From water rock-interaction to methanogenesis: How climate induced raise of groundwater inputs might favor CH4 fluxes in the mid latitude/altitude Frasne peatland, Jura Mountains, France.

Abstract

From water rock-interaction to methanogenesis: How climate induced raise of groundwater inputs might favor CH4 fluxes in the mid latitude/altitude Frasne peatland, Jura Mountains, France. Abstract Peatlands are socio-ecosystems that constitute an inherent part of the Critical Zone in which water quality and quantity are key components of biogeochemical functions that drive peat accumulation, carbon and vegetation dynamic. Because peatlands store a huge stock of carbon, shelter a specific biodiversity, and impact hydrological dynamics at the watershed scale, they gather the main environmental challenges of the 21st century. There is therefore an imperative need to evaluate their reactivity to ongoing climate change and human disturbances, especially as changes in water inputs and quality could alter their ecological equilibrium and biogeochemical dynamics. In order to investigate the possible relationships between water origins and chemistry and biogeochemical processes affecting C (Carbon) exchanges between peatland and atmosphere, this study focused on a sphagnum dominated peatland. The site belongs to the French Observatory of Tourbières and the Zone Atelier Arc Jurassien (French Jura Mountains; 46.826 N, 6.1754 E; 850 m a.s.l), and is located in a karstified syncline overlain by fluvio-glacial deposits. Chemical and isotopic characterization combining δ13CDIC (Dissolved Inorganic Carbon), δ18OH2O, δ2HH2O, 87Sr/86Sr, Dissolved Organic Carbon (DOC) concentration and physico-chemical parameters (T, Eh, pH, O2) has been performed in Feb 2021 over 10 piezometers tapping both surface and deep peat layers, rainwater, outlet and surrounding karstic springs. In addition, one complete (Feb 2020-2021) of monthly evaluation of δ18OH2O, δ2HH2O DOC and physico-chemical parameters has been performed. Preliminary results from nested panpipes piezometers highlight vertical gradients for DOC concentration, δ18OH20 and δ13CDIC and physico-chemical parameters. Acid surface water (pH ranging from 4.4 to 5.5) seems to mainly interact with vegetation as suggested by high DOC (24 to 62 mg/L, mean = 43 mg/L), low bicarbonate (0 to 51 mg/L, mean = 24 mg/L) concentrations and depleted δ13CDIC (-3.6 to-20 ‰, mean =-9.7 ‰). In contrast, deep peat pore waters harbor circumneutral pH, have low DOC (13 to 53 mg/L, mean = 24 mg/L), high bicarbonate (138 to 472 mg/L, mean = 325 mg/L) concentrations and enriched δ13CDIC (from-7 to + 8 ‰, mean = 3.5 ‰). These enriched δ13CDIC were compared with δ13CDIC modeled assuming either a unique biogenic origin of DIC or a double geogenic and biogenic origin implying alteration of car-bonates. Both these approaches suggest hotspots of methanogenesis mainly in deep peat layers where groundwater inputs from the regional karstic system are hypothesized. Expected modifications in local precipitation and regional groundwater supply contributions due to ongoing climate changes implying possible greater winter recharge over Jurassic an-ticlines therefore could have feedback on carbon methane dynamics. In particular greater groundwater inputs combined with warmer conditions could favor greater DIC reduction under anoxic conditions, providing more CH4 production. In parallel, such a methane stock could be destabilized under climate change, further degassing at the peat surface and altering the peatland C balance and storage socio-ecosystemic service. sciencesconf.org:ozcartereno2020:362518

Full text

From water rock-interaction to methanogenesis: How
climate induced raise of groundwater inputs might
favor CH4 fluxes in the mid latitude/altitude Frasne
peatland, Jura Mountains, France.
Abstract
Peatlands are socio-ecosystems that constitute an inherent part of the Critical Zone in
which water quality and quantity are key components of biogeochemical functions that drive
peat accumulation, carbon and vegetation dynamic. Because peatlands store a huge stock
of carbon, shelter a specific biodiversity, and impact hydrological dynamics at the watershed
scale, they gather the main environmental challenges of the 21st century. There is there-
fore an imperative need to evaluate their reactivity to ongoing climate change and human
disturbances, especially as changes in water inputs and quality could alter their ecological
equilibrium and biogeochemical dynamics.
In order to investigate the possible relationships between water origins and chemistry and
biogeochemical processes affecting C (Carbon) exchanges between peatland and atmosphere,
this study focused on a sphagnum dominated peatland. The site belongs to the French Ob-
servatory of Tourbi`eres and the Zone Atelier Arc Jurassien (French Jura Mountains; 46.826
N, 6.1754 E; 850 m a.s.l), and is located in a karstified syncline overlain by fluvio-glacial
deposits. Chemical and isotopic characterization combining δ13CDIC (Dissolved Inorganic
Carbon), δ18OH2O, δ2HH2O, 87Sr/86Sr, Dissolved Organic Carbon (DOC) concentration
and physico-chemical parameters (T, Eh, pH, O2) has been performed in Feb 2021 over
10 piezometers tapping both surface and deep peat layers, rainwater, outlet and surround-
ing karstic springs. In addition, one complete (Feb 2020-2021) of monthly evaluation of
δ18OH2O, δ2HH2O DOC and physico-chemical parameters has been performed.
Preliminary results from nested panpipes piezometers highlight vertical gradients for DOC
concentration, δ18OH20 and δ13CDIC and physico-chemical parameters. Acid surface wa-
ter (pH ranging from 4.4 to 5.5) seems to mainly interact with vegetation as suggested by
high DOC (24 to 62 mg/L, mean = 43 mg/L), low bicarbonate (0 to 51 mg/L, mean = 24
mg/L) concentrations and depleted δ13CDIC (-3.6 to -20 ‰, mean = -9.7 ‰). In contrast,
deep peat pore waters harbor circumneutral pH, have low DOC (13 to 53 mg/L, mean = 24
mg/L), high bicarbonate (138 to 472 mg/L, mean = 325 mg/L) concentrations and enriched
δ13CDIC (from -7 to + 8 ‰, mean = 3.5 ‰).
These enriched δ13CDIC were compared with δ13CDIC modeled assuming either a unique
biogenic origin of DIC or a double geogenic and biogenic origin implying alteration of car-
bonates. Both these approaches suggest hotspots of methanogenesis mainly in deep peat
layers where groundwater inputs from the regional karstic system are hypothesized. Ex-
pected modifications in local precipitation and regional groundwater supply contributions
due to ongoing climate changes implying possible greater winter recharge over Jurassic an-
ticlines therefore could have feedback on carbon methane dynamics. In particular greater
groundwater inputs combined with warmer conditions could favor greater DIC reduction
under anoxic conditions, providing more CH4 production. In parallel, such a methane stock
could be destabilized under climate change, further degassing at the peat surface and altering
the peatland C balance and storage socio-ecosystemic service.
sciencesconf.org:ozcartereno2020:362518