This pages is a `subpage of versicolor.ca/sandylakebedford/Surface Waters/Lit&Links/Lake Stratification & EC/salt content
Excerpts are taken from:
Nutrients and Algae Water Quality Guidelines (PDF, 70 pages)
B.C. Ministry of Environment and Climate Change Strategy, 2021. (Reformatted from: British Columbia Ministry of Environments, 1985. Water quality criteria for nutrients and algae). Water Quality Guideline Series, WQG-16. Prov. B.C., Victoria B.C. Document written for B.C. but its consideration of the nuances of trophic classifications should apply more broadly. “In summary, the criteria which are proposed here are designed to protect particular water uses. Few previous attempts have been made by other government agencies to specify standards for nutrients or algae on such a detailed basis. The criteria are intended to serve as the basis for more specific water quality objectives which will require a detailed evaluation of individual streams or lakes (or parts thereof). The criteria values are conservative and therefore favour protection.”
Below, I have copied some of the text that provides comments on the relationship of oxygen levels to trophic status, and to phosphorous levels in particular. Some additional paragraphing has been added to facilitate reading on a monitor (versus a print document), also some bolding.
PDF p5
For lakes a well defined relationship exists between phosphorus, generally measured at spring overturn, and the amount of algal biomass in a lake during the growing season. Since phosphorus is much less difficult to measure than algal biomass, and can be easily related to other important lake characteristics such as water clarity and hypolimnetic dissolved oxygen, the lake criteria are specified as total phosphorus.
In examining what levels of phosphorus could be suggested for protecting particular water uses, data from the scientific literature and from lake studies conducted in British Columbia were examined.
For water-based recreation and aesthetics, a major consideration is water clarity. As such, there is a distinct preference for oligotrophic lakes which are generally defined as having less than 10 ug/L phosphorus. This value, or a value close to this, has also been used by other jurisdictions as a water quality standard and suggested by other authors as being a value which ensures lakes are acceptable for recreation. The criterion which is suggested for this water use is a total phosphorus concentration at spring overturn of 10 ug/L. Some qualification is required since spring overturn phosphorus is only a valid estimator of summer algal biomass, water clarity, and oxygen deficit, if the lake’s summer epilimnetic water exchange rate is less than six months. For lakes with more rapid flow-through characteristics, a mean summer phosphorus concentration should be used. This requirement applies to the criteria suggested below as well.
PDF p6
It would appear that, in general, a higher concentration of phosphorus is required to optimize fish production than is desirable for recreation and drinking water supply (10 ug/L). This is particularly important for non-salmonid (warm water) species which may require much higher phosphorus concentrations for optimum fish production.
Some lakes would be best maintained at a low phosphorus concentration (5-10 ug/L) if an increase could cause a change in the food chain. If the lake is sensitive to oxygen depletion because of morphometric characteristics, it might consequently exhibit hypolimnetic oxygen depletion at low phosphorus concentrations (<10 ug/L).
Generally, symptoms of hypolimnetic oxygen depletion begin to occur at 10 ug/L and this is sometimes a major constraint to lake enrichment. However, many lakes, if they are highly flushed or have very large hypolimnion to epilimnion ratios, may be able to have high phosphorus concentrations (10-15 ug/L or higher) and a consequent high fish production with no adverse oxygen depletion. This situation assumes that the principal use of the lake is for fish production and that recreation or drinking water supply are minor or unimportant, since a phosphorus concentration of 10-15 ug/L or higher would likely interfere with these uses.
The criterion range given (5-15 ug/L) is a basis for setting lake specific concentrations in lakes where salmonids are the most important species. The procedure requires detailed knowledge of the chemical, physical and biological processes of that particular lake.
In summary, the criteria which are proposed here are designed to protect particular water uses. Few previous attempts have been made by other government agencies to specify standards for nutrients or algae on such a detailed basis. The criteria are intended to serve as the basis for more specific water quality objectives which will require a detailed evaluation of individual streams or lakes (or parts thereof). The criteria values a:re conservative and therefore favour protection. These criteria will be subject to periodic review and to modification as understanding of the subject area increases. The criteria are summarized below.
Insert Table PDF p. 6-7:
PDF p 41
5.1 Trophic Classification of Lakes
Trophic Classification of Lakes The concept of trophic levels in lakes (Naumann 1919) is based on the grouping of lakes into categories (oligotrophy, mesotrophy and eutrophy) based on the level of biological production of lakes. Trophic levels can be characterized in a variety of ways, and some of these are summarized in Table 4.
A principal value of the trophic system is that there is a basis on which persons dealing with lakes can communicate the basic chemical and biological conditions of a lake. For instance, “mesotrophic” conveys a variety of lake characteristics, including water clarity, oxygen depletion, algal biomass, phosphorus concentration, etc., (see Table 4) and transition from, for instance, oligotrophy to mesotrophy is generally associated with a number of significant changes (algal biomass, water clarity, oxygen depletion).
It should also be noted that the limnological terms of oligotrophy, mesotrophy and eutrophy carry with them synonyms of value judgement which are also used in a qualitative way: good, fair and poor (Chapra and Dobson, 1981). Similar value judgements were used by Vollenweider (1968) in describing phosphorus loadings. He designated the oligotrophic and eutrophic loading rates as “permissible” and “dangerous”, respectively.
Bernhardt (1983) made specific connections between the trophic state and the water use. For instance he felt that for drinking water supply the required trophic state was oligotrophy but mesotrophy could be tolerated. Other Bernhardt guidelines are shown in Table 5.
The combination of some judgement on appropriate trophic levels for particular water uses and good quantification of the trophic levels gives some starting point for suggesting quantitative criteria for different land uses. However, many lakes are multiple use and uses may have conflicting water requirements. Oligotrophy (<10 ug/L phosphorus or 2 ºg/L chlorophyll a) maybe an acceptable state for water supply for drinking water, however, oligotrophy may not provide sufficient production to support fisheries (particularly some species) at a desired level.
INSERT TABLE 4, PDF p 42
PDF p 44
The key role of phosphorus in determining lake algal production makes the exercise of proposing water quality criteria much easier than for streams.
A variety of relationships have been described which allow correlation of phosphorus loading with chlorophyll a, with water clarity and with hypolimnetic oxygen depletion (Vollenweider 1968; Janus and. Vollenweider 1981; Rast and Lee 1978; Rast et al. 1983). Phosphorus/ chlorophyll and phosphorus/water clarity correlations for British Columbia are described in Nordin and McKean (1984), Since these relationships are well documented, the use of phosphorus as the key water quality variable appears to be justified, but algal biomass can also provide a useful means of evaluating biological water quality and corroborating conclusions reached using phosphorus, if necessary.
PDF p 45
5.4 Phosphorus and Water Uses: Proposed Criteria
5.4.1 Introduction
In addition to the data cited above for phosphorus and chlorophyll in B.C. lakes, there are numerous examples from the literature and from other geographical areas which can be used as guidelines for setting water quality criteria for phosphorus in lakes.
Because of the positive and significant correlation between phosphorus and algal standing crop/water clarity/oxygen depletion, it is possible to specify criteria for phosphorus concentrations in most cases.
However, some situations may require specifying criteria for other properties (algal biomass/water clarity/oxygen depletion), and this can be accommodated by using correlations such as those given in Table 6. Similarly, criteria for nitrogen ·could be established using the ratio between total nitrogen and phosphorus from algal demand (7 or 8:1) to provide the basis for a criterion in a nitrogen limited environment.
INSERT TABLE 6, PDF p 46
PDF P48
5.4.4 Criteria for Aquatic Life
For protection of aquatic life in lakes, Ontario (1979) proposed a total phosphorus concentration for the ice-free period of 10 ug/L or less. This value was specified to prevent oxygen depletion in lake hypolimnia. The International Joint Commission (1930) also suggested that 10 ug/L should be used as a concentration which should not be exceeded to prevent deoxygenation of the hypolimnion of Lake Erie.
The 10 ug/L concentration of total phosphorus to prevent oxygen depletion has some technical support from other sources as well. Walker (1979) showed that hypolimnetic oxygen depletion (HOD) was correlated with the trophic state of the lake. Cornett and Rigler (1979) felt that HOD could be predicted from the phosphorus retention of the lake. Mathias and Barica (1980) noted that the rate of winter HOD was related to the trophic status of the lake, but that the relationship should also consider basin morphometry. Welch et al. (1976) also showed a correlation between winter HOD and phosphorus. Welch and Perkins (1979) describe the correlation between HOD and P loading.
The best correlations with HOD are found with phosphorus loading, and examples of these are given in Jones and Lee (1982) and Rast et al. (1983), However, because of the difficulty in using loading as a factor in protection of aquatic life, it would seem acceptable to use phosphorus concentration as the most convenient quantification for a criterion.
PDF p49
In the correlations and models above, concentration has a poorer fit with HOD than loading because of the range of morphometry and hydrology of any large data set. However, in the general case, concentration, loading and biological response (of which HOD is one component) are well correlated.
Using lakes with typical morphometry and hydrology, the occurrence of anaerobic or near anaerobic conditions in the hypolimnion are usually encountered at phosphorus concentrations of 10 to 12 ug/L, Large lakes, or lakes with large hypolimnia generally do not respond as directly (in terms of hypolimnetic oxygen deficit) to higher nutrient concentrations or loadings.
Oxygen demand can originate from organic material or inorganic chemicals. An input of one mg of phosphorus will result in 0.1 g of algal biomass (dry weight) in one limnological cycle, After settling into the hypolimnion, 0.1 g exerts a biochemical oxygen demand of 140 mg for mineralization. Ammonia has an oxygen demand when it is nitrified. Two moles of ammonia requires three moles of oxygen for oxidation (Stumm and organ 1970)
Rast and Lee (1978) suggested that an average summer chlorophyll a of 2 ºg/L and a corresponding mean summer Secchi disc of 4, 5 m imply a hypolimnetic oxygen depletion of 0.3 g O2/m2/day at a loading rate on the threshold between oligotrophy and mesotrophy (Vollenweider s permissable loading rate). Corresponding approximate values for the excessive loading rate are: 6 ºg/L average summer chlorophyll, 2.7 m average summer Secchi and a hypolimnetic oxygen depletion of 0.6 g 02 / m2 / da y . With these very approximate depletion rates or the oxygen depletion relationships noted above, risk of oxygen depletion in lakes can be assessed.
The onset of anaerobiosis at the bottom of the hypolimnion is a major change for lake biota. Generally, a change in benthos can be observed with the onset of even partial anaerobiosis. Zooplankton vertical migration (and consequent growth, reproduction and survival) are affected by low hypolimneti0c oxygen. Fish can be affected by a change in food organisms (benthos, zooplankton), and directly by loss of a summer cool water refuge due to low oxygen concentrations. Low oxygen concentration at the sediment/water interface can initiate release of P from the sediments, and begin a general acceleration of the eutrophication process.
In some cases it may be necessary to suggest concentrations of phosphorus. which can be directly related to conditions which affect aquatic organisms other than fish. However, when protection of aquatic life is considered, fish are the group which generally receives the most attention.
No criteria exist for a minimum concentration of phosphorus which would enhance the level of biological production to benefit fish production but create minimal consequences to other aquatic biota.
PDF p50
Interior lakes in B.C. where trout are the important species, generally have nutrient concentrations which are higher than the coastal salmon lakes, even when these are fertilized. Smaller interior lakes which are very productive (in terms of trout) often have phosphorus concentrations exceeding 10 ºg/L, and in some cases several times this value.
A key consideration in an acceptable level of nutrients appears to be whether or not a lake is thermally stratified.
A small lake which is stratified and has a phosphorus concentration greater than 10 or 15 ug/L generally has some degree of hypolimnetic oxygen depletion which may be a constraint to fish habitat (loss of cool water refuge) or food supply (particularly change in benthos).
Shallow lakes which do not stratify do not have this oxygen depletion problem and a higher level of nutrients may be tolerable, although with increasing productivity the risk of winter kill increases. Two major factors determine winter oxygen depletion. Mathias and Barica (1980) and Welch et al. (1976) note the effects of lake productivity (nutrients/ chlorophyll) and of morphometry (primarily lake depth).
Warm water fisheries (e.g. bass) must also be considered in another category. With species such as bass, hypolimnetic oxygen is of minor concern since temperature preferences are higher and habitat requirements are different. For warm water fish a phosphorus concentration below 10 ug/L is likely to be undesirable since the level of fish production would be quite low. Lake phosphorus concentrations up to 40 ug/L may be tolerable, depending on lake characteristics and the species considered.
The lack of either empirical or experimental data is a major impediment to suggesting criteria for nutrient concentrations for fish or aquatic life as noted above, except for salmonids and perhaps only for coastal lakes
For lakes where salmonids are the important species of aquatic life, a maximum of 15 ug/L of total phosphorus and a minimum of 5 ug/L are recommended during spring overturn (lake residence > 6 months) or as the mean summer epilimnion concentrations (lake residence <6 months) (See section 5.4.1 for monitoring guidelines).
No attempt is made here to propose a range of optimum phosphorus concentrations for lakes where other groups of sport or commercial fisheries are important, and several factors must be taken into account to apply the criterion which is suggested above. Some lakes, for example, may have marginal hypolimnetic oxygen concentrations at concentrations of phosphorus as low as 7 or 8 ug/L (Nordin and McKean 1984). In such a case an objective would have to be chosen at the low end of the criterion range suggested.
In contrast, some lakes may be amenable to a concentration as high as 15 ug/L if a favourable food chain response exists and the lake had a sufficiently large hypolimnion volume, such that no serious oxygen depletion would occur. Such a concentration would mean that uses such as drinking water or recreation might be impaired to some degree. The chlorophyll a concentration range which corresponds to 5-15 ug/L phosphorus is 1.0-3.5 ug/L
Selected from the PDF p. 54 ff (8. Bibilography)
Links added.
Cornett, R. J., and Rigler, F. H. 1979. Hypolimnetic oxygen deficits: Their prediction and interpretation. Science, 205: 580-581. PDF
Mathias, J. A., and Barica, J. 1980. Factors controlling oxygen depletion in ice-covered lakes. Canadian Journal of Fisheries and Aquatic Sciences, 37: 185-194.
Walker, W. W. 1979. Use of hypolimnetic oxygen depletion rate as a trophic state index for lakes. Water Resources Research, 15: 1463-1470.
Welch, E. B., and Perkins, M. A. 1979. Oxygen deficit – phosphorus loading relation in lakes. Journal of the Water Pollution Control Federation, 51: 2823-2828