title: Dissolved organic carbon dynamics in a riparian aquifer: effects of hydrology and nitrate enrichment.
abstract: The capacity of riparian soils to remove nitrate (NO3) from ground water is well established, but the effects of ground water NO3(-)-enrichment on C dynamics are not well studied. We incubated horizontal cores of aquifer material extracted from beneath moderately well-drained (MWD) and poorly drained (PD) soils in a riparian forest in Rhode Island, USA for 132 d, and dosed (flow rate, 170 mL d(-1); dissolved O2, 2 in PD and 5 mg L(-1) in MWD cores) with ground water amended with either Br-, Br(-)+ NO3- (10 mg N L(-1)), or Br(-) + NO3(-) + DOC (20 mg C L(-1)). The DOC was extracted from forest floor material and added during the first 56 d of the experiment. Addition of NO3- had limited effect on CO2 production while DOC amendment had a significant effect in the PD but not in the MWD mesocosms. Total CO2 production (mg CO2-C kg(-1) soil) was 6.3, 7.0, and 10.1 in the PD and 3.6, 4.0, and 4.5 in the MWD cores amended with Br-, Br(-) + NO3-, and Br(-) + NO3(-) + DOC, respectively. Carbon balance (C(bal) = DOC(in) - (DOC(out) + CO2-C) showed a net C retention of 8.0 mg C kg(-1) soil in the DOC-amended MWD cores (equivalent to 50% of the DOC added), and a net C loss of 8.3 mg C kg(-1) soil in similarly treated PD cores. The lack of C retention in the PD cores was ascribed to reductive dissolution of minerals implicated in DOC sorption. These findings underscore that there is marked variation in C dynamics in riparian aquifers that has the potential to influence the fate of NO3- and DOC in the landscape.
authors.affiliation: School of Natural Resources, 2021 Coffey Road, 210 Kottman Hall, Ohio State Univ., Columbus, OH 43210, USA. jacinthe.1@osu.edu
authors.forename: P A
authors.initials: PA
authors.lastname: Jacinthe
authors.forename: P M
authors.initials: PM
authors.lastname: Groffman
authors.forename: A J
authors.initials: AJ
authors.lastname: Gold
mesh_terms: D002244:Carbon / Q000032:analysis / Q000378:metabolism*; D017753:Ecosystem; D004784:Environmental Monitoring; D009566:Nitrates / Q000737:chemistry* / Q000378:metabolism*; D012988:Soil Microbiology; D014197:Trees; D014881:Water Supply
chemical_list: D009566:Nitrates; D002244:Carbon