Impacts on Water Quality at a Newly Opened and Extracted Peatland: Influence of Internal Processes and Hydrological Connectivity in Horticultural Peat Harvesting
Creators: Little-Devito, Mika
Publisher: name: University of Alberta Library
Year: 2024

<p>Horticultural peat harvesting continues to expand in Canada, yet the impact to downstream water quality during the initial stages of peatland opening and peat extraction are poorly understood. Major changes can occur to the hydrology and internal processes within a peatland during the transition to a drained, extracted, peat field that can influence the availability and export of nutrients. In addition to changes occurring within the harvested field, drainage ditch composition and beaver (Castor canadensis) dams can further modify the water quality exported to downstream ecosystems. The objective of this study was to investigate changes to the in-field processes and hydrological connectivity that may influence the outflow water quality during the understudied period when a peatland is opened and initially extracted in the continental Boreal Forest in Alberta, Canada. Water levels, volumetric flow, depth of ice, and aeration depth were measured along with water chemistry (electrical conductivity (EC), major ions, pH, and nutrients (dissolved and particulate nitrogen (N), phosphorus (P), and carbon (C))) in surface water and groundwater in natural and harvested peat fields, and at the outflows of the peatland complex. Sampling was initiated in the fall of 2018, prior to peatland disturbance, and continued monthly from March through October in 2019 and 2021, capturing the perimeter ditching, vegetation mulching, internal ditching, and peat extraction. In situ ion availability was measured in surface peat layers, alongside surface and below ground temperature, soil moisture, and peat aeration in 2021. Perimeter ditching had little impact on the peat field hydrology; however, ditching increased the catchment contributing area and magnitude of flow to the outflow and extended the flow duration throughout the year compared to the reference. Mulching the vegetation increased water levels, surface temperatures, and initial concentrations of total dissolved N and P in porewaters within the harvested peat field, although N and P concentrations were not sustained at peak levels. Internal ditching and ongoing extraction decreased water levels below 100 cm, but soil moisture remained high and aeration was shallow. Nutrient concentrations in the harvested field were elevated relative to the reference, likely due to decomposition. Internal ditches did not consistently mirror the harvested field; higher nutrient concentrations were common and water was sourced from precipitation, surface, and deep peat porewaters in variable proportions throughout the year. Compared to natural peatland areas, harvesting activities greatly decreased peat water storage capacity, encouraged ice formation, and increased spring runoff in a landscape dominated by summer runoff. Transport of high stores of nutrients in the harvested field and internal ditches was dependent on hydrological connectivity that varied both seasonally and interannually. Thus, nutrient concentrations were often poor indicators of mass discharge and leaching risk. When ditches reached underlying mineral sediments, EC, pH, and P concentrations in outflow waters differed drastically relative to reference and harvested peatland porewaters, and drainage ditches acted as a source of predominantly mineral sediments. Waters exiting the main outflow ditch into the downstream outflow swamp had higher P and TSS concentrations, but similar N and DOC concentrations relative to an adjacent reference outflow swamp. Increased flow encouraged beavers to establish a dam at the harvesting operation outflow. Downstream of the beaver dam, ammonium and dissolved P concentrations rose above peat field outflow levels, but sediment concentrations were reduced. Although internal processes increased nutrient availability in the harvested fields, this study shows that hydrological connectivity, ditch substrate, and presence of beaver are key players governing the water quality exported downstream.</p>