What have we learned about water quality in the Western Durham nearshore, compared to other parts of Lake Ontario and to other lakes?
If we compare the open-water total phosphorus water quality in the Ajax and Pickering area to other regions and lakes around the province, it is clear that the open water conditions are similar to other lakes around the province, and sometimes better.
If we focus in on different zones, we can see some similarities and differences between the total phosphorus concentrations from the Ajax and Pickering nearshore in comparison to other regions around Lake Ontario. As a recap, here are the definitions of the different zones displayed:
Ontario Ministry of the Environment Definitions in Howell et al. (2012b):
Tributary: in the rivers or creeks
Embayment: areas within a bay (e.g. Frenchman’s Bay, Cobourg Harbour, Jordan Harbour, etc)
Shoreside: wadeable area to approximately 1.2 m depth
Nearshore: from approximately 3 m depth to 5 km offshore
Background: the last kilometre of the sampling area (often 4 to 5 km from the shoreline) used as a reference
If we use data collected from other nearshore studies around Lake Ontario (Howell et al., 2012b; Makarewicz et al., 2012), we can see some similarities and some differences with the Canada and United States shores of the Lake.
Ajax and Pickering shoreside concentrations are similar to Grimsby and Coburg data collected by the Ontario Ministry of the Environment in 2008. The shoreside concentrations for Ajax and Pickering are lower than the concentrations observed in the Toronto nearshore, and the American side of Lake Ontario. All of the shoreside conditions along Lake Ontario, including Ajax and Pickering, are elevated compared to the entire nearshore. There is no nearshore or shoreside water quality objective to compare them to (although the open-water objective is displayed on the graph).
Nearshore concentrations show the same trends as the shoreside concentrations. Nearshore concentrations are similar to Grimsby and Coburg data collected by the Ontario Ministry of the Environment in 2008. The nearshore concentrations in Ajax and Pickering are lower than the concentrations observed in the Toronto nearshore, and the American side of Lake Ontario.
Leon et al. (2012) also sampled the Ajax and Pickering nearshore in 2008. If we look at their total phosphorus distribution data, we see that similar to TRCA Leon et al. (2012) found:
- Elevated concentrations are observed by the shoreline and the outfall.
- Concentrations appear higher in the west than the east although symbols are in increments of 5 mg/L.
- Majority of the variability is within 1 km of the shoreline.
- Total phosphorus decreases by at least 80% within 1 km of the outfall.
- Tributaries affect total phosphorus during high runoff periods.
There has been one other study in the region completed by Malkin et al. (2010). Similar to elevated creek concentrations observed by TRCA, these authors have shown that Duffins Creek is a local source of total phosphorus. However, in contrast to the TRCA they did not find repeated seasonal patterns in total phosphorus at sites 2-12m depth. This is likely because of the short timeframe for the Malkin et al. (2010) study (2 years of data).
Finally, we do see overlap between the concentrations measured in the Ajax and Pickering nearshore by TRCA and by Malkin et al. (2010). (Due to copyright protection, we cannot post the images from Malkin et al. (2010), only the abstract.)
If we consider the nearshore background conditions for Ajax and Pickering, other sites along Lake Ontario, cottage country lakes from the Muskoka area, Lake Simcoe, and so on, we also see similarities and differences in average total phosphorus concentrations.
Background concentrations in Ajax and Pickering are below the International Joint Commission and the Ontario Ministry of the Environment water quality objectives for open water total phosphorus concentrations. The observed concentrations are similar to other sites along the Canadian shores of Lake Ontario, and are lower than the background concentrations from the American side of Lake Ontario.
In addition, the background concentrations are also similar to cottage country lakes that the Ontario Ministry of the Environment studies in the Muskoka region, and even Six Mile Lake – notable because it is a provincial park. The background concentrations are also lower than those observed in Lake Nippising, the third largest lake in Ontario, excluding the Great Lakes.
Despite elevated concentrations from the shoreside to 1 km from the shore, nearshore background conditions are similar to other lakes around the province (including cottage country and provincial parks), and sometimes better. Cottage lakes can also have high shoreside concentrations due to leaky septic tanks.
Average total phosphorus background conditions in the Ajax and Pickering nearshore are:
- Lower than the United States side of Lake Ontario, and some cottage country and provincial park lakes.
- Similar to the 2008 study completed by the Ontario Ministry of the Environment.
Background data collected by the TRCA in 2008 are similar to background data collected by the Ontario Ministry of the Environment. The higher variability in the TRCA data is due to the multi-year program (2007 – 2012). The data from Howell et al. (2012b) and Makarewicz et al. (2012) are from one year (2008).
Take Home Messages
- Open water total phosphorus concentrations in Lake Ontario are similar to many smaller lakes including those in Muskoka, and in provincial parks.
- Ajax and Pickering shoreside concentrations are lower than Toronto and the United States side of Lake Ontario.
- Ajax and Pickering nearshore conditions are similar to Grimsby and Cobourg.