FISHERY BULLETIN: VOL. 70, NO. I 



C/m^/year) , application of nutrients at a level 

 that would increase primary and secondary pro- 

 duction seemed reasonable. 



Data used in this presentation have been ob- 

 tained from Stephens et al, (1969') and Kennedy 

 et al. (1971^). 



METHODS 



ANALYTICAL PROCEDURES 



Chlorophyll a, nutrients, oxygen, and total 

 CO2 were all measured as described previously 

 (Strickland and Parsons, 1968); bacteria were 

 enumerated from plate counts after 24 hr in- 

 cubation at room temperature on Millipore uni- 

 versal medium; major phytoplankton species 

 were enumerated after settling preserved sam- 

 ples; conductivity was measured using a Beck- 

 man Solu Bridge (Cedar Grove, N.J.). Primary 

 productivity was measured as the difference in 

 uptake of '^COo in light and dark bottles; how- 

 ever, on a few days the dark-bottle uptake was 

 exceptionally high and this requires further in- 

 vestigation. For the purpose of this presenta- 

 tion, data have been used only for days when 

 the dark-bottle uptake was less than 20 9f of the 

 maximum light-bottle uptake. 



Radiation was measured with an Epply pyra- 

 nometer and corrected to give photosynthetically 

 available radiation (PAR) as described previ- 

 ously (Parsons and Anderson, 1970). Light 

 attenuation was routinely measured with a 

 Secchi disc (SD), and an empirical relationship 

 between SD depth (m) and the vertical extinc- 

 tion coefficient was established using a Schiiler 

 meter (maximum response at 430 nm). This 

 relationship for light at 430 nm was: 



K4.30 _ 

 in — 



2.1 

 SD depth 



The (total) extinction coefficient for the water 

 column was then found from Jerlov's (1957) 



' Stephens, K., R. Neuman, and S. Sheehan. 1969. 

 Chemical and physical limnological observations, Babine 

 Lake, British Columbia, 1963 and 1969, and Great Cen- 

 tral Lake, British Columbia, 1969. Fish. Res. Board 

 Can., Manuscr. Rep. 1065: 41-52. 



* Kennedy, 0. D., K. Stephens, R. J. LeBrasseur, T. R. 

 Parsons, and M. Takahashi. 1971. Primary and sec- 

 ondary production data for Great Central Lake, B.C., 

 1970. Fish. Res. Board Can., Manuscr. Rep. 1127. 379p. 



light attenuation curves. Mean radiation (Im) 

 for the water column of depth (dm) was deter- 

 mined from the expression 



im — 



h (1- 



u^nK 



-e-^^m) 



where h was the surface radiation and k was 

 the attenuation coefficient for light below the 

 surface meter. The expression was also used 

 to determine the light at various depths in re- 

 lation to the photosynthetic activity at those 

 depths. 



NUTRIENT ADDITIONS 



The choice of a suitable fertilizer for the 

 waters of Great Central Lake has been discussed 

 previously (Parsons et al, in press). The nu- 

 trient addition consisted of a commercial grade 

 of ammonium phosphate and ammonium nitrate 

 which contained trace quantities of other ele- 

 ments essential for plant growth. The mixture 

 is known commercially as 27-14-0 (27% N; 

 14% P2O5; 0% K2O) and has an N:P ratio of 

 10:1. 



The ammonium nitrate and ammonium phos- 

 phate were dissolved separately in 5-ton amounts 

 (total) and the concentrated solutions mixed be- 

 fore distribution. A small quantity of organic 

 material was added to the dissolved inorganic 

 fertilizer at a dilution of 6 liters of fish solubles 

 (obtained from B.C. Packers Ltd.) for every 

 2 tons of nutrient solution. The dissolved ferti- 

 lizer was distributed at 10 gal/min (38 liters/ 

 min) in the wake of a vessel travelling at approx- 

 imately 8 knots. The area of nutrient additions 

 is shown in Figure 1, together with sampling 

 stations 1, 2, and 3. Station 1 was sampled dur- 

 ing 1969 and 1970, Station 2 was sampled during 

 1970, and Station 3 was sampled sporadically 

 during 1970 in order to check on the flow of 

 nutrients in a westerly direction; in addition, 

 areal surveys for chlorophyll a, transparency, 

 and bacteria were carried out over the whole lake 

 in order to determine within-lake variation. 



The area over which nutrients were added 

 represented ca. 3 sq mi (8 km-) of lake surface; 

 however, from studies on lake circulation it was 

 apparent that the material was transported east 



14 



