DMI-01-013

Experimental Harvesting within Riparian Buffers of Northern Alberta: Determining the impacts of timber harvesting on stream water quality and development of a physically based predictive model for water quality
Sponsor: 
Tolko Forest Industries – High Level Lumber Division
Lead Researcher: 
P McEachern, E.E. Prepas, PhD, D. Chanasyk, PhD, University of Alberta
Body: 
The objective of this research was to determine and model the impacts of watershed disturbance on water quality in northern Alberta. The research consists of two projects; The first was focused on the impact of harvesting on stream water quality and the second considered the impact of forest fire on phytoplankton in lakes.

The project took place in the area of High Level, Alberta. Two streams in a steeply sloped mountain valley and four streams in a lowland setting were monitored for hydrologic and chemical patterns in two pre-harvest years, one post-harvest year and one post-harvest post-scarification year. The area harvested in the stream basins ranged from 20% to 50%, with the exception of one mountain basin where no harvest had previously taken place.

Harvesting was found to have caused increases in groundwater levels in mountain basins and a decline in total water discharge from the harvested mountain catchment. Harvesting in lowland catchments did not impact groundwater levels, however caused a 20% increase in the total water yield in two streams located in basins with a high percentage of harvested area. There was no apparent change to total water yield in the stream located in basin with a low percentage harvest. Generally, ion flux declined in harvested basins. Scarification caused an increase in flux rates for the treated mountain catchment, however flux rates were still lower than pre-harvest rates. Exceptions were in the dissolved nitrogen which remained at pre-harvest flux rates and dissolved phosphorus where flux rate increased 23% compared to pre-harvest condition. Following scarification in lowland watersheds, flux rates increased markedly in the basin with 50% harvest and flux rates declined in basins with lower harvest levels, but remained above pre-harvest conditions.
To determine the potential impacts of forest fire in peatland dominated catchments, the project tested nitrogen (N), phosphorus (P) and light limitation of pelagic phytoplankton with in situ microcosms in three lakes from a Boreal Subarctic ecozone. To assess if phytoplankton assemblages were influenced by water chemistry, changes following fire, phytoplankton species were identified from 10 lakes in unburnt and 10 lakes in burnt catchments.

For the 20 lakes surveyed, phytoplankton species richness was 36% lower in lakes from burnt compared to unburnt catchments. Phytoplankton communities in boreal forest lakes may be particularly sensitive to catchment disturbances such as fire due to changes in phosphorus and carbon loading from peatland enhance nitrogen, and light limitation.