Heat transport in the Red Lake Bog, Glacial Lake Agassiz Peatlands

Abstract. Northern peatlands cover more than 350 million ha and are an important source of methane (CH 4 ) and other biogenic gases contributing to climate change. Free-phase gas (FPG) accumulation and episodic release has recently been recognized as an important mechanism for biogenic gas flux from peatlands. It is likely that gas production and groundwater flow are interconnected in peatlands: groundwater flow influences gas production by regulating geochemical conditions and nutrient supply available for methanogenesis, while FPG influences groundwater flow through a reduction in peat permeability and by creating excess pore water pressures. Water samples collected from three well sites at Caribou Bog, Maine, show substantial dissolved CH 4 (5-16 mg L −1 ) in peat waters below 2 m depth and an increase in concentrations with depth. This suggests production and storage of CH 4 in deep peat that may be episodically released as FPG. Two min increment pressure transducer data reveal approximately 5 cm fluctuations in hydraulic head from both deep and shallow peat that are believed to be indicative of FPG release. FPG release persists up to 24 h during decreasing atmospheric pressure and a rising water table. Preferential flow is seen towards an area of relatively lower hydraulic head associated with the esker and pool system. Increased CH 4 concentrations are also found at the depth of the esker crest, suggesting that the high permeability esker is acting as a conduit for groundwater flow, driving a downward transport of labile carbon, resulting in higher rates of CH 4 production.

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“…These data reveal a temperature inversion that occurs in the late fall as seen in another peatland study (e.g., McKenzie et al, 2007) (Fig. 9).…”

Section: Pressure Datasupporting

confidence: 79%

Using hydrologic measurements to investigate free-phase gas ebullition in a Maine peatland, USA

Bon

Reeve

Slater

et al. 2014

Hydrol. Earth Syst. Sci.

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“…One source of error is the effect of temperature variations on the gas content estimated from the CRIM model. As previously stated, we assumed the temperature of the pore water throughout the peatland is 4.8°C and that variation in peat water temperature below 1 m is normally less than 4°C during the month of August [ McKenzie et al , 2007]. To specifically address the potential error that may be attributed to our lack of detailed temperature data we conducted a sensitivity analysis as shown in Figure 11.…”

Section: Resultsmentioning

confidence: 99%

“…For higher velocities around 0.045 m ns −1 , this maximum possible error is reduced to 1.2% estimated gas content. Based on consistencies of peat temperature observed by McKenzie et al [2007], we believe that it is unlikely that the temperature estimates are off by more than 4°C, and this is accounted for in the following error analysis.…”

Section: Resultsmentioning

confidence: 99%

Geophysical evidence for the lateral distribution of free phase gas at the peat basin scale in a large northern peatland

Parsekian¹,

Comas²,

Slater³

et al. 2011

J. Geophys. Res.

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[1] Northern peatlands contribute to the global carbon cycle by way of gas emissions in the form of biogenic carbon dioxide and methane originating in the subsurface. Determining how much gas is present and where it is trapped is essential to understanding the role of northern peatlands on the global carbon cycle, particularly in regard to methane cycling. In this study, spatial variability in free phase gas content was estimated using ground penetrating radar (GPR) along a 1.4 km transect crossing distinct peat landforms including a bog crest, midslope lawn, and fen. Variations in gas content and distribution were observed in landforms crossed by this transect. Estimated gas content up to 25% by volume was observed in landforms dominated by woody surface vegetation. In areas of the midslope lawn, the estimated gas content was greater than 15%, while estimated gas contents between 0% and 7% were found in the fen. Changes in estimated gas content of up to 20% were observed over distances of 100 m across a transition between a stand of 10 m tall trees and an adjacent fen. The mean of the estimated errors in gas content is 1.3%, suggesting that these large changes in estimated gas content between landforms can be clearly determined using geophysical methods. A geophysical image of the distribution of free phase across this transect reveals evidence for gas storage in deep peat in intervals as thin as 0.35 m. These data support conceptual models based on accumulation and storage of free phase gas in deep peat.

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“…In applying the Complex Refractive Index Model to estimate gas content we accounted for variability in ɛ r ( w ) due to differences in temperature between the top (12.5°C) and bottom (4.5°C) of the peat column based on data previously collected at the Red Lake II study site during the summer season of 1998. McKenzie et al [2007] showed vertical temperature variation from over a 4 m depth profile with intervals deeper than 2.5 m showing little variation throughout 1998–1999, suggesting that the lower layers of peat have consistent temperature conditions. Detailed estimates of vertical variations in porosity are not available from the study sites.…”

Section: Petrophysical Modelmentioning

confidence: 99%

Variations in free‐phase gases in peat landforms determined by ground‐penetrating radar

et al. 2010

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[1] The spatial variability of biogenic gas produced by methanogenic archaea is difficult to assess within saturated peat soils and is often poorly quantified. This study uses ground-penetrating radar to noninvasively estimate the vertical distribution of biogenic free-phase gas (FPG) in two distinct peat landform types in the Glacial Lake Agassiz Peatland, Minnesota: a near-crest bog and a midslope lawn (i.e., both as defined by surface vegetation communities). Ground-penetrating radar velocities retrieved from common midpoint surveys were modeled using the Complex Refractive Index Model to estimate free-phase gas volumes along one-dimensional vertical profiles. Near-crest bog landforms are characterized by vertical variability in gas content with accumulations along the peat column up to 24% by volume of FPG localized within the deep peat (e.g., 2-4 m depth). Midslope lawn sites show lower total volumes (up to 12% free-phase gas) and less variability that result in a more even free-phase gas distribution throughout the vertical profile. High-resolution data also suggests the presence of thinner layers (<1 m) containing up to 40% free-phase gas at a near-crest site. Our results suggest that spatial distribution of free-phase gas along the peat column may vary in the Glacial Lake Agassiz Peatlands depending on peat landform. Statistical analysis supports vertical variability of ground-penetrating radar velocity data with a 95% confidence limit. Our results could potentially be upscaled using surface vegetation communities to estimate landscape-scale gas storage potential in peat landforms.

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Heat transport in the Red Lake Bog, Glacial Lake Agassiz Peatlands

Cited by 37 publications

References 34 publications

Using hydrologic measurements to investigate free-phase gas ebullition in a Maine peatland, USA

Using hydrologic measurements to investigate free-phase gas ebullition in a Maine peatland, USA

Geophysical evidence for the lateral distribution of free phase gas at the peat basin scale in a large northern peatland

Variations in free‐phase gases in peat landforms determined by ground‐penetrating radar

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