Journal
HYDROLOGICAL PROCESSES
Volume 28, Issue 18, Pages 4938-4952Publisher
WILEY
DOI: 10.1002/hyp.9983
Keywords
northern peatlands; isotope hydrology; seasonal recharge; bogs; fens
Categories
Funding
- National Science Foundation [0628611]
- Syracuse University
- Directorate For Geosciences
- Division Of Earth Sciences [0628611] Funding Source: National Science Foundation
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Ground water recharge is assumed to occur primarily at raised bog crests in northern peatlands, which are globally significant terrestrial carbon reservoirs. We synoptically surveyed vertical profiles of peat pore water delta O-18 and delta H-2 from a range of bog and fen landforms across the Glacial Lake Agassiz Peatlands, northern Minnesota. Contrary to our expectations, we find that local-scale recharge penetrates to not only the basal peat at topographically high bog crests but also transitional Sphagnum lawns and low-lying fen water tracks. Surface landscape characteristics appear to control the isotopic composition of the deeper pore waters (depths >= 0.5m), which are partitioned into discrete ranges of delta O-18 on the basis of landform type (mean +/- standard deviation for bog crests = -11.9 +/- 0.4%, lawns = -10.6 +/- 0.1%, fenwater tracks= -8.8 +/- 1.0%). Fen water tracks have a shallow free-water surface that is seasonally enriched by isotope fractionating evaporation, fingerprinting recharge to underlying pore waters at depths >= 3m. Isotope mass balance calculations indicate on average 12% of the waters we sampled from the basal peat of the fen water tracks was lost to surface evaporation, which occurred prior to advection and dispersion into the underlying formation. These new data provide direct support for the hypothesis that methane production in deeper peat strata is fuelled by the downward transport of labile carbon substrates from the surface of northern peat basins. Copyright (C) 2013 John Wiley & Sons, Ltd.
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