Water Stewardship Information Sources
| ID | 1338 |
|---|---|
| Citation | Nordin, RN, Swain, L, Nijman, R, Rocchini, R and Wetter, D. 2001. Phosphorous in the Okanagan Valley Lakes: Sources, Water Quality Objectives and Control Possibilities. BC Ministry of Environment. |
| Organization | Ministry of Environment |
| URL | http://www.env.gov.bc.ca/wat/wq/objectives/okphosphorus/okphosphorus.html |
| Abstract/Description or Keywords | Over the last 20 years phosphorus inputs to the Okanagan Valley lakes have affected water quality. The economic value of this water resource is high and a considerable effort has already been made to maintain a good level of water quality. This report analyses the present situation and investigates new ways of controlling phosphorus inputs in the future. The phosphorus concentration in a lake is a measure of its biological productivity or trophic state. This is because phosphorus controls algal growth and hence major uses of the water. Phosphorus however does not affect the growth of nuisance weeds to any extent. The Okanagan Valley lakes are a combination of eutrophic lakes (Ellison and Wood), oligotrophic lakes (Okanagan and Kalamalka) and mesotrophic lakes (Skaha and Osoyoos). Over the past ten years there has been some increase in phosphorus concentrations. The increase has been most apparent in Kalamalka Lake, with lesser increases in Okanagan, Skaha and Osoyoos lakes and only minor changes in Ellison and Wood Lakes. Water quality objectives for total phosphorus are proposed in this report for each lake. They are intended to protect. the major water uses and are, by necessity, a compromise between higher values required for fisheries and lower values required for recreation and drinking water use. The main body of Okanagan Lake is the only lake where the phosphorus level presently equals the proposed objective level of 0.010 mg/L. Elsewhere, the objectives are exceeded to a greater or lesser extent. In Kalamalka Lake, the phosphorus level, 0.010 mg/L, is somewhat higher than the objective, 0.008 mg/L. Phosphorus levels in Skaha Lake, 0.025 mg/L, and Osoyoos Lake, 0.030 mg/L, are substantially higher than the objective which is set at 0.015 mg/L for both lakes. The level in Wood Lake, 0.075 mg/L, exceeds the objective, 0.015 mg/L, by an even greater margin. The general relationships between phosphorus levels in a lake and critical phosphorus loadings do not appear to hold for the Okanagan Valley lakes. This is due to their relatively long water-residence time and other unique characteristics. However, measurement of lake phosphorus concentrations and comparison to the water quality objectives will serve as a measure of how well phosphorus loadings are being brought under control. Since 1970, phosphorus loadings from municipal effluents have been reduced 70 percent to Okanagan Lake, 80 percent to Skaha Lake and virtually 100 percent to Osoyoos Lake. Rough estimates indicate that with an expenditure of about $20 million, the main treatment plants can be upgraded and phosphorus removal can be maintained or improved to the 95 percent level for the coming decade. Spray irrigation of all treated effluents on land will achieve almost 100 percent removal of phosphorus from this source. However, the cost in addition to treatment plant upgrading would be at least a further $170 million, half of which would be needed for land acquisition. Rough estimates indicate that phosphorus loadings from septic tanks and agriculture are of equal or perhaps greater importance than phosphorus from municipal effluent in Okanagan and Skaha Lakes. In Wood, Kalamalka and Osoyoos Lakes these diffuse sources presently constitute the most important source of phosphorus. Costs to reduce phosphorus loadings from septic tanks, the most important source of phosphorus from diffuse sources, are about $50 million for the valley as a whole. Costs to reduce agricultural loadings cannot yet be assessed due to lack of proper information. Until now the major effort in reducing phosphorus loading to the lakes has been with municipal treatment plants. Although there is room for some improvement, the cost of removing the last fraction of phosphorus from this source is very high. Even with complete removal of phosphorus from municipal plants, phosphorus loadings from diffuse sources need to be reduced in the future in order to meet water quality objectives and thereby maintain important uses of the water. Reduction of phosphorus from septic tanks and agricultural sources would appear, from the analysis to date, to offer the most promise in the near future. A phased program for dealing with septic tanks could probably be drawn up fairly quickly. More site-specific and pertinent information on agricultural sources will be required before a plan to control them can be prepared, although feedlots and winter-feeding areas will be priority areas for control. For Wood and Kalamalka Lakes a number of special control measures deserve consideration. These include lake precipitation and aeration techniques for Wood Lake and flow restriction methods. These methods will restrict water from Wood Lake, which contains relatively high levels of phosphorus, from flowing into Kalamalka Lake. |
| Information Type | website |
| Regional Watershed | Okanagan |
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| Project status | complete |
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