AGRICULTURAL LAND-USE PRACTICES AND NITRATE CONTAMINATION IN THE ABBOTSFORD AQUIFER, BRITISH-COLUMBIA, CANADA

Spatial and temporal variation of nitrate contamination was assessed i n a study area within the Canadian portion of the Abbotsford/Sumas Aqu ifer that covers an area of 100 km(2). Elevated nitrate concentrations were observed over a wide portion of the aquifer. Only minor decrease s in nitrate concentrations were measured with depths up to 20 m below the water table. The results are consistent with a wide-spread, non-p oint source of contamination. The spatial distribution of high nitrate concentrations appeared to correlate with agricultural land use patte rns. A nitrogen budget calculation was performed based on nitrogen add itions and losses to the root zone of the agricultural land in a study area located over the aquifer, using 1971, 1981 and 1991 census data. Nitrogen additions exceeded N removals by 134, 185, and 245 kg N ha(- 1) in 1971, 1981, and 1991, respectively, indicating a high potential for nitrate leaching to occur. The increase in the nitrogen surplus wa s primarily the result of changes in land use. In particular, the agri cultural land base decreased by almost 20%, and there was a shift from animal production systems which require a local land base for crop pr oduction and grazing to animal production where the feed is imported. The N balance calculations were internally consistent with N budgets c onstructed for individual agricultural operations over the aquifer, an d confirm that agricultural production is a primary contributor to ele vated nitrate concentrations in the aquifer. The results highlight the potential for intensification of animal production, and the de-coupli ng of animal and crop production, to affect ground water quality. (C) 1998 The Department of Agriculture and Agri-Food. Published by Elsevie r Science B.V. All rights reserved.