title: A decade of boreal rich fen greenhouse gas fluxes in response to natural and experimental water table variability.
abstract: Rich fens are common boreal ecosystems with distinct hydrology, biogeochemistry and ecology that influence their carbon (C) balance. We present growing season soil chamber methane emission (FCH4), ecosystem respiration (ER), net ecosystem exchange (NEE) and gross primary production (GPP) fluxes from a 9-years water table manipulation experiment in an Alaskan rich fen. The study included major flood and drought years, where wetting and drying treatments further modified the severity of droughts. Results support previous findings from peatlands that drought causes reduced magnitude of growing season FCH4, GPP and NEE, thus reducing or reversing their C sink function. Experimentally exacerbated droughts further reduced the capacity for the fen to act as a C sink by causing shifts in vegetation and thus reducing magnitude of maximum growing season GPP in subsequent flood years by ~15% compared to control plots. Conversely, water table position had only a weak influence on ER, but dominant contribution to ER switched from autotrophic respiration in wet years to heterotrophic in dry years. Droughts did not cause inter-annual lag effects on ER in this rich fen, as has been observed in several nutrient-poor peatlands. While ER was dependent on soil temperatures at 2 cm depth, FCH4was linked to soil temperatures at 25 cm. Inter-annual variability of deep soil temperatures was in turn dependent on wetness rather than air temperature, and higher FCH4in flooded years was thus equally due to increased methane production at depth and decreased methane oxidation near the surface. Short-term fluctuations in wetness caused significant lag effects on FCH4, but droughts caused no inter-annual lag effects on FCH4. Our results show that frequency and severity of droughts and floods can have characteristic effects on the exchange of greenhouse gases, and emphasize the need to project future hydrological regimes in rich fens.
authors.affiliation: Department of Integrative Biology, University of Guelph, Science Complex, Guelph, ON, N1G 2W1, Canada.|Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2H1, Canada.
authors.forename: David
authors.identifier: 0000-0002-5976-1475
authors.initials: D
authors.lastname: Olefeldt
authors.affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA.
authors.forename: Eugénie S
authors.initials: ES
authors.lastname: Euskirchen
authors.affiliation: U.S. Geological Survey, Menlo Park, CA, 94025, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Harden
authors.affiliation: School of Forest Resources and Environmental Sciences, and USDA Forest Service, Michigan Tech University, Northern Research Station, Houghton, MI, 49931, USA.
authors.forename: Evan
authors.initials: E
authors.lastname: Kane
authors.affiliation: U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA.
authors.forename: A David
authors.initials: AD
authors.lastname: McGuire
authors.affiliation: U.S. Geological Survey, Menlo Park, CA, 94025, USA.
authors.forename: Mark P
authors.initials: MP
authors.lastname: Waldrop
authors.affiliation: Department of Integrative Biology, University of Guelph, Science Complex, Guelph, ON, N1G 2W1, Canada.
authors.forename: Merritt R
authors.initials: MR
authors.lastname: Turetsky
mesh_terms: D057486:Carbon Cycle; D002245:Carbon Dioxide; D017753:Ecosystem; D005740:Gases; D060587:Groundwater; D012987:Soil
chemical_list: D005740:Gases; D012987:Soil; D002245:Carbon Dioxide
keywords: carbon dioxide; climate change; ecosystem respiration; methane; peatland; soil temperature; water table; wetland