Peat porewaters have contrasting geochemical fingerprints for groundwater recharge and discharge due to matrix diffusion in a large, northern bog-fen complex

Zeno F. Levy, Donald I. Siegel, Paul H. Glaser, Scott D. Samson, Soumitri S. Dasgupta

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Abstract

Although northern peatlands represent a globally significant reservoir for carbon, considerable uncertainty exists concerning solute transport systems within large (>1000 km2) peat deposits. We therefore delineated geochemical gradients linked to groundwater recharge and discharge along a 6 km transect within the 1200 km2 Red Lake Peatland of northwestern Minnesota. We used ratios of Ca/Mg and 87Sr/86Sr to distinguish discharge of calcareous groundwater (∼1.4 and 0.7155, respectively) to the peatland from the mineral substratum along a topographic gradient from a bog crest downslope to an internal fen water track and bog islands. In contrast, the stable isotopes of the porewaters (δ18O from −12.8 ‰ to −7.8 ‰) show that the active pore-spaces in these peat profiles have been flushed by recharge from the near-surface peat. We hypothesize that back-diffusion of groundwater-derived solutes from the peat matrix to active pore-spaces has allowed the geochemical signal from paleo-hydrogeologic discharge to persist into the current regime of dilute recharge. This effect has not been observed previously on the landform-scale and has important implications for carbon cycling in peatlands.

Original languageEnglish (US)
Pages (from-to)941-951
Number of pages11
JournalJournal of Hydrology
Volume541
DOIs
StatePublished - Oct 1 2016

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peat
peatland
recharge
groundwater
bog
fen
pore space
porewater
matrix
carbon
solute transport
landform
solute
stable isotope
transect
lake
mineral
water

Keywords

  • Bogs
  • Fens
  • Geochemistry
  • Hydrogeology
  • Isotopes
  • Matrix diffusion
  • Peatlands

ASJC Scopus subject areas

  • Water Science and Technology

Cite this

Peat porewaters have contrasting geochemical fingerprints for groundwater recharge and discharge due to matrix diffusion in a large, northern bog-fen complex. / Levy, Zeno F.; Siegel, Donald I.; Glaser, Paul H.; Samson, Scott D.; Dasgupta, Soumitri S.

In: Journal of Hydrology, Vol. 541, 01.10.2016, p. 941-951.

Research output: Contribution to journalArticle

Levy, Zeno F.; Siegel, Donald I.; Glaser, Paul H.; Samson, Scott D.; Dasgupta, Soumitri S. / Peat porewaters have contrasting geochemical fingerprints for groundwater recharge and discharge due to matrix diffusion in a large, northern bog-fen complex.

In: Journal of Hydrology, Vol. 541, 01.10.2016, p. 941-951.

Research output: Contribution to journalArticle

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abstract = "Although northern peatlands represent a globally significant reservoir for carbon, considerable uncertainty exists concerning solute transport systems within large (>1000 km2) peat deposits. We therefore delineated geochemical gradients linked to groundwater recharge and discharge along a 6 km transect within the 1200 km2 Red Lake Peatland of northwestern Minnesota. We used ratios of Ca/Mg and 87Sr/86Sr to distinguish discharge of calcareous groundwater (∼1.4 and 0.7155, respectively) to the peatland from the mineral substratum along a topographic gradient from a bog crest downslope to an internal fen water track and bog islands. In contrast, the stable isotopes of the porewaters (δ18O from −12.8 ‰ to −7.8 ‰) show that the active pore-spaces in these peat profiles have been flushed by recharge from the near-surface peat. We hypothesize that back-diffusion of groundwater-derived solutes from the peat matrix to active pore-spaces has allowed the geochemical signal from paleo-hydrogeologic discharge to persist into the current regime of dilute recharge. This effect has not been observed previously on the landform-scale and has important implications for carbon cycling in peatlands.",
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T1 - Peat porewaters have contrasting geochemical fingerprints for groundwater recharge and discharge due to matrix diffusion in a large, northern bog-fen complex

AU - Levy,Zeno F.

AU - Siegel,Donald I.

AU - Glaser,Paul H.

AU - Samson,Scott D.

AU - Dasgupta,Soumitri S.

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AB - Although northern peatlands represent a globally significant reservoir for carbon, considerable uncertainty exists concerning solute transport systems within large (>1000 km2) peat deposits. We therefore delineated geochemical gradients linked to groundwater recharge and discharge along a 6 km transect within the 1200 km2 Red Lake Peatland of northwestern Minnesota. We used ratios of Ca/Mg and 87Sr/86Sr to distinguish discharge of calcareous groundwater (∼1.4 and 0.7155, respectively) to the peatland from the mineral substratum along a topographic gradient from a bog crest downslope to an internal fen water track and bog islands. In contrast, the stable isotopes of the porewaters (δ18O from −12.8 ‰ to −7.8 ‰) show that the active pore-spaces in these peat profiles have been flushed by recharge from the near-surface peat. We hypothesize that back-diffusion of groundwater-derived solutes from the peat matrix to active pore-spaces has allowed the geochemical signal from paleo-hydrogeologic discharge to persist into the current regime of dilute recharge. This effect has not been observed previously on the landform-scale and has important implications for carbon cycling in peatlands.

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