Introduction
    Drainage Basin Characteristics
    Lake Basin Characteristics
    Water Quality
    Biological Characteristics (Introduction)
    Biological Characteristics (Plants)
    Biological Characteristics (Invertebrates)
    Biological Characteristics (Fish)
    Biological Characteristics (Wildlife)
    References

Water Quality

Water quality concerns most lake users. How does the water taste and smell? Is it clear or green? Can I swim in it or drink it? Lakes described in the Atlas vary from the cool, clear Kananaskis Lakes, to the warm, green Nakamun Lake, to the salty, but clear Oliva Lake. Many aspects of lake water are determined by natural features of the drainage basin, local weather patterns, and shape and size of the lake basin. Changes in the drainage basin, such as forest clearing, construction of dams, diversion of water and disposal of industrial, agricultural and domestic wastes also have a direct impact on water quality. Evaluation of lake water depends on how the water is used. A saline lake such as Miquelon has poor water quality for a town's drinking water supply, but excellent water quality for swimming or boating.

Many of the lakes described in the Atlas have algal blooms (or "green scum") in summer and have likely been this productive or fertile for millennia. However, detailed water quality information has only been collected for Alberta lakes since 1980. Thus there is relatively little information on the impacts of human settlement on Alberta's lakes, or on deterioration or change in the quality of their water.

Eight lakes described in the Atlas have two basins or are two distinct lakes (Amisk, Baptiste, Kananaskis, La Biche, Mann, Ste. Anne, Sandy and Skeleton) and one lake has three basins (Buffalo). In this section, each lake or basin is considered distinct, but there are few water quality data for about 12 other lakes, therefore the total number of lake basins with good water quality data is about 100. Except where noted, the chemistry described is the average for the euphotic zone in the open-water period. When comparisons are made with lakes on the Canadian Shield, data from the Experimental Lakes Area in northwestern Ontario are used.

Major Ions and Related Characteristics

Lake water contains minute amounts of chemicals, often called salts. This general term describes chemicals which, when dissolved in water, separate into positively and negatively charged particles called ions. Common cations (positively charged ions) include calcium (Ca), magnesium (Mg), sodium (Na) and potassium (K); anions (negatively charged ions) include bicarbonate (HCO₃), carbonate (CO₃), sulphate (SO₄) and chloride (Cl). The ions may join in various combinations to form salts such as calcium carbonate. The units used for chemicals reported in each lake description are those familiar to most lake scientists - weight per unit volume (mg/L or µg/L). One milligram per litre (mg/L) is equivalent to one part of chemical per one million parts of water; one microgram per litre (µg/L) is equivalent to one part per one billion. Two other measures of chemicals are also used by lake scientists, micromoles and microequivalents (conversions between these scales are given in Section 2 of the Appendix). A micromole is a measure of the number of atoms per unit volume. A microequivalent is a measure of the charge contributed by that substance. When the major cations and anions in a water sample are expressed as microequivalents and totalled, the groups will be approximately equal.

Water in lakes described in the Atlas contains on average about 50% more dissolved substances than do freshwater lakes around the world. These chemicals come with water that runs over the soils and rocks in the drainage basin and percolates below the surface before entering a lake, or fall directly on the lake in rain or snow or with dust. Water in lakes described in the Atlas is generally rich in calcium and magnesium from weathering of carbonates. Carbonates are part of the natural buffering capacity in lake water, and consequently protect lakes from acidification by neutralizing acids. In some cases the water may have a strong flavour; in extreme cases such as some of the saline lakes in southeastern Alberta, the shore may even look crusty or salty.

Salinity

Because anions and cations carry electrical charges, water containing them can conduct electricity, and its ability to do so gives a measure of the total quantity of charged particles (ions) dissolved in it. This is known as the specific conductivity of water. Another measure of the total ion content of lake water is total dissolved solids (TDS). Specific conductivity (or conductivity) is measured with an instrument that passes an electrical current through a sample of the lake water between two platinum electrodes; units are micro-Siemens per centimetre (µS/cm). Total dissolved solids is the weight of salts remaining after filtered lake water is evaporated at 103°C to 105°C, in units of mg/L. In the Atlas's freshwater lakes, total dissolved solids are consistently less than conductivity (62% on average). In saline lakes such as Oliva Lake, TDS exceeds conductivity.

Throughout the world, lake water ranges from very dilute (conductivity less than 10 µS/cm) to more saline than seawater (which has a conductivity of about 32,000 µS/cm). For example, lakes on the Canadian Shield have an average conductivity of 19 µS/cm; these lakes are in hard rock, granite basins and are as dilute as any group of lakes in the world. Lakes described in the Atlas have higher salinity (range from 81 to 60,000 µS/cm conductivity or from 50 to 84,000 mg/L TDS) than water found in hard rock basins such as the Canadian Shield. The salinity of lake water described in the Atlas is representative of the waters found throughout most of Alberta and regions extending from southern Manitoba to the interior of British Columbia, excluding some lakes in the Rocky Mountains, small lakes on the western edge of the Canadian Shield in the remote northeast corner of Alberta and lakes situated in northern peatlands, none of which is included in the Atlas. Lake Athabasca is the only Atlas lake which has part of its drainage basin on the Canadian Shield, and it also has the lowest salinity. The distribution of salinity in lake water described in the Atlas is presented as a frequency histogram in Figure 16; most lakes (89) have fresh water (defined for the Atlas as having TDS less than 500 mg/L), 7 have slightly saline water (between 500 and 1,000 mg/L TDS), 5 have moderately saline water (between 1,000 and 5,000 mg/L TDS) and 4 have saline water (more than 5,000 mg/L TDS).

Water from saline lakes not only tastes different from fresh water, but fewer species of plants and animals are found there. When water reaches the salinity of Oliva Lake (twice the salinity of seawater), a white crust is evident along the water's edge. The saline lakes have higher ionic content as a result of two factors: first, they are in a region where evaporation greatly exceeds precipitation (up to three-fold) and thus there is a trend towards concentration of all ions in surface runoff and precipitation. Second, saline lakes have inputs of saline groundwater.

pH

The pH indicates the acidity or alkalinity of water. The term pH refers to the concentration of hydrogen ions on a negative logarithmic scale extending from 1 (acidic) to 14 (basic). A decrease of one unit in pH corresponds to a 10-fold increase in the concentration of hydrogen ions. When the pH is less than 7 the solution is acidic, at pH 7 it is neutral, and above this it is alkaline. All of the lake water described in the Atlas has pH between 7 and 10 and is thus alkaline. Water that falls in the drainage basin of these lakes flows over rocks and percolates through glacial deposits and soils that are rich in carbonate salts and thus free hydrogen ions are neutralized. The capacity of soils to neutralize hydrogen ions, called buffering capacity, is relatively high over much of Alberta. Also, the pH of precipitation in this region is relatively high, because the prevailing winds are from the west and the distance from major industrial centres is great. In contrast, lakes in northwestern Ontario, on the Canadian Shield, where rocks and soils are less able to neutralize hydrogen ions, have a pH between 5.6 and 6.7. Similarly, stained or brown water lakes in northern Alberta have a pH as low as 5. Farther east, where lakes are still on the Canadian Shield and near large industrial and urban centres, the pH in lake water can drop to 4 or less due to acidic rain. Many aquatic animals are intolerant of a pH below 5.7, and thus where acidic rain has lowered the pH of lake water below this level, many animal species do not survive. The most devastating impact of acidic rain on aquatic animals has been documented for the lakes in southern Sweden and Norway, which are situated in carbonate-poor, hard rock basins downwind of the polluted air from the rest of Europe. In Alberta, carbonate-rich glacial deposits and soils protect lakewater against such impacts.

Buffering Capacity and Hardness

Total alkalinity is a measure of the capacity of water to neutralize strong acid. It is measured by determining how much strong acid will lower the pH of a water sample to a specific level; units are mg/L equivalent to calcium carbonate (CaCO₃). For lakes described in the Atlas, this capacity is linked to the amounts of bicarbonate and carbonate ions. In the poorly buffered lakes on the Canadian Shield, total alkalinity is generally less than 15 mg/L CaCO₃. In brown water lakes in northern Alberta total alkalinity can be less than 5 mg/L CaCO₃. In contrast, the range of total alkalinity for Atlas lakes is from 40 mg/L CaCO₃ for the dilute Lake Athabasca to 25,000 mg/L CaCO₃ for the saline Oliva Lake (Fig. 17); they are all strongly buffered lakes. Most of the Atlas lakes (86%) are categorized as high alkalinity because alkalinity is greater than 100 mg/L, the remainder are classified as relatively low alkalinity for prairie lakes.

Water that is rich in calcium and magnesium is called hard water, a term that comes from the amount of soap needed to form a lather - hard water needs more soap to form a lather than soft water. As with alkalinity, water hardness or total hardness is expressed as mg/L equivalent calcium carbonate (CaCO₃). All lakes described in the Atlas have hard water:

In contrast, lakes on the Canadian Shield and some brown water lakes in northern Alberta have soft water; total hardness of these lakes is generally less than 10 mg/L CaCO₃.

Major Ions

The major ions described in the Atlas (listed in Table 4), are vital to the health of plants and animals in lakes. For example, calcium is a structural component of vertebrate bones, and it forms the shells of many invertebrate animals, especially clams and snails. The use of these major ions by plants and animals does not directly affect the amounts in water because the requirements of these organisms are small compared to concentrations in lake water.

Concentrations of three cations, magnesium, sodium and potassium, are relatively constant over time and at various depths in the water column. In contrast, calcium concentrations are more variable overtime and depth within lakes. Calcium concentrations are lowest in the surface waters when large amounts of algae are growing. When carbon dioxide is absorbed from the water for photosynthesis, pH increases and the relatively insoluble salt, calcium carbonate, comes out of solution and precipitates onto the leaves of rooted plants, or on the bottom of the lake, or even forms crystals in the open water. Calcium concentrations in lakes described in the Atlas are low for hardwater lakes, and there is no pattern with increasing TDS (Fig. 18). In Atlas lakes, relatively low concentrations of calcium are balanced by concentrations of Na, K, and Mg that are 2 to 3 times the world average for freshwater lakes (Table 4).

When people think of salt, they often think of sodium chloride (table salt). Although sodium concentrations are high in these 100 lakes, chloride concentrations are low as a result of the distance from the ocean and limited use of road salt in this region compared to eastern Canada and northeastern United States. For example, the amount of chloride has tripled in Lake Erie and Lake Ontario over the past half century due to the use of road salt in their drainage basins. The ions in freshwater lakes can come from salts such as calcium carbonate, calcium bicarbonate, sodium sulphate and potassium sulphate. Fresh water contains many salts and has quite a different composition from seawater (Table 4). Similarly, the saline lakes in Alberta have relatively high concentrations of sulphate and bicarbonate and low concentrations of chloride.

Sulphate concentrations are quite variable among lakes in the Atlas (over 200-fold in the freshwater lakes) and these concentrations are linked to inputs from atmospheric sources, surface runoff and groundwater, and consumption of sulphide in bottom mud. Oxygen is absent in water in the bottom mud and some bacteria consume sulphates, with hydrogen sulphide as a byproduct. Hydrogen sulphide produces the characteristic rotten egg smell when stagnant muddy water is stirred up. Sulphate is also used in these sediments to produce highly insoluble compounds such as pyrite and ferrous sulphide.

Bicarbonate and carbonate (along with a relatively small amount of carbon dioxide) make up inorganic carbon in lake water described in the Atlas. Inorganic carbon is used by algae in a process called photosynthesis. Water and inorganic carbon are combined by plants in the presence of adequate light, nutrients and the pigment chlorophyll to produce organic carbon or solid plant material. Approximately half the weight of organic material in living cells is carbon. Most plants obtain their carbon through photosynthesis; animals are unable to photosynthesize and therefore must obtain carbon from the carbon-rich bodies of plants and animals (Fig. 19). The amount of carbon fixed in a given time is an important measure of the productivity of a lake; it is often expressed as milligrams of carbon fixed per square metre of lake surface area per unit time (mg C/m² per day) to allow comparisons to be made between lakes of different depths. Photosynthesis takes place in the euphotic zone or trophogenic zone, the zone which extends from the lake surface to the depth that 1% of the surface light will penetrate.

Bicarbonate is the highest among the anions in many of the Atlas lakes, and these lakes are referred to as bicarbonate-type. In summer, inorganic carbon concentrations are generally higher in water over the bottom mud than in the waters near the surface of the lake, as a result of decomposition of organic material by bacteria in the bottom sediment.

Temperature

Temperature, oxygen and pH are often described as the "master variables" structuring aquatic habitats. The temperature of water changes much less rapidly than that of air, so aquatic plants and animals are protected from sudden changes and only have to adjust gradually. As well, the range of temperatures in temperate zone fresh water (0°C to 26°C) is much less than in air. The unique physical properties of water play an important role in structuring the annual temperature patterns in a lake; water at 4°C is heavier than water that is either cooler or warmer. Temperature patterns that develop in water are determined by air temperatures and wind. Water temperature, as with most variables described in this section, is usually measured as a series of measurements from the water surface to the lake bottom, at the deepest part of the lake (Fig. 20).

Studies during the 1980s on 20 lakes located from north of Peace River to south of Kinsella, Alberta, indicate that maximum ice thickness can vary from a minimum of 40 cm to almost 1 m, although the average maximum ice thickness is approximately 60 cm. In Alberta, the duration of ice cover is approximately five months, ranging from more than six months in the mountain lakes and in the northeastern part of the province, to no more than four months in saline lakes and many shallow lakes and reservoirs in southern Alberta. In any individual lake, freeze-up and ice-out will vary from year to year depending on weather patterns. At Narrow Lake, where records of the date of freeze-up and ice-out were kept for six years (1983-1989), the date of first ice-cover extends from 1 to 26 November, and of ice-melt from 19 April to 7 May.

In winter in Alberta, water near the lake bottom is usually near 4°C, whereas water near the surface is colder and approaches 0°C just under the ice. This pattern is illustrated in Figure 21 with data from a shallow lake (Figure Eight) and a relatively deep lake (Narrow). After the ice melts in spring, surface waters in Alberta warm quickly. The thermal patterns observed during the open-water season depend on whether a lake is relatively shallow and the entire depth of water mixes during summer, or whether it is deep enough to be divided into seasonal thermal layers.

In shallow lakes, such as Figure Eight, the entire water column warms during the first few weeks in spring. When the whole water column is the same temperature, all the water in the lake will mix together. In calm weather, the surface water will warm up more rapidly than the deeper water. By May or June the surface layer will approach 15°C to 20°C and the deeper water may be several degrees cooler. The temperature difference between the surface and bottom waters is reduced over the summer, as intermittent periods of cooler air temperatures and strong winds reduce surface water temperatures. By late summer the temperature of the entire water column is uniform or isothermal. Occasionally during brief periods of calm, warm weather, the surface waters may be slightly warmer than the waters over the bottom mud. This fairly uniform condition continues through the fall, as water temperatures drop and eventually reach 4°C. Isothermal water is usually well-mixed. When it becomes sufficiently cold, a layer of ice will form and the annual temperature cycle repeats itself.

After ice-out in deeper lakes, such as Narrow, the surface water may warm so rapidly that there is little mixing of this water with the deep water (Fig. 21). Soon, a distinct warm surface layer is separated from the cool bottom waters by a layer where the water temperature changes rapidly. This transition layer is often a repository for small particles and plankton. The three layers have names of Greek origin: epilimnion, or "top of the lake", metalimnion, or "middle of the lake" and hypolimnion, or "bottom of the lake". When these zones form, a lake is said to be thermally stratified. During summer, the depth of the epilimnion increases, as a result of wind mixing and periods of cooler air temperatures. With the onset of cooler air temperatures in fall, the epilimnion deepens faster and the metalimnion becomes less clearly defined until eventually the entire water column reaches 4°C. With sufficient time and wind, the lake may mix for a while before ice forms. But if the onset of ice-cover comes soon after the whole lake is the same temperature, there may be little mixing before the ice forms. In deep lakes, the bottom waters have relatively constant temperatures year-round, but in shallow lakes, bottom water temperatures may range from 2°C to over 20°C.

There are many deviations from this general pattern of annual temperature cycles in lakes. High salt content can change the density of water in any particular layer and alter the patterns described. Very large lakes such as Cold Lake tend to have delayed dates of ice formation, lower temperatures under ice in winter, and delayed dates of ice-off in spring relative to the smaller lakes in the same region. Lakes fed with water from high mountain streams such as the Kananaskis Lakes tend to have cooler water in summer than lakes farther from the mountains. As a consequence of the inputs of warm water from a thermal generating plant, Wabamun Lake has a shorter period of ice-cover than other lakes just west of Edmonton, and one part of that lake remains ice-free most of the winter. The size and shape of the ice-free area at Wabamun Lake can change rapidly, depending on air temperatures, and wind speed and direction.

Oxygen

Just as terrestrial plants and animals require oxygen, so do most aquatic organisms. Aquatic creatures do not breath air, but they can extract dissolved oxygen from their watery medium. Some life stages of animals, such as trout fry, require high concentrations of dissolved oxygen and will not tolerate amounts below about 10 mg/L. Other organisms such as sticklebacks, fathead minnows and many benthic invertebrates are tolerant of lower concentrations and may even survive short periods with no dissolved oxygen. Concentrations of dissolved oxygen in lakes in the Atlas range from 0 to above 20 mg/L.

Oxygen enters lake water from three sources: from the air, as a byproduct of photosynthesis and with groundwater. Most oxygen inputs are in the top layers of the lake. Oxygen from the atmosphere enters the lake only at the surface. Under ice-cover, no oxygen can enter the lake from the air. Oxygenated groundwater is more likely in shallow water than in deep water. Photosynthesis, and thus the addition of oxygen by green plants, takes place only in the euphotic zone during daylight hours. Because plants and animals use oxygen for respiration around the clock, oxygen is being continuously taken out of the euphotic zone, although the rate of replenishment during the day often exceeds the rate of uptake. In the deeper, darker water, oxygen is only being taken out. In or near the bottom mud, oxygen demand is often high due to bacterial decomposition. Under very unusual conditions, an algal bloom may die off suddenly in a shallow lake, and oxygen demand for decomposition may be so much higher than the input with photosynthesis that oxygen concentrations will approach zero throughout the water column for a few hours or days. Many animals will perish during the period of uniformly low dissolved oxygen concentrations, and the condition is called summerkill.

The amount of oxygen that can dissolve in water depends on water temperature, elevation above sea level and salinity. More oxygen can dissolve in cold water than in warm water; at 4°C, one litre of water can hold (or is saturated at) about 12 mg of oxygen, at 20°C it is saturated at 8 mg per litre of oxygen. Similarly, fresh water holds more oxygen than saline water and saturation increases with increased pressure. Water at the surface usually has higher concentrations of dissolved oxygen than water deeper in the lake. This effect may be modified somewhat by the fact that warmer surface water cannot hold as much oxygen as colder, deeper water. An example of highly oxygenated deep water is found in Upper Kananaskis Lake in summer.

The amount of dissolved oxygen in lakes usually decreases under ice-cover primarily due to respiration by all organisms, but mainly bacteria. In shallow lakes, oxygen depletion can proceed rapidly under ice (Fig. 22). If concentrations throughout the water column drop close to zero, as occurred in Figure Eight Lake in February 1986, many fish species (such as yellow perch and walleye) and some invertebrates (such as clams) will not survive and a condition called winterkill will develop.

Oxygen loss under ice is often expressed as milligrams of oxygen consumed per square metre of lake surface area per unit time (mg oxygen/m² per day). Most of this oxygen loss is due to respiration, primarily by bacteria which break down organic matter in the bottom mud. Oxygen loss from November through February is fairly predictable based on depth of the water column, an estimate of summer algal productivity and water temperature; measured rates of under-ice oxygen depletion for lakes described in the Atlas range from 0.2 to 1.0 mg O₂/m² per day. In some as yet poorly understood situations, algal blooms can develop under ice during midwinter (November through February). These conditions are relatively uncommon, although one spectacular bloom was recorded during the winter of 1985-86 in shallow Driedmeat Lake. Under-ice algal blooms are more common in March and April when light levels are relatively high. These late winter under-ice algal blooms can result in increasing oxygen content, as illustrated in Figure 22; therefore predicting oxygen concentrations in March and April is more difficult than earlier in the winter.

During the ice-free season in shallow lakes, the distribution of dissolved oxygen concentrations is variable, shifting from fairly uniform when the water is well-mixed, to highly stratified when the water column is weakly thermally stratified (Fig. 22).

Compared with shallower lakes, the water in deeper lakes is often not as well-mixed in fall prior to ice cover. Oxygen concentrations are usually higher in the top layer of water than over the bottom sediments during late fall and the early period after ice formation. Under ice, oxygen consumption proceeds as described for shallow lakes, except the larger volume of water protects the lake against winterkill. Oxygen concentrations in the water over the bottom mud often approach zero, particularly in the more productive deep lakes such as Baptiste. After the ice melts, some oxygen is introduced from the atmosphere into the surface layer, but because the surface water usually warms up quickly, there is only limited oxygen transported by mixing into the deeper waters. During summer, oxygen depletion can be rapid in the hypolimnion or deeper water, and most of the deep lakes in regions covered by the Atlas, such as Narrow (Fig. 22), Amisk and Ethel, have little or no oxygen in the hypolimnion by late summer. Summer oxygen depletion rates are expressed as milligrams of oxygen per square metre of the area of the top of the hypolimnion per unit time (mg O₂/m² per day). For individual lakes, summer oxygen depletion rates are probably slightly higher than winter rates since higher algal production and water temperatures in summer promote increased oxygen consumption by bacteria. In fall, as the epilimnion deepens, the mixed layer increases and the oxygen content of the lake slowly increases until ice forms and the annual cycle repeats itself. The distribution of oxygen in lake water is thus a result of interactions of lake morphometry, wind, air temperatures and biological activities within the lake.

Nutrients

Most users of lakes in Alberta are concerned about water quality for recreation - is the water murky or clear? Is there green scum on the surface? Are there dense masses of plants in the water? These questions refer to the lake's fertility-the quantity of plant nutrients in the water. A nutrient is a chemical that plants need for growth. Phosphorus and nitrogen are familiar nutrients because they are applied to crops or vegetable gardens to help them grow. The same nutrients, plus carbon, are essential for the growth of algae that turn lakes green in summer and for the large water plants called aquatic macrophytes or "weeds".

Phosphorus

Concentrations of phosphorus often affect recreational water quality in Alberta lakes. Phosphorus is often present in the surface waters of freshwater lakes (<500 mg/L TDS) in smaller quantities than algae need for maximum growth, thus it is referred to as the limiting nutrient. Unlike nitrogen and carbon, phosphorus is not present as a gas in the atmosphere. Once phosphorus in the surface water of a lake is exhausted, algae stop growing and soon die. If more phosphorus is added to a lake where it is the limiting nutrient, larger algal populations will result until their growth is again limited by nutrients or light. Macrophytes, the large shoreline aquatic plants, may not respond as directly to phosphorus in the water as do algae. Many of these large plants take their required nutrients from the bottom sediments through roots, rather than from the open water.

In contrast to the freshwater lakes, algae in saline lakes (> 500 mg/L TDS) in Alberta are limited by chemicals other than phosphorus. In these saline lakes, algal populations (both numbers of algal cells and numbers of species) decline as salinity increases. Some scientists believe that high concentrations of one nutrient (sulphate) may interfere with incorporation by algae of another nutrient (molybdate), thus inhibiting cell growth, which may explain the clear water in phosphorus-rich, saline lakes such as Miquelon, Peninsula and Oliva.

Lake scientists, or limnologists, discuss phosphorus as four forms. Two forms (total dissolved phosphorus (TDP) and soluble reactive phosphorus (SRP)) are dissolved. Particulate phosphorus is incorporated into particles suspended in the water-for example, in soil or tiny plants and animals. Total phosphorus (TP) is the sum of particulate and dissolved phosphorus. A water sample is analyzed for phosphorus by treating it with specific chemicals. Water for the dissolved fractions is first poured through a fine filter and then treated. For both dissolved and total phosphorus, the treated water sample turns blue (Fig. 23), and the intensity of the blueness is directly proportional to the phosphorus concentration. Particulate phosphorus is estimated from the difference between TP and TDP. SRP is a portion of TDP. Only phosphorus data since 1980 are included in the Atlas because earlier data are not reliable.

Total phosphorus concentration has proved to be a powerful predictive tool for lake management, particularly recreational water quality. In the lakes presented in the Atlas, total phosphorus concentrations range from 5 to 13,000 µg/L in the euphotic zone during the open-water period. In freshwater lakes described in the Atlas, TP concentrations cover a smaller range (5 to 453 µg/L TP, Fig. 24) and are strongly linked to algal abundance or green scum in a lake. For example, total phosphorus concentration in the clear Kananaskis Lakes averages 5 µg/L, whereas in murky Nakamun Lake the average is 88 µg/L. In the freshwater lakes, approximately 60% of the total phosphorus is in the particulate fraction and 40% is in the dissolved fraction at any one time. Soluble reactive phosphorus concentration, which is generally present in very low concentrations (average 7 µg/L for the 27 freshwater lakes which have SRP data), approximates the main form of phosphorus which plants use to grow. In saline lakes, phosphorus concentrations in the euphotic zone, or upper layer, tend to be higher than in freshwater lakes and increase with increasing salinity, from 36 to 13,000 µg/L TP (Fig. 24). Total phosphorus concentration in the moderately saline Cooking Lake averages 251 µg/L, and in saline Oliva Lake 13,058 µg/L. In the saline lakes, total phosphorus is not related to algal growth because growth requirements are easily met by supply; total dissolved phosphorus is a higher proportion of total phosphorus than in freshwater lakes (TDP averages 62% of TP in the moderately saline lakes, 92% of TP in the saline lakes).

Phosphorus sources and cycling have been the focus of many water quality studies in Alberta in the 1980s. Natural sources of phosphorus include external inputs - runoff over land, and dust and precipitation directly onto the lake - and internal inputs - from sources within the bottom sediments of the lake (Fig. 25). The relative importance of various external sources of phosphorus, such as runoff and the atmosphere (dust and precipitation), is determined by the ratio of the drainage basin area to the lake area, and by the geology and land use in the drainage basin. As rain or snow-melt water runs over or just below the surface of the ground, it picks up dissolved and particulate substances, including phosphorus. In general, more phosphorus is lost per unit time from a square metre of land with soft rock and/or rich soil overlying it (as is common in Alberta) than from hard rock basins, and from cleared as compared to forested land. For example, differences in rocks, soils and vegetation in the drainage basin account for much of the disparity between lakes on the Canadian Shield where total phosphorus concentration in lake water is typically less than 15 µg/L, and freshwater lakes described in the Atlas where the amount of phosphorus can be as much as 30 times higher. Further, more phosphorus is lost from areas of intense human usage (cattle feedlots, intense cultivation and urban centres) than from areas with limited cultivation (pastureland or land with only an occasional house or cottage). Atmospheric loading consists of phosphorus which falls directly onto the lake surface in rain, snow or dust. For the 25 lakes described in the Atlas where external phosphorus loading has been calculated, the proportion of total phosphorus from the atmosphere ranges from one-twentieth to two-thirds of total external loading. Atmospheric loading is the largest portion of external phosphorus loading for lakes with a small drainage basin relative to the size of the lake basin, and where the natural vegetation is undisturbed.

Internal phosphorus inputs involve transfer from the bottom mud or sediments up into the open water. Bottom sediments for most of the 100 lakes in the Atlas are made up primarily of organic material produced in the lake, supplemented with material swept in from the drainage basin. Most phosphorus in the bottom sediments is associated with sediment particles; some of this phosphorus is loosely bound, or attached to sediment particles. Under certain conditions, this loosely bound phosphorus can move into the water surrounding the sediment particles, or porewater. Once phosphorus is in the porewater, it can be transferred to the water that overlies the sediment. Bottom sediments contain large amounts of phosphorus compared to the open water.

In shallow lakes, bottom sediments gradually warm as the summer progresses. Bacterial activity and chemical reactions consume dissolved oxygen. When this happens, some of the phosphorus stored in the bottom sediments is typically released to the overlying water. The process is illustrated with data from Figure Eight Lake (Fig. 26), where phosphorus accumulation over bottom sediments is evident much of the year. Recent evidence suggests that phosphorus is also transferred fairly rapidly in summer from the bottom sediments into the overlying water, even when dissolved oxygen concentrations are relatively high in the overlying water. This transfer involves chemical diffusion, groundwater flow through the bottom sediments and activity of small organisms such as bacteria and worms which live on the lake bottom. Once phosphorus has moved to the overlying water, wind action mixes this nutrient-rich water into the euphotic zone, and algae respond with a burst of growth. Recycling of phosphorus from the bottom sediments takes place continually during the warm summer months, and may result in the green scums known as algal blooms. This process is important in most lakes in the Atlas. Limnologists now believe that for many lakes in Alberta, the bottom sediments annually provide more phosphorus than the total of all the external sources such as runoff and precipitation. Transfer of phosphorus from the bottom sediments to the overlying water also takes place in the deep cool waters of thermally stratified lakes and under ice in winter, although the rate is slower than in shallow warmer water during summer. Coefficients used to estimate phosphorus loading for lakes described in the Atlas were developed from studies in central Alberta and are found in Section 3 of the Appendix.

One of the unresolved questions about Alberta lakes is: Why does phosphorus in the bottom sediment in Alberta lakes return so quickly to the water compared to lakes on the Canadian Shield, where relatively little phosphorus is transferred by this route? Two features of lakes described in the Atlas which may be related to this condition are the relatively low total iron and calcium concentrations. These two chemicals are thought to regulate phosphorus cycling in lakes. Detailed information on iron cycling is not available for most Alberta lakes. For many lakes, total iron concentrations in the water column are below the detection level of the method used. For those Atlas lakes with reliable iron data, total iron concentrations are often similar to or less than total phosphorus concentrations. In contrast, total iron concentrations are usually several times higher than total phosphorus concentrations in freshwater lakes in other parts of Canada. Total iron concentrations in Atlas lakes range from 7 to 285 µg/L in the freshwater lakes (average less than 67 µg/L), which is very similar to the values reported for the Canadian Shield. In contrast, for lakes on the Canadian Shield phosphorus concentrations are much lower than for lakes described in the Atlas. Total iron concentration for lakes described in the Atlas are only 10% of the world average for fresh water. In saline lakes, total iron concentrations tend to be higher, ranging up to 1,454 µg/L in Peninsula Lake. Many lakes in the Atlas have low calcium concentrations (average 28 mg/L Ca) compared to other hardwater lakes. In two lakes and two dozen ponds in Alberta where calcium concentrations have been experimentally increased, phosphorus appears to be more effectively sealed in the bottom mud.

Nitrogen and Carbon

Nitrogen and carbon are two essential nutrients for primary producers. Both nutrients are usually present in much higher concentrations than phosphorus in lake water, and in excess of the needs of aquatic plants. The ratio of inorganic carbon to total nitrogen to total phosphorus averages from 3,500 to 20 to 1 in the freshwater lakes described in the Atlas. In contrast, the ratios required for growth of freshwater plants average from 80 to 10 to 1. Nitrogen and carbon are present as gases in the atmosphere, and can dissolve in water. Although about half of the total phosphorus in lake water described in the Atlas is tied up in living plants and animals, most of the nitrogen is associated with dissolved organic matter in the water and most of the carbon is dissolved inorganic carbon such as bicarbonate.

Some species of blue-green algae can use nitrogen gas directly and incorporate it into organic compounds through a process called nitrogen fixation. Other algae require inorganic forms of nitrogen that are dissolved in the water: nitrite and nitrate (NO₂ + NO₃ -nitrogen) and ammonium (NH₄ -nitrogen). Ammonium, nitrogen in dissolved organic molecules, and nitrogen contained in the cellular structure of organisms are analyzed together as total Kjeldahl nitrogen (TKN). Total nitrogen (TN) is the sum of NO₂ + NO₃ and TKN.

In summer, amounts of inorganic nitrogen tend to be very low in the euphotic zone of Alberta lakes compared to that in the euphotic zone of lakes throughout much of the rest of the world. The average total inorganic nitrogen concentration for lake water described in the Atlas is less than 50 µg/L during the ice-free period, or less than one-twentieth of the world average for fresh water. In the saline lakes described in the Atlas, the average was slightly higher, 136 µg/L inorganic nitrogen. Ammonium averages more than 75% of inorganic nitrogen in the euphotic zone of lakes described in the Atlas. The low NO₂ + NO₃ -nitrogen concentrations given in the Atlas reflect low inputs with precipitation and runoff and possibly low rates of nitrogen recycling from the bottom sediments compared to rates of phosphorus recycling. The relative importance of ammonium increases in the more productive lakes and in the saline lakes (Table 5). Because concentrations of nitrogen in samples may change in the transport time from the lake to the laboratory, values for nitrogen presented in the Atlas may overestimate the amount of inorganic nitrogen in the lake water.

In contrast to inorganic nitrogen, total nitrogen concentrations for lakes in the Atlas, particularly the eutrophic and saline lakes, are relatively high compared to other lakes around the world. The average total nitrogen concentrations in the euphotic zone of freshwater lakes during summer range from 200 to over 10,000 µg/L TN (Fig. 27); the average for freshwater lakes is one-third (1,081 µg/L TN) that of saline lakes (3,336 µg/L TN). The lowest amounts of total nitrogen are recorded in the less productive freshwater lakes (Table 5). Most of the total nitrogen in the water is dissolved organic nitrogen. In the euphotic zone of lakes described in the Atlas, organic nitrogen averages more than 95% of the total nitrogen. For example, in the euphotic zone of the north basin of Amisk Lake, on average 82% of organic nitrogen is dissolved. Limnologists know very little about how dissolved organic nitrogen influences and interacts with algal production in Alberta. However, it is known that the amount of nitrogen which can be used directly by algae (inorganic nitrogen and possibly some organic nitrogen) can influence the composition of the algal community. Generally, low concentrations of available nitrogen favour the development of blue-green algae species such as Anabaena spp. and Aphanizomenon sp., which can fix atmospheric nitrogen.

The rate of carbon fixation is often the unit used to describe production in ecosystems. Carbon is measured in three forms: dissolved inorganic carbon (DIC or HCO₃ Plus CO₃) (see Major Ions section), dissolved organic carbon (DOC) and total particulate carbon (TPC). In lakes described in the Atlas, DIC is the overwhelming portion of total carbon, followed by DOC and TPC. For the north basin of Baptiste Lake, for example, DIC is 91%, DOC 8% and TPC 1 % of total carbon. Although aquatic studies in many regions have focused on carbon, limnologists in Alberta have yet to do any detailed studies on carbon.

Transparency

Transparency, or water clarity, in most lakes is affected mainly by the amount of algae in the water. The clarity of water is measured throughout the world by estimating the depth that a black and white plate, called a Secchi disk, can be seen. This depth is called the Secchi depth. Average Secchi depths for the lakes and reservoirs in the Atlas range from over 6 m in Ghost Reservoir (which is very clear), to 0.4 m in some of the most productive lakes such as Little Fish Lake. Secchi depth provides a simple and quick estimate of a lake's fertility. Transparency of water is also measured with a light sensor that is lowered into the water, so that light intensity can be recorded at various chosen depths. Generally the euphotic zone, or zone with sufficient light for photosynthesis, is defined as extending from the lake surface to the depth which receives 1% of light recorded just below the surface. If no data were collected with a light meter, the depth of the euphotic zone may be approximated as twice the Secchi disk depth. The extent of light penetration delineates the depth of rooted aquatic plants in lakes and the depth of most algal growth.

Turbidity and colour also affect water transparency. In some reservoirs and shallow lakes, the water may contain suspended silt as well as algae. Turbidity is a measure of particle scattering or the amount of suspended material such as mud, silt and algae and is presented as NTU, the standard international unit. Turbidity ranges from less than 1 to 33 NTU in the euphotic zone of the 41 lakes for which turbidity was measured. All these lakes are considered not very turbid. Turbidity for the 32 freshwater lakes averages 3 NTU, and for the nine slightly saline to saline lakes, it averages 12 NTU. Some lake water is highly stained or coloured. Colour is a measure of the amount of humic material in the water. It is measured by comparing filtered lake water to a mixture of platinum (Pt)-cobalt compounds, and is presented as units of Pt. Colour is often high in water that flows through muskeg and bogs and picks up humic matter. The scale in the Atlas is: very clear (colour less than 4 mg/L Pt), not highly coloured (from 4 to 55 mg/L Pt), and highly coloured (more than 55 mg/L Pt). Colour in the euphotic zone of the 26 lakes in the Atlas which have this information, ranges from 2 to 62 mg/L Pt. The 19 freshwater lakes are less coloured (an average of 13 mg/L Pt) than the 7 saline lakes (average colour 35 mg/L Pt). All but two of the lakes, Lessard with 2 mg/L Pt and Little Fish with 62 mg/L Pt, fall in the not highly coloured range. The relatively low colour values for lakes in the Atlas reflect a combination of little humic matter in many of the drainage basins and long water residence times. More coloured water is typical of lakes with large bogs or muskeg in their drainage basins; lakes on the Canadian Shield have on average more than twice the colour of the lakes described in the Atlas. Similarly, brown water lakes in northern Alberta have more coloured water.

Trophic Status

The information provided in the water quality section in each lake description in the Atlas includes an assessment of the lake's level of fertility. Lake scientists call this assessment the trophic status of the lake. Trophic is a Greek word meaning nourishment. Eutrophic, or well-nourished, lakes are very rich in nutrients, so that the water is green with algae during most of the summer. Almost thirty percent of Atlas lakes are eutrophic (Table 6). Oligotrophic, or poorly nourished, lakes have very low concentrations of nutrients and low algal abundance and hence the water is clear. Ten percent of lakes reported in the Atlas are oligotrophic. They include lakes that are fed by nutrient-poor water from the Rocky Mountains. Moderately productive lakes are called mesotrophic. Thirty-two percent of lakes described in the Atlas are mesotrophic. Five percent of lakes described in the Atlas fall between oligotrophic and mesotrophic and are classified as oligo-mesotrophic. Twenty-four percent of the lakes reported in the Atlas have such large quantities of nutrients that the growth of algae is enormous, and the water resembles pea soup during part of the summer. This condition is termed hyper-eutrophic. Because the prairie and parkland soils of Alberta are naturally fertile and phosphorus is poorly bound in bottom sediments, many of the lakes outside of the mountains are eutrophic or hyper-eutrophic. They have likely been this way since the last glaciation ended 12,000 years ago. Some lakes may have become more eutrophic over the past century, largely as a result of land clearing, but very few in Alberta have been studied long enough to confirm this.

Limnologists assess trophic status directly by measuring the concentrations of nutrients in the water of freshwater lakes, or indirectly in all lakes by measuring water transparency or the amount of algae present. Scientists around the world have developed several classification schemes for trophic status. The one used throughout this book was developed during a worldwide study of lake fertility by countries of the Organisation for Economic Co-operation and Development (OECD). It is based on a measurement of chlorophyll a. Chlorophyll a is one of the photosynthetic pigments that, under appropriate conditions, converts sunlight to new growth in green plants. To measure chlorophyll, algae from a water sample are collected onto a filter and then the chlorophyll is extracted from the algal cells with a solvent. The colour density of the extract is analyzed and the amount of chlorophyll is calculated. The main type of chlorophyll found in all algal cells is designated with an "a", and the term chlorophyll a is used or implied throughout the Atlas. The OECD trophic category is based on the maximum chlorophyll a concentration measured for a lake (Table 6). Overall average chlorophyll a concentration is 20 µg/L for all Atlas lakes (Fig. 28); 19 µg/L in the freshwater lakes; 34 µg/L in the slightly and moderately saline lakes, and only 6 µg/L in the saline lakes, despite the excessive nutrient concentrations recorded there. In the freshwater lakes, seasonal patterns of chlorophyll a and total phosphorus concentrations are closely related over time (Fig. 29).

The average concentrations of chlorophyll a, phosphorus and other constituents reported in the Atlas are based on samples collected for one or two years during the period that the lake is free of ice-usually May through October. Typically this is the period that water quality is important to lake users and also when limnologists can best assess some aspects of it. For six Alberta lakes, information has been collected on phosphorus and chlorophyll a concentrations almost continuously since 1980. One of these lakes (Narrow Lake), is classified as oligo-mesotrophic, another (Ethel Lake) is mesotrophic, two (Amisk and Wabamun lakes) are eutrophic and two (Baptiste and Nakamun lakes) are hyper-eutrophic. The data collected on these lakes will permit scientists to determine to what extent these important water quality indicators vary naturally from year to year, and what factors are responsible for yearly variation. Limnologists currently believe that year-to-year variation in these trophic indicators is related to variability in nutrient inputs as well as climatic variables such as air temperature. The variation recorded for total phosphorus and chlorophyll a concentrations in Ethel Lake over this period is illustrated in Figure 29; chlorophyll a was generally lower during years with cool April air temperatures (such as 1982) than for years with warm April air temperatures (such as 1980).

Many users of Alberta lakes are concerned about how to protect or enhance water quality. Once the factors determining a lake's water quality are established, a concerted plan for water quality management can be developed by lake users and agencies responsible for this resource.

E.E. Prepas