Proceedings - Teaching and Learning Centre - Simon Fraser ...

Fraser River Action Plan 3rd Research Workshop
Agricultural Impact on Water Quality in the Sumas River Watershed
H. Schreier, C. Berka and K. Hall
Institute for Resources and Environment
University of British Columbia
The Sumas River basin contains some of the best agricultural land in Canada. The dairy and vegetable producers
remain the dominant agricultural force, but over the past five to ten years, hog and poultry operations have
undergone considerable intensification leading to an oversupply of manure. The combined nutrient application
(manure and fertilizers) on many fields is exceeding the crop demand and absorption capacity of the soils by 100
- 200 kg/ha/year. This is leading to pollution of the surface water resource. The water quality was monitored at
15 stations over a one-year period. Results showed elevated nitrate values in the late summer in Lonzo (alias
Marshall) Creek, which receives groundwater inputs from the Abbotsford Aquifer. In contrast, some streams
have been more affected by manure management and direct surface runoff during the early winter period of
October to December. Consistently low dissolved oxygen and elevated ammonia levels, both failing to meet the
criteria set by the province, were observed in the Arnold Slough and Central Canal area (see Figure 1).
A GIS resource database was created for the watershed, and land use changes were examined quantitatively
between 1954 and 1991 using large scale historic aerial photos. The latter source was also used to document the
introduction of new farms into the watershed since 1954. Similarly, changes in animal numbers between 1986
and 1991 were obtained from the agricultural census data. The results suggested that agricultural intensification,
including the expansion of hog and poultry operations, is largely responsible for the generation of excessive
nutrients. This is now the major non-point source of pollution for the stream system. A nitrogen mass balance
was used to determine excessive nutrient applications within each contributing area draining to a sampling
station, and the results were then related to water quality. Significant negative correlations were obtained
between excessive rates of nitrogen loading to the land and dissolved oxygen levels in the stream. Positive
correlations were obtained between excess nitrogen loadings and ammonia levels in the stream during the winter
season. Animal stocking densities were calculated for each contributing area also. The densities in some areas
exceeded the standards used by several European countries to regulate manure application rates.
Nutrient production and application is clearly excessive in the watershed. The overall surplus nitrogen
application in the watershed typically ranged between 135 to 185 kg/ha/year. The effects of this surplus
application is most evident in the late fall/early winter period when plant uptake is minimal and there is heavier
rainfall. A number of steps need to be taken to reduce the generation of manure, the applications of N, P and K,
and to protect the stream. Manure processing, best management practices, better storage of manure and timing of
its application, reduction of fertilizer use, and development of buffer zones are all positive measures that can
reduce the impact of agricultural non-point source pollution on the stream ecosystem.
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