| | Why was this study conducted? | What did we learn? | More information
A provincial survey of 27 small streams in Alberta was conducted in 1995 and 1996, under the Canada-Alberta Environmentally Sustainable Agriculture (CAESA) Agreement. The survey's goal was to determine if there were relationships between the intensity of agricultural practices in natural drainage basins and the water quality of the streams which flow through them. The results showed that streams that drain high intensity agricultural land have more nutrients in the water than streams which drain moderate or low intensity land.
Why Was This Study Conducted?
Monitoring of Alberta's major rivers had been conducted prior to 1995, but little was known about the water quality of its smaller streams. The effects of agricultural practices on these streams was of particular interest.
For this two-year study, areas of high, moderate and low agricultural intensity were defined on the basis of fertilizer and chemical use, and livestock density. Using information from a variety of databases, 27 small streams in areas of different agricultural intensity, were scientifically selected for the survey.
Up to 20 water samples were collected from each of these streams throughout the growing seasons of 1995 and 1996. Samples were analysed for nutrients, suspended solids, bacterial content, and common pesticides.
What Did We Learn?
The results confirmed that the intensity of agriculture, as defined in this study, has a direct effect on nutrient concentrations, and to some extent, on bacteria counts and colour levels.
Nutrients
Guidelines for total nitrogen (TN) and total phosphorus (TP) were exceeded more frequently in streams draining high intensity areas than in streams draining moderate or low intensity agricultural lands. As well, the degree with which the samples exceeded the guidelines was greatest in the high intensity areas. None of the samples exceeded human drinking water guidelines for nitrate (10 mg/L). Nor did any of the samples exceed ammonia levels set under the guidelines for the protection of aquatic life.
Pesticides
Samples were analysed for 13 pesticides. Nine of these pesticides were detected in the survey streams. Pesticides were detected in 44% of the samples. Many samples had detections of more than one pesticide. Streams draining land with the highest rates of pesticide use, had the highest frequency and degree of detection. Runoff from fields also influenced the concentrations of pesticide detected.
Concentrations of the detected pesticides were generally well below guidelines for the protection of aquatic life or human drinking water. However, guidelines have not been set for many of the pesticides detected. Triallate, imazamethabenz, MCPA and 2,4-D were the most frequently detected compounds. Triallate and trifluralin were also detected in stream sediments.
In general, pesticide concentrations were directly related to their rate of application. However, detections were found in a few areas where there was little or no pesticide use. These detections are probably due to movement by wind of the pesticides from distant fields.
Though few of the survey streams are used for the irrigation of crops, it should be noted that guidelines for herbicide content of irrigation water were frequently exceeded. Use of these waters on cultivated fields could adversely affect crop yields.
Bacteria
Bacteria counts were conducted in only some of the survey streams. Non-compliant samples for fecal bacteria appeared in all the streams sampled. The proximity of livestock operations to the sampling locations, rather than the level of agricultural intensity, was the primary influence on the specific results. The small number of samples may also account for some of the variability found.
Sediments
Sediment levels were related more to runoff events and the hydrology of the stream basins than to the intensity of agricultural practices in the watershed.
Colour
All the surveyed streams, regardless of agricultural intensity, had a high frequency of non-compliance with water quality guidelines for the colour of the sample after suspended particles are removed. However, streams in high intensity areas exceeded guidelines for colour to a greater degree than other streams.
More Information
This fact sheet on the Provincial Stream Survey is one of a series of special information bulletins on agriculture and resource management produced by Alberta Agriculture, Food and Rural Development. The other factsheets are Assessing Alberta's Water Quality and Haynes Creek Watershed Study.
For more information on sustainable agriculture contact your regional conservation co-ordinator or your district office of Alberta Agriculture, Food and Rural Development. Or telephone the Alberta Government RiteLine, toll-free, at 310-0000. |
|