Coarse Filter - Freshwater
To help sustain the NWT’s biodiversity and cultural landscapes, the NWT Protected Areas Strategy (PAS) aims to protect special natural and cultural areas, and core representative areas within each of the territory’s 45 ecoregions. To date, the PAS Science Team has focused its analyses primarily on terrestrial areas, which only capture limited aspects of freshwater biodiversity. However, freshwater is a critically important ecological component and physical force in the NWT. To evaluate whether freshwater biodiversity is also represented within protected areas, the PAS Science Team has developed a coarse-scale freshwater classification.
Freshwater Classification
In conservation science, the underlying idea of the coarse filter approach is that by protecting samples of environmental features, many species and communities, and the ecological processes that support them, will also be protected. In areas such as the NWT, where species data is sparse, the coarse filter approach is the primary tool for representing biodiversity in regional conservation planning.
The PAS Science Team developed a coarse-scale freshwater classification for the Mackenzie River Basin and several watersheds in the adjacent Queen Elizabeth drainage basin. The classification describes the dominant regional patterns of environmental conditions that influence freshwater ecosystems and biotic processes. The challenges of finding datasets to classify this collective 'Basin' include obtaining datasets that are meaningful for freshwater systems, that cover the entire basin under study, and that provide an adequate level of detail for analysis. Chosen datasets were surficial geology, permafrost, accumulated catchment size, density of lakes, eskers and glaciers/icefields.
The classification is not intended to predict species distribution or specific habitats. Instead, the resulting abiotic classification units (i.e., based on physical and chemical characteristics) can be the foundation for a freshwater coarse filter analysis to evaluate whether the diversity of freshwater habitats within the NWT is well represented in protected areas, and whether additional protection may be required. The classification can also be used for more detailed watershed planning as more information becomes available and for ongoing uses in freshwater and fisheries planning and management throughout the NWT. More detailed biotic and abiotic fine filter data such as waterfalls and rapids can be added to analyses, where it exists, to better inform our decisions.
How was the freshwater classification created?
Work on a coarse scale freshwater classification for the Mackenzie River and portions of the adjacent Queen Elizabeth drainage basin began in 2006, and a first draft of the classification was completed in early 2007. The work was reviewed by freshwater experts at a workshop held in Yellowknife in early November 2007. Based on the advice and feedback received at the workshop, the classification was revised to better characterize freshwater systems of the Mackenzie River Basin.
A first step was to create Ecological Drainage Units for the Basin. Ecological Drainage Units (EDUs) are areas distinguished by:
- watershed boundaries,
- landscape features (landform and geology), and
- climate.
The interaction of these three factors influences broad patterns of aquatic ecosystems, such as channel morphology, hydrology, temperature and nutrient regimes. The best available data on these broad patterns is the ecozones of Canada and the National sub-sub drainage basins (i.e., smaller basins that nest within sub drainage basins). These two datasets were combined to divide the Basin into 21 EDUs that are useful for exploring the impacts of larger scale effects such as rainfall or climate change.
The smallest analysis unit, water catchments, is small drainage areas immediately surrounding segments of streams. There are over 65,000 catchments in the Basin. The PAS Science Team analyzed the direction of flow through the catchments to get accumulated upstream catchment information and classified four catchment sizes based on total area of upstream catchments.
The EDUs and the catchments are used to analyze physical components of the Basin. The component datasets used for the classification are based both on data availability and usefulness as surrogates for freshwater ecosystems and biotic processes and include:
- Surficial geology (12 classes): influences sediment load, substrate size, infiltration, ground water–surface water interaction, water chemistry, nutrient concentrations
- Permafrost (6 classes): influences water temperature, surface flow/drainage.
- Amount of glacial coverage: influences water temperature, which in turn influences fish distribution and water chemistry, amount and timing of affected stream flow, turbidity, etc.
- Amount of waterbodies/lakes: sinks for sediment load, influences water chemistry, etc.
- Amount of eskers: have different ecology than the surrounding Shield, so influence local ground water flow and availability in an otherwise surface flow dominated landscape.
- Presence of glaciers/icefields – these are rare in the Basin and contribute to difference in flow regime and water temperature.
In early 2013, the PAS Science Team finalized the report detailing the coarse filter freshwater classification project. The report is online and can be downloaded [pdf].
This background information is available for use by contacting the PAS Secretariat at nwt_pas@gov.nt.ca.
Related links
- Ecozones of Canada: areas representation of very large scale climate, landform, geology, and broad vegetation types available from A National Ecological Framework for Canada at the EcoMap project.
- Sub-sub drainage basins: cover the entire landmass of Canada and were delineated on maps in 1980 based on “classic drainage areas” and mean annual discharge from streams. They are part of the Atlas of Canada National Frameworks Data courtesy of GeoGratis.
- Freshwater classification for British Columbia [link]
- The Catchments dataset represents modeled approximate catchment areas for each individual river segment and lake in the 1:1 million scale drainage network, to be used in the absence of more accurate drainage divide data. The dataset is part of Natural Resources Canada's Atlas of Canada National Frameworks Hydrology Data.
- Mackenzie River Basin Board: Formed through a transboundary agreement between the Northwest Territories, Alberta, British Columbia, Saskatchewan, the Yukon and the Government of Canada to ensure a healthy and diverse aquatic ecosystem in the Mackenzie River Basin.
- NWT Water Stewardship Strategy: An initiative by the Government of the Northwest Territories and the Government of Canada to ensure water in the NWT remains healthy now and for future generations.
