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The role of gas exchange in the inorganic carbon, oxygen, and 222 Rn budgets of the Amazon River 1
Author(s) -
Devol Allan H.,
Quay Paul D.,
Richey Jeffrey E.,
Martinelli Luiz A.
Publication year - 1987
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.1987.32.1.0235
Subject(s) - alkalinity , tributary , hydrology (agriculture) , carbon dioxide , atmosphere (unit) , dissolved organic carbon , carbonic acid , chemistry , environmental science , environmental chemistry , geology , meteorology , physics , cartography , geotechnical engineering , organic chemistry , geography
Dissolved oxygen, 222 Rn, pCO 2 , alkalinity, respiration rate, and discharge have been measured at eight mainstem and seven tributary stations during February–March 1984 in a 1,700‐km stretch of the Amazon River between Vargem Grande and Obidos in Brazil. Air–water gas exchange rates were estimated two ways: measurements of the flux of 222 Rn into floating domes yielded an average boundary layer thickness of 78 µ m, and oxygen mass balance calculations resulted in an average of 38 µ m. Given a boundary layer thickness on the order of 50 µ m, CO 2 loss to the atmosphere in the entire reach would have been 37.4 kmol s −1 , which is about equal to the total tributary dissolved inorganic carbon (DIC) input (43 kmol s −1 ) and is about half of the total fluvial DIC input to the section (97.7 kmol s −1 ). Thus, CO 2 evasion is a major component of Amazon River DIC balance. Because gas exchange within the section was rapid relative to water travel time through the section, a quasi‐steady state was maintained between respiratory input and evasion of CO 2 . Dissolved 222 Rn activities in the mainstem varied from 3.5 to 8.3 dpm liter −1 and were always highly supersaturated with respect to the atmosphere. Dissolved radon was also not supported by decay of 226 Ra (0.59–0.70 dpm liter −1 ) in the mainstem. A 222 Rn mass balance indicated that direct groundwater input into this stretch of the Amazon mainstem probably accounted for no more than 1% of water discharge.