Scaling effects of riparian peatlands on stable isotopes in runoff and DOC mobilization

C Tunaley (Corresponding Author), D Tetzlaff, C Soulsby

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Abstract

We combined 13 months of daily isotope measurements in stream water with daily DOC and 15 min FDOM (fluorescent component of dissolved organic matter) data at three nested scales to identify how riparian peatlands generate runoff and influence DOC dynamics in streams. We investigated how runoff generation processes in a small, riparian peatland-dominated headwater catchment (0.65 km2) propagate to larger scales (3.2 km2 and 31 km2) with decreasing percentage of riparian peatland coverage. Isotope damping was most pronounced in the 0.65 km2 headwater catchment due to high water storage in the organic soils encouraging tracer mixing. At the largest scale, stream flow and water isotope dynamics showed a more flashy response. The isotopic difference between the sites was most pronounced in the summer months when stream water signatures were enriched. During the winter months, the inter-site difference reduced. The isotopes also revealed evaporative fractionation in the peatland dominated catchment, in particular during summer low flows, which implied high hydrological connectivity in the form of constant seepage from the peatlands sustaining high baseflows at the headwater scale. This connectivity resulted in high DOC concentrations at the peatland site during baseflow (∼5 mg l−1). In contrast, at the larger scales, DOC was minimal during low flows (∼2 mg l−1) due to increased groundwater influence and the disconnection between DOC sources and the stream. High frequency data also revealed diel variability during low flows. Insights into event dynamics through the analysis of hysteresis loops showed slight dilution on the rising limb, the strong influence of dry antecedent conditions and a quick recovery between events at the riparian peatland site. Again, these dynamics are driven by the tight coupling and high connectivity of the landscape to the stream. At larger scales, the disconnection between the landscape units increases and the variable connectivity controls runoff generation and DOC dynamics. The results presented here suggest that the processes occurring in riparian peatlands in headwater catchments are less evident at larger scales which may have implications for the larger scale impact of peatland restoration projects.
Original languageEnglish
Pages (from-to)220-235
Number of pages16
JournalJournal of Hydrology
Volume549
Early online date27 Mar 2017
DOIs
Publication statusPublished - Jun 2017

Fingerprint

peatland
mobilization
stable isotope
runoff
headwater
connectivity
low flow
isotope
catchment
baseflow
antecedent conditions
effect
summer
water storage
hysteresis
dissolved organic matter
organic soil
water
damping
seepage

Keywords

  • Riparian peatland
  • stable isotopes
  • dissolved organic carbon
  • scaling
  • high frequency
  • connectivity

Cite this

Scaling effects of riparian peatlands on stable isotopes in runoff and DOC mobilization. / Tunaley, C (Corresponding Author); Tetzlaff, D; Soulsby, C.

In: Journal of Hydrology, Vol. 549, 06.2017, p. 220-235.

Research output: Contribution to journalArticle

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keywords = "Riparian peatland , stable isotopes, dissolved organic carbon, scaling, high frequency, connectivity",
author = "C Tunaley and D Tetzlaff and C Soulsby",
note = "Acknowledgments The authors would like to thank the European Research Council ERC (project GA 335910 VeWa) for funding the VeWa project. Part of this work was funded through the Natural Environment Research Council (NERC) (project NE/K000268/1). We would also like to thank our NRI colleagues for all their help with field and laboratory work, especially Jason Lessels, Matthias Sprenger, Jonathan Dick, Audrey Innes and Ann Porter. We would like to also thank Iain Malcolm (Marine Scotland Science) for providing AWS and Girnock flow data. Please contact the authors for access to the data used in this paper.",
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N1 - Acknowledgments The authors would like to thank the European Research Council ERC (project GA 335910 VeWa) for funding the VeWa project. Part of this work was funded through the Natural Environment Research Council (NERC) (project NE/K000268/1). We would also like to thank our NRI colleagues for all their help with field and laboratory work, especially Jason Lessels, Matthias Sprenger, Jonathan Dick, Audrey Innes and Ann Porter. We would like to also thank Iain Malcolm (Marine Scotland Science) for providing AWS and Girnock flow data. Please contact the authors for access to the data used in this paper.

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N2 - We combined 13 months of daily isotope measurements in stream water with daily DOC and 15 min FDOM (fluorescent component of dissolved organic matter) data at three nested scales to identify how riparian peatlands generate runoff and influence DOC dynamics in streams. We investigated how runoff generation processes in a small, riparian peatland-dominated headwater catchment (0.65 km2) propagate to larger scales (3.2 km2 and 31 km2) with decreasing percentage of riparian peatland coverage. Isotope damping was most pronounced in the 0.65 km2 headwater catchment due to high water storage in the organic soils encouraging tracer mixing. At the largest scale, stream flow and water isotope dynamics showed a more flashy response. The isotopic difference between the sites was most pronounced in the summer months when stream water signatures were enriched. During the winter months, the inter-site difference reduced. The isotopes also revealed evaporative fractionation in the peatland dominated catchment, in particular during summer low flows, which implied high hydrological connectivity in the form of constant seepage from the peatlands sustaining high baseflows at the headwater scale. This connectivity resulted in high DOC concentrations at the peatland site during baseflow (∼5 mg l−1). In contrast, at the larger scales, DOC was minimal during low flows (∼2 mg l−1) due to increased groundwater influence and the disconnection between DOC sources and the stream. High frequency data also revealed diel variability during low flows. Insights into event dynamics through the analysis of hysteresis loops showed slight dilution on the rising limb, the strong influence of dry antecedent conditions and a quick recovery between events at the riparian peatland site. Again, these dynamics are driven by the tight coupling and high connectivity of the landscape to the stream. At larger scales, the disconnection between the landscape units increases and the variable connectivity controls runoff generation and DOC dynamics. The results presented here suggest that the processes occurring in riparian peatlands in headwater catchments are less evident at larger scales which may have implications for the larger scale impact of peatland restoration projects.

AB - We combined 13 months of daily isotope measurements in stream water with daily DOC and 15 min FDOM (fluorescent component of dissolved organic matter) data at three nested scales to identify how riparian peatlands generate runoff and influence DOC dynamics in streams. We investigated how runoff generation processes in a small, riparian peatland-dominated headwater catchment (0.65 km2) propagate to larger scales (3.2 km2 and 31 km2) with decreasing percentage of riparian peatland coverage. Isotope damping was most pronounced in the 0.65 km2 headwater catchment due to high water storage in the organic soils encouraging tracer mixing. At the largest scale, stream flow and water isotope dynamics showed a more flashy response. The isotopic difference between the sites was most pronounced in the summer months when stream water signatures were enriched. During the winter months, the inter-site difference reduced. The isotopes also revealed evaporative fractionation in the peatland dominated catchment, in particular during summer low flows, which implied high hydrological connectivity in the form of constant seepage from the peatlands sustaining high baseflows at the headwater scale. This connectivity resulted in high DOC concentrations at the peatland site during baseflow (∼5 mg l−1). In contrast, at the larger scales, DOC was minimal during low flows (∼2 mg l−1) due to increased groundwater influence and the disconnection between DOC sources and the stream. High frequency data also revealed diel variability during low flows. Insights into event dynamics through the analysis of hysteresis loops showed slight dilution on the rising limb, the strong influence of dry antecedent conditions and a quick recovery between events at the riparian peatland site. Again, these dynamics are driven by the tight coupling and high connectivity of the landscape to the stream. At larger scales, the disconnection between the landscape units increases and the variable connectivity controls runoff generation and DOC dynamics. The results presented here suggest that the processes occurring in riparian peatlands in headwater catchments are less evident at larger scales which may have implications for the larger scale impact of peatland restoration projects.

KW - Riparian peatland

KW - stable isotopes

KW - dissolved organic carbon

KW - scaling

KW - high frequency

KW - connectivity

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EP - 235

JO - Journal of Hydrology

JF - Journal of Hydrology

SN - 0022-1694

ER -