0.025 





 to 



-^ 



TO 



Q. 



3 



control acetone HCH rep.#1 HCH rep.#2 



Fig. 10. Net 48 h change in ammonium specific uptake rates in the untreated 

 control, acetone control and HCH experimental container for the shelf 

 experiment. For the untreated control, acetone control and HCH 

 experimental containers of the oceanic experiment, the measured 

 values (and not the changes) are shown because the initial 

 measurements for this experiment are not available. 



ammonium levels increased in the experimental containers 

 suggests that HCH acted to increase net ammonium fluxes in 

 both shelf and oceanic areas. 



The proportion of new to total nitrogen production (new 

 plus regenerated) in the plankton can be related to the flux of 

 carbon from surface waters (Eppley & Peterson, 1979). 

 Therefore, any change in this ratio would affect the 

 biogeochemical cycling of carbon as well as nitrogen. This is 

 a subject of broad importance because the biological flux of 

 carbon from surface waters is a major sink for atmospheric CO, 

 and may be an important sink forrising levels of this greenhouse 

 gas. The changes observed in our experiments suggest that 

 atmospheric input of pollutants like HCH can decrease the 

 amount of carbon exported from surface waters by increasing 

 the amount that is regenerated in siiii. 



We feel that these results provide a basis for preliminary 

 quantitative extrapolation for several reasons. This is one of 

 the few studies to examine the effects of pollutants on natural 

 populations of open ocean plankton. The amount of HCH 

 added to the experimental containers (80-90 ng/1) was 

 approximately 10 times the highest level of HCH yet measured 

 in ocean water (Hinckley el ai. Subchapter 8. 1 . 1 , this volume). 

 However, it is not unreasonable that localized, higher 

 concentrations of HCH exist in the ocean. Also, although it is 

 difficult to assess the effect of chronic (long-term ) exposure of 

 marine plankton systems to pesticides, we suspect that the 

 changes in nitrogen cycling also would have been observed at 

 lower HCH concentrations in longer experiments. 



In addition to the potential increased regeneration induced 

 by exposure to HCH, the literature on pollutant effects on 

 plankton indicates that there are significant differences among 

 the sensitivities ofplankton populations to pollutants. Although 

 little information on the specific effects of HCH is available, a 

 number of studies with other pollutants have shown that marine 

 algal community changes are a much more sensitive indicator 

 of toxic effect than specific measurements done on unialgal 

 cultures. For example, in a number of studies, diatom 

 populations were particulariy sensitive among the organisms 

 studied (Maloney& Palmer, 1956:Men/,elt'r«/., 1970; Mosser 

 el ai, 1972; Fisher el ai. 1974). This suggests that the 



combined effects of pollutants on carbon flux are greater than 

 this preliminary HCH experiment suggests because diatoms 

 are typically associated with high levels of new production and 

 their sensitivity to pollutants would further reduce carbon flux. 



The results of the experiments can be interpreted in terms 

 of the known biological differences between the shelf and 

 oceanic regimes. The shelf and oceanic waters of the subarctic 

 North Pacific differ markedly in the amount and character of 

 phytoplankton productivity (Sambrotto&Lorenzen. 1986). In 

 shelf areas of the eastern Bering Sea, intense, diatom-dominated 

 blooms occur in the spring and summer months (Sambrotto 

 el ai. 1986). However, in oceanic areas, the phytoplankton 

 crop remains low throughout the year, despite an abundance of 

 surt'ace layer nutrients, most likely due to intense grazing 

 pressure by both macro- and microzooplankton (Frost, 1990). 

 Thus the shelf and oceanic experiments provide insight into the 

 reactions of two distinct plankton systems to airborne HCH. 



A complete analysis of the causality of the effects observed 

 in the nitrogen system is not possible given the limited 

 measurements made and the known complexity of plankton 

 systems. However, observations on specific components of the 

 community over the course of the experiments offer some 

 insight as to the biological changes accompanying the changes 

 in nitrogen cycling. Unfortunately, ciliate abundance data are 

 available only for the shelf experiment and do not reflect any 

 distinct effect of HCH. Volume restrictions at the end of the 

 experiments contributed to the scatter in other measurements 

 relating to biomass as well. For example, the chl a change for 

 the replicates in the oceanic experiment varied widely and 

 obscured the detection of any possible difference between the 

 experimentals and acetone control. 



However, changes in the bacterial community are apparent, 

 particularly if the data are examined on a per-cell basis ( Hanson 

 el ai. 1988; Fig. 11). On this basis, HCH suppressed cell- 

 specific activity on the shelf, while oceanic cell-specific 

 activities increased. These differences closely parallel the 

 observed changes in phosphate, which were also opposite in 



300 



^250 



control 



acetone HCH rep.#1 



HCH rep #2 



Fig. 1 1 . Net 48 h change in specific activity of thymidine incorporation per 

 bacterial cell {based on the data in Figs. 3 and 4) in the untreated 

 control, acetone control and HCH experimental container for the shelf 

 experiments. 



368 



