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:
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
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
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 low.
District of Muskoka Lake System Health Program[1]
In adopting the Lake System Health Program, the District of Muskoka Official Plan provides that:
"F.16 Recreational water quality monitoring and modeling is an important component of Lake System Health. Recreational water quality will continue to be monitored and modeled by The District of Muskoka as one measure of a waterbody's capacity to sustain development.
F.17 The District of Muskoka will continue, through its development review and approvals function, to ensure that water quality is protected and will require Municipalities to adopt provisions in Area Municipal official plans and zoning by-laws in order to achieve this objective."
The 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. Unfortunately, no data has ever been prepared 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. Also, the District only tests Jessop and Waseosa for phosphorous once every two years, rather than the 5-10 times per year which is deemed to be ideal.
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 |
3.4m |
9.9 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 was reported as having a long-term average of phosphorus of 9.9 ug/L but is incorrect in reporting that it does not contain cold-water fish. The dissolved oxygen levels are near the minimum required to support lake trout but it has been confirmed there is a small and fragile naturally reproducing population. There is also a naturally reproducing population of cisco (lake herring) - a potential prey for lake trout. 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. Benthic testing conducted in association with the District of Muskoka suggests the lake is still reasonably healthy, but the low "EOT" count shows the lake is under stress from human activities.
As mentioned, these studies by the Muskoka Heritage Foundation are not complete. In particular, the District has not been monitoring Palette, Jessop and Ripple lakes. Information obtained through testing with the Ministry of Environment Lake Partner Program is also incomplete and, in a number of instances, are not up to date, but the available data can be used to fill some of the gaps in the Lake System Health Program.
From the incomplete data from the Lake Partner program it would appear that:
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
Jessop Lake has a high phosphorus content, which with the exception of anomalous low readings in 1997 and 2010, hovers at or above the threshold of 14.4 micrograms per litre despite the very low concentration of development. Given the high percentage of vacant lots, this lake could easily be pushed over the edge.
Palette Lake is Over Threshold. The threshold for Palette was determined to be 5.22 µg/L by the District of Muskoka's Lake System Health Program. The practice established by the District to quantify the phosphorous level of the lake is to discard the higher of the two samples taken in any given year, and to average the lower of 5 bi-annual samples.
Ontario Ministry of the Environment Lake Partner program testing over the last eight years reveals an alarming trend:
|
2003 |
8.5 |
8.7 |
|
2004 |
7.8 |
8.8 |
|
2005 |
8.3 |
9.7 |
|
2006 |
10.0 |
11.1 |
|
2007 |
7.2 |
9.5 |
|
2008 |
14.4 |
14.8 |
|
2009 |
19.7 |
20.1 |
|
2010 |
9.8 |
13.8 |
Discarding the highest reading each year and considering only the lower of the two readings, we can see the average phosphorous reading is 10.7 µg/L - more than twice the threshold and the readings are well above the threshold in each and every single sample. And while there is some fluctuation, the general trend is an ever increasing concentration of phosphorous.
Ripple Lake test results vary wildly from year to year, suggesting it is highly susceptible to outside influences such as run-off. The minimum annual readings range from 5.8 to 12.7µg/L of phosphorus during the period from 2003 to 2009. The high years approach the threshold value of 13.12 µg/L Ripple is fed in part from Palette Lake to the east, separated only by a narrow strip of land. As Palette is well above its threshold of phosphorus concentration, it may be a major contributor of phosphorous in years of high water flow. It is unknown how the inflow from Waseosa affects the situation, but it may serve to dilute the phosphorous concentrations in Ripple, at least at the surface.
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