title: Contribution of sediment respiration to summer CO2 emission from low productive boreal and subarctic lakes.
abstract: We measured sediment production of carbon dioxide (CO(2)) and methane (CH(4)) and the net flux of CO(2) across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were made in situ under ambient light conditions. The flux of CO(2) between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m(-2) day(-1) from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated to dissolved organic carbon (DOC) concentration in the water (r(2) = 0.61). The net flux of CO(2) across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed layer (r(2) = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration. Lakes with DOC concentrations <5.6 mg L(-1) had net consumption of CO(2) in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic (<2.6 mg L(-1)) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources.
authors.affiliation: Department of Ecology and Environmental Science, Umeå University, SE-901 87, Sweden. grete.algesten@emg.umu.se
authors.forename: Grete
authors.initials: G
authors.lastname: Algesten
authors.forename: Sebastian
authors.initials: S
authors.lastname: Sobek
authors.forename: Ann-Kristin
authors.initials: AK
authors.lastname: Bergström
authors.forename: Anders
authors.initials: A
authors.lastname: Jonsson
authors.forename: Lars J
authors.initials: LJ
authors.lastname: Tranvik
authors.forename: Mats
authors.initials: M
authors.lastname: Jansson
mesh_terms: D002244:Carbon / Q000032:analysis / Q000378:metabolism; D002245:Carbon Dioxide / Q000032:analysis* / Q000378:metabolism; D017753:Ecosystem; D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry*; D008697:Methane / Q000032:analysis / Q000378:metabolism; D012621:Seasons; D013548:Sweden
chemical_list: D002245:Carbon Dioxide; D002244:Carbon; D008697:Methane