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Automated determination of carbon dioxide, oxygen, and nitrogen partial pressures in surface waters
Author(s) -
Carignan Richard
Publication year - 1998
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1998.43.5.0969
Subject(s) - epilimnion , carbon dioxide , supersaturation , partial pressure , gas analyzer , chemistry , analytical chemistry (journal) , oxygen , nitrogen , environmental chemistry , hypolimnion , nutrient , organic chemistry , eutrophication
An automated system capable of accurate determinations of O 2 , CO 2 , and N 2 partial pressures ( p ) in surface waters is described. The system is composed of a programmable data logger‐controller, an infrared CO 2 analyzer, a polarographic O 2 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 p O 2 measurements to atmospheric readings. p N 2 is calculated by subtracting p O 2 + p H 2 O + p CO 2 from total dissolved gas pressure. Complete (>99%) equilibration of internal gases with water p CO 2 occurs within 4 min. Equilibration half‐times for p O 2 range from 7.1 min at 21°C to 9.4 min at 05°C. The equilibration half‐time for p N 2 is 15.1 min at 15°C. Observations conducted in a small oligotrophic Shield Lake show that the epilimnion is usually supersaturated with both CO 2 (50–150 µatm) and O 2 (500–4,000 µatm), with both gases exhibiting marked daily variations. The epilimnetic supersaturation (up to 2%) with respect to atmospheric O 2 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.