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Threats to Water Availability in Canada
- Publishing Information
- Environment Canada Steering Committee, Production Team, Editors, Authors, External Reviewers
- Threats to Water Availability in Canada - A Perspective
- Short Chapter Summaries
- 1. Water Allocations, Diversion and Export
- 2. Dams, Reservoirs and Flow Regulation
- 3. Droughts
- 4. Floods
- 5. Municipal Water Supply and Urban Development
- 6. Manufacturing and Thermal Energy Demands
- 7. Land Use Practices and Changes - Agriculture
- 8. Land-Use Practices and Changes - Forestry
- 9. Land-Use Practices and Changes - Mining and Petroleum Production
- 10. Climate Variability and Change - Groundwater Resources
- 11. Climate Variability and Change - Rivers and Streams
- 12. Climate Variability and Change - Lakes and Reservoirs
- 13. Climate Variability and Change - Wetlands
- 14. Climate Variability and Change - Crysophere
- 15. Integrated and Cumulative Threats to Water Availability
7. Land Use Practices and Changes - Agriculture
Brook Harker,1 John Lebedin,1 Michael J. Goss,2 Chandra Madramootoo,3 Denise Neilsen,4 Brent Paterson5 and Ted van der Gulik6
1 Agriculture and Agri-Food Canada, Prairie Farm Rehabilitation Administration, Regina, SK
2 University of Guelph, Chair of Land Stewardship, Guelph, ON
3 McGill University, Department of Agricultural and Biosystems Engineering, Montreal, QC
4 Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland, BC
5 Alberta Agriculture, Food and Rural Development; Irrigation Branch, Lethbridge, AB
6 B.C. Ministry of Agriculture, Food and Fisheries; Resource Management, Abbotsford, BC
- Current Status
- Future Trends and Emerging Issues
- Knowledge and Data Needs
- View short chapter summary
Land and Water Use
Agriculture accounts for 3% of Canada’s gross domestic product, making it one of the largest sectors in the country. Approximately 7% of Canada’s land base is used for agriculture, amounting to 67.5 million ha. Prairie Provinces account for 82% of this total, while Ontario and Quebec contribute only 13%, although the productivity in these two provinces is generally greater on a per hectare basis. Of the agricultural land base, 46 million ha are improved farmland such as cropland and summerfallow, with 20 million ha as unimproved pasture land (Statistics Canada, 2002).
Although agriculture is not Canada’s largest user of water, it is the largest net consumer. Nationally, 44.61 billion m3 of surface water are withdrawn by major users from Canada’s rivers (1996). However agriculture (1991) withdrew only about 9% compared with thermal power (64%) and manufacturing (14%). Even though, overall, only about 10% (4.5 billion m3) of water withdrawn is actually consumed, agriculture consumes 71% of the water it diverts, making it by far the greatest consumer. Furthermore, there are marked differences among Canadian regions related to agricultural water use. About 85% of agricultural withdrawals (surface and ground water) are used for irrigation (primarily in the West) and 15% is used for watering livestock (Environment Canada, 2002a,b). Groundwater use, though relatively small in comparison to surface water volumes, provides 26% (6.2 million people) of domestic water supply overall, with 82% of rural Canadians (about 4 million people) relying on groundwater for supply (Science Council of Canada, 1988).
Sustainable agricultural development and an increase in improved farmland require continued access to reliable, good quality water resources. The importance of water to agriculture cannot be overstated. Agriculture’s use of water for irrigation of crops, livestock watering, processing, and sustaining farm families in urban and rural areas alike is of utmost importance.
Impacts of Farming on the Hydrologic Cycle
As agricultural land use in Canada has increased, the natural hydrology of the landscape has changed, affecting the relative availability and in some cases the quality of water. It is widely perceived, but not well understood, that the quality of surface and ground water is likely deteriorating in agricultural areas due to increased loading from nutrients, pesticides and pathogens.
The production of crops in both irrigated and rain-fed systems affects water flow in the landscape. The diversion and redistribution of water through irrigation and drainage have significant impacts on the natural hydrologic cycle. Crop type and management can change infiltration and flow of water through the soil profile, and hence modify patterns of surface and subsurface flow. This combination has sometimes resulted in increased peak runoff events and silt loading to rivers, decreased base flows in small streams and waterways, and reduced surface infiltration on which groundwater recharge in some areas may be dependent to sustain wetlands and water supply.
Effects of crop type on runoff and sediment loss are well known (Table 2). Runoff is likely to be less with those crops that provide permanent soil cover such as pasture, hay and perennial horticultural crops like tree fruits that have a grass cover.
Conservation tillage: For annually seeded crops, conservation tillage practices, developed and widely accepted over the past 15 to 20 years can greatly reduce surface losses of water, sediment and nutrients to waterways. Under such practices, a 30% or greater cover of residue from the previous crop is left on the soil surface. For example, a 60% reduction in surface runoff was reported for no-till corn in Quebec when compared with conventional tillage (McRae et al., 2000). In Saskatchewan, at the watershed scale, snowmelt runoff from long-term, zero-tillage was less than half that from conventionally tilled fields, and runoff from summer storms was also reduced (Elliott et al., 1998). Adoption of conservation tillage practices has resulted in fewer days when soils are left bare and exposed to erosion. McRae et al. (2000) reported that between 1981 and 1996, the number of bare soil days per hectare per year was reduced by 2% in Quebec, and 44% in Newfoundland, with the average for Canada being around 20%.
Drainage and irrigation: Due to Canada’s climatic conditions, systems for both good drainage and irrigation are often essential for successful agricultural production. In eastern Canada and the coastal areas of B.C. where there is a surplus of precipitation at certain times of the year, drainage is required to remove excess soil water. Natural internal drainage and surface drainage are insufficient to ensure that the water table is lowered rapidly enough for early seedbed preparation and planting. Therefore, artificial drainage in the form of horizontal subsurface drains ("tile" drainage) is often required to provide better conditions for farm machinery operation.
Conversely, irrigation may be required on the Prairies and other regions of Canada where the range in annual precipitation (as low as 300 mm in southwest Saskatchewan to 550 mm in Beausejour, Manitoba) is often insufficient to meet the evaporative demands placed on crops. In regions where irrigation is widely practiced (predominantly Alberta and British Columbia), up to 35 to 40% of annual precipitation within affected watersheds is diverted for irrigation purposes. This constitutes a major change from the natural hydrologic processes in these basins.
Consumptive Use – Irrigation
Much of the water required for irrigation throughout the growing season must be captured during spring snowmelt and stored behind dams or in reservoirs for later use. This storage promotes significant evaporative losses throughout the year. In addition, the diverted water that is ultimately used in crop production results in gaseous losses through evapotranspiration, which will generally exceed those losses found under natural vegetation cover. The remainder of the diverted irrigation water is unavailable to crops, either being stored in the soil below the rooting zone, lost to groundwater, or is returned to river systems through surface flow.
About 75% of all agricultural water withdrawals in Canada take place on the Prairies, mainly for irrigation. Alberta has approximately 630,000 ha of irrigated land, or about 60% of the total irrigated cropland in Canada. In the South Saskatchewan River basin (SSRB) of Alberta, irrigation consumes about 2.2 billion m3 of water each year from the river system, equivalent to 28% of the total annual river flow. Under the Apportionment Agreement with the Prairie Provinces, 50% of the annual natural flow of water in the SSRB must flow to Saskatchewan. Apportionment and irrigation therefore account for 78% of the current Alberta water commitments in the SSRB, leaving about 22% of the flow for all other uses, including municipal, industry and the environment. As a result of increased water demands from all sectors, some Alberta watersheds are near or at full allocation and under water diversion moratoriums.
The challenge for agriculture has been to adopt management practices that will optimize the amount of water diverted per unit of crop yield, through improved efficiencies in storage, distribution, and on-farm utilization. As an example, the St. Mary River Irrigation District in Alberta has reduced the total amount of diverted water "lost" in return flows to the river system to less than 7%. This is indicative of more efficient usage and thus a smaller requirement for diversion per unit of crop produced. These efficiencies have resulted from the development of internal storage reservoirs, lining of irrigation canals, replacement of surface canals by pipelines, and conversion of flood irrigation systems to high efficiency pivot sprinkler systems (Irrigation Water Management Study Committee, 2002).
The majority of irrigation in Canada is through sprinkler systems. This type of irrigation has significantly less impact on surface hydrology than traditional flood irrigation. Flood irrigation often results in surface water losses of up to 50% (Irrigation Water Management Study Committee, 2002). In Alberta, the change from flood irrigation to pivot sprinkler irrigation has essentially eliminated these losses. In British Columbia, the use of micro-irrigation systems (trickle or drip irrigation) has further increased the optimization of water use for crop production, and has the potential to eliminate surface loss and restrict subsurface losses.
The present focus is to improve irrigation effectiveness through higher efficiency irrigation systems, improved water management, scheduling irrigation to meet crop water demands, suppression in evaporation losses and production of higher value crops. In British Columbia’s Okanagan Valley, irrigation methods started with flood irrigation in the 1940s. These systems were converted to more efficient sprinkler irrigation methods in the late 1950s and 1960s. Today, 30% of the fruit tree growing area has converted from sprinkler irrigation to micro-irrigation systems that offer an increase in efficiency of 70% to 90% over sprinkler methods (Ted van der Gulik, personal communication). Mulches are being used to reduce evaporative losses in horticultural crops. For newly planted trees, the reduction in evaporation losses has been shown to be as much as 50%, but reduces to 10% as the trees get larger.
In Alberta, conversion from flood irrigation to more efficient centre pivot systems has increased irrigation system efficiencies by 40%. Seepage losses in 1991 from canal systems in the 13 irrigation districts were estimated to be 471.76 million m3. A more detailed analysis in 1999 following extensive rehabilitation efforts showed that seepage losses were 89.75 million m3. It is estimated that projected canal rehabilitation will further reduce seepage losses to about 54 million m3, which represents 1.5% of the gross volume of water diverted on an annual basis (Irrigation Water Management Study Committee, 2002).
The current demand for irrigation in eastern Canada is relatively small. This is because the region usually experiences an annual surplus of precipitation over evapotranspiration. The total land area irrigated in the region is approximately 100,000 ha. This is mainly for high value horticultural crops in the fruit and vegetable industries. Irrigation is required during the months of June, July and August, to supplement rainfall and help meet crop evapotranspiration requirements. The main methods of irrigation in eastern Canada are sprinkler and drip systems.
The shift to efficient irrigation systems does not necessarily translate into water savings unless these systems are managed correctly. Advances in irrigation scheduling technology (using soil moisture or climate/weather data), allow farmers to schedule water applications on a daily basis. In British Columbia, irrigation scheduling with fully automated systems controlled by units that monitor evaporative demand (Parchomchuk et al., 1996), has been shown to reduce water use by 20 to 30% (Neilsen and Neilsen, 2002).
Need for reliable potable water: In some areas, buyers are starting to require farm audits confirming that potable quality water is being used to irrigate and wash crops that are sent to the fresh market. Many surface water supplies will not meet such requirements without some form of treatment, which may prove difficult to obtain. There is, accordingly, a trend towards the use of groundwater, even though the resource is poorly understood in many parts of the country.
Consumptive Use – Livestock
Livestock production is an important component of Canada’s agri-food industry. At present, approximately 15.5 million head of cattle and calves, 14 million head of hogs and 140 million poultry are produced throughout Canada (Statistics Canada, 2002). Production of quality livestock requires a stable supply of high-quality water, as indicated in Table 1. Groundwater provides nearly all of the water used to produce livestock in Canada (Science Council of Canada, 1988).
|Animal Type||Water (L/day)|
From Agriculture and Agri-Food Canada (2000), Health of Our Water - Toward Sustainable Agriculture in Canada.
In some areas of the country, such as Quebec, expansion of the intensive livestock industry has been restricted as a result of concerns about water quality. Current livestock management promotes reduced water use through improved techniques. For example, in dairy operations water can be saved through initiatives that include: scraping or sweeping milkhouse floors before washing, reusing equipment rinse water to wash floors, using high pressure nozzles for washing, installing water-saving sinks, and using the first rinse water from milk lines to water calves.
The beneficial effects of land drainage for crop production are well understood. Surface drainage systems include shallow ditches designed to drain surface depressions in fields, and deeper ditches designed to intercept overland flow and seepage, and to prevent water from re-entering agricultural land. Such systems eventually drain into natural waterways. Surface drainage systems may increase runoff, which may be of poor quality and contain high quantities of nutrients, agri-chemicals and sediment. Soil conservation techniques, such as grassed waterways and buffer strips, have been shown to significantly reduce over-land movement of water and to improve the quality of water in surface drains (Table 2). Considerable work is required to further clarify the value and to achieve universal adoption of a range of such beneficial management practices throughout Canada.
|Crop and year||Accumulated rainfall (mm)||Diversions and grass waterways||Up and down slop cultivation|
|Runoff(mm)||Soil loss(kg/ha)||Runoff(mm)||Soil loss (kg/ha)|
From: Table 8-3, Agriculture and Agri-Food Canada (2000), Health of Our Water - Toward Sustainable Agriculture in Canada.
Source: McRae et al. (2000).
Subsurface drainage systems can influence the downstream quality of surface drainage waters by transporting large volumes of water (which may contain pathogens, nutrients and agri-chemicals) into natural watercourses. One method of controlling water and nutrient losses from subsurface drainage is through a water table management system. This system has been used successfully in Quebec (Madramootoo et al., 2001) and in Ontario (Drury and Tan, 2000). Water drainage is reduced at specified times in the growing season and stored water may then be used for subsurface irrigation during periods of water shortage. Reduced water losses through tile drains resulting in decreased nitrate losses of up to 39% have been demonstrated using this technique. Losses of nutrients and water to tile drains may also be reduced by planting winter cover crops which act as a sink for nutrients and water at the end of the main crop growing season (Milburn et al., 1997).
Land and Water Use
Market conditions require that Canada’s farmers provide cost-efficient, high-quality food for a growing world population. This will mean more competition for instream flow, and for the use and regulation of water bodies, resulting in more pressure to further develop water resources, diversions and conveyance, with attendant social and environmental considerations.
The relative cost of water: Increased competition with instream users (such as fisheries and recreation) and consumptive uses (such as domestic and other industries), will require agriculture to respect the true economic value of water and ensure optimum use is attained. Increasing demand and a willingness to pay on the part of high-value enterprises, such as rural subdivision, golf courses, and water recreation, are increasing pressure on agriculture to seek alternate supplies such as municipal effluent, or to make their supplies available by simply selling their lands or water rights.
The Hydrologic Cycle
Expansion of the agricultural land base, and increasing agricultural demands for water and water management, have the potential for further impacts on the hydrologic cycle. But this incremental effect may be much less than previously, due to the adoption of on-farm beneficial management practices such as conservation-tillage. Still, there are tradeoffs even with these actions, and practices that reduce one hazard (e.g., surface runoff and soil erosion) may well enhance risks associated with another. For example, although minimum-tillage may reduce losses of water and some pollutants to surface drainage, this practice may increase infiltration into the soil and leaching to groundwater. This can enhance the movement of mobile nutrients and some pesticides to subsurface drains and to deeper groundwater along preferential pathways (e.g., cracks and worm holes) in the soil profile (Drury et al., 1996; Gaynor et al., 2002; Drury and Tan, 2000).
Increased percolation may also reduce anticipated overland flow to local sloughs and storage ponds. As well, the higher organic matter content in reduced-tillage fields such as no-till tends to filter the coarse soil particles from runoff, thereby enhancing the ratio of fine to coarse soil particles in runoff (Bernard et al., 1992). The decomposing organic matter in reduced-tillage fields can also bring about increased concentrations of soluble nutrients, particularly phosphorus, in surface runoff (Pesant et al., 1987). Such increased nutrient loadings might even be sufficient to offset the benefits of an otherwise reduced volume of runoff, by enhancing the potential for eutrophication.
Past agriculture programs (e.g., Agriculture and Agri-Food Canada’s Permanent Cover Program) have encouraged the removal of marginally productive agricultural lands from annual cropping, returning them to long-term permanent cover under alfalfa hayland and pasture. The newly announced national GreenCover program, part of Agriculture and Agri-Food Canada’s new Agriculture Policy Framework (Agriculture and Agri-Food Canada, 2002) is an expansion of that thrust. Such steps will tend to further reduce surface runoff and enhance groundwater recharge, while further filtering potential loadings to streams of sediment, nutrients, pesticides, and in some cases pathogens.
Consumptive Use – Irrigation
An increasing demand for more dams, reservoirs, and diversions will come with increased demand for irrigation. As already indicated, many watersheds now have their water resources fully allocated and greater irrigation efficiencies will be required if irrigation acreage is to expand, while maintaining acceptable streamflows for other uses. In limited areas, improved irrigation efficiencies may actually dictate an increase in irrigation water used per unit of land, where crops are now receiving insufficient water for optimum growth. For example, in Alberta and British Columbia, evaluation of irrigation system practices found that for some crops, producers were under-irrigating and could improve production by increasing the amount of water applied (Ted van der Gulik, personal communication; Irrigation Water Management Study Committee, 2002). Continued improvements in irrigation and conveyance efficiencies will free up some water for other uses.
Wireless and computer technologies might allow farmers to obtain required irrigation scheduling data directly from local weather stations. This technology can also be used to evaluate and monitor crop diseases that are climate based, reducing the amount of chemical pest control applications and the exposure window of water supplies to chemicals. Additional weather stations are required in agricultural areas. As well, GPS-type monitoring might be used for soil and crop moisture, similar to that being employed for fertilizer and pesticide applications. The challenge remains to have the technology adopted by the majority of crop producers in order that the efficiencies gained become fully realized, in the form of reduced water use and improved water quality on a watershed scale.
The cost of farming is also causing the agriculture industry to increase its use of water resources. Expensive farmland that was not irrigated before is being converted to produce higher value crops that often require irrigation to ensure that production levels can be maintained annually. As agriculture progresses toward crop, diversification and the planting of higher value crops it is likely that water demand will generally increase.
Increased water use is required for irrigation systems that now serve crop cooling and frost protection functions to ensure productivity and quality. Nutrient delivery to crops through irrigation systems, in an effort to improve nutrient management, may result in increased water use. In eastern Canada, not only will there be an expected increase in water demand as farmers move towards the planting of higher value horticultural crops, but also because of the fact that severe droughts have been experienced in the region over the past few years.
Wider need for potable water: Water for irrigation and washing of plant products that are eaten raw requires potable water quality, as does the adoption of improved quality assurance programs on dairy farms. Treatment costs which will be required as most surface water sources are not considered potable without some level of treatment, may be significant. The trend towards the increasing use of, as yet often poorly defined groundwater resources, will continue. Competition between agricultural and domestic users for potable water sources and the associated infrastructure required can be expected to increase.
Consumptive Use – Livestock
It is expected that the intensive livestock industry, driven by provincial policy targets to increase livestock production, will continue to grow in some regions of Canada (Agriculture and Agri-Food Canada, 1998). This may be limited because of the increased competition for water, or constraints to land and water quality presented by manure management.
Awareness is increasing as to the potential impact that drainage systems have on soil moisture relationships, and on both surface and ground water volumes and quality. Drainage system design will increasingly take these factors into account.
Agriculture and Climate Change
Effect of climate variability on agriculture and water demand: Issues of climate variability and climate change are expected to have significant effects on agricultural practices, which in turn will affect water demand and availability. Climate variability is encouraging an increase in the adoption of irrigation to ensure higher yields and to compensate for drought stresses. For example, contracts for potato production in Manitoba require the availability of irrigation water in times of drought. Irrigation use for frost protection is increasing as is misting to cool crops.
It is generally recognized that climate change has the potential to have the greatest impact on the Prairies and in central B.C. Changes reflected in the hydrographs of snowmelt streams in response to recent climate variability (which may affect the timing of water availability), have already been documented (Leith and Whitfield, 1998; Whitfield, 2001). In addition, glacial melt-water flows, which contribute significant volumes of water to rivers such as the Bow (Alberta) and Columbia (B.C.) during the summer months, will cease to exist as key glaciers disappear within the next 50 to 60 years. This will have significant impacts (10% of flow) on water availability for irrigation and instream flows for the protection of aquatic life. Additional storage may therefore be required on these rivers in order to meet all water demands and pressure to use more groundwater can be expected.
Climate change is expected to result in increased average temperatures across Canada. For example, based on climate change modelling, projections indicate a 37% increased demand for irrigation water in the Okanagan Valley, B.C., which may exceed availability in irrigation districts dependent on tributary streamflow (Neilsen et al., 2001). In addition, the area where crops require irrigation may increase northward in the Prairies, and east to Ontario, Quebec and the Atlantic Provinces.
Effect of agriculture on climate change: Agriculture may contribute to climate change largely because of the release of the key greenhouse gases methane and nitrous oxide, and ways are being sought to reduce their production (e.g., carbon sequestration, improved fertilizer application).
Knowledge and data needs relating to threats to freshwater availability, both to, as well as from, agriculture and its land use practices, have been grouped into four main categories as follows.
Understanding Water Balances
Agriculture not only consumes water, but irrigation and drainage practices also contribute to the recharge of groundwater aquifers and the generation of runoff to surface waters. A better understanding of agricultural needs for water and the balance between its water demands and returns to the ecosystem is needed. There is good knowledge on water use for many crops grown in Canada. However, in irrigated systems, much of this knowledge is based on outdated assumptions related to irrigation technologies of the past. There is a general need to better understand:
- the potential for using less water: including the development of more drought-tolerant crops, and the use of lower moisture-use crops and management practices to optimize crop production, particularly during times of water shortage
- water use requirements of specialty crops: for many of the high value and niche market species being introduced to Canadian agriculture and horticulture
- regional water uses: including knowledge of the volumes of water withdrawn, used for irrigation and returned (e.g., this information is quite good in Alberta, but is generally lacking in other areas)
- agriculture and wetlands relationships: including the effect of agricultural water use and drainage on wetlands and riparian areas, and the base streamflows necessary to protect aquatic life
- land management effects: on the soil water balance and partitioning of precipitation, and how this influences water availability for all users, at scales ranging from the field to a region, and
- potential climate impact: including variable weather and climate change, on agricultural water needs and the availability of water, as well as the effect of land management on the water-related consequences of climate variability.
There is also a need to:
- establish and maintain monitoring networks: to identify long-term trends in water harvesting, use, and quality under different land management practices
- document groundwater supplies: to understand their extent, availability and quality. While this natural resource is often poorly understood, it is widely believed that the quality of surface and ground water may be deteriorating in agricultural areas (pesticides, nutrients and pathogens), and
- enhance local weather forecasting (Mesonet scale): with increased station density nationally, to optimize water use and support climate monitoring and prediction in agricultural areas.
Clarifying Institutional Frameworks
We need an improved understanding of the proper role of institutions in the allocation and protection of water resources used by agriculture. This includes a requirement for clear policies on water allocation, particularly during times of water shortage and between competing uses.
Employing Integrated Strategies
Effective progress requires the adoption of integrated planning and adaptive techniques to reduce agricultural threats to water availability. These should include:
- a watershed approach: incorporating appropriate agricultural practices into integrated watershed management plans to account for numerous water use activities
- water reuse: promoting water reuse where practical, including urban wastewater use by agriculture, such as from the canning and processing industries
- enhanced decision making: developing decision support and information systems, to improve water use efficiency and increase understanding of groundwater availability and vulnerability to agricultural practices, and
- adaptation strategy: incorporating processes to reduce the impact of climate variability on the need for water.
Sustained Agricultural Productivity
More intensive use of land for agricultural production, including increased areas under irrigation will continue in Canada. To deal effectively with existing and emerging water availability issues, specific actions in the following three generalized areas will clearly be required:
- targeted monitoring: investment in targeted monitoring is required to determine trends, assess limitations, and conduct ecological impact assessments of the effects of agricultural practices on water availability
- research: continued research to ensure that the best knowledge and technologies are available for land and water management with emphasis on reduced crop water needs and improved water use efficiency; understanding the effect of land management practices on water availability, runoff/leaching characteristics and water quality and wetlands relationships; and exploring opportunities for water reuse and improved drought-adaptive strategies, and
- develop standards and codes of practice: the development and adoption of scientifically credible practices and standards and codes for agricultural enterprises is required to ensure protection of surface and ground water availability.
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