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Surface water contamination
Most Albertans drink treated surface water from rivers, streams, lakes or dugouts. Freshwater aquatic life depends on good quality surface water, and surface water is also used for irrigation.
Agriculture in general and irrigation in particular is the largest single use of surface water in the province. Farm acres on which pesticides and fertilizers are used have almost tripled in Alberta in the last 25 years, and cattle numbers increased by 25% between 1991 and 1996. The industry continues to grow.
The influence of this growing industry on surface water quality in Alberta was assessed by several studies conducted in the 1990s. The results indicate that agricultural practices are contributing to the degradation of surface water quality, and the potential for impacts increases as agricultural intensity increases.
Alberta farmers recognize the importance of clean water to their families and their businesses. They look for sound information to maintain the competitive advantage given by our relatively clean and abundant surface water supplies. They also know remediation of water quality problems is difficult and expensive.
Contaminant pathways
Contaminants can enter surface water in dissolved form and as particulates attached to sediment. Transport paths include runoff, return flow channels and subsurface drain effluent.
Runoff is water that runs across the surface of the land during snowmelt and heavy rains, on top of frozen, compacted or saturated soil, or moving laterally just below the soil surface. Most runoff in southern Alberta occurs during the spring.
Return flow channels carry runoff, unused irrigation water and subsurface drain effluent back to rivers. About 40% of total flow in the Bow River is from return flows. The Bow’s largest return flow is Crowfoot Creek. Return flows account for 20% of flow in the Oldman River. The largest return flows in the Oldman River are the Little Bow River and Expanse Coulee.
Groundwater discharge can also add significant amounts of contamination to surface water, especially where land is tile drained, or where natural groundwater discharge accounts for a significant portion of the surface supply.
Nutrients and bacteria
Sewage, fertilizers and manure are the major sources of nitrogen, phosphorus and bacteria in Alberta surface waters. Table 1 summarizes nutrient and bacteria content in terms of the most sensitive water quality guidelines. The studies showed phosphorus and bacteria often exceeded water-quality guidelines. Nutrients and bacteria increased with distance along the Bow and Oldman Rivers, and with distance along irrigation canals and return flow channels. The Calgary and Lethbridge waste-water treatment plants are the largest single sources of nutrients and bacteria to the Bow and Oldman Rivers, respectively.
Runoff from intensive livestock operations, cattle wintering sites, summer-fallow, and fertilized and manured fields often contains high amounts of nutrients and bacteria. Bacteria and nutrients tend to be higher in return flows than in streams.
Phosphorus
Phosphorus is a common surface-water problem. Agriculture is the major contributor of phosphorus in most Alberta lakes. Excess phosphorus in surface water promotes eutrophication and excessive algal growth. The resulting decrease in oxygen can cause fish kills, and can make certain trace elements dissolve more easily. Surface water in Alberta is particularly prone to phosphorus contamination because many Alberta lakes, streams and rivers are naturally eutrophic. Natural background phosphorus levels in Alberta soils are higher than those in eastern North America.
The risk of phosphorus accumulation in surface water increases with the amount of excess phosphorus in the soil. Most farm fields, but particularly manured fields, are a source of excess phosphorus, especially during runoff events. Most crops require about ten times more phosphorus than the amount that can cause eutrophication in surface water. Manure application rates that meet crop nitrogen requirements will supply excess phosphorus.
Nitrogen
Nitrogen in surface water also contributes to eutrophication, but nitrogen is usually lower than phosphorus in surface water in Alberta.
Drinking water with high nitrate (dissolved nitrogen) has been linked to stomach cancer and negative reproductive outcomes in humans, and to lower productivity in livestock. Nitrate occurs in all Alberta surface waters, but at concentrations far lower than the guidelines for human and livestock drinking water and for irrigation. In contrast, nitrate levels in eastern Canada exceed drinking-water guidelines in some locations. Surface drains accessed by livestock tend to have high and erratic nitrate levels, which sometimes exceed guidelines for human drinking water, though not for livestock water.
Bacteria
Bacteria in water can cause respiratory, gastro-intestinal, eye, ear and skin problems. Fecal coliforms have traditionally been used to indicate bacterial contamination. However, some species occur naturally, so the measurement of bacteria is gradually being replaced by use of Enterococci and Esherichia coli (E. coli), which are definite indicators of the presence of fecal contamination from warm-blooded animal sources. Surface water in Alberta almost always contains some bacteria, so it should be boiled or treated before using. Guidelines for irrigation and contact recreation are sometimes exceeded. Fecal coliforms and other micro-organisms can generally survive in water for about 30 to 60 days.
Pesticides
Pesticides include herbicides, insecticides and fungicides used in cities and on farm fields. Pesticides that are highly soluble in water are usually the most prone to contaminate surface water, but pesticides that attach to sediment can enter surface water through wind and water erosion. Some pesticides are much more persistent in the environment than others. The greatest pesticide losses to surface water take place when rainfall or irrigation occurs soon after application.
Some of the most frequently detected pesticides in surface water in southern Alberta are listed in Table 2. Pesticides from both rural and urban sources were detected in 56% of the 941 surface-water samples collected throughout Alberta, and in 97% of samples from the Oldman River Basin. Pesticide levels, as indicated by both concentration and frequency of detection, increase downstream in rivers and canals, are higher in small streams than in rivers, and are usually the highest in return flows. Most pesticide detections were acceptable for humans, livestock and aquatic life, but dicamba and MCPA frequently exceeded irrigation guidelines.
The following considerations should be noted when assessing pesticide results:
- Guidelines do not exist for many pesticides.
- Alberta guidelines apply to water containing a single pesticide, but 37% of the surface water samples analyzed contained more than one pesticide.
- The frequency of detection increases significantly as analyses become more precise. Most analyses for the Western Irrigation District study were four times more accurate than for other studies shown in Table 2.
- Water often contains higher concentrations of pesticide breakdown products than of the applied compound, but most studies do not analyze for breakdown products.
- Current data suggest exposure to even low levels of pesticides can effect humans and aquatic life in ways not considered by current guidelines, including effects on endocrine, nervous and immune systems, particularly due to fetal exposure.
- Canadian guidelines often allow for higher pesticide concentrations than allowed by the European Commission.
- Pesticide concentrations vary substantially on a seasonal basis, so frequent sampling is often required to determine true levels.
The concentration and frequency of detection for most pesticides tends to increase as agricultural use of the pesticide increases. Pesticides were detected in 67%, 31% and 2% of Alberta streams draining land with high, medium and low pesticide use, respectively. Some pesticides are detected in basins where they are not applied. Pesticides are most commonly detected in the summer months, and pesticides can persist from one spring to the next. The frequency of detection also increases as the intensity of runoff increases.
The common detection of pesticides in Alberta surface water is consistent with results from elsewhere in the world. Although pesticide levels in surface water in Alberta are generally acceptable for aquatic life, more than half of samples from urban and agricultural streams in the United States exceed guidelines for aquatic life.
Trace elements
Plants and animals require low levels of trace elements, but at higher levels most trace elements are toxic. Natural sediment is by far the most important source of trace elements, although sewage, manure and fertilizer can also be sources. Some trace elements are not soluble, and are transported to surface water only with soil erosion. Other trace elements, such as arsenic and selenium, are highly soluble under certain conditions.
Most trace elements in rivers increase with distance downstream, mainly due to additions from industry, sewage effluent, and sediment in tributaries and return flows. Lead, copper, mercury, iron, aluminum and cadmium sometimes exceeded aquatic-life guidelines in studies of southern Alberta surface water, including the Bow and Oldman Rivers. Selenium, copper, arsenic, manganese and mercury are sometimes higher in return flow streams than in rivers.
The highest trace element concentrations occur in sloughs and lakes subject to evaporation, and in surface water that receives a significant amount of groundwater discharge or subsurface drain effluent.
Selenium is a common contaminant in closed drainage basins in irrigated areas of the western United States, because it is leached from bedrock that is naturally high in this element. Excess selenium in these areas is responsible for a high proportion of deaths and deformities in water fowl. Bedrock in southern Alberta is similar to that in the western United States, indicating selenium may be a potential contaminant here too. Selenium is not detected in most surface water in southern Alberta, but it sometimes exceeded aquatic life guidelines in return flow streams that are affected by manure and receive groundwater discharge or subsurface tile drain effluent. The combined selenium load from two such drains constituted up to 18% of the total selenium load in the Oldman River.
Salts
The majority of salts in water are derived from natural sources in sediment. They can be transported both in the dissolved form and with sediment. Excess salinity (total salt content) and sodicity (sodium) in irrigation water can decrease crop productivity. Salt guidelines for drinking water are mainly based on taste, although excess sodium can be a problem for people with heart disease.
Surface water in southern Alberta is generally low in salt. Salinity increases slightly with distance along rivers, and sodicity doubles between the beginning and end of both the Bow and the Oldman Rivers. However, no salinity or sodicity parameters exceeded guidelines for irrigation or drinking water in the Bow, Oldman or South Saskatchewan Rivers. Salt levels in rivers are highest in the fall, when flow volumes are lowest.
Sewage effluent is by far the largest point source of salt to the Bow and Oldman Rivers, but runoff from fertilized or manured fields and cattle feeding areas can also add salt to surface water. The highest salt loadings to surface water occur during spring runoff and heavy rainfalls. For example, spring runoff in the Western Irrigation District exceeded salt guidelines in about 25% of samples.
Salt levels in return flows are approximately double that in rivers. The percent of samples that exceeded irrigation guidelines in return flows are about 7% for salinity and 3% for sodicity. About 3% of return flow samples exceeded salinity guidelines for drinking water. The highest salt levels occur in return flows in areas with saline or sodic soils, and in areas where subsurface drain tiles discharge to surface water.
Return flows have a minimal impact on salt levels in the Bow and Oldman Rivers. Return flows with high salinity levels often have relatively low flow volumes, and therefore do not add significant amounts of salt to surface water. The total amount of salt in irrigation water tends to decrease with flow through irrigated land, indicating that salt is deposited on land with irrigation water. Salt levels in the Bow and Oldman Rivers and their return flow streams did not increase between 1967 and 1998.
What are we doing now?
Agricultural water quality studies in 2000 and beyond will focus on locations where surface water quality is being affected. Important goals will be to determine which land uses have the greatest potential to contaminate surface water, and to develop practices that minimize impacts on surface water, while maintaining a healthy agricultural industry.
An Irrigation Branch technologist takes a sample
for water quality analyses from an irrigation canal.
Water quality guidelines
Water quality guidelines recommend maximum limits for various substances and conditions which may be found in water supplies. These parameters include nutrients, pesticides, bacteria and pathogens, trace metals, salts, pH, suspended solids, temperature and turbidity.
Guidelines are suggested for specific uses of water, including human drinking water, contact recreational activities, the protection of freshwater aquatic life, irrigation, and livestock watering. Maximum allowable concentrations in the guidelines typically provide a protection factor of 10 to 100 times the identified safe limits.
In Canada, human drinking water guidelines are set by the federal government and apply to water used for all domestic purposes, including cooking, personal hygiene and laundry. They are based on current scientific knowledge of human health and assume life-long use of the water being tested. They also assume water for domestic supplies is properly treated.
Surface water quality guidelines for use in Alberta are set by the provincial government. A new set of guidelines issued in November 1999 focuses on agricultural, recreational and aesthetic objectives and on the protection of freshwater aquatic life.
The guidelines for livestock drinking water are based on regular use of the water supply for domestic animals, and on human health concerns related to the consumption of the livestock. The guidelines for water applied to irrigated crops are based on knowledge of crop reactions to regular use.
Recreational guidelines are based largely on the microbiological content of surface water bodies used for contact activities.
The guidelines for the protection of freshwater aquatic life are set to ensure the survival of plants and animals that live in or near surface water bodies and to sustain their natural aquatic ecosystems.
This fact sheet on the Agricultural Impacts on Groundwater Quality in the Irrigated Areas of Alberta is one of a series of information bulletins on agriculture and resource management produced by the Irrigation Branch, Alberta Agriculture and Food. For more information contact Rod Bennett of the Irrigation Branch, at (403) 381-5883 or use the Alberta Government Riteline, toll-free, at 310-0000.
The contents of this page are no longer available.
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