How does Toronto and Region Conservation Authority (TRCA) conduct its sampling of nearshore water quality in Western Durham?
TRCA monitors water quality monitoring in the Ajax and Pickering nearshore, extending from the Rouge River in the west, to Carruthers Creek in the east.
This monitoring program examines the water quality conditions in the nearshore environment in an effort to understand the nutrient dynamics (the variability over time and space), and guide management decisions.
Preliminary investigations were completed in August 2006, when sampling design, sampling procedures, and logistics were determined. More intensive sampling began in 2007.
From 2007-2010, 8 transects were followed sampling water quality predominantly in the surface water at 7 sites along each transect varying in distance from 0 m to 3 km from shore (0 m, 100 m, 400 m, 1 km, 1.5 km, 2 km, 3 km; Figure 1).
In addition to the surface samples taken, additional samples were taken within the water column for Transect 6 at middle and bottom depths.
In 2010, an expert peer review of the sampling design was completed by Dr. Martin Auer (Professor of Civil and Environmental Engineering at Michigan Technological University). His suggestions included increasing the sampling distance to 5 km and adding samples at depth to gain an understanding of the nutrients throughout the water column.
In response, TRCA revised the sampling plan in 2011 to include middle and bottom depths along all transects. To compensate for the increased number of samples, the number of transects was reduced from 8 to 4 extending from the Pickering Nuclear Generating Station to Carruthers Creek, and surrounding Duffins Creek.
Samples were taken at 100 m, 1 km, 3 km, and 5 km from shore at the surface, middle, and bottom of the water column (Figure 2). The transects were extended to 5 km from shore to compare the shoreline water chemistry with “background” nutrient levels.
In 2014, we increased our sampling locations closer to the shore to integrate the original study design from 2007-2009, and the study design used between 2011 and 2013 (Figure 3). In addition, we added some transects closer to the shore by Petticoat Creek and Frenchman’s Bay.
Samples were taken at varying distances based on the transect location. Generally, the lake surveys included sampling 5 transects up to 5 km from the shore with samples taken at the surface when less than 1 km from the shore and at depth when the distance is 1 km or greater from the shoreline. Shoreside lake surveys were completed by sampling the surface waters of 4 additional transects up to 400 m from the shore.
The 2014 sampling design was very difficult to complete in one day even using two boat crews. We realized that we needed to scale back and focus our efforts on the samples by the shore.
As a Conservation Authority, our efforts at improving water quality and water quantity occurs from the land. As a result, we decided to add a transect close to the shore by a large storm drain in between Duffins and Carruthers Creek (Figure 4). However, overall we needed to reduce the number of samples we took so sampling could be complete within one day.
Our analysis of the 2014 data at the 3 km and the 5 km sites showed that there was no statistical difference between the lake surface water quality at these distances for our nutrients of interest.
As a result of these tests, in 2015 we removed many of the 3 km and 5 km sampling locations. Since we are able to supplement our dataset with offshore data from Environment and Climate Change Canada, reducing these sampling points will not impact our understanding of water quality in the region.
We also decided to remove the middle sampling locations until a more rigorous analysis could be completed on those results from previous years. Samples are being taken at the surface and bottom of the lake at all 1 km, 3 km, and 5 km sites; closer to the shore (e.g. 0 m, 100 m and 400 m) samples are only being taken at the surface since the surface and bottom waters are well mixed.
This lake sampling design was followed from 2015 to 2018.
From 2019 to the present, TRCA has continued sampling the lake under a “maintenance design” (Figure 5). We are sampling two locations 400 m from the shore, the outfall and drinking water intake sites, a mid-nearshore site, and a station that will tell us about lake background at 5 km.
Sample Collection
Samples were collected at each station using a Niskin water sampler (Figure 6). If samples were taken at depth, a number of these samplers were arranged on a line lowered into the lake and messengers were sent down to tell the samplers to close in quick succession of each other. Samples were placed in bottles and stored on ice in coolers for transport to the lab.
For the 2019 maintenance design, sampling was conducted in the same way but from the R.V. Ken Higgs monitoring vessel (Figure 7).
Sample Analysis
Once water samples have been collected from the lake, they are submitted for analysis at the York-Durham Regional Environmental Laboratory.