Based on total phosphorus (TP) and chlorophyll-a (chl-a), over half (54% and 57%, respectively) of the sampled lakes and reservoirs in Alberta are productive and classified as eutrophic or hypereutrophic. Based on Secchi depth, the percentage of lakes and reservoirs classified as eutrophic or hypereutrophic increases to 78%.
- Median TP concentrations ranged from 2.25 μg/L at Spray Lake Reservoir (last sampled 2014), to 2,350 μg/L (4.14 mg/L) at Gooseberry Lake (East basin; sampled in 1985). 34 of 288 (12%) lakes with TP measurements were classified as oligotrophic, 97 (34%) were classified as mesotrophic, 85 (29%) were classified as eutrophic and 72 (25%) were classified as hypereutrophic (Figure 2).
- Alberta’s current surface water quality guideline for TP is narrative, not numeric. For lakes, the guideline calls for “no increase in…phosphorus over existing conditions”, and “where…phosphorus have increased due to human activity, develop lake-specific nutrient objectives and management plans where warranted”. Assessing trends requires sufficient data collection frequency. Trends in trophic status for lakes across the province will be provided in future years as data become available through repeated sampling over time.
- Median chl-a concentrations ranged from 0.68 mg/m3 at Elbow Lake (last sampled 2008) to 275 mg/m3 at Antler Lake (last sampled 2019). Of the 284 lakes with chl-a data, 36 (13%) were classified as oligotrophic, 86 (30%) were classified as mesotrophic, 68 (24%) were classified as eutrophic and 94 (33%) were classified as hypereutrophic (Figure 3).
- There are no provincial or federal water quality guidelines for chl-a.
- Median Secchi depth ranged from 7.6 m at Jarvis Lake (last sampled 2016) to 0.1 m at Pakowki Lake (last sampled 1998). 7 (3%) of the 273 lakes with Secchi depth measurements were classified as oligotrophic, 53 (19%) were classified as mesotrophic, 106 (39%) were classified as eutrophic and 107 (39%) were classified as hypereutrophic (Figure 4).
- There are no provincial or federal water quality guidelines for Secchi depth.
Variation across Alberta
- Figures 2, 3 and 4 show that lakes in the foothills and montane regions of Alberta differ compared to the rest of the province. These lakes show lower productivity, lower algal growth, and better water clarity.
- Considering the province broadly, productive lakes (mesotrophic, eutrophic and hypereutrophic) exist across most of Alberta, while low-productivity lakes (oligotrophic) are mostly located in the foothills and montane regions.
- Alberta’s nutrient-rich geology and numerous environmental factors result in water quality conditions conducive to (excessive) algae growth across much of the province.
- Constructed reservoirs in the southern portions of the province receive surface water diversions from nutrient-poor rivers and thus have trophic classifications influenced by the source river waters instead of natural geology or agricultural land-use in their watersheds.
Figure 1. Scatterplot of average chlorophyll-a (chl-a) concentration (y-axis) vs. average total phosphorus (TP) concentration (a-axis) from Alberta Lakes surveyed from 1980 to 2019. Axes are log-scaled to linearize the relationship.
View full-size Figure 1 (PNG, 172 KB)
Figure 2. Lake trophic status based on median total phosphorus concentration across Alberta lakes between 1980 and 2019.
View full-size Figure 2 (JPEG, 778 KB)
Figure 3. Lake trophic status based on median chlorophyll-a concentration across Alberta lakes between 1980 and 2019.
View full-size Figure 3 (JPEG, 765 KB)
Figure 4. Lake trophic status based on median Secchi depth across Alberta lakes between 1980 and 2019
View full-size Figure 4 (JPEG, 760 KB)
Figure 5. Importance of local ‘in-lake’ (in blue) and regional (in pink) environmental factors (vertical axis) explaining variation (horizontal axis) in monthly and seasonally aggregated phytoplankton and cyanobacteria community composition in 75 lakes and reservoirs across Alberta. Total explained variation is divided into spatially dependent (lighter bars) and spatially independent (darker bars) components for July and August (July only for cyanobacteria).
View full-size Figure 5 (JPG, 184 KB)
Scientists, water managers and lake watershed stewardship groups have long-questioned if regional (for example, climate and land-use factors) and local environmental conditions (for example, lake basin depth, TP, water temperature) differ spatially in lakes across Alberta. They also question whether those differences can be used to classify lake water quality. In other words, can factors related to a lake’s location be used to predict water quality and specifically algal productivity (or trophic status)?
A recent study by AEP (Loewen et al. 2020) investigated the relative importance of co-occurring local (in blue) and regional (in pink) environmental factors (including TP and Secchi) explaining variation in planktonic algae and cyanobacteria communities in 75 lakes and reservoirs across Alberta (Figure 5 (JPG, 184 KB)). The study results showed that planktonic algae communities have relatively little variation across the province and that associations with environmental factors were largely independent of location. Lake basin elevation and nutrients (including phosphorus and nitrogen) were the few factors displaying spatial dependence and, even then, it was evident only in July and August data. This finding speaks to: (1) the primary importance of phosphorus (for planktonic algae and cyanobacteria) and nitrogen (for planktonic algae only) nutrients and (2) the fact that lakes in the foothills and montane regions of Alberta differ compared to the rest of the province.
Data collection and analysis
Water quality data was collected through AEP’s Provincial Lentic (lake) Monitoring Program and the Alberta Lake Management Society’s LakeWatch Program.
Of the 291 lakes and reservoirs, 288 had TP data, 284 lakes had chl-a data and 273 lakes had Secchi depth measurements. Values below method detection limits (MDL) were replaced with a value of ½ MDL for calculation purposes. To provide as current of a snapshot of lake trophic status as possible based on available datasets, only the three most recent years of data prior to and including the last sampled year for each lake were included in the calculation of median TP, chl-a or Secchi depth values. Trophic status was assigned for each parameter based on the Organisation for Economic Co-Operation and Development’s trophic classification system (OECD 1982). All analyses and generation of supporting figures were performed in R 4.0.0 (R Core Team 2020). Maps (Figs. 2-4) were produced in ArcGIS Desktop 10.7.1.
Note that while the 3 trophic indicators are often closely related, they do not always show a relationship. As Secchi depths are determined from light penetration and water turbidity, the measured depths are not only affected by algal growth but also other factors including silt and fine particulates from erosion (e.g., glacial flour) or dissolved organic matter. Thus, shallow Secchi depth measurements can occur in low productivity lakes when turbidity is influenced strongly by these other factors.
Access data and learn about how Alberta’s Environmental Science Program monitors Alberta’s water quality and quantity: Environmental monitoring.
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