|Wednesday, April 06|
Litter decomposition and nutrients dynamics of four macrophytes in intact and restored freshwater marshes of Canada
* Dan Dong, McGill University, Canada
Tim Moore, McGill University, Canada
Pascal Badiou , Institute for Wetland and Waterfowl Research Ducks Unlimited , Canada
Christian von Sperber , McGill University, Canada
Janice Neumann , McGill University, Canada
The restoration of drained wetlands offers opportunities to rewet soils, inhibit decomposition and enhance the nutrient retention in decomposing litters. Yet, the rates of decomposition and nutrient dynamics of macrophyte litters in intact and restored wetlands have not been well addressed. We conducted a 2.1-year litterbag experiment of four common freshwater macrophytes (Phalaris arundinacea, Phragmites australis, Scirpus cyperinus and Typha spp.) in 8 freshwater marshes (3 intact, 4 restored and 1 treatment) within two sites in Manitoba and Ontario, Canada. The marshes varied in terms of the restoration age, inundation periods and the surrounding land uses. Litter decomposition rates (k) followed the order of P. arundinacea (0.42 ± 0.03 yr-1) > T. spp. (0.31 ± 0.03 yr-1) > P. australis (0.19 ± 0.01 yr-1) > S. cyperinus (0.13 ± 0.01 yr-1) in most wetlands and were positively correlated to the initial litter N concentration. Litters decomposed fastest under seasonally inundated conditions. N and P retention from litters were analyzed from mass remaining and the N and P concentration after 2.1 years. Both initial litter N and P abundance and wetland surrounding land uses significantly affected the N and P retention in litters. At the end of this decomposition experiment, the N:P ratio of all litters converged to 20 to 28:1 regardless of initial litter N:P ratio or N or P concentrations. The effectiveness of wetland restoration on slowing decomposition and enhancing nutrient accumulation depends on the quality of the input litters and wetland characteristics including inundated periods and surrounding land uses.
Can phenolic enrichments along with rewetting strengthen enzymic latch and impede carbon emissions in post-extracted peatlands?
* Talal Asif, Université Laval, Canada
Line Rochefort, Université Laval, Canada
Chris Freeman, Bangor University, United Kingdom
Christian Dunn, Bangor University, United Kingdom
Peatlands act as vast carbon (C) reservoirs by regulating decomposition over millennia. Unfortunately, in the recent past, considerable changes such as drainage and peat extraction due to anthropogenic activities have been observed in the peatlands. These land conversions disturbed the functioning of peatlands by increasing organic matter decomposition: hence converted long-term C sink to atmospheric C source. Therefore, the current study aimed to combine rewetting with phenolic addition on a large scale to strengthen enzymic latch and to test how it can suppress enzyme activities, reduce peat decomposition, and limit greenhouse gas (GHG) emissions.
On the potential for peat-block transplants to restore industrially contaminated Sphagnum peatlands
* Colin McCarter, McMaster University, Canada
Paul Moore, McMaster University, Canada
Mike Waddington, McMaster University, Canada
For centuries, industrial processes have inadvertently been contaminating peatlands that degrade peatland functions, such as carbon sequestration. Returning functionality to these degraded peatlands remains a challenge due to adverse hydrological conditions and elevated pollutant concentrations, such as nickel (Ni) and copper (Cu), at the peat surface. To overcome these challenges, a successful restoration technique will need to limit periods of hydrological (soil water tension > 100 mbar) and chemical stress (Ni and Cu concentration > 10-6 mmol mL-1) in the capitula of the restored Sphagnum moss. To limit chemical stress, it is necessary to minimize the upward transport of Ni and Cu to the capitula. As such, the height of the restored Sphagnum moss above the degraded peat (the water and contaminant source) and the hydraulics of the Sphagnum species will likely impact both the hydrological and chemical stress. To examine if the peat-block restoration (i.e., acrotelm transplant) approach, adopted in previous PERG projects, could be used to restore a peatland contaminated by Ni and Cu, we undertook a modelling feasibility study using coupled hydrological and solute transport models in Hydrus-1D. The exceedance of critical capitula hydrological and chemical thresholds that correspond with increased Sphagnum physiological stress were assessed using a series of modelled scenarios with varying peat-block thicknesses (5 to 30 cm), Sphagnum species (S. fuscum, S. rubellum, S. magellanicum, and generic Sphagnum), and initial contaminant loads (i.e., distance from a smelter). When the remnant peat contaminant load was largest and the transplant thickness was 5 cm, the combined hydrological and chemical thresholds in the capitula were exceeded after at least 2 years, while thicker transplants did not exceed the concentration threshold after 10 years. In general, the generic Sphagnum exceeded the hydrological threshold most, followed by S. magellanicum, S. rubellum, and S. fuscum, respectively. A Monte Carlo and sensitivity analyses showed that our modelling results were generally robust. Based on these results, we suggest that targeting S. fuscum and S. rubellum (i.e., densely growing Sphagnum spp.), would likely provide a suitable peat-block for transplant. This research provides a critical path forward for restoring contaminated and degraded peatlands.
Hydrological controls of carbon emissions from vacuum extracted peatlands
* Miranda Hunter, University of Waterloo, Canada
Ian Strachan, Queen's University, Canada
Maria Strack, University of Waterloo, Canada
Disturbance of northern peatlands through land use change may turn these long-term carbon sinks into sources of carbon dioxide (CO2) and methane (CH4). Vacuum extraction of peatlands is an understudied human-caused disturbance. The peatland sectors are subdivided into fields bounded by drainage ditches, spaced 30 m apart. The surface vegetation and top portion of the acrotelm are removed prior to extraction. Currently, few studies in Canada have quantified carbon emissions from actively extracted peatlands. We conducted research during the summers of 2019 and 2021 at two actively extracted peatland sectors in Seba Beach, Alberta, where extraction began 5 (Young sector) and 12 years ago (Intermediate sector). The objectives of this study were to i) assess the influence of sector age and distance from the drainage ditches on CO2 and CH4 emissions and ii) determine the environmental drivers of these carbon emissions at the plot scale. Sixteen transects were created across the two sectors, perpendicular to the drainage ditches. Carbon dioxide and CH4 emissions were measured in the ditches, and 2 m, 5 m and 15 m from the drainage ditches, using the dynamic closed chamber method. In addition, we measured water table depth, volumetric water content (VWC), soil temperature, and pore gas concentration over the summers. We observed that the ditches were hotspots of CO2 and CH4, with significantly higher emissions compared to the fields. There was no significant difference in carbon emissions between field transect positions. Soil temperature and VWC were important controls on carbon emissions, though their strength and direction were site specific. There was a significant negative relationship between CO2 flux and VWC at the intermediate sector, and a positive relationship at the young sector. Analysis of continuous water table measurements showed rapid fluctuations during early summer. A domed shaped water table was observed between drainage ditches at the intermediate site, with the shallowest water table in the center of the fields. This did not cause significant differences in surface (top 20 cm) VWC along this gradient, likely due to strong capillary water movement. These results will help inform future management and restoration of these peatlands.
Ecological Indicators of Carbon Storage at Two Restored Horticultural Peatlands in Quebec, Canada
* Andrew Rutland, University of Waterloo, Canada
Maria Strack, University of Waterloo, Canada
Scott J. Davidson, University of Plymouth, United Kingdom
The declaration of restoration success is as important as the act of restoration itself. One of the primary goals in peatland restoration is the return of the carbon (C) sequestration function found in undisturbed peatlands. However, this function can be difficult to measure and can take years to return even after the peatland has been revegetated. The re-establishment of peat mosses and other vegetation in the years following restoration have been well documented and can be used as indicators of long-term vegetation communities. This study sought to evaluate whether these vegetation indicators can also be used to predict net ecosystem exchange and the return of the carbon sequestration function in restored peatlands. The closed chamber method was used to measure carbon fluxes at two restored post-extraction horticultural peatlands, approximately 20 years post-restoration, in the Bas-Saint-Laurent region of Quebec, Canada. We established 27 collars for carbon flux measurements that were located near permanent plots where vegetation survey data since restoration was available. Each permanent plot was categorized as one of three outcomes: ‘A’ representing plots that have long been dominated by Sphagnum mosses, ‘B’ representing plots that had recently become dominated by Sphagnum mosses, and C representing plots that contain bare peat and little moss. Catotelm respiration, biomass, tree flux was also estimated near all plots. Measured fluxes showed that Outcome A plots had significantly lower average net ecosystem exchange rates than those classified as Outcome C and were mostly net sinks of C under full light conditions, though seasonal modelled results indicated that all plots are still net emitters of carbon. Vegetation community often reflects long-term biogeochemical conditions like water table level at a site, and fluxes in this study were primarily controlled by soil temperature and water table position, further hinting at a connection between NEE and vegetation community. Ultimately, vegetation community shows some promise as an ecological indicator of carbon storage, though more research at other sites is needed.