The impact of agricultural land uses on water and sediment quality in the Agassiz/Harrison Hot Springs watershed, B.C..
Creators: name: Addah, Jody
Publisher: name: University of British Columbia
Year: 2009

description: Non-point source pollution is a significant threat to surface water quality, particularly from agricultural land uses. The Agassiz / Harrison Hot Springs watershed, which contains various pesticide and manure intensive land uses, was studied in order to determine correlations between land use types and water quality. The technique of correlating water quality with land uses has been well documented in the literature. With the development of computer software applications such as Geographical Information Systems (GIS), spatial analysis of land uses combined with the incorporation of water quality has become more practical. Two techniques were applied to determine the impact of agricultural land uses on water quality. The first, examined land uses within a 100 m buffer around major water courses. This method assumes that land uses adjacent to watercourses are the most relevant to water quality. The second technique divided land into contributing areas and assumes that all land uses within a sub-watershed, regardless of distance from the watercourse, impact water quality. Correlations at each sampling station were determined between various water quality parameters and the total area of different land uses upstream from the sampling point. A wide variety of water quality parameters were examined, including nitrate, nitrite, ammonia, orthophosphate, pH, specific conductivity, dissolved oxygen and chlorophyll a concentrations. Sediment quality was also taken into consideration through the measurement of copper, lead, zinc, manganese, and iron in the &lt;0.063 fim clay/silt fraction. Other sediment characteristics such as loss on ignition and grain size distribution were also examined. Whenever possible, these parameters were compared to provincial water quality guidelines in order to determine the overall state of the watercourses within the watershed. Water quality parameters were combined with a bioassay experiment using the moss Fontinalis antipyretica. Moss stems were placed within mesh bags at select locations within the watershed. Indicators examined were shoot growth, and concentrations of chlorophyll a and chlorophyll b in each stem. Except for significant differences in shoot growth between stations H4 and H2 (Hogg Slough), the variability of the results was not significant enough to confirm differences in water quality. This is likely because variable environmental conditions between sampling stations made it difficult for the bioassay to determine subtle differences in water quality. As a result, it was concluded that the use of Fontinalis antipyretica is not feasible as a bioassay in small agricultural watercourses. Another technique utilized to determine water quality was X A D resin adsorption of the pesticide atrazine, which is the primary pesticide used on surrounding corn fields. Bench scale results of the technique showed that recovery of atrazine was affected by pH and the presence of organic matter. Results from the field showed significantly lower recoveries. No significant correlation between corn area and recoverable atrazine could be determined, likely due to variability of site conditions and contamination due to windblown transport of atrazine applied in neighbouring fields. Use of the buffer technique to determine land use/water quality correlations was found to be a more effective method than examining contributing areas. Overall the buffer technique gave stronger correlations to known agricultural impacts to water quality. It was found that grazing pastures within the Agassiz / Harrison Hot Springs watershed had the greatest impact on water quality, resulting in higher nutrient concentrations in water and increased zinc concentrations in sediments. These impacts are thought to come directly from manure which has been stored or spread onto surrounding fields. Corn and hay/silage fields did not appear to correlate with any particular degradation of water quality, although certain sites appeared to be impacted due to manure application on these surrounding land uses. The primary areas of degradation within the Agassiz / Harrison Hot Springs watershed are Agassiz Slough and Hogg Slough. Degradation within Agassiz Slough is directly connected with the presence of stormwater outfalls along the watercourse. Along with elevated concentrations of nutrients, there were concentrations of copper above the severe effect level and high levels of zinc and lead present in the sediments outside of the sewer outfall sampling station. Similarly, Hogg Slough had elevated concentrations of nutrients combined with high concentrations of zinc in the sediments. However, the source of degradation in Hogg Slough is primarily manure runoff from surrounding pastures and manure storage. Specific sites of degradation also included station D5 (McCallum Slough), C3 (Miami Creek), and 13 (Clarke Ditch). Levels of nitrite, dissolved oxygen, pH and iron were outside of accepted water quality guidelines at some stations. Iron and pH, however were assumed to be the result of background concentrations.