Points of Interest

What have we learned about water quality around points of interest in the Western Durham nearshore?

If we look at the water quality along Lake Ontario from the Pickering Nuclear Generating Station to Carruthers Creek, the majority of the area falls below the open water objective set by the International Joint Commission and the Ontario Ministry of the Environment, Conservation and Parks.

Near the shoreline, concentrations are elevated. What happens if we zoom into an area with something that is considered a point of interest such as a creek mouth, storm drains, the Pickering Nuclear Generating Station, the municipal drinking water intake, or the diffuser for the Duffins Creek Water Pollution Control Plant?

To look at the changes around these points of interest, we took the average of all the data from rings (with a 250 m radius) around the point of interest.

Looking at the data in this manner is slighted skewed as it does not integrate the entire area surrounding the point of interest, but the results are based on only a couple of points of data. Nonetheless, it provides some information about the water quality within 1 km of the point of interest, as well as what background conditions might be.

It is important to recognize that our sampling locations have changed over time. No shoreside samples were collected between 2011 and 2013. In addition, only early spring samples were collected in 2010.

This means that when we look at the data, we should look at changes within a year (i.e., the different results from one year) and not between the different years (i.e., do not compare 2008 to 2011 to 2018).

Before examining the data, we must understand the format that the data are in:

Lake Ontario Waterfront nearshore monitoring points of interest — Figure 1: An illustration describing the bar graphs used to summarize the concentrations around the points of interest.

Creeks

The image below shows Rouge River, Duffins Creek and Carruthers Creek. These streams all deliver nutrients from the land to the lake. Buffer rings are drawn around the mouth of each creek, and these rings increase incrementally by 250 m from the point of interest.

This means that the rings are 250 m, 500 m, 750 m, and 1000 m from the point of interest. The sampling locations from 2007 to 2009 are shown in red on the image (Figure 2).

However, the number of and the locations of sites sampled change depending on the year (see Sampling Design).

Carruthers Creek

The following plots show the average concentration of all data within each of the buffer rings.

It is important to recognize that the average concentration, and concentration ranges are greatest at the creek mouth (i.e., 0 m), and generally decrease as you move away from the creek mouth towards the open lake.

The difference between years is not as important because the sampling locations changed after 2010, and in 2010 there was only data for April as the program was under review.

After 2010 there were some years with not as many samples close to shore, and with no samples right at the creek mouth — therefore no red bars on the graph.

In 2019, we began our maintenance sampling design and only one site at 400 m is monitored within the first kilometer of the shoreline.

Despite the changing sample locations, what is obvious is that concentrations by the creek mouth are higher and they decrease moving towards open waters.

In addition, although average nitrate + nitrite concentrations are similar in most years, the ranges often show a decreasing trend as you move away from the river mouth. The decline in total phosphorus concentrations suggests that Carruthers Creek is the main phosphorus source along the path of the transect.

In 2018, water levels in the lake were very high and shorelines experienced flooding. Nutrient concentrations in the buffer rings show higher total phosphorus in the lake background at this time.

Figure 3: Average total phosphorus and soluble reactive phosphorus concentrations from sampling locations within 250 m buffer rings from the mouth of Carruthers Creek. The black vertical lines represent the minimum and maximum concentration. The black horizontal line represents the detection limit for the majority of the total phosphorus samples and the soluble reactive phosphorus samples from 2007-2014. The dashed horizontal line represents the total phosphorus water quality objective for open waters set by the International Joint Commission.

Figure 4: Average nitrate + nitrite concentrations from sampling locations within 250 m buffer rings from the mouth of Carruthers Creek. The black vertical lines represent the minimum and maximum concentration.

Rouge River

Similar to Carruthers Creek, in many years the highest nutrient concentrations are observed at the mouth of Rouge River, and they generally decrease as you move farther from the mouth of the river. There are some exceptions suggesting that, at times, there are additional sources affecting this area.

In some years, although average nitrate + nitrite concentrations are similar, the ranges show a decreasing trend as you move away from the river mouth. In other years, average nitrate + nitrite concentrations are higher at a distance from shore, further supporting that there are additional sources affecting these waters.

Figure 6: Average nitrate + nitrite concentrations from sampling locations within 250 m buffer rings from the mouth of Rouge River. The black vertical lines represent the minimum and maximum concentration.

Duffins Creek

The observations in the rings originating from Duffins Creek are not as clear as those from Carruthers Creek or the Rouge River. This is because there are additional sources of nutrients within the vicinity of the mouth of Duffins Creek.

The 250 m to 500 m ring contains influences from the storm drain west of Duffins Creek mouth. Nutrient concentrations in close proximity to the storm drain are elevated and increase the average nutrient concentrations observed within the ring.

Similarly, the concentrations within the 750 m to 1000 m ring are also higher than expected as the concentrations by the Pickering Nuclear Generating Station also influence the area. To further complicate the results, the outfall to the Duffin Water Pollution Control Plant also intersects this area.

Figure 8: Average nitrate + nitrite concentrations from sampling locations within 250 m buffer rings from the mouth of Duffins Creek. The black vertical lines represent the minimum and maximum concentration.

Other locations of interest are the Pickering Nuclear Generating Station, and the storm drain located west of Duffins Creek. The buffer rings around their locations are illustrated below:

Buffer rings surrounding the Pickering Nuclear Generating Station and the storm drain located west of Duffins Creek — Figure 9: Buffer rings surrounding the Pickering Nuclear Generating Station, and the storm drain located west of Duffins Creek. Concentric rings increase by 250 m. The red dots represent the sampling locations from 2007-2009. Map Source: Data provided by Ontario Ministry of Natural Resources.

Storm Drains

The nearshore region close to the storm drain west of Duffins Creek has been identified as a location where high nutrient concentrations are present.

Elevated concentrations are observed in the lake near the storm drain — however, concentrations do not decrease as nicely as with the creeks when you move away from the shore. This is because there are other nutrient sources influencing the buffer rings.

The yellow bar in the graphs below represents the band from 250 m to 500 m from the storm drain. The concentrations are elevated because the mouth of Duffins Creek is within this distance of the storm drain.

The dark blue bar represents the band from 750 m to 1000 m. It is higher than expected because it includes some of the shoreside sampling locations from the surrounding transects and it is also on the outskirts of the Duffin Water Pollution Control Plant outfall.

In 2014, TRCA transformed the storm drain channel into a pilot treatment system in an effort to reduce the nutrients exiting the watershed to the nearshore of Lake Ontario. Monitoring of the storm drain during storm events in 2015 suggested the effort was successful.

Figure 10: Average total phosphorus and soluble reactive phosphorus concentrations from sampling locations within 250 m buffer rings near the storm drain west of Duffins Creek. The black vertical lines represent the minimum and maximum concentration. The black horizontal line represents the detection limit for the majority of the samples. The dashed horizontal line represents the water quality objective for total phosphorus in open waters set by the International Joint Commission.

Figure 11: Average nitrate + nitrite concentrations from sampling locations within 250 m buffer rings near the storm drain west of Duffins Creek. The black vertical lines represent the minimum and maximum concentration.

Pickering Nuclear Generating Station

Near the Pickering Nuclear Generating Station, mean concentrations and concentration ranges are similar in all the rings between 0 m and 1000 m from the shore. One possible explanation for this is a continual influence from Frenchman’s Bay.

Circulation patterns in this region are complicated, however, and it is possible that the circular gyres are the reason that the water quality appears well mixed in the region. However, since there is no sampling transect near this region, that cannot be confirmed.

Between 2015 and 2017, higher concentrations in the 750-1000 m band suggests additional influences affected these distances.

Figure 12: Average total phosphorus and soluble reactive phosphorus concentrations from sampling locations within 250 m buffer rings near the Pickering Nuclear Generating Station. The black vertical lines represent the minimum and maximum concentration. The black horizontal line represents the detection limit for the majority of the samples. The dashed horizontal line represents the water quality objective for total phosphorus in open waters set by the International Joint Commission.

Figure 13: Average nitrate + nitrite concentrations from sampling locations within 250 m buffer rings near the Pickering Nuclear Generating Station. The black vertical lines represent the minimum and maximum concentration.

The final two points of interest in the Ajax and Pickering study area are the Duffin Water Pollution Control Plant outfall and the Durham Region Ajax Water Supply plant intake.

Duffin Creek Water Pollution Control Plant Outfall

Similar to the creek mouths and storm drains, the area immediately surrounding the outfall of the Duffin Creek Water Pollution Control Plant has elevated nutrient concentrations.

These concentrations decrease as the distance increases from the outfall, and generally apporach background concentrations by 1000 m away from the source.

At times, the blue bars representing the concentrations within 500 to 1000 m from the outfall seems high because it overlaps areas where other nutrient sources contribute to the concentration observed such as the storm drain, or Duffins Creek.

Figure 14: Average total phosphorus and soluble reactive phosphorus concentrations from sampling locations within 250 m buffer rings near the Duffin Creek Water Pollution Control Plant outfall. The black vertical lines represent the minimum and maximum concentration. The black horizontal line represents the detection limit for the majority of the samples. The dashed horizontal line represents the water quality objective for total phosphorus in open waters set by the International Joint Commission.

Figure 15: Average nitrate + nitrite concentrations from sampling locations within 250 m buffer rings near the Duffin Creek Water Pollution Control Plant outfall. The black vertical lines represent the minimum and maximum concentration.

Durham Region Ajax Water Supply Plant Intake

Unlike the creek mouths, the water quality around the drinking water supply plant intake approaches the concentrations observed in the lake background. The intake was intentionally placed farther from the shore to ensure the water taken from the lake is of good quality, and away from potential nutrient sources.

Figure 16: Average total phosphorus and soluble reactive phosphorus concentrations from sampling locations within 250 m buffer rings near the Regional supply plant drinking water intake. The black vertical lines represent the minimum and maximum concentration. The black horizontal line represents the detection limit for the majority of the samples. The dashed horizontal line represents the water quality objective for total phosphorus in open waters set by the International Joint Commission.

Figure 17: Average nitrate + nitrite concentrations from sampling locations within 250 m buffer rings near the Drinking water intake. The black vertical lines represent the minimum and maximum concentration.

Take Home Messages

Nutrient concentrations are elevated at creek mouths and storm drains, and concentrations decline as you move away from the creek mouth or storm drain.
Nutrient concentrations by the Pickering Nuclear Generating Station have a small range compared to the creeks, and decrease to near background within 1 km of the Plant.
Nutrient concentrations by the Duffin Creek Water Pollution Control Plant outfall decrease to near background within 1 km of the outfall.
Nutrient concentrations by the regional water supply plant intake are close to background concentrations.
Multiple sources affect the nearshore area by Duffins Creek, as observed by the overlapping buffer rings and concentrations.