Trophic Status of Lakes Relating to Water Quality
Water Quality
The water quality of a lake is often the focus of concerns because it is directly related to recreation, fishing, aquatic vegetation and surface water uses. It is often a good place to begin when setting lake management goals and objectives.
Lake Water Quality Monitoring and Assessment
Measuring the lake's chemical, biological and physical composition is essential to understanding how the lake works and identifying appropriate lake management options. Initial measurements will establish parameters that can characterize the trophic status and overall ecology of the lake.
Common Lake Sampling Procedures
A good way to gather lake water quality data is to sample surface water parameters on 5 to 10 occasions from May to September. Samples should be collected at one or more pre-selected mid-lake locations. Lakes with distinct bays need more sampling sites than round ones. Given the considerable differences in summer weather (e.g., variation in rainfall and temperature), it will take a minimum of three to five years of data collection to be able to statistically describe "average" conditions.
The parameters most often used to describe the trophic status of a lake are total phosphorus, Secchi transparency and chlorophyll-a. The amount of phosphorus limits the growth of chlorophyll-a. More generally, phosphorus is the limiting nutrient in lake for plant growth. Generally all lakes in the District of Muskoka have a recorded trophic status that is interpreted as nutritional and the processes associated with it.
Those lakes, which have low levels of phosphorus, algae and nutrients, are generally considered to be the most desirable for cottage development.
The following are the main trophic status categories for cold-water lakes:
a. Oligotrpohic - Total phosphorus content is less than 10 micrograms per litre (10 ug/l) with sufficient oxygen to support a lake trout habitat; there are also low nutrients and low plant growth
b. Mesotrophic - Total phosphorus content is between 10 and 20 micrograms per litre (10 - 20 ug/l). It is borderline for cold-water fish but supports warm water species such as pickerel and bass
c. Eutrophic - Greater than 20 micrograms per litre (>20 ug/l) and contains high nutrients and high plant growth, and the existence of phosphorus. This combination consumes oxygen (in part from increased algae growth) and can lead to the death of certain species of fish such as lake trout which have trouble existing in lakes with a high phosphorus content.
A typical lake is said to age from a young, oligotrophic lake to an older eutrophic lake.
The fish community can also be a useful indicator of water quality. Trout have the most critical requirements for good water quality. They need well-oxygenated water and prefer temperature of 50 to 65 degrees Fahrenheit. Oxygen must be present below the thermocline in midsummer - a condition usually found only in oligotrophic lakes and occasionally in some mesotrophic lakes. Dr. Schiefer's 2005 assessment confirms that the deep-water dissolved oxygen levels in Lake Waseosa are very low.
District of Muskoka Lake System Health Monitoring Program[1]
The 2006 Lake Data Sheets were provided by the Muskoka Heritage Foundation, and were prepared for Waseosa, and Jessop (Jingo). These Lake Data Sheets form part of this section. No data was prepared or available for Ripple and Palette Lakes and it appears that the District of Muskoka never undertook Heritage Foundation studies of these lakes. This data deals with lake sensitivity, long term Secchi disk monitoring, phosphorus average and ability to sustain cold-water fish, such as lake trout. The following information has been extracted from the above data sheets which appear as appendices to this Lake Plan and also contain long term monitoring data.
|
Lake |
Flushing Rate Sensitivity |
Long Term Secchi disk |
Phosphorus Average |
Cold Water Fishery |
|
Waseosa |
Moderate |
3.6m |
12.52 ug/L |
No |
|
Ripple |
|
No Data Provided |
No Testing |
|
|
Palette |
|
No Data Provided |
No Testing |
|
|
Jessop |
|
~2m |
15.00 ug/L |
No |
In analyzing the above data from the Muskoka Heritage Foundation, Lake Waseosa is reported as having a long-term average of phosphorus of 12.52 ug/L and does not contain cold-water fish. It would therefore fall into the mesotrophic category but has remnants of an oligotrophic status. The trend line over 20 years shows an increase in phosphorus content. The dissolved oxygen levels are very low and, therefore, the lake is unable to support lake trout but can support herring, which is the last type of cold-water fish to be present. Low oxygen content can result in phosphorus cycling from deep lake sediment. This increases the risk of major algae blooms (including blue/green algae) such as occurred in 2005 in Three Mile Lake and a few years earlier in Sturgeon Bay.
Unfortunately, these studies by the Muskoka Heritage Foundation are not complete. In addition, the information obtained under the Ministry of Environment Lake Partner Program is also incomplete and, in a number of instances, are not up to date.
From the incomplete data from the Lake Partner program it would appear that:
1. The water clarity ratings of the lakes would be in the following order from the lowest to the highest:
- Jessop - 2 metres from the surface
- Waseosa - 2.9 metres from the surface
- Palette - 3.4 metres from the surface
- Ripple - 4.7 metres from the surface
2. Jessop Lake has a high phosphorus content of 13.9 micrograms per litre.
3. Jessop Lake has a high spring phosphorus content of above 15, which places it in the mesotrophic or lower category.
4. Ripple Lake has a high phosphorus reading of 13 micrograms per litre.
5. Palette Lake has a phosphorus reading of 8.6 micrograms per litre.
Concerns About the Future
The number of people living on a lake and using the lakes for recreational purposes such as swimming and boating will have a direct effect on water quality, which, in turn, will affect the natural qualities of the environment of the surrounding areas.
As new developments occur and seasonal dwellings are used more frequently and/or converted to full-time use, the increase in occupancy is likely to increase the amount of phosphorus finding its way into the lake water. This will increase the impact and stress on water quality. In addition to lots that can presently be legally developed, the creation of any new undeveloped lots would have an additional negative impact on the water quality and could severely limit their future use and enjoyment.
The Lake Waseosa Ratepayers' Association is continuing to participate in the Lake Partner program in order to help collect and compile accurate and complete data for the lakes covered by this Lake Plan.
[1] Provided by the Muskoka Heritage Foundation