Phosphorus is the nutrient that controls the growth of algae in most Ontario lakes. For this reason any increase in phosphorus in the lake will increase the quantity of algae that can grow. High levels of phosphorus can lead to algal blooms and in some cases affect the habitat of cold water fish such as lake trout.
The Provincial Water Quality Objective for Total Phosphorous (TP) in inland lakes in Ontario is < 20 μg/L (micrograms per litre) While some degree of TP is important for lake health to ensure productivity of aquatic life, readings consistently above 20 μg/L are often associated with nuisance, and potentially harmful, algae. In Palmerston Lake, septic systems and naturally occurring organic material on the forest floor are the main sources of TP, especially during and after a rain event.
In Palmerston Lake, TP readings in recent years have been predominantly in the healthy oligotrophic range – below 10 μg/L – although a couple of exceptions have occurred. According to the Mississippi Valley Conservation Authority, these exceptions most likely were caused by increased runoff following a rain storm event. As rain water flows over the soil toward the lake, it collects phosphorus from all the organic matter present on the ground. When this water, high in phosphorus, filters into the lake it briefly increases the total phosphorus levels of the lake. Levels return to normal once the TP has been used up by aquatic organisms or flushed downstream.
Phosphorous concentrations are also one of the main factors determining whether or not a lake will be deemed by the Province to have the capacity to tolerate further lakeside development. Read about the Lake Shore Capacity Assessment planning tool the Province uses to assist in this determination.
Other useful sources:
- Mississippi Valley Conservation Authority State of the Environment Report 2010: Palmerston Lake
- “Long-term Trends in Water Quality from the Lake Partner Program” by Anna DeSellas and Andrew Paterson, Ontario Ministry of Environment and Climate Change, Nov. 22, 2017. View the full report here.
- Ontario Ministry of Environment and Climate Change, “Water Quality in local lakes”
- Integrated Monitoring Report 2016 Report, March 2017, Mississippi Valley Conservation Authority
Further information can be found at the Ontario Ministry of Environment and Climate Change web site for water quality. An interactive map can be found here and complete data files can be found here. See also the Palmerston Lake Stewardship Report presented at the 2019 AGM
Water clarity is measured using a Secchi Disk, a round plate that’s painted black and white. The disk is attached to a rope and is lowered into the lake until it’s at a depth where it can no longer be seen. This is called the ‘Secchi depth’. The higher the Sechi depth reading, the clearer is the water. In Ontario’s inland lakes, 55% register a Secchi depth greater than 4 metres; 39% register a Secchi depth of between 2 and 4 metres; and 6% measure less than 2 metres. In Palmerston Lake, Secchi depths are usually above 5 metres according to MCVA reports.