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Data Sources and Methods for the Freshwater Quality Indicator


3.1 Data source

Water quality data for 2008 to 2010 were obtained from a number of monitoring programs managed by federal and provincial authorities, as well as by federal-provincial agreements, across the country. The complete list can be found in Annex 1.

Freshwater quality guidelines were obtained from the Canadian Council of Ministers of the Environment (CCME) water quality guidelines for the protection of aquatic life, the United States Environmental Protection Agency (U.S. EPA), and provincial and territorial sources. A complete list of water quality guidelines used by each jurisdiction can be found in Annex 2.

Drainage regions used in the regional Freshwater Quality Indicator (WQI) correspond to those defined in Statistics Canada’s Standard Drainage Area Classification.Footnote[1]

The upstream drainage area of core monitoring stations was delineated using Natural Resources Canada’s National Hydro Network.Footnote[2]

Human activity in the drainage basin of core monitoring stations was characterized using population density from Statistics Canada’s 2006 Census of Population, mine locations using Natural Resources Canada’s 2006 Census of Mines, point-source agricultural activity locations using Statistics Canada’s 2006 Census of Agriculture, and land cover using Natural Resources Canada’s land cover maps.Footnote[3],Footnote[4]

3.2 Spatial coverage

The national WQI is calculated using a set of core stations selected to be representative of surface freshwater quality across Canada and the human pressure exerted on it. The 2008-2010 national WQI was calculated using 172 core stations.

The local WQIis reported for the 172 core stations for which 2008-2010 data are available, and 156 additional local stations across Canada. The number of core stations changes every year due to missing data. For this year’s report, water quality is reported at 172 core stations compared to 173 stations in last year’s report. Core stations are added or removed depending on whether they meet data standards and requirements of the WQI.

Core station selection

Among Canada’s 25 drainage regions, 16 were selected based on population density for the WQI core network (Figure 1). Within the 16 selected drainage regions, core stations were selected to avoid overlapping drainage areas and to ensure stations are independent of one another. The upstream drainage area of monitoring stations was delineated by Statistics Canada using the National Hydro Network.Footnote [5] Where upstream drainage areas of monitoring stations overlap, the most downstream station was retained for the core network, as this station is impacted by the maximum area in the river basin and, to some degree, reflects the cumulative impact of all upstream stresses. For 14 large rivers, including the Athabasca and North Saskatchewan rivers, core stations were established in the upper, mid and lower portions of the river as well as the most downstream stations on each tributary when available. Additional core stations were established on these rivers, as water travels thousands of kilometres from source to mouth. Water quality changes along the way and cannot be summarized by a unique downstream monitoring station. The final selection of core stations ensures monitoring stations are well distributed among provinces, territories and drainage regions.

Figure 1: Geographic extent of the 16 drainage regions selected for the core network

Figure 1: Geographic extent of the 16 drainage regions selected for the core network

Water quality was also assessed at monitoring stations known as “local stations” that were not included in the core network. Information on water quality at individual core and local stations can be found in the CESI interactive freshwater quality map.

3.3 Temporal coverage

The WQI was calculated using a minimum of four samples per year from 2008 to 2010 for southern sites. A minimum of three samples per year is allowed for northern and remote stations because winter access can be difficult. A sensitivity analysis concluded that no significant difference existed in the water quality score when the mid-winter sample was excluded.Footnote [6] Three years of data are used to dampen temporal variability in WQI results caused by annual fluctuations in weather and hydrology.Footnote [7] By using a three-year roll-up, theWQIis more representative of the overall freshwater quality at a station. It minimizes the effects of events such as high or low flow, by avoiding one sample driving the WQI score up or down.

Minimum sampling requirements were not met at 12 core stations: 11 in Manitoba and 1 in New Brunswick. The stations are remote, making sampling during the winter months difficult, dangerous and costly. These stations, however, were closely evaluated by local water quality experts, and were included because the data were consistent with previous years and were considered representative of local water quality.

Sample timing and frequency varies among monitoring stations and is set according to the monitoring program objectives. There are up to 60 samples for a given parameter at some stations.

3.4 Data completeness

Data quality assurance / quality control (QA/QC) is performed within each monitoring program providing data for the WQI. Each monitoring program follows standardized methods for sample collection in the field. Chemical analyses are performed in Canadian laboratories accredited by the Canadian Association for Laboratory Accreditation or the Standards Council of Canada.

The data undergo an additional QA/QC process by Environment Canada to ensure the dataset meets minimum data requirements and that standards for calculation are respected. This process leads to removal of parameters due to low sampling frequencies or because detection limits are higher than guidelines used in the calculation. Unusually high or low values in the monitoring datasets are double-checked and confirmed through consultation with the data provider. WQI scores and station information from the monitoring programs are stored in a centralWQIdictionary, which facilitates the verification of the number of samples, the timing location of monitoring stations, and calculations.

3.5 Data timeliness

The WQI was calculated using data from 2008 to 2010, the most recent data available from all monitoring programs. For 10 core stations, data from late December 2007 or early January 2011 were used to meet requirements for minimum number of samples.