control acetone HCH rep #1 HCH rep #2 



Fig. 6. Net 48 h change in phosphate concentration in the untreated control, 

 acetone control and HCH experimental containers. Initial values for 

 each experiment are given in Table 1 . 



are the observed changes in phosphate (Fig. 6). However, in the 

 oceanic experiment, the net consumption of phosphate was 

 greater in the HCH treated experimentals than in the presence 

 of acetone alone. 



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

 opposite in shelf and oceanic experiments and the effects of 

 HCH cannot be distinguished from acetone alone. In this 

 category are the changes in N + N (Fig. 7) and silicate (Fig. 8). 

 Acetone slowed the net consumption of ambient N + N in the 

 shelf experiment (Fig. 7) but resulted in a net increase in 

 N + N in the oceanic experiment (Fig. 7). Likewise, the 

 presence of acetone slowed the consumption of silicate in the 

 shelf experiment ( Fig. 8 ) and produced a net increase in silicate 

 in the oceanic experiment (Fig. 8). 



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

 in both shelf and oceanic experiments, and in both locations the 

 effects of HCH are distinct from acetone alone. The observed 

 net changes in ambient ammonium are in this category (Fig. 9). 

 In both the untreated and acetone-treated containers in both 

 shelf and oceanic experiments, the ammonium concentrations 



control 



acetone HCH rep,#1 HCH rep.#2 



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



Fig. 8. Net 48 h change in silicate concentration in the untreated control, 

 acetone control and HCH experimental containers. Initial values for 

 each experiment are given in Table I. 



0.6^ 



0.4 



0.2 







-0.2 



-0.4 





control acetone 



HCH rep.#1 HCH rep. #2 



Fig. 7. Net 48 h change in N+N concentration in the untreated control, 

 acetone control and HCH experimental containers. Initial values tor 

 each experiment are given in Table 1. 



Fig. 9. Net 48 h change in ammonium concentration in the untreated control, 

 acetone control and HCH experimental containers. Initial values for 

 each experiment are given in Table 1 . 



decreased. However, in all containers treated with HCH, the 

 ammonium concentrations increased during the 48-h 

 experiment. 



Like the changes in ammonium levels, the specific rates of 

 ammonium uptake were higher in the HCH-treated containers 

 attheendofbothexperiments(Fig. 10). In the shelf experiment, 

 ammonium uptake rates increased in the acetone and HCH 

 containers at 48 h. In the oceanic experiment, the ammonium 

 uptake rates in the HCH-treated containers were markedly 

 higher than either the untreated or acetone-treated containers at 

 48 h. 



Discussion 



The most significant findings from our experiments were 

 the effects of HCH on plankton nitrogen cycling (Figs. 9,10). 

 The results clearly indicate that the added HCH produced a 

 measurable effect beyond that ofthe acetone carrier alone. The 

 ambient ammonium pool is extremely dynamic and reflects the 

 net result of uptake and regeneration processes. The fact that 

 both the specific rates of ammonium uptake and the ambient 



367 



