Premium
Downstream Changes in Free Carbon Dioxide in an Upland Catchment from Northeastern Scotland
Author(s) -
Dawson J. J. C.,
Hope D.,
Cresser M. S.,
Billett M. F.
Publication year - 1995
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1995.00472425002400040022x
Subject(s) - carbon dioxide , outgassing , hydrology (agriculture) , environmental science , dissolved organic carbon , drainage basin , environmental chemistry , chemistry , carbon dioxide in earth's atmosphere , geology , geotechnical engineering , cartography , organic chemistry , geography
Significant losses of free carbon dioxide (CO 2 ) to the atmosphere are likely to occur when soil‐water, supersaturated with free CO 2 , enters streams and equilibrates with atmospheric CO 2 . Spatial changes in dissolved free CO 2 downstream from the river source should therefore demonstrate progressive equilibration with atmospheric CO 2 . Data on the spatial and diurnal variation in the concentration of dissolved free CO 2 are described for a small headwater stream draining an acidic heather [ Calluna vulgaris (L.) Hull] moorland catchment in northeastern Scotland. The degree to which free CO 2 exceeded the concentration expected for atmospheric equilibration decreased rapidly downstream, from an excess partial pressure ( ep CO 2 ) of >10 at the source of the stream to ca. 1.5 over a distance of 2 km downstream, suggesting that free CO 2 was being lost from the water by outgassing as the water equilibrated with atmospheric CO 2 . Diurnal variation of ±1.0 CO 2 units was also measured at the lowest point in the stream, with levels of CO 2 being highest during the early morning and late evening (measurements were not taken during times of darkness) and lowest in the period from late morning to midafternoon. An estimate of the flux of C as free CO 2 suggests that it comprises ca. 10% of the combined fluxes of dissolved organic carbon (DOC) and particulate organic carbon (POC). These results suggest that outgassing from and transport within river systems of soil‐derived CO 2 forms an important component of the C flux from terrestrial ecosystems back to the atmosphere or to the ocean.