 

 change occurred. 



There also was a difference between the shelf and oceanic 

 response on the basis of bacterial activity (thymidine 

 incorporation; Fig. 4). There was little difference between the 

 treatments and controls in the shelf experiment. However, in 

 the oceanic experiment, acetone markedly depressed activity. 

 The presence of HCH appeared to make up for this inhibition 

 in that bacterial activity in the HCH experimentals were similar 

 to the untreated control. 



Changes in ciliate abundance are only available for the 

 shelf experiment (Fig. 5). Ciliate numbers decreased in all 

 containers. However, the decrease in the acetone control was 

 less than either the untreated control or the HCH experimental. 



The 48-h changes in the concentration of dissolved 

 inorganic nutrients fall into one of three distinct categories: 



/. The effect of treatments on net 48-h changes are similar 

 in both shelf and oceanic experiments and the effects of HCH 

 cannot be distinguished from acetone alone. In this category 



140 



T 120 



- 100 

 I 80 



I 60 



TO 



^ 40 



Q) 

 O 



03 20 



CD ^'-' 



HCH Rep#1 



HCH Rep#2 



Fig. 4. Net 48 h change in bacterial activity (thymidine incorporation) in the 

 untreated control, acetone control and HCH experimental containers. 

 Initial values for each expenment are given in Table 1 . 



c3 



Fig. 5. Net 48 h change in ciliate concentration in the untreated control, 

 acetone control and HCH experimental container for the shelf 

 experiment. 



366 



