title: Transport and transformation of soil-derived CO2, CH4and DOC sustain CO2supersaturation in small boreal streams.
abstract: Streams are typically supersaturated in carbon dioxide (CO2) and methane (CH4), and are recognized as important components of regional carbon (C) emissions in northern landscapes. Whereas there is consensus that in most of the systems the CO2emitted by streams represents C fixed in the terrestrial ecosystem, the pathways delivering this C to streams are still not well understood. We assessed the contribution of direct soil CO2injection versus the oxidation of soil-derived dissolved organic C (DOC) and CH4in supporting CO2supersaturation in boreal streams in Québec. We measured the concentrations of CO2, CH4and DOC in 43 streams and adjacent soil waters during summer base-flow period. A mass balance approach revealed that all three pathways are significant, and that the mineralization of soil-derived DOC and CH4accounted for most of the estimated stream CO2emissions (average 75% and 10%, respectively), and that these estimated contributions did not change significantly between the studied low order (≤3) streams. Whereas some of these transformations take place in the channel proper, our results suggest that they mainly occur in the hyporheic zones of the streams. Our results further show that stream CH4emissions can be fully explained by soil CH4inputs. This study confirms that these boreal streams, and in particular their hyporheic zones, are extremely active processors of soil derived DOC and CH4, not just vents for soil produced CO2.
authors.affiliation: Groupe de Recherche Interuniversitaire en Limnologie (GRIL), Département des sciences biologiques, Université du Québec à Montréal, C.P. 8888, Succursale Centre-ville, Montréal, Québec H3C 3P8, Canada. Electronic address: terhi.rasilo@gmail.com.
authors.forename: Terhi
authors.initials: T
authors.lastname: Rasilo
authors.affiliation: Groupe de Recherche Interuniversitaire en Limnologie (GRIL), Département des sciences biologiques, Université du Québec à Montréal, C.P. 8888, Succursale Centre-ville, Montréal, Québec H3C 3P8, Canada. Electronic address: hutchins.ryan@gmail.com.
authors.forename: Ryan H S
authors.initials: RHS
authors.lastname: Hutchins
authors.affiliation: Groupe de Recherche Interuniversitaire en Limnologie (GRIL), Département des sciences biologiques, Université du Québec à Montréal, C.P. 8888, Succursale Centre-ville, Montréal, Québec H3C 3P8, Canada. Electronic address: clara.ruiz.glez@gmail.com.
authors.forename: Clara
authors.initials: C
authors.lastname: Ruiz-González
authors.affiliation: Groupe de Recherche Interuniversitaire en Limnologie (GRIL), Département des sciences biologiques, Université du Québec à Montréal, C.P. 8888, Succursale Centre-ville, Montréal, Québec H3C 3P8, Canada. Electronic address: del_giorgio.paul@uqam.ca.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Del Giorgio
keywords: Carbon dioxide; Headwater streams; Methane