Representative regional sampling of carbon dioxide and methane concentrations in hemiboreal headwater streams reveal underestimates in less systematic approaches
2014 (English)In: Global Biogeochemical Cycles, ISSN 0886-6236, Vol. 28, no 4, 465-479 p.Article in journal (Refereed) Published
Boreal headwater streams have been identified as hotspots for water-air exchange of greenhouse gases (GHG´s). Despite these findings GHG concentrations and fluxes in headwaters are to a great extent unexplored at large (regional/national) scales. This study was the first to systematically determine the concentrations of CO2 and CH4 in hemiboreal (southern boreal and boreonemoral) headwater streams. The use of a headspace sampling method focusing on GHG´s in combination with a statistically representative selection of more than 200 streams across two regions in Sweden was the basis for defining the base flow supersaturation level of CO2 and CH4. All streams were supersaturated relative to the atmosphere in CO2 (median concentration, 1.9 (±1.1) mg C L-1) and the majority in CH4 (median concentration, 7.1 (±54.0) µg C L-1 for the 82% of streams in which CH4 was detected). The spatial variability in both CO2 and CH4 was high but positively related to total organic carbon, mean annual temperature and proportion of peatland in the catchment. There were however regional differences in the spatial controls, which is something that predictive models need to consider. The large and representative data set allowed for comparison between a headspace and an alkalinity-based method for determining CO2 in these headwaters. More than 50% of the streams contained no alkalinity which made the alkalinity based determination of CO2 impossible. In addition, half of the streams with alkalinity alkalinities low enough (<0.07 mEq L-1) to make the CO2 determination very uncertain. The streams with low pH and no alkalinity contained median CO2 concentrations that were 45% higher than the streams containing alkalinity. Therefore large scale generalizations about the supersaturation of CO2 from such headwaters will be significantly underestimated if (1) headwaters are underrepresented, and (2) the headwaters are sampled but CO2 is calculated from their alkalinity.
Place, publisher, year, edition, pages
2014. Vol. 28, no 4, 465-479 p.
Research subject Earth Science with specialization in Environmental Analysis
IdentifiersURN: urn:nbn:se:uu:diva-222225DOI: 10.1002/2013GB004715ISI: 000335809500010OAI: oai:DiVA.org:uu-222225DiVA: diva2:710993