The CO2 dynamics and hydrology of an experimental Sphagnum farming site
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Date
2017-01-23
Authors
Brown, Catherine
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Publisher
University of Waterloo
Abstract
Sphagnum farming (or cultivation) is a recent land management strategy in reclaimed peatlands. The goal of Sphagnum farming is to cultivate Sphagnum fibers on a cyclic basis. Sphagnum moss is non-vascular and requires high and stable moisture availability at the growing surface to reduce capillary stresses. However, specific hydrological requirements to maximize Sphagnum biomass accumulation (CO2 uptake) are uncertain, and there is interest in evaluating the water management design (i.e. irrigation) that is best suited for effective water distribution in Sphagnum farming operations. The purpose of this thesis was to evaluate the hydrological thresholds to increase Sphagnum CO2 uptake in an experimental Sphagnum farming site, and to provide recommendations on how irrigation can be used to increase productivity and upscale the size of operations. The experimental site is in a block-cut peatland south of Shippagan, New Brunswick. From May to July 2014, six 20 x 50 m Sphagnum cultivation basins were established within the lowered trenches of the block-cut peatland, each with a different type of active water management design. The CO2 fluxes were monitored with the closed chamber method, along with hydrological data collected from July 10 to August 14 in 2014, and May 11 to August 22 in 2015. A CO2 and water balance were calculated for each basin for the 2015 study period.
Research has demonstrated that CO2 uptake by Sphagnum moss in post-extraction peatlands is affected by the position of the water table (WT). At this experimental site, CO2 uptake by the moss was not limited by dry (WT -15 to -25 cm) or wet (WT < -15 cm) treatments. When the mean WT was shallow (< 25 cm), the fluctuations in WT were found to be more important in limiting/increasing CO2 uptake. Carbon dioxide uptake was highest where the range in seasonal WT position was < 15 cm. A WT position of -10 to -15 cm is recommended to reduce WT fluctuations and limit excess moisture at the surface. Productivity has the potential to be further improved by maintaining the daily WT fluctuations < ± 7.5 cm from the seasonal WT mean. When these conditions were met, moss grew by a mean of 1.8 mm/month.
To maintain hydrological conditions necessary for maximum biomass accumulation, topographical features of the reclaimed peatland, such as baulks, drainage canals and adjacent trenches, are important considerations for site scale water flow. Water regulation canals are important hydrological features because they have stabilizing effects on WT levels when they are water input sources, and behave as water sinks when water tables are high in the peat basins. The majority of the water flow occurred towards the deep primary drainage canals. The baulks not adjacent to drainage canals formed water mounds, limiting water flow between the basins. An unmanaged trench that is a relic of the block-cut extraction outside but adjacent to the experimental area, was a large source of ground water input to the site. Leveling the site to a common datum and establishing buffer zones adjacent to drainage canals and adjacent un-restored trenches could reduce water transfer within the sites.
Pumping water into the canals was necessary to reduce the water deficit from high ET and low P during a dry study period. The variability in WT position increased with distance from the water input feature (canals or sub-surface pipes). Increasing the irrigation density (ratio of pipe/canal length to basin area) of the water management design will assist in maintaining stable WT positions. To upscale production sites, irrigation features (canals and pipes) should be installed in ways that complement the topography of the site. Installing these features upslope, and increasing their density (maximum spacing of 12 m) will reduce pumping demands and maintain a stable WT. Post-extraction vacuum harvested sites may be better suited for Sphagnum farming than block-cut sites, as they are more accessible to machinery and less landscape manipulation is required. Future studies should evaluate the feasibility of establishing Sphagnum farming sites on post-extraction vacuum harvested peatlands.
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Keywords
Sphagnum farming, carbon dioxide, water table range, straw mulch, moss layer transfer technique, peatland, block-cut peatland, water balance, Peatland hydrology, CO2 peatland balance