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Cumulative effects of agricultural intensification on nutrient and trace metal pollution in the Sumas River watershed, Abbotsford, B.C. Smith, Ione Marie

Abstract

The Sumas River transboundary watershed is characterized by an asbestos landslide in a headwater tributary and intensive hog and poultry operations in the flat Sumas Prairie floodplain. The quality of water and sediment in the Sumas River watershed is important from the point of view of fish habitat and recreation. A recent intensification of agricultural activities has renewed concerns about environmental impacts in the region, notably with regard to non-point source pollution. This study used land use indicators such as livestock density, nitrogen application surpluses, and crop cover along with the analysis of water and sediment samples to investigate cumulative effects of agricultural intensification on an aquatic ecosystem. Long-term trends were explored using historical data to track changes over time. Water quality results indicated that nitrate levels have significantly increased during the wet season since 1993 in the Sumas River and in tributaries that are surrounded by intensive agricultural operations. Marshall Creek, which is influenced by the Abbotsford Aquifer, has experienced significant increases in nitrate during the dry season since 1993. Levels of ammonium have risen above provincial water quality guidelines for aquatic health in the Sumas Canal. Tributaries throughout the watershed were often eutrophic during summer months, with algal blooms observed at several sites. Trace metals associated with agricultural operations (Cu, Fe, Mn, and Zn) and the asbestos landslide (Ni, Cr, Co, Mg) were investigated by measuring the dissolved, bioavailable (using the diffusive gradient thin film technique (DGT)), and sedimentbound metal fractions. DGT results indicated that bioavailable Zn levels were consistently highest in Marshall Creek. Spatially, sediment concentrations of Cu, Fe, and Zn increased in the downstream direction of the Sumas River. Temporally, severa sediment bound elements (Cu, K, P, and Zn) have significantly increased in tributaries associated with intensive agricultural operations since 1993. Livestock density was significantly correlated to higher levels of nutrients and trace metals in water and sediment. Nitrate was also significantly correlated to nitrogen surplus applications, the percent clay content within sediment, and the amount of corn and pasture crops cultivated adjacent to the sampling sites. The results indicate that more effective manure management practices are needed in order to stabilize water and sediment quality within the watershed. Substantial improvements in manure storage infrastructure, increases in manure exports, or a limit on livestock density may be required to remediate water and sediment quality. The current environmental state of the Sumas River watershed warrants renewed attention from private landowners and all levels of government.

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