title: Climatic variability, hydrologic anomaly, and methane emission can turn productive freshwater marshes into net carbon sources.
abstract: Freshwater marshes are well-known for their ecological functions in carbon sequestration, but complete carbon budgets that include both methane (CH4 ) and lateral carbon fluxes for these ecosystems are rarely available. To the best of our knowledge, this is the first full carbon balance for a freshwater marsh where vertical gaseous [carbon dioxide (CO2 ) and CH4 ] and lateral hydrologic fluxes (dissolved and particulate organic carbon) have been simultaneously measured for multiple years (2011-2013). Carbon accumulation in the sediments suggested that the marsh was a long-term carbon sink and accumulated ~96.9 ± 10.3 (±95% CI) g C m(-2)  yr(-1) during the last ~50 years. However, abnormal climate conditions in the last 3 years turned the marsh to a source of carbon (42.7 ± 23.4 g C m(-2)  yr(-1) ). Gross ecosystem production and ecosystem respiration were the two largest fluxes in the annual carbon budget. Yet, these two fluxes compensated each other to a large extent and led to the marsh being a CO2 sink in 2011 (-78.8 ± 33.6 g C m(-2)  yr(-1) ), near CO2 -neutral in 2012 (29.7 ± 37.2 g C m(-2)  yr(-1) ), and a CO2 source in 2013 (92.9 ± 28.0 g C m(-2)  yr(-1) ). The CH4 emission was consistently high with a three-year average of 50.8 ± 1.0 g C m(-2)  yr(-1) . Considerable hydrologic carbon flowed laterally both into and out of the marsh (108.3 ± 5.4 and 86.2 ± 10.5 g C m(-2)  yr(-1) , respectively). In total, hydrologic carbon fluxes contributed ~23 ± 13 g C m(-2)  yr(-1) to the three-year carbon budget. Our findings highlight the importance of lateral hydrologic inflows/outflows in wetland carbon budgets, especially in those characterized by a flow-through hydrologic regime. In addition, different carbon fluxes responded unequally to climate variability/anomalies and, thus, the total carbon budgets may vary drastically among years.
authors.affiliation: Department of Environmental Sciences, University of Toledo, Toledo, OH, USA.
authors.forename: Housen
authors.initials: H
authors.lastname: Chu
authors.forename: Johan F
authors.initials: JF
authors.lastname: Gottgens
authors.forename: Jiquan
authors.initials: J
authors.lastname: Chen
authors.forename: Ge
authors.initials: G
authors.lastname: Sun
authors.forename: Ankur R
authors.initials: AR
authors.lastname: Desai
authors.forename: Zutao
authors.initials: Z
authors.lastname: Ouyang
authors.forename: Changliang
authors.initials: C
authors.lastname: Shao
authors.forename: Kevin
authors.initials: K
authors.lastname: Czajkowski
mesh_terms: D057486:Carbon Cycle; D002980:Climate; D005618:Fresh Water; D062070:Hydrology; D008697:Methane / Q000032:analysis*; D009820:Ohio; D012621:Seasons; D053833:Wetlands
chemical_list: D008697:Methane
keywords: carbon budget; carbon dioxide; carbon sequestration; dissolved organic carbon; eddy-covariance; methane; particulate organic carbon