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Data Sources and Methods for the Freshwater Quality in Canadian Rivers Indicator

3. Data

3.1 Data source

Water quality data for 2010 to 2012 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 in Canadian Rivers Indicator (WQI) correspond to those defined in Statistics Canada's Standard Drainage Area Classification.Footnote [1]

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

Human activity in the drainage basin of core monitoring sites 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 pollutant releases from industrial and commercial facilities using Environment Canada's 2007 National Pollutant Releases Inventory, 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 sites selected to be representative of surface freshwater quality across Canada where human pressure is greatest. The 2010–2012 national WQI was calculated using 172 core sites.

The local WQI is reported for the 172 core sites and 164 additional local sites across Canada for which 2010–2012 data are available. The number of core sites changes year to year because samples are sometimes missed or lost so the site does not have the minimum data required.

Core site selection

Among Canada's 25 drainage regions, 16 were selected, based on human population density, from the available water quality monitoring network to create the WQI core network (Figure 1). Within the 16 selected drainage regions, core sites were selected to ensure site drainage areas do not overlap and are thus independent of one another. For this analysis, the upstream drainage area of each monitoring site was delineated by Statistics Canada using the National Hydro Network.Footnote [5] Where upstream drainage areas of monitoring sites overlapped, the site furthest downstream was retained for the core network, as the downstream site 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 sites were established in the upper, mid and lower portions of the river as well as the most downstream sites on each tributary when available. Additional core sites were included on these rivers, because water travels thousands of kilometres from source to mouth. Water quality changes along the way and cannot be summarized by a unique downstream monitoring site. The final selection of core sites ensures monitoring sites are well distributed among provinces, territories and drainage regions.

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


Long description

The map of Canada shows the drainage regions included in the Freshwater Quality in Canadian Rivers Indicator core network. Of Canada's 25 drainage regions, 16 are used for the calculation of the Freshwater Quality in Canadian Rivers Indicators.

Water quality was also assessed at monitoring sites (local sites) not included in the core network. Information on water quality at individual core and local sites can be found in the interactive freshwater quality map.

3.3 Temporal coverage

The WQI was calculated using a minimum of four samples per year from 2010 to 2012 for the majority of sites. A minimum of three samples per year is allowed for northern and remote sites because winter access can be difficult. A sensitivity analysis concluded no significant difference existed in the water quality index 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, the WQI is more representative of the overall freshwater quality at a site. 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 sites: eight in Manitoba, two in Newfoundland Labrador, one in Saskatchewan, and one in New Brunswick. The sites are remote, making sampling during the winter months difficult, dangerous and costly. These sites, 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 sites and is set according to the monitoring program objectives. There are up to 56 samples for a given parameter at some sites.

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 site information from the monitoring programs are stored in a central WQI dictionary, which facilitates the verification of the number of samples, sample timing and the location of monitoring sites, and calculations.

3.5 Data timeliness

The WQI was calculated using data from 2010 to 2012, the most recent data available from all monitoring programs. For 10 core sites, data from late December 2009 or early January 2013 were used to meet requirements for minimum number of samples.

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