| | Salinity on the prairies | Saline seep mechanism | Salinity mapping in Alberta | Applications | Salinity classification | Salinity control and management | References
Salinity mapping assists agencies in:
- targeting salinity control activities
- focusing on the areas with the best opportunity for cost-effective control
- creating a database with saline areas specified by the legal land location
- generating the colour-coded salinity maps from the database
- calculating the areas affected by each salinity type
- applications at the provincial and farm levels
- creating regional and provincial salinity maps and database
- monitoring changes in salinity from provincial to farm level
- targeting provincial soil salinity control programs
Salinity on the Prairies
Dryland salinity is a major soil degradation problem on the Canadian Prairies (Acton, 1995). In Alberta, approximately 1.6 million acres (or 647 485 ha) of dryland are affected by secondary salinity with an average crop yield reduction of 25 per cent (Alberta Agriculture, 1991). The problem is caused by groundwater redistributing salts and accumulating these at the surface. The problem is present in the other provinces and states within the northwestern Great Plains region. The extent and severity of the dryland saline seep problem is increasing, in particular after a few wet years.
Many studies have been done to estimate the extent of salinity in western Canada. The exact area affected is difficult to establish because of the large extent of the problem and the ability of salts to move up to the surface and back into the soil profile.
Over the years researchers tried to find a way to record the type, extend, severity or controls methods; however, the methods differed and most of the time only produced estimates.
Alberta - 647 485 ha (1.6 million ac)
Saskatchewan - 1.3 million ha (3.3 million ac)
Manitoba - 243 000 (0.6 million ac)
A procedure for salinity mapping developed by AAFRD, Conservation and Development Branch, assists municipalities in targeting salinity control activities. The mapping also focuses on those areas with the best opportunities for cost-effective control. For each mapped municipality, a database is created with saline areas specified by the legal land location. The colour-coded salinity maps are generated from the database. The database calculates the area affected by each salinity type.
Saline Seep Mechanism
Generalized saline mechanism
The development of saline soils is related to the flow of groundwater (see figure). Groundwater is the water in the soil and underlying strata. Under saturated flow conditions, when the moisture content is at or above field capacity, groundwater is able to move under the influence of gravity. In saturated flow systems, excess groundwater builds up in a recharge area to the point where lateral groundwater flow occur. As the groundwater flows between particles of rock and soil, it dissolves and transports soluble salts. The groundwater emerges at the soil surface in a discharge area. When the water evaporates, the salts are left behind on the soil surface. Over time, the salts accumulate in the discharge area, and eventually the salt concentration becomes so high that plant growth is restricted.
Groundwater can also move under unsaturated conditions through the smaller soil pores by the process of adhesion (Stolte et al. 1994). That is, when soil moisture content is close to field capacity, soil particles will yield water molecules to other soil particles with lower moisture levels. Unsaturated flow is common around sloughs, dugouts and other water bodies. Like saturated flow, it can dissolve and transports salts to the soil surface.
For saline soils to form, the water table needs to come close enough to the soil surface to allow capillary (wick) action to raise the groundwater to the soil surface. In general, the water must be within 2 m (6 ft) of the soil surface for this occur, but the critical depth ( the depth beyond which water cannot wick to the soil surface) varies with soil texture (Henry et al. 1987).
Saturated groundwater flow systems may be local, intermediate or regional (Toth 1963; Kwiatkowski et al. 1994). In a local flow system, the recharge area is usually within a few hundred meters of the discharge area. An intermediate system consists of several interconnected local systems, and extends beyond 1 km (0.6 miles). A regional system has its recharge area at the water divide of a basin while the discharge area lies at the bottom of the basin. Regional systems may extend over several kilometers.
Salinity Mapping in Alberta
The purpose of classifying and mapping salinity is to identify various types and extent to quantify the issue and move toward recommended management practices. The maps provide an excellent extension tool to local agents and let farmers know the extent of salinity issues beyond their property. Analyses of the data allow policy makers to design and target programs specific to the extent and the nature of the problem.
In Alberta, an initiative existed in the 1990s to map the surface (visible) salinity in cooperation with counties. 22 counties (and Special Areas) were mapped. Data sources for the map included: aerial photos, extensive field checking, ground water and assessment records. Data from the municipal level mapping activity will be combined in a larger and comprehensive research salinity database. This will serve both the research and agricultural community.
Reports and maps were produced on a county basis. Limited hard copies are still available from the Conservation and Development Branch. With the popularity of Internet the reports have been produced as electronic PDF files that can be downloaded. Likewise, the county salinity maps can be downloaded as a PDF file.
Remember the scale of the maps produced was 1:100,000 which is the scale of most county maps. Even though computers allow one to enlarge the image the scale of the original map should not be forgotten. Salinity patches may occur beyond the original map polygons but were not mapped due to the intended final scale.
Click here to go to a complete listing of the counties with salinity maps and reports.
Applications
The salinity databases have a number of applications. Most importantly, the municipality can use the information to target its salinity control programs. Because the information is in digital format, it is simple to calculate statistics on the areas affected by the different salinity types. These statistics allow the municipality to focus on those saline areas which can be easily controlled with low-cost methods.
For example, the County of Wheatland, typical of the many municipal districts in Southern and Central Alberta with salinity problems, has 4 026 saline seeps which occupy a total of 23 494 ac (9 508 ha). The seep sizes vary from about 170 m2 to 314 ha (775 ac). Most of the seeps (73%) are smaller than 2.0 ha (4.94 ac). The average size of contact saline seeps is 1.60 ha (3.96 ac), of depression bottom seeps, 3.39 ha (8.38 ac), and of coulee bottom seeps, 9.1 ha (22.5 ac). Depression bottom salinity is the most common type (26.0% of the total saline area), followed by coulee bottom salinity (23.5%), contact/slope change salinity (15.3%), slough ring salinity (3.7%), outcrop salinity (2.0%), and artesian salinity (0.5%).
Salinity database can also be used by district staff to provide salinity control recommendations to farmers and ranchers.
The data can also be used for monitoring the impact of natural and farm management factors on the extent of visible salinity. This would allow municipalities to assess the effectiveness of current salinity control programs.
Salinity Classification
Based on hydrogeology, surface water flow, geology, topography, and soils, eight types of salinity are recognized within the Province of Alberta. This classification system is helpful in salinity control programs because the cause of the salinity determines which control practice is appropriate.
Dryland salinity types
Irrigation salinity types
Salinity Control and Management
Cost-effective agricultural practices are used to help prevent and control saline seeps. Specifically, cropping systems that intercept excess soil water in a recharge area before it is able to move below the root zone.
Recommended management systems for the types of salinity found in Alberta are as followed:
Salinity types and management systems in Alberta
Salinity Type | Control |
| contact/slope change salinity | - salt-tolerant grasses in saline area and alfalfa in upslope recharge area recharge area may be about three times area of seep) |
| outcrop salinity | - salt-tolerant grasses in saline area |
| artesian salinity | - salt-tolerant grasses in saline area
- relief wells connected to suitable outlets |
| depression bottom salinity | - salt-tolerant grasses in saline area and along edge of depression in band 50 to 150 m (165 to 490 ft) wide |
| coulee bottom salinity | - salt-tolerant grasses in saline area
- appropriate water management |
| slough ring salinity | - deep-rooted and salt-tolerant grasses in a 20 to 60 m (65 to 195 ft) band around slough
- appropriate water management |
| irrigation canal seepage salinity | - appropriate water management to prevent canal seepage (canal lining, cut-off curtains) and/or subsurface drainage area |
| natural/irrigation salinity | - appropriate water management for irrigation related salinity
- salt-tolerant grasses for natural salinity |
References
Acton, D.F. and Gregorich, L.J. (editors). 1995. The health of our soils. Centre for Land and Biological Resource Research, Research Branch. Agriculture and Agri-Food Canada.
Brown, P.L., Halvorson, A.D., Siddoway, F.H., Mayland, H.F., and Miller, M.R. 1982. Saline seep diagnosis, control, and reclamation. United States Department of Agriculture. Conservation Research Report No. 30. 22 pp.
Alberta Agriculture. 1991. Dryland Saline Seep Control. Agdex 518-11. Alberta Agriculture and Agriculture Canada. 12 pp.
Hendry, M.J., Cherry, J.A., and Wallick, E.I. 1986. Origin and distribution of sulfate and fractured till in Southern Alberta, Canada. Water Resources Research, Vol. 22, No.1, Pages 45-61, January 1986.
Henry, L., Harron, B., and Flaten, D. 1987. The nature and management of salt-affected land in Saskatchewan. Saskatchewan Agriculture. Agdex 518. 23 pp.
Kwiatkowski, J., Marciak, L.C, Wentz, D., and King, C. 1995. Salinity mapping for resource management within the County of Wheatland, Alberta. Alberta Agriculture, Food and Rural Development and Agriculture and Agri-Food Canada. Edmonton.
VanderPluym, H. 1982. Salinity in western Canada. Pages 9-23 in First Annual Western Provincial Conference of Water and Soil Research and Management, Soil Salinity. Lethbridge.
Page developed by Jan Kwiatkowski.
For more information contact Tom Goddard |
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