Relationship between agricultural land use and surface water quality using a GIS: Sumas River Watershed, Abbotsford, B.C.
Creators: name: Berka, Caroline Svatava
Publisher: name: University of British Columbia
Year: 2009

description: The Sumas Prairie is one of the most intensively used agricultural floodplains in Canada. Dairy farmers are the traditional occupants of the floodplain, but the past 20 years have seen the development of turf and vegetable farms, and large hog, chicken and turkey operations. Nutrient management and related water contamination have been recognized as major issues over the past decade, but due to the non-point nature of the pollution it has been difficult to analyse the contributing sources and to mitigate the impacts. The Sumas River watershed was thus investigated as an illustration of how land use activity affects water quality with a focus on non-point source pollution from agriculture. A Geographic Information System (GIS) was used to integrate resource data for the watershed, which included surficial geology, soils, current and historic land use, agricultural intensification and population growth. River sediments and water quality were analysed in seasonal, spatial and historical contexts. GIS overlay techniques were used to summarize land use activities within the drainage areas to sampling points, or "contributing areas". Indices of land use activities were developed within the contributing areas and correlated to the water quality parameters to identify significant relationships. Examples of land use indices included nitrogen loadings over contributing areas and animal stocking densities. Zinc concentrations in river sediment were elevated from those measured twenty years ago and are attributed to agricultural sources while high chromium and nickel concentrations occur from natural sources. The nutrient concentrations and fecal coliform counts in stream water increased dramatically in the rainy season. Manure, particularly when spread in the wet season due to lack of winter storage, is likely entering the stream via runoff. Dissolved oxygen levels were low in this same period, and on a site specific basis year round. One tributary, Marshall Creek, was found to have elevated nitrate levels in the summer with the suspected source being contaminated groundwater from the neighbouring Abbotsford aquifer. Animal stocking densities and surplus nitrogen loadings were found to be high, as compared to values found in the literature. Significant relationships were identified between surplus nitrogen applied to farm land, amount of clay soil texture by area, and ammonia-N concentrations in the wet season. Similarly, these two land indices were negatively correlated with dissolved oxygen levels in both the wet and dry seasons. Nitrate-N concentrations were positively correlated to amount of clay and organic soils in the contributing area, but negatively correlated to the amount of sandy texture. The results indicate agricultural best management practices need to be more aggressively pursued in the watershed, with regard to amount of manure and time of application. Areas with higher nitrogen loadings coincided with areas of water quality degradation. Techniques developed in this research can be used to evaluate the impact of non-point source pollution from agriculture on stream water quality in a quantitative manner and provide watershed managers with a tool to address non-point source pollution. The densification of animals and farms on the floodplain, emergency responses due to frequent flooding, and the impact of contaminated groundwater on the stream, are issues that should be given renewed attention.