An automated system capable of accurate determinations of O2, CO2, and N2 partial pressures (p) in surface waters is described. The system is composed of a programmable data logger-controller, an infrared CO2 analyzer, a polarographic O2 electrode, and a barometer linked to a submersed gas exchanger made of thin-walled (100 μm) silicone elastomer tubing. Oxygen electrode calibration and drift problems are eliminated by continuously referencing pO2 measurements to atmospheric readings. pN2 is calculated by subtracting pO2 + pH2O + pCO2 from total dissolved gas pressure. Complete (>99%) equilibration of internal gases with water pCO2 occurs within 4 min. Equilibration half-times for pO2 range from 7.1 min at 21°C to 9.4 min at 0.5°C. The equilibration half-time for pN2 is 15.1 min at 15°C. Observations conducted in a small oligotrophic Shield Lake show that the epilimnion is usually supersaturated with both CO2 (50-150 μatm) and O2 (500-4,000 μatm), with both gases exhibiting marked daily variations. The epilimnetic supersaturation (up to 2%) with respect to atmospheric O2 indicates that primary production slightly exceeds community respiration in the epilimnion. The system appears adequate for metabolic and gas flux studies, even in the most oligotrophic waters.
CITATION STYLE
Carignan, R. (1998). Automated determination of carbon dioxide, oxygen, and nitrogen partial pressures in surface waters. Limnology and Oceanography, 43(5), 969–975. https://doi.org/10.4319/lo.1998.43.5.0969
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