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New Zealand Journal of Marine and Freshwater Research abstracts

Environmental effects on gross production and respiration in a facultative oxidation pond

D. E. IRVING*
F. I. DROMGOOLE

Department of Botany University of Auckland Private Bag, Auckland New Zealand

Abstract Oxygen exchange by effluent samples taken at weekly intervals from a facultative oxidation pond was investigated over a 7 month period. Concentrations of ammonia, nitrate, nitrite, total and reactive phosphorus, alkalinity, total inorganic carbon, and free CO2 were measured over 12 months. Gross daily oxygen production within the community compensation depth ranged from 8 gO2 m2 in winter to 43 gO2 irr2 in summer. The corresponding range for dark respiration was 5-17.5 gO2 m~2d~'. On average, light saturated rates of net oxygen production and total net production extended to the upper 2 and 15% of the 1.3 m mean depth profile respectively. Community respiration to gross production ratios ranged from 1.58-7.14. Light saturated rates of net oxygen production and dark rates of oxygen consumption increased with seasonal rise in pond temperature as did net production per unit detectable pigment. However, the most important factor affecting the rate of oxygen production was the concentration of detectable pigment. In laboratory studies, oxygen exchange rates were optimal at pH 5-8, but rates declined rapidly as the pH was increased from 8.0-8.5. Pond pH varied between 6.7 and 7.8 throughout the year. Net CO2 uptake under saturating irradiance (at pH 4.5) was maximal at 30 (iM CO2, and compensation was reached at about 5 |iM CO2. The minimum concentration of free CO2 observed in the pond was 190 uM.

Keywords oxidation pond; algae; photosynthesis; respiration; production; pigment; pH; CO2; nitrogen; phosphorus

New Zealand Journal of Marine and Freshwater Research, 1986, Vol. 20: 1-8 Received 18 May 1984; accepted 17 June 1985

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