in a second particulate nitrogen increase. The maximum particulate nitrogen level was 400 /xg/ 

 liter, compared with a baseline level between 60 and 85 /xg/liter. 



Sub-ponds created within ponds B (B,. B^, Bj) and C (C,, Cj. C,) also were subjected to 

 phosphaus manipulation. These sub-ponds consisted of containers constructed of clear poly- 

 ethylene sheeting, each containing an area of about 2 m^ and open at the top and bottom. Syringe 

 pumps were set up to deliver phosphate solution at a steady rate over a long period of time. In 

 each pond one sub-pond was not subject to manipulation but was used as a control for the enclosures. 

 Sub-ponds Bj and Cj were supplied with phosphorus at a rate of 0.5 mg P/day (about 2pig P/liter- 

 day) and Bj and Cj at a rate of 2.5 mg P/day (about lOjxg P/liter-day) starting at 2200 hours, 29 

 July 1970. Only two sets of primary productivity data are available at present, one for before 

 and one for after treatment. The data are somewhat variable but do appear to have a general trend 

 foi- increased productivity in the treated ponds, especially marked in the case of pond Cj. In 

 pond C3 the productivity rose from a net rate of 0.02 ^g C/liter-hour to 2.45 ^gC/liter-hour. A 

 slight increase in pH was also evident. Quantitative phosphorus determination and "P kinetic 

 studies were done (nominally at 5-day intervals) through mid-September. By 11 August the phos- 

 phate concentration had increased tenfold in the high level treatment subponds. 



The treated sub-ponds were tested for nitrogen fixation before and during phosphaus infusion. 

 No evidence of nitrogen fixation was found by the acetylene reduction technique. Some '^N nitro- 

 gen fixation determinations were also made; the results of these are not available as yet. There 

 was no consistent increase in particulate nitrogen within these sub-ponds during treatment. 



The rate of ammonia production within the pond area was measured using an isotope dilution 

 technique. A quantity of '^N ammonia was added to a water sample, the initial '^N enrichment of 



the ammonia fraction in the water determined, and then the enrichment determined again following 

 24 hours of incubation. This yields the rate of supply of ammonia from other nitrc^en fractions in 

 the water (dissolved and particulate organic, animal excretion, plant excretion, etc.) but does not 

 take into account any supply from the sediments to the pond waters. The information is an indica- 

 tion of the metabolic activity of the microorganisms responsible for nitrc^en regeneration, and gives 

 a good idea of the amount of nutrient available for plant growth as a result of such in situ regenera- 

 tion. 



Due to mass spectrometer problems, not all tlie samples have been analyzed. The few 

 currently available results are given here: 



These rates are extremely low compared with measurements carried out in otiier waters. Upon 

 completion of nutrient analyses, it will be possible to calculate turnover times from this infor- 

 m;ition. From the hunted data avaikible here, turnover times would appear to be on the order of 

 several days. 



Tables XIII-XVI contain selected data lliat are currently available for ponds B, C, and D. 



39 



