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. |
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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 |
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Comments | |
Project status | complete |
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