Water Quality Objectives for Okanagan Lake: Overview
Prepared pursuant to Section 5(e) of the
Library and Archives Canada Cataloguing in Publication Data
Main entry under title:
to the report: Phosphorus in the Okanagan Valley lakes :
Water quality – British Columbia – Okanagan
TD227.B7W37 2005 363.73’946’097115 C2005-960145-0
THIS DOCUMENT is one in a series that establishes ambient water quality objectives for British Columbia. It is based on a report prepared by Limnos Water Associates for the Ministry of Water Land and Air Protection, Penticton and Kamloops, BC. This report is designed to be an update and expansion of a report produced by the Ministry of Environment in 1985. The 1985 report recommended water quality objectives for all the main stem lakes in the Okanagan Valley for one indicator only, the spring phosphorus concentration. This report confines itself to Okanagan Lake but recommends water quality objectives for additional parameters to provide guidance for long-term water quality protection.
Okanagan Lake is an extremely important water body for a number of uses. There are numerous natural processes and human activities which affect the water quality of Okanagan Lake. The two major influences include nutrient input from non-point sources (e.g., agriculture, forest harvesting, septic tank systems, watershed sources, dust fall and precipitation) and hydrology (e.g., response time and climate change).
The water quality objectives recommended are designed with consideration of three major uses: recreation and aesthetics, drinking water and aquatic life (fisheries). A review of extensive background information provided the basis for the recommended objectives. Although there have been a variety of changes in different components of the ecosystem, some components, like phytoplankton and zooplankton, have shown remarkable stability with few changes over the period of record. The recommended water quality objectives are shown in Table 1.
Purpose of Water Quality Objectives
WATER QUALITY OBJECTIVES (WQO) are tools for the effective management of water resources. They describe conditions that water managers have agreed should be met to protect the most sensitive designated uses of fresh, estuarine, and coastal marine waters. They are used in conjunction with other management tools such as effluent controls and pollution prevention planning to achieve high standards of water quality.
Water quality objectives are prepared for specific bodies of fresh, estuarine and coastal marine surface waters of British Columbia as part of the Ministry of Water, Land and Air Protection’s mandate to manage water quality. Objectives are prepared only for those water bodies and water quality characteristics that may be affected by human activity now or in the near future.
WATER QUALITY OBJECTIVES are based on an evaluation of historical norms for a particular water body as well as the BC approved and working water quality guidelines and the Canadian Council of Ministers of the Environment (CCME) water quality guidelines. Water quality guidelines are safe limits of the physical, chemical, or biological characteristics of water, biota (plant and animal life) or sediment which protect water use. Water quality objectives are established in British Columbia for water bodies on a site-specific basis. They are derived from the guidelines by considering local water quality, water uses, water movement, waste discharges and socioeconomic factors.
Water quality objectives (WQO) are based on best available information in time. When insufficient information exists, provisional WQO may be applied until the data required to develop permanent WQO are available. Provisional objectives are deliberatively conservative and a monitoring or study program is required that will lead to the establishment of permanent objectives.
Water quality objectives are set to protect the most sensitive designated water use at a specific location. Designated water uses include:
Each objective for a location may be based on the protection of a different water use, depending on the uses that are most sensitive to the physical, chemical or biological characteristics affecting that water body.
WATER QUALITY OBJECTIVES routinely provide policy direction for resource managers for the protection of water uses in specific water bodies. Objectives guide the evaluation of water quality, the issuing of permits, licenses and orders, and the management of fisheries and the province's land base. They also provide a reference against which the state of water quality in a particular water body can be checked, and help to determine whether basin-wide water quality studies or enhanced protection measures should be initiated.
Water quality objectives are also a standard for assessing the Ministry's performance in protecting water uses. While water quality objectives have no legal standing and are not directly enforced, these objectives become legally enforceable when included as a requirement of a permit, license, order, or regulation, such as the Forest Practices Code Act, Water Act regulations or Waste Management Act regulations.
WATER QUALITY OBJECTIVES are established to protect all uses which may take place in a water body. Monitoring (water or environmental sampling) is undertaken to determine if all the designated water uses are being protected. The monitoring usually takes place at a critical period of time when the water quality objectives are least likely to be met. It is assumed that if all designated water uses are protected at the critical time, then they also will be protected at other times when the threat is less.
For some water bodies, the monitoring period and frequency may vary, depending upon the nature of the problem, severity of threats to designated water uses, and the way the objectives are expressed (i.e., mean value, maximum value).
Okanagan Lake is the most important and valuable lake in British Columbia. The lake serves as the economic and cultural backbone of the Okanagan Valley. Without the presence of the lake, the communities and the economy would be so different it would be difficult to imagine. The lake is the focus of life in the valley, a source of recreation and drinking water for an ever-growing population as well a habitat for a wide range of organisms. Changes in the lake have the potential of affecting a wide range of economic and aesthetic values and the general social fabric and structure of the communities that border the lake.
Okanagan Lake, because of its importance, is also one of the most studied lakes in the province, at least in the past 35 years. Before 1967 there was little technical data gathered but since then there have been a number of studies which have provided an understanding of the scientific and technical details and a basic understanding of the biology, chemistry, physics, hydrology, geography and geology of the lake and its watershed.
Despite a large volume of technical information on the lake to date, there is far from sufficient knowledge to completely understand many of the complex biological, chemical and physical processes that are necessary to manage the lake with a high level of certainty. While some progress is being made, caution still needs to be used before taking actions which may be difficult to reverse.
This report was designed to update existing water quality objectives for the Okanagan lakes (Ministry of Environment, 1985). Water quality objectives are designed to provide guidance for the public and goals for the government managers of this valuable public resource. The 1985 report proposed water quality objectives for phosphorus only. The goal of this report is to propose a broader suite of aquatic measures to guide the management of Okanagan Lake water quality in the future.
OKANAGAN LAKE is situated in south central British Columbia and is a part of the Columbia River drainage basin. The lake is 113 km long and quite narrow, generally two to four kilometer wide. It has a surface area of 351 km2 with a catchment area of about 6,200 km2 and is the largest of the five main and interconnected lakes in the main stem of the Okanagan Valley.
The average precipitation in the Okanagan Valley is low (315 mm). Only 12% of the precipitation reaches the lake with 85% being lost to evaporation and evapotranspiration. About 2% of the water flows out from the lake. The main inflow from the watershed tributary creeks to the lake takes place generally in May and June. There is some evidence that water availability will decrease with global warming.
The amount of water in Okanagan Lake and subsequent lake level is a result of the balance between the amount of water that enters the lake and the water that leaves the lake. A key fact is that the amount of water that enters (and leaves) the lake is a very small volume relative to the lake volume. In an average year an input of 880 Mm3 (no outflow) would raise the lake by 2.5 metres but add only 3.3% to the volume of water in Okanagan Lake. Evaporation from the lake surface removes almost a metre of water in an average year.
Three major population centres are located along Okanagan Lake: Vernon at the north, Kelowna midway down the lake, and Penticton at the south end. Population growth in the area is expected to continue at rates exceeding the provincial average.
THERE ARE THREE MAJOR uses of the lake: water supply (irrigation and drinking water), aquatic life (including, but not restricted to, fish), and recreation and aesthetics (swimming, boating, water skiing, etc.). There are 919 licenses at present that have been issued to allow a variety of local water utilities, government organizations, and individuals to use water from Okanagan Lake.
Fifteen species of fish were collected from the lake during the Okanagan Basin Study. Kokanee are regarded as the most important species in Okanagan Lake, especially with respect to the sport fishery over the last 20 years. The non-fish aquatic life resources (e.g., zooplankton) of the lake also need to be protected, although their economic value is difficult to evaluate.
The 1980 survey indicated 7.2 million beach days for the year. The survey indicated tourists spend 80% of their vacation days at the beach and the average length of stay was 9.7 days. Water quality was identified as one of the major considerations for tourist beach users along with safety and scenery.
BEEN many efforts to reduce the major inputs of phosphorus
from sewage treatment plants (STPs) to Okanagan Lake. A reduction
of approximately 95% of the point source phosphorus load has
been achieved (44 tonnes in 1970; 2.1 tonnes in 2001). Various
regulations and guidance pertaining to timber harvest (Forest
and Range Practices Act, agriculture (**), best management
plans for storm water control are thought to have also reduced
loading to Okanagan Lake but with efficiencies less than for
the point source sector. Total phosphorus loading to Okanagan
Lake is estimated to have decreased by 30% since 1970 with
60-74% being from natural processes plus timber harvest activities,
and 26-40% from NPS (agriculture, septic tanks and storm water),
Water Quality Assessment
Water quality of Okanagan Lake was assessed with respects to several chemical and biological parameters: water clarity (secchi disk), dissolved oxygen content, phosphorus concentration, nitrogen concentration, N:P ratio, chlorophyll a, phytoplankton, zooplankton, trace contaminants in biota, and bacterial indicators.
Phytoplankton productivity, measured as chlorophyll a, appears to influence the water clarity of Okanagan Lake. This was consistent with observations made in the literature. Whereas the spring- time water clarity of the lake has not changed appreciably from 1980 to 2005, the fall secchi data showed a decrease in water clarity during periods of higher run off in certain years. Seasonal data sets are limited but comparison of the OBS (1971) , OBIA (1976-79) and OLAP (1996-2004) shows a consistent decrease (1970- 9.0m; 1976-78- 7.6m; 2001- 6.5m) over the period of study.
Although dissolved oxygen content is not a concern in the main lake, deep water oxygen depletion is a concern in Armstrong Arm of the lake.
Phosphorus data collected in February or March over a 25-year period showed little change in the total phosphorus concentration other than response to annual inflow of water into the lake. The 25-year WLAP data set for total phosphorus (TP) in Okanagan Lake south of the bridge averaged out at 7 µg/L and north of the bridge 8 µg/L. The Vernon Arm now has essentially the same concentration of TP as the main body of the lake. The TP concentration was substantially lower in year 2003 (12 µg/L) as compared to the year 1985 concentration of 25 µg/L. As a result, changes in water quality objectives from the 1985 report are recommended based on recent and historical data and a reasonable expectation that they will be met and provide a higher level of protection for the lake.
The long-term spring monitoring indicated a significant increase in nitrate concentration in Okanagan Lake. Similar trend was observed for adjacent Kalamalka Lake but not in nearby Mabel or Sugar lakes. However, there was no evidence that the concentration of total nitrogen (and total phosphorus) has changed significantly over the past 30 years.
The N:P (Total N: Total P) ratio is a key factor in understanding the aquatic food chain response to nutrient limitation. The present spring N: P ratio of about 28:1 is reasonably balanced and would not encourage the proliferation of cyanobacteria. Although there is a clear phosphorus limitation in spring and early summer and likely co-limitation of N and P in summer and fall, there is no evidence that the concentration of total N and P have changed significantly over the past 30 years.
Phytoplankton and zooplankton characteristics (e.g., community composition, abundance and biomass) have been used as indicators of environmental quality. Chlorophyll a has also been employed as a surrogate of phytoplankton biomass. The MWLAP data collected during spring months showed fairly consistent concentrations of chlorophyll a with some inter-annual variations but no noticeable changes over the period of record (1975-2002) in Okanagan Lake. Similar trends were observed for zooplanktons biomass in the north and south basins of the lake.
Limited monitoring indicated that the concentrations of trace contaminants (e.g., DDT, mercury and pesticides) in rainbow trout and Mysis tissues were below safe consumption guidelines for humans but wildlife protection guidelines need to be evaluated further with additional testing. Additional monitoring will be required for detailed assessment of trace contaminants in biota. Monitoring of bacterial indicators, E. coli, should also be undertaken near the drinking water intakes to protect human health.
Water quality objectives proposed for Okanagan Lake and its basins are summarized in Table 1. The objectives are based on the B.C. approved water quality guidelines, the Canadian water quality guidelines developed by the Canadian Council of Ministers of the Environment, designated water uses, and ambient water quality characteristics.
The proposed water quality objectives may already be met in a water body, or may describe water quality conditions which can be met in the future. To limit the scope of the work, water quality objectives are currently prepared only for those water bodies and water quality characteristics that may be affected by human activity now and in the foreseeable future.
The major water uses considered for the purpose of setting water quality objectives in this report are: recreation and aesthetics, drinking water, and aquatic life. Inclusion of all these uses was necessary for long-term management and protection of the lake.
There are many stations which are presently monitored to assess lake water quality in Okanagan Lake. In terms of strategic allocation of resources, it is recommended to concentrate sampling on four sites: the north, central and south basins plus Armstrong Arm, to provide continuity in the evaluation of the lake.
There are lingering concerns over biological pathogens, viruses, bacteria, protozoa, and biochemical active constituents like pharmaceuticals and hormone mimics that could be discharged to the lake from sewage treatment plant outfalls. Monitoring of these locations should be the responsibility of the discharger to ensure discharges are not having a negative effect.
The following program is recommended for water quality objectives monitoring.