Water Quality Criteria for Nutrients and Algae
pursuant to Section 2(e) of the
R.N. Nordin Ph.D.
signed by Ben Marr
Updated: August 7, 2001
THE MINISTRY OF ENVIRONMENT, LANDS AND PARKS (now called Ministry of Water, Land and Air Protection) develops province-wide ambient water quality guidelines for variables that are important in the surface waters of British Columbia. This work has the following goals:
Ambient water quality objectives for specific waterbodies will be based on the guidelines and also consider present and future uses, waste discharges, hydrology/limnology/oceanography, and existing background water quality. The process for establishing water quality objectives is more fully outlined in Principles for Preparing Water Quality Objectives in British Columbia, copies of which are available from the Water Quality Section of the Environmental Quality Branch.
Neither guidelines nor objectives which are derived from them, have any legal standing. The objectives, however, can be used to calculate allowable limits or levels for contaminants in waste discharges. These limits are set out in waste management permits and thus have legal standing. The objectives are not usually incorporated as conditions of the permit.
The definition adopted for a guideline is:
The guidelines are set after considering the scientific literature, guidelines from other jurisdictions, and general conditions in British Columbia. The scientific literature gives information on the effects of toxicants on various life forms. This information is not always conclusive because it is usually based on laboratory work which, at best, only approximates actual field conditions. To compensate for this uncertainty, guidelines have built-in safety factors which are conservative but reflect natural background conditions in the province.
The site-specific water quality objectives are, in most cases, the same as guidelines. However, in some cases, such as when natural background levels exceed the guidelines, the objectives could be less stringent than the guidelines. In relatively rare instances, for example if the resource is unusually valuable or of special provincial significance, the safety factor could be increased by using objectives which are more stringent than the guidelines. Another approach in such special cases is to develop site-specific guidelines by carrying out toxicity experiments in the field. This approach is costly and time-consuming and therefore seldom used.
Guidelines are subject to review and revision as new information becomes available, or as other circumstances dictate.
These criteria are based on a detailed analysis given in a technical document. Criteria are specified separately for streams (including brooks, rivers and creeks) and lakes (including ponds and reservoirs). The criteria for streams are specified as biomass of periphytic algae. The criteria for lakes are specified as phosphorous concentration. In rare cases where a lake is shown to be nitrogen limited, nitrogen criteria can be derived. Refer to the technical document for details.
It is not possible to specify a single phosphorous concentration to achieve protection of aquatic life in lakes.
Criteria are proposed to protect water resources in British Columbia from degradation caused by excessive amounts of algae which may impair human use of lakes and streams. Where problem concentrations of algae occur, over-supply of nutrients (generally phosphorous) is the cause. A general goal in dealing with the eutrophication problem is to quantify the amounts of algae which cause problems, and the concentrations of phosphorous which may be associated with algal problems, in order to set limits which would protect specific uses.
Because of fundamental differences between lakes and streams, the criteria are specified in terms of different parameters and different measurement units. For lakes, a clear relationship has been established between phosphorous and algal biomass whereas no such relationship exists in streams. Thus for lakes, phosphorous concentration provides the best indicator of actual or potential problems. For streams there are many factors which determine the amount of algae which will be present and phosphorous is much less important. Thus for streams, the algal biomass itself must be measured to determine actual or potential problems.
For lakes, phosphorous concentrations are measured at spring overturn (if the epilimnetic water residence time is greater than six months) or measured through the growing season (if the epilimnetic water residence time is less than six months). The timing of spring overturn in lakes can vary considerably in different parts of the province and even from year to year in an individual lake. Spring overturn can be considered to occur when the water column is isothermal prior to the presence of significant algal growth (less than 0.5 µg/L chlorophyll a). Samples should be taken from near the surface (one metre), near the bottom, and at one or two intermediate depths. Mean growing season phosphorous concentration should be calculated by sampling at three-week intervals over the summer growing period (generally May to September) from near the surface, at the middle of the epilimnion and near the bottom of the epilimnion. The mean concentration over the summer growing period is then compared to the criterion.
For lakes, a general correspondence between phosphorous concentration and mean growing season chlorophyll a, as well as water clarity or hypolimnetic oxygen deficit, exists. For example, a phosphorous concentration of 10 µg/L results in a chlorophyll a concentration of 2.0 to 2.5 µg/L. The potential thus exists for setting chlorophyll a criteria or water clarity criteria, however this is advantageous only in special cases. In general it is best to use phosphorous concentration as the criterion.
For streams, the criteria levels apply to naturally growing periphytic algae as opposed to algae growing on artificial substrates. Sub-samples are to be taken randomly from the stream section and the mean biomass of the sample is to be compared to the criterion. The criterion should not be exceeded by the mean sample value obtained at any one time.
No criteria for protection of estuarine or marine waters from eutrophication are proposed due to the lack of information available on levels of nutrients or algal biomass which would be desirable in BC coastal waters.