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TECHNICAL REPORTS
Landscape and Watershed Processes

Dissolved Organic Carbon Dynamics in a Riparian Aquifer

Effects of Hydrology and Nitrate Enrichment

^a School of Natural Resources, 2021 Coffey Road, 210 Kottman Hall, Ohio State Univ., Columbus, OH 43210
^b Inst. of Ecosystem Studies, Millbrook, NY 12545
^c Dep. of Natural Resources Science, Univ. of Rhode Island, Kingston, RI 02881

^* Corresponding author (jacinthe.1{at}osu.edu)

Received for publication May 10, 2002. The capacity of riparian soils to remove nitrate (NO^-₃) from ground water is well established, but the effects of ground water NO^-₃-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^- + NO^-₃ (10 mg N L^-1), or Br^- + NO^-₃ + 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 NO^-₃ 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^- + NO^-₃, and Br^- + NO^-₃ + 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.

Abbreviations: DO, dissolved oxygen • DOC, dissolved organic carbon • DOC_in, dissolved organic carbon in input solution • DOC_out, dissolved organic carbon in core effluent • MBC, microbial biomass carbon • MWD, moderately well drained • PD, poorly drained • PDOM, patches of decomposed organic materials • SOC, soil organic carbon

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JEQ 2003 32: 1167-1172. [Full Text]