Water Stewardship Information Sources

Citation Pellett, K. 2011. A review of twenty years of nutrient enrichment in the Salmon River watershed, Vancouver Island (1989-2010). Prepared for BC Hydro.
Organization BC Hydro
URL http://a100.gov.bc.ca/appsdata/acat/documents/r40300/10.CBR.04_Salmon_20years_1386168011381_6166228483.pdf
Abstract/Description or Keywords The feasibility of enriching the Salmon River watershed with nutrients was explored
beginning in the summer of 1988. The first nutrient applications were conducted in 1989
above the BC Hydro diversion dam in Grilse and Norris creeks. Other sites were added
over time including several in the mainstem Salmon River and two in the Memekay River
through 2010. Following two decades of nutrient treatments, members of the BC Hydro
Fish and Wildlife Compensation Program (FWCP) board requested a detailed review of
the program, conditional to future financial support.

An investigation of the bio-physical response to varying nutrient treatments was
conducted including the effect of nutrient quantity, application timing and stream flow.
Biological response was characterized by increased periphyton accrual, accelerated
juvenile steelhead growth, and changes in adult steelhead abundance/ distribution.
Nutrient concentrations in untreated reaches were found to follow similar seasonal
patterns. Phosphorus (P) levels decreased throughout the treatment period (typically
June to September) while nitrogen (N) concentrations increased. The addition of
nutrients was found to increase P immediately downstream of treatment sites but
decreased proportionally with distance. N decreased in reaches of increased
productivity but appeared to recover at the estimated spiralling distance for most sites
(5-15 km). Periphyton accrual in treated reaches (chlorophyll a) was found to be
significantly higher compared to control sites in most years. The source of nutrients
(product or application method) did not appear to influence monitoring results despite
frequent changes to the program.
Nutrient quantity and earlier application timing were found to be positively correlated with
the magnitude of biological response (r2
=0.42 and 0.47, respectively) while stream flow
was negatively correlated (r2
=0.48). Steelhead fry were found to be significantly
heavier in treated reaches (α 0.05) during eleven of twelve years. The magnitude of the
response averaged 104% (1.56 g) and varied between 11% and 218%. The response
was found to be similar at sites 350 m and 3.8 km downstream of the nutrient source
(p=0.40) suggesting a spiralling distance of nearly 4 km in Grilse Creek.
The average age of steelhead smolts captured at the diversion dam (1989-2002) was
found to be consistent with nutrient treatments on the Keogh River at 2.15 years. The
length of two year old smolts was found to be highly correlated to the quantity of
nutrients applied to Grilse Creek two years prior (r2
=0.84) suggesting early growth
sustained as fry may be driving increased size and abundance of smolts under enriched
conditions.
Periphyton accrual did not correlate with the magnitude of juvenile steelhead growth
response although it was found to be strongest near the nutrient source. High nutrient
loading in Grilse Creek (100 kg P or more) produced an exponential algal growth
response while only a moderate response was associated with lower loading rates (15-
80 kg P).
The density of steelhead fry in the Salmon River is positively correlated with the number
of adults observed during March snorkel counts in an 11.5 km index reach. Both fry and adult densities have been approaching target levels in recent years (2006-2011) and the
density of adults in the upper watershed is currently at the highest level formally
documented. Further investigation into bio-physical effects of nutrient enrichment is
recommended by continuing monitoring in non-treatment years.
Information Type report
Regional Watershed Vancouver Island North
Sub-watershed if known Salmon River
Aquifer #
Comments
Project status complete
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