The phosphorus loads we report for Lake Simcoe are a measurement of the amount of phosphorus entering the lake from all sources on an annual basis.​

Since 2000, the average phosphorus load has been about 85 tonnes per year. Although this is above the Lake Simcoe Protection Plan (LSPP)​ target of 44 tonnes, it has declined since the 1980-90s when the average was well over 100 tonnes per year. ​​

 

​As you can see on the graph, there are years of higher phosphorus loads and years of lower phosphorus loads. This variation is being driven mostly by changes in tributary (or river) flow rate (or how much water is entering Lake Simcoe) which, in turn, is driven by yearly differences in precipitation. 

The year with highest phosphorus loading on the graph (2008) also had the highest tributary flow. 2008 was a very wet year with higher than average precipitation, a mild winter with several snow melt events, and rain during the winter months that fell on frozen ground and ran directly into rivers. All of these factors create perfect conditions for high runoff, high tributary flow, and high phosphorus loading. 

One of the major threats to the LSPP, and our efforts to reduce phosphorus loading in Lake Simcoe, is climate change​. With warmer winters, we are receiving more rain. So even though we have reduced the phosphorus concentration in the water, more tributary flow means less change in the phosphorus loading. 

To circle back to our cups of tea example, even though we are drinking weaker tea, we are drinking more cups and getting the same amount of caffeine!

Phosphorus in the Sediment

​Phosphorus is also found in the sediments in the lake. Although plants predominately get their phosphorus from the sediment, not all sediment phosphorus is accessible to plants. As a result of decreasing light penetration, plants are generally not found in water any deeper than 10 metres in Lake Simcoe and therefore sediment at depths greater than 10 metres is considered a phosphorus “sink".

Phosphorus deposits in the sediment are not evenly distributed throughout the lake. In a lake-wide survey, our researchers recorded the locations of high and low concentrations of sediment. In Cook's Bay, for instance, there is a very low concentration of sediment phosphorus because it is consumed by the large amounts of aquatic plants. In Kempenfelt Bay and near Beaverton, sediment phosphorus is much higher because there are fewer plants to consume the phosphorus.

Phosphorus in the Plants

Two of the main users of phosphorus are plants and algae. In Lake Simcoe, zebra mussels have filtered out most of the algae which has resulted in higher water clarity, which allows the sunlight to penetrate deeper into the water, encouraging abundant plant growth.

Aquatic plants get up to 97% of their phosphorus from lake sediments. When they die, some of the phosphorus in their tissues is released back into the water, while some remains bound in the plant tissue that will join the sediment. Where these sediments are at a water depth of less than 10 metres deep, the plant tissue phosphorus may be used to fuel plant growth in subsequent years. If the plant material is transported to waters deeper than 10 metres, the phosphorus will become essentially locked away in the sediments.​

Positive Changes are Happening

The cycle of phosphorus tells us that there are significant reservoirs of phosphorus in Lake Simcoe and that these reservoirs have been caused by many years of excessive loads. While the lake has many natural processes for absorbing excess phosphorus, when these processes get overwhelmed, the result can be excessive plant growth or algal blooms; indicating a system out of balance. 

It has taken many decades for Lake Simcoe to accumulate this much phosphorus and it will take many more to return it to an ecologically sustainable state.

This means that the efforts we are making today may not show immediate results, but positive change is happening. We are now seeing improvements in dissolved oxygen, decreasing phosphorus concentrations and the return of some environmentally sensitive species in the watershed.​

What We're Doing

Continued monitoring - We continue to monitor the phosphorus sources throughout our watershed. Monitoring helps better understand how wet and dry years impact our management plans and how we can adapt to new challenges.

Phosphorus offsetting policy – This is a first-of-its-kind policy​ in Canada and was developed specifically to control phosphorus from new development. As of January 1, 2018, any new development in the watershed is required to control 100% of the phosphorus leaving the property.

If 100% of the phosphorus can't be managed on the site, then developers must pay a fee so that projects to “offset" the phosphorus can be completed elsewhere in the subwatershed. Fees collected for offsets are at a 2.5:1 ration, meaning, for every 1 kg. of phosphorus that can't be controlled, the property developer must pay for 2.5 kgs. to be controlled elsewhere. Over time, the restoration projects that are implemented with offset fees, will allow a greater reduction of phosphorus overall.

Some of the types of restoration projects to reduce phosphorus can include engineered wetlands and stormwater pond retrofits. ​

Retrofitting stormwater management - We encourage retrofitting stormwater ponds because we now know how to incorporate retrofits that lessen their phosphorus contributions to the lake. ​Older stormwater management ponds were designed to address stormwater quantity, not quality. Retrofitting a pond like this would incorporate both water quantity and quality into the design.

Low Impact Development - We promote better stormwater management through the use of sustainable low impact development (LID) practices which can be applied to new undeveloped lands as part of the subdivision process, and to existing developed lands through retrofitting. Low impact development techniques such as raingardens, bioswales, green roofs, permeable pavement and dry ponds can be used to manage a significant amount of phosphorus in new developments. 

Plantings - We plant trees along streambanks to prevent erosion. This keeps the soil intact, slows water velocity which reduces erosion and allows a portion of the water to infiltrate into the ground rather than run-off directly in the stream.

What You Can Do

You can help reduce phosphorus in stormwater run-off by:

1. Purchasing phosphate free soaps and detergents.
2. When using water outside, direct the excess to the lawn or garden and not through the stormwater system.
3. Wash your car at the car wash, where the water will be properly treated. If you must do it yourself, wash your car on the lawn, so that the water soaks into the ground.
4. Use native plants in your lawn and garden. They've adapted to survive in our climate and therefore don't have the same need for watering or fertilizer. If you fertilize, look for phosphate free fertilizer.
5. All fertilizers have 3 numbers on them. The middle number represents phosphorus, so look for a fertilizer where the middle number is "0".
6. Make a donation to the Lake Simcoe Conservation Foundation​. Their work supports many LSRCA projects for a cleaner and healthier Lake Simcoe watershed.