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Headwater gas exchange quantified from O 2 mass balances at the reach scale
Author(s) -
Rovelli L.,
Attard K. M.,
Heppell C. M.,
Binley A.,
Trimmer M.,
Glud R. N.
Publication year - 2018
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.1002/lom3.10281
Subject(s) - environmental science , wind speed , hydrology (agriculture) , trace gas , atmospheric sciences , diel vertical migration , carbon dioxide , meteorology , chemistry , ecology , geography , geology , geotechnical engineering , organic chemistry , biology
Headwater streams are important in the carbon cycle and there is a need to better parametrize and quantify exchange of carbon‐relevant gases. Thus, we characterized variability in the gas exchange coefficient ( k 2 ) and dissolved oxygen (O 2 ) gas transfer velocity ( k ) in two lowland headwaters of the River Avon (UK). The traditional one‐station open‐water method was complemented by in situ quantification of riverine sources and sinks of O 2 (i.e., groundwater inflow, photosynthesis, and respiration in both the water column and benthic compartment) enabling direct hourly estimates of k 2 at the reach–scale (~ 150 m) without relying on the nighttime regression method. Obtained k 2 values ranged from 0.001 h −1 to 0.600 h −1 . Average daytime k 2 were a factor two higher than values at night, likely due to diel changes in water temperature and wind. Temperature contributed up to 46% of the variability in k on an hourly scale, but clustering temperature incrementally strengthened the statistical relationship. Our analysis suggested that k variability is aligned with dominant temperature trends rather than with short‐term changes. Similarly, wind correlation with k increased when clustering wind speeds in increments correspondent with dominant variations (1 m s −1 ). Time scale is thus an important consideration when resolving physical drivers of gas exchange. Mean estimates of k 600 from recent parametrizations proposed for upscaling, when applied to the settings of this study, were found to be in agreement with our independent O 2 budget assessment (within < 10%), adding further support to the validity of upscaling efforts aiming at quantifying large‐scale riverine gas emissions.