This section of the report presents results from the control plots, the phosphorus experi- 

 ments and the interactions of nitrogen nutrition with primary production. The field program 

 started on 18 May and was terminated 14 September 1970. 



The quantitative phosphorus analyses consist of the determination of dissolved reactive, 

 dissolved unreactive (organic), particulate reactive, and particulate unreactive phosphorus. This 

 elaborate scheme was in part necessitated by the presence of dissolved organic acids and par- 

 ticulate iron-rich suspensions in tundra waters, as both of these fractions may contain substan- 

 tial quantities of phosphorus not intimately involved in the biological phosphorus cycling in the 

 ponds. Phytoplankton uptake, microbial regeneration, and physicochemical transports were 

 assessed by "P tracer techniques in combination with the addition of antibiotics and metabolic 

 poisons. 



Primary productivity was measured using '"C labeled bicarbonate, with incubation under 

 natural light. Only phytoplankton productivity was routinely determined, and the quantitative con- 

 tribution of benthic plants is not known. Chlorophyll a, pH and alkalinity data were obtained 

 for each productivity measurement. Light, dark and net productivities are all reported since 

 1) dark uptake tends to represent a substantial proportion of the total uptake and 2) dark uptake 

 data may be used independently to estimate heterotrophic activity in the water. 



In conjunction with the biolc^ical and chemical aquatic work a number of routine physical 

 measurements were made at the study ponds. East-west transects were established across ponds 

 C and E, and depth of thaw profiles were obtained at intervals across these transects by the frost 

 probe technique. Vertical profiles of air, water and sediment temperatures were obtained from 

 thermocouple strings placed near the centers of ponds C and E. Additional air temperatures, mid- 

 depth water temperatures, and sediment surface temperatures for ponds B, C, E, and F together 

 with water levels for ponds B, C, and E were measured. 



Pond D, which had a surface area of 750 m\ a mean depth of 20 cm, and a volume of 150 m', 

 was subjected to enrichment with phosphate, and the effects on primary production, phosphorus 

 cycling, and nitrogen cycling were monitored. The first addition, on 25 July, involved the addi- 

 tion of 46 g phosphorus, designed to produce a final concentration of about 300 //g P per liter of 

 pond water. A second addition of phosphorus was made on 28 July, this time designed to produce 

 a somewhat higher final concentration of phosphorus. 



The initial phosphorus addition appeared to result in a slow increase in primary productivity. 

 The second, somewhat excessive, addition had the initial effect of depressing photosynthesis to 

 some extent immediately and totally on the day following treatment. This was followed by a 

 rapid recovery, with a steady increase in photosynthetic rate to higher levels than otherwise had 

 occurred in the ponds throughout the summer. The persistence of these high rates will be 

 determined upon completion of sample processing. 



The first addition of phosphaus to pond D resulted in a concentration of 174 /tg/literof 

 dissolved reactive phosphorus one day after the enrichment, compared with a value of 2.6 prior 

 to the treatment. The second addition resulted in a phosphaus concentration of 780 /ig/liter. 

 The rate of decline from this high level was rapid. Dissolved unreactive pliosphorus appeared 

 to decline duiing treatment and then to slowly decrease. 



There were no apparent changes in organic nitrc^en nutrient levels in the pond following 

 manipulation. Measurements of nitrogen location using acetylene reduction did not indicate nitro- 

 genase activity before or after treatment. The behavior of the particulate nitrogen fraction was 

 of interest. There appeared to be a clear positive response to the original phosphorus addition, 

 which was further augmented by tiie sec:ond phosphorus addition. Tlie peak in particulate nitrc^en 

 lasted only a short time and was followed by a rapid decline to pietreatment levels. This pre- 

 sumably was due to limitation by a different nutrient. Addition of anmionia at this point resulted 



38 



