Water Stewardship Information Sources

Citation Hudson, R and Tolland, L. 2002. Roberts Creek Study Forest: effects of partial retention harvesting on nitrate concentration in two S6 creeks three years after harvesting. Forest Research Technical Report TR-019. Vancouver Forest Region.
Organization FLNRO
URL https://www.for.gov.bc.ca/rco/research/projects/rcsf/TR019.pdf
Abstract/Description or Keywords The Flume Creek Paired Watershed Experiment (Roberts Creek
Study Forest, Sunshine Coast, BC) was implemented in the
early 1990s to provide information on the effects of forest
harvesting on drinking water quality. Three study creeks were
identified: F4 (39 ha catchment area), F5 (61 ha) and F6 (16
ha). The study creeks have been monitored for streamflow
more or less continuously, using high frequency event based
automatic sampling to obtain detailed water quality data.
Variable retention (VR) and strip shelterwood treatments were
applied to F4 and F5 respectively, in two stages. In the summer
of 1998, about half of the target volume on each creek was
harvested; the remainder of the cut was taken in summer 1999,
leaving F4 and F5 at 39% and 17% harvested. F6 was kept as
the control creek. This divided the data into four periods: prelogging,
year 1 (the logging phase following the first entry) and
years 2 and 3 (one and two years after logging).
Prior to treatment, nitrate concentration exhibited pulse behavior
with the highest concentrations occurring just after fall
freshet. Subsequent storms produced nitrate pulses of diminishing
concentration as the season progressed. Several parameters
were used to assess the changes in nitrate status following
logging, including arithmetic and flow-weighted mean concentration,
seasonal nitrate flux, and change in peak concentration
of paired nitrate pulses relative to the control. Ratios of each
parameter for treatment periods relative to control periods were
calculated. Overall, nitrate levels at F5 were about 4, 30 and
60 times that of its unlogged state in years 1, 2 and 3 respectively,
while at F4 the nitrate levels changed by factors of 12
and 18 times in years 2 and 3, and were unchanged in year 1.
These results are somewhat unexpected. It had been thought
that F4 would experience a larger change in nitrate concentration
than F5, proportional to harvesting intensity. Instead, the
change in nitrate levels at F5 were 3 times the changes at F4.
Therefore, the response is likely due in part to differences between
the watersheds as opposed to purely a treatment effect.
It is speculated that the riparian zone of F5 stores more nitrate
than that of F4, and that the large response in water
chemistry is due to riparian disturbance.
Information Type report
Regional Watershed sunshine coast
Sub-watershed if known Flume Creek
Aquifer #
Comments
Project status complete
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