Water Stewardship Information Sources
| Citation | Mavinic, DS, Stockner, JG, Ward, PRB, Hrudey, SE. 2012. Drinking water quality with sockeye salmon introduction in Coquitlam Reservoir. Metro Vancouver. |
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| Organization | Metro Vancouver |
| URL | http://www.metrovancouver.org/services/water/WaterPublications/Drinking_Water_Quality_with_Sockeye_Salmon_Introduction_in_the_Coquitlam_ReserviorOct_2012.pdf |
| Abstract/Description or Keywords | Coquitlam Reservoir is currently a primary source of high quality drinking water for municipalities in the Metro Vancouver Region. The reservoir is a shared resource, with BC Hydro using water that is diverted out of the basin for power generation at the Buntzen power plant. Fisheries requirements for water in the lower Coquitlam River mean that significant flows of water are also maintained in the lower Coquitlam River, via the Coquitlam Dam. First Nations’ oral history of the Coquitlam River, describe an abundant salmon run in previous centuries. Closure of the first Coquitlam dam in 1905 and the absence of a fish ladder, meant that salmon were no longer able to navigate the river, and the anadromous sockeye run that utilized the pre-existing lake and upper Coquitlam river became lake bound or blocked below the dam. In recent years, initiatives for restoring salmon runs in the Coquitlam River, including the sockeye salmon population that depended on Coquitlam Lake for rearing, have been discussed. Key questions have been posed, such as what should be the maximum sockeye escapement permitted in the reservoir, given the excellent raw water quality at present, and a need to prevent taste and odour problems in the municipal water supply. Reports commissioned and completed in the period 2006 to 2007 by Metro Vancouver and BC Hydro were synthesized in 2007, with a recommendation to pursue six primary questions relating to water quality and salmon in the reservoir. These included the requirement for limnological data collection, together with a paleolimnology study, that would enable us to provide a reliable opinion about risk assessment and numbers of salmon. Metro Vancouver agreed to fund a detailed field and analysis program, and provided staff, boats and funding for the study. The limnology study commenced in April 2008, and terminated at the end of the field season in 2010. A risk assessment to identify an appropriate number of sockeye salmon that may be introduced into the Coquitlam Reservoir without compromising drinking water quality was completed in 2011. This report presents a summation of the research results of the limnology study, incorporating also a high level risk assessment for water quality. Also included is a study to determine the potential for creation of disinfection by-products in the municipal supply, due to the possibility of increased nutrients from re-introduced salmon populations. The Expert Committee (panel) overseeing the work consisted of Drs. John G. Stockner, Don S. Mavinic and Peter R.B. Ward. Dr. Steve E. Hrudey was involved at the beginning and near the end of the study, to contribute to the findings in regard to risk assessment. Key findings of the work were as follows: The reservoir was confirmed as being of extremely low biological productivity (ultraoligotrophic), and was among the lowest in productivity of lakes studied in the south coastal climate zone. Low biogenic growth was due to nutrient limitation, brought about by the extremely small inputs of particulate and dissolved phosphorus relative to the size and depth of the reservoir. Annual input of total dissolved phosphorus (TDP) to the reservoir, on average for the summer growing period from inflowing creeks, was as low as 430 to 650 kg. The areal phosphorus loading was less than 0.1 g per m2 per year, a value that was lower than oligotrophic lakes of similar depth. Relatively fast flushing times for the epilimnion, with residence times of only 100 to 135 days, implied that a significant proportion of the phosphorus annually entering the reservoir was flushed out. The configuration of the reservoir sills, with the inflows and outflows occurring at approximately the same depth as the epilimnion, facilitated fast flushing in summer months. During the peak summer (August) period, the rate of photosynthetic carbon (C) production ranged from 0.3 to 0.6 g C/m2 /day. Average chlorophyll concentrations over the summer season were also low, < 0.5 µg/L. The carbon cycle was dominated by photosynthetic phytoplankton. Phytoplankton populations in the reservoir were very low and dominated by small opportunistic species, e.g. micro-flagellates, pico-cyanobacteria and dinoflagellates, that can effectively reproduce and are typical of the C production cycle in low-nutrient systems like Coquitlam reservoir. The most ubiquitous species from July to October was a colonial blue-green with very small cells, Merismopedia, attaining moderate densities. The minute cell-size, (2.5 µm), caused Merismopedia to make only a small contribution, to total phytoplankton biomass. Zooplankton population concentrations were also extremely low, in the range 1 to 3 individuals per L during the summer period. The most abundant zooplankton class in Coquitlam Reservoir were copepods, while the cladoceran Daphnia supported the greatest biomass. Peak densities occurred in May-June for copepods, July to August for Daphnia and other cladocerans, with a second, smaller peak in September. Paleolimnological work, based on sediment cores taken from the bottom muds of the reservoir, showed that there had been no major shift in productivity over the 200 year period covered by the core samples. The only significant change in the record was a small and gradual increase in lake productivity that began at the time of dam construction and impoundment in the early 1900’s, a trend that has continued to the present. The results of diatom-based phosphorus nutrient models showed no statistically significant difference between 200+ yr sediments and those from the most recent decade. Stable isotope-based models of the lake’s nitrogen budget show that ocean derived salmon nutrients have not constituted a large or measurable role in the lake’s nutrient budget prior to impoundment, based on micro-fossil and chemical analyses of the cores collected. Implications are that the pre-dam annual salmon escapement was no more than modest numbers, likely up to a few tens of thousands per year. An experiment to determine the production of disinfection by-products (DBPs), such as haloacetic acids (HAAs) and total trihalomethanes (THMs) from reservoir waters showed that DBP formation was insensitive to the concentration of various combinations of phosphorous (P) and nitrogen (N) nutrients after water treatment for a multi-day period. The results of this experiment suggest that the nature of the molecular carbon compounds from live, or recently senesced algae were not quickly halogenated. Concerns about the addition of nutrients to the reservoir from the decomposition of spawned out sockeye salmon were addressed. A calculation for the number of returning adult sockeye salmon that would be a threshold for potential change of the very low productivity state of the reservoir was carried out. A number was difficult to determine because the details of the P cycling from salmon carcasses are system dependent (lake shoreline, stream, etc.) and are not well understood. Numbers of 15,000 +/- 5,000 sockeye spawners would bring an estimated approximate 11% in TDP concentration in the reservoir, a value unlikely to cause significant effects on plankton production. Modelling work for sockeye salmon returns using the PR (primary production) model, developed by the Department of Fisheries and Oceans (DFO) to help understand capacity of lakes to support juveniles, provided a similar range of numbers of fish. Previous reports (LGL 2005, LGL 2006) have cited the lack of availability of suitable gravels for spawning sockeye salmon. The present situation is that as few as 1,500 females could spawn with the reservoir water level held in the range of full supply level down to 140 m in the fallwinter months, and about 4 times this number of salmon if the water levels were in the range of full supply level down to 144 m. It was concluded in the LGL reports that in a self sustaining system, carbon production must be sufficient to sustain juvenile growth and survival. However with Coquitlam reservoir’s present very low C production, it would not be possible to achieve large populations of returning sockeye salmon for two reasons: insufficient areas of gravel substrate for spawning and a low production pelagic habitat for rearing. A risk assessment that looked at turbidity, pathogens, contaminants and focused on aspects such as taste and odour problems associated with returning sockeye salmon populations, acknowledged that an escapement of up to 15,000 +/- 5000 sockeye salmon per year would be unlikely to alter algal populations or create taste and odour problems in the raw water. However, an overall risk that Metro Vancouver must address is that re-introduction of returning sockeye into Coquitlam Reservoir, resulting in a limited annual sockeye return, could conceivably lead to subsequent calls for additional measures (e.g. fertilization of Coquitlam Reservoir), to artificially enhance the productivity of the reservoir, and thereby enhance the annual numbers of returning sockeye. This situation would carry the substantial risk of degraded drinking water quality and would not be consistent with Metro Vancouver’s responsibility to provide clean, safe drinking water to the region. A good baseline for nutrients and plankton in the reservoir has now been established. An ongoing, low intensity, monitoring program is considered prudent, to monitor the future trends, particularly factors such as phytoplankton that may lead to future taste and odour problems. The allowance of a natural increase of up to 15,000 +/- 5000 adult sockeye would take a long period (one decade to several decades) and would provide a long period for monitoring of any potential changes to the phytoplankton community and any potential changes to water quality. One of the objects of this low intensity, long term program would be to provide a management indicator to help ensure that future reservoir productivity does not move to a higher trophic status, e.g. from ultra-oligotrophic to oligotrophic. It would also be sensible for Metro Vancouver to implement water quality monitoring on a monthly basis including composite sampling on Capilano and Seymour reservoirs as well where, like Coquitlam Reservoir, conditions are likely to change as climate changes. |
| Information Type | report |
| Regional Watershed | Lower Fraser |
| Sub-watershed if known | Coquitlam River |
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| Comments | |
| Project status | complete |
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