|Wednesday, April 06|
Introduction par / by Line Rochefort
On learning and applying hydrological principles to peatland restoration in Canada
* Jonathan Price, University of Waterloo, Canada
The physics and theory of water flow in saturated and unsaturated media was established decades before interest in the hydrology of peat and peatlands became fashionable. Peat is a porous matrix, as are the mineral sediments for which these principles were developed. However, the physical properties and surface chemistry of peat are so different from those of mineral sediments, that new approaches and interpretations were necessary to understand peatland hydrology, and particularly how to effectuate peatland restoration. This required a parallel approach in which the fundamental behaviour of water in peat had to be established, and how this was relevant to the degradation of peatlands, and eventually, their restoration. Early research showed undisturbed and drained and harvested peatlands could have substantially similar water budgets, but with changes in how and where water was stored or released. Seasonally deeper water tables in impacted systems accelerate peat decomposition, so the hydraulic and physical properties of peat change, altering its hydrological response to weather, and ecological function. Non-vascular Sphagnum mosses, the dominant peat-forming species in boreal peatlands, is itself the matrix through which water moves, from living plants near the surface, to partly decomposed organic remains that is the peat itself. The particular species, and their state of decomposition influences how and where water is stored, and rates of horizontal and vertical water flow, thus runoff and evaporation, respectively. It turns out that Sphagnum itself is sensitive to the quality of the substrate it formed, and that degradation of the peat caused by drainage and harvesting, for example, renders a harsh surface typically unsuitable for Sphagnum regeneration. The development of a method to transfer moss diaspores for peatland restoration, required consideration, and often manipulation of the hydrology from micro-sites to field-scale, to facilitate the requisite moisture conditions for Sphagnum to thrive, and return a degraded peatland into a functioning ecosystem. This presentation is about the steps and stumbles to get the hydrology right for restoration.
Years of extraction determines CO2 and CH4 emissions from an extracted peatland in eastern Quebec
* Laura Clark, McGill University, Canada
Ian Strachan, McGill University, Canada
Maria Strack, University of Waterloo, Canada
Nigel Roulet, McGill University, Canada
Draining and extraction of peatlands fundamentally alters the controls of CO2 and CH4 emissions. Carbon emissions from peatlands undergoing extraction is not well constrained due to a lack of measurements from extraction sites. We determine the effect that production duration (years of extraction) has on the CO2 and CH4 emissions from an actively extracted peatland over three years (2018-2020) of measurements. We studied five sectors identified by the year when extraction began (1987, 2007, 2010, 2013, 2016). Higher average CO2 and CH4 emissions were measured from the drainage ditches (CO2: 2.05 (± 0.12) g C m-2 d-1; CH4: 72.0 (± 18.0) mg C m-2 d-1) compared to the field surface (CO2: 0.9 (± 0.06) g C m-2 d-1; CH4: 9.2 (± 4.0) mg C m-2 d-1) regardless of sector. For peat fields, CO2 fluxes were highest from the youngest sector, opened in 2016 (1.5 (± 0.2) g C m-2 d-1). The four older sectors all had similar mean CO2 fluxes (~0.65 g C m-2 d-1) that were statistically different from the mean 2016 CO2 flux. A spatial effect on CO2 fluxes was observed solely within the 2016 sector, where CO2 emissions were highest from the centre of the peat field and declined towards the drainage ditches. These observations occur as a result of the surface contouring that operators create to facilitate drainage. The domed shape and subsequent peat removal resulted in a difference in surface peat age, hence different humification and lability. 14C dating confirmed that the remaining peat contained within the 2016 sector was younger than peat within the 2007 sector and that peat age is younger toward the centre of the field in both sectors. Fourier Transform Infrared Spectrometry (FTIR) (1630/1090 cm-1) values indicated that peat humification increases with increasing years of extraction. Laboratory incubation experiments showed that CO2 production potentials of surface peat samples from the 2016 sector increased toward the center of the field and were higher than samples taken from the 1987 and 2007 sectors. In contrast to pristine and restored peatlands, peatlands under extraction are a net source. Our results indicate that C emissions are high in the first few years after a sector is opened for extraction and then decline to half its original value and remain at this level for the next several decades.
Modeling soil respiration and its influencing factors for an ongoing peat extraction site
* Hongxing He, McGill University, Canada
Laura Clark, McGill University, Canada
Oi Yin Lai, McGill University, Canada
Rachel Kendall, McGill University, Canada
Ian Strachan, McGill University, Canada
Nigel Roulet, McGill University, Canada
By removing vegetation, installing drainage ditches and harvesting peat, peat extraction changes the hydrological and thermal regimes of the peatlands, which makes the peatlands a strong source of CO2 emissions. We adopted the CoupModel (www.coupmodel.com) to simulate the soil CO2 emissions and its associated abiotic drivers for an ongoing extraction site, located in Rivière-du-Loup, Quebec. COUP was first evaluated against three-year (2018-2021) manual chamber measurements of CO2 flux, multi-layered soil moisture and temperature profile, and water table depth data. The validated model was then used to assess the sensitivity of climate on the simulated CO2 emissions. Over 2018-2021, the average CO2 emissions measured mainly over summer was 0.73 ± 0.46 g CO2-C m-2 d-1, with 0.76 ± 0.31 g C m-2 d-1 for 2018, 0.81 ± 1.1 for 2019 (0.57 ± 0.42 g C m-2 d-1 removing the two extreme data), and 0.76 ± 0.31 g C m-2 d-1 for 2020. COUP reproduced the measured summer flux data well with an R2 of 0.5 and a mean bias of 0.2 g C m-2 d-1 and simulated the hydrology and thermal conditions well. Using the simulated data and integrated over a full year, the emission average over 2018 -2021 was reduced to 0.42 g C m-2 d-1, or 153 g C m-2 yr-1. We further performed a long-term (1994-2021) simulation using available climate data from the nearby station. The simulated 27-year annual CO2 emission was 137 ± 24 g C m-2 yr-1, ranging from 80 to 190 g C m-2 yr-1. Overall, the annual variation of the soil respiration was small both in our simulations and the measured data. Our simulated annual CO2 emission rate, 137-153 g C m-2 yr-1 for the studied field is c.a. half of the Tier 1 default emission factor 280 (110 - 420) g CO2-C m-2 yr-1 provided in the IPCC 2013 wetland supplement, also much lower than current emission factors, 310 g CO2-C m-2 yr-1 (by an IPCC Tier 2 methodology) for drained areas used for peat extractions in Canadian national greenhouse gas reporting. We also discuss the coupled hydrological-C dynamics and examine mitigation of management strategies.
Horticultural Additives influence soil biogeochemistry and increase CO2 emissions from peat
* Bidhya Sharma, McGill University , Canada
Tim Moore, McGill University , Canada
Klaus-Holger Knorr, University of Münster, Germany
Henning Teickner, University of Münster, Germany
Peter Douglas, McGill University , Canada
Isabel Strachan, McGill University , Canada
Nigel Roulet, McGill University , Canada
Peat is used as chief ingredient of growing media in horticulture. An average of 11.3 ×10^9kg of peat is extracted in Canada every year. Though the extraction comes at a high carbon cost, the high cation exchange capacity, water retention capacity, low bulk density and appropriate physical properties make peat based growing media desirable for soilless ornamental horticulture and food production. Peat in its natural form is acidic and low in nutrient compositions. For its suitability as a growing media, peat is mixed with liming agents, nutrients, surfactants, perlite among several other possible additives. We assessed the change in soil biogeochemistry and CO2 fluxes because of horticultural additives. We obtained samples of raw peat and additive mixed growing media (n=52) from four different peat extraction companies in Canada. Our analysis shows that the key soil biogeochemical parameters Carbon: Nitrogen ratio, pH, dissolved organic carbon, bulk density, Carbon content differs significantly (p<0.01) between raw peat and growing media. There is more than two-fold increase in CO2 from growing media as compared to raw peat. Further experiment using 13C-CO2 measurements showed longer-term contribution of carbonates, that is added for liming purpose, borne CO2 to the total flux. In addition, CO2 fluxes correlated with decomposition proxies ranging from pH, humification index (derived from FTIR analysis), C:N ratio to Von post for raw peat, but such correlation ceased to be true for growing media. IPCC (2007) calculates that all C from harvested peat is lost in the atmosphere in the first year. However, our initial results we estimate less than 10% of C loss in the first year from growing media.