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Biogeosciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/bg-2017-485
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Dec 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).
Response of hydrology and CO2 flux to experimentally-altered rainfall frequency in a temperate poor fen, southern Ontario, Canada
Danielle D. Radu and Tim P. Duval Department of Geography, University of Toronto Mississauga, Mississauga, ON, Canada, L5L 1C6
Abstract. Predicted changes to the precipitation regime in many parts of the world include intensifying the distribution into lower frequency, large magnitude events. The corresponding alterations to the soil moisture regime may affect plant growth and soil respiration, particularly in peatlands, where large stores of organic carbon are due to gross ecosystem productivity (GEP) exceeding ecosystem respiration (ER). This study uses a combined lab and field approach to examine the effect of changing rainfall frequency on peatland moisture controls on CO2 uptake in an undisturbed cool temperate poor fen. Lab monoliths and field plots containing mosses, sedges, or shrubs received either 2.3, 1, or 0.5 events per week, with total rainfall held constant. Decreasing rain frequency led to lower near-surface volumetric moisture content (VMC), water table (WT), and soil tension for all vegetation types, with minimal effect on evapotranspiration. The presence of sedges in particular led to soil tensions > −100 cm of water of a sizeable duration (37 %) of the experiment. Altered rainfall frequencies affected GEP but had little effect on ER: overall low-frequency rain led to reduced net CO2 uptake for all three vegetation types. VMC had a strong control on GEP and net ecosystem exchange (NEE) of the Sphagnum capillifolium monoliths, and decreasing rainfall frequency influenced these relationships. Overall, communities dominated by mosses became net sources of CO2 after three days without rain, whereas sedge communities remained net sinks for up to 14 days without rain. Results of this study demonstrate the hydrological controls of peatland CO2 exchange dynamics influenced by changing precipitation frequency and suggest these predicted changes in frequency will lead to increased vascular plant growth and limit the carbon-sink function of peatlands.

Citation: Radu, D. D. and Duval, T. P.: Response of hydrology and CO2 flux to experimentally-altered rainfall frequency in a temperate poor fen, southern Ontario, Canada, Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-485, in review, 2017.
Danielle D. Radu and Tim P. Duval
Danielle D. Radu and Tim P. Duval
Danielle D. Radu and Tim P. Duval

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Short summary
Climate change can shift rainfall into fewer, more-intense events with longer dry periods, leading to changes in peatland hydrology and carbon cycling. We manipulated rain events over three plant types (moss, sedge, and shrub) of a peatland. We found increasing regime intensity led to drier surface soils and deeper water tables, reducing plant carbon uptake. Mosses became sources of CO2 after > 3 consecutive dry days. This study shows peatlands may be smaller sinks for carbon due to rain changes.
Climate change can shift rainfall into fewer, more-intense events with longer dry periods,...
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