Forest harvesting impacts on dissolved organic carbon in Alberta’s southern Rocky Mountains: implications on shallow subsurface fate and transport

• Author / Creator

  Mueller, Derek J

• Dissolved organic carbon (DOC) is an important constituent of source water quality from forested headwaters regions that can have implications on downstream drinking water treatment. Landscape disturbances such forest harvesting are known to alter biotic and abiotic controls regulating subsurface DOC fate and transport in some forested regions. The objective of this thesis was to evaluate potential harvest-associated impacts on the magnitude, seasonal timing, and chemical character of hillslope DOC in Alberta’s southern Rocky Mountains. This study explored the influences of harvesting, hillslope position (lowland vs upland) and depth in the soil profile on the transport and fate of shallow subsurface DOC. These potential impacts were assessed by comparing soil pore water, shallow groundwater and stream water DOC as well as mineral soil-DOC adsorption parameters from a reference and harvested catchment. Harvesting resulted in elevated DOC concentrations in soil pore water (p < 0.01) and, to a lesser extent, in shallow groundwater compared to the reference catchment. Additionally, soil pore water DOC from harvested plots was more aromatic (p = 0.01). Temporal trends were investigated over the snowmelt period showing the magnitude of DOC was consistent during snowmelt periods, while the DOC chemical composition was temporally variable among catchments. No difference in DOC concentration or aromaticity was observed between reference and harvested streams, providing evidence that hillslope scale impacts were muted at the catchment scale. Vertical transport of DOC in the soil profile can also be affected by adsorption to mineral soil as water percolates through the soil profile. While DOC adsorption to soils was not influenced by harvesting, adsorption of DOC was strongly influenced by variation in soil properties (pH, soil organic carbon, extractable iron and aluminum) that control mineral soil - DOC exchange among B- and C-horizons. B-horizon soils had a 33% lower sorption affinity and had a 65% greater desorption term than C-horizon soils. This study provides valuable insight into DOC dynamics in this region and helps to evaluate forest harvesting as a potential source water protection strategy.

• Subjects / Keywords

  • hydrology
  • carbon

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-brv5-b876

• License

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