Recharge rate estimation with environmental tracers in semi-arid environment
Ward, Bret Nathan
Determining the impact of agricultural practices on water quality is an area of study that is important to Saskatchewan. Many of the province's groundwater reservoirs are found in productive agricultural areas and are recharged by water that has been distributed over this area. New cropping systems require increased nitrogen fertilizer inputs, and hog manure is one way of acquiring the additional nitrogen. The application of manure as a fertilizer has resulted in increased public concern regarding potential groundwater contamination. In an effort to address these concerns a study has been conducted on lands receiving hog manure. A landscape approach was used on three small watersheds to study local recharge characteristics. The watersheds are analyzed by landscape position (depression, toe, midslope, shoulder, and upper). Hog manure was applied for the first time to the watersheds in 1999. The objectives of the study were to determine deep leaching rates for the study area and their relationship to hill slope position. The method adapted to determine a deep drainage rate uses tritium as a water tracer. Tritium peaks (representing 1963 waters) occurred just beneath the active zones. The active zone, as defined by seasonal changes in soil moisture, extended to 1.1 m depth for upper slope positions and 1.4 m depth for lower slope positions. The tritium analysis indicates that recharge is between 0.0 and 18.7 mm yr-1 with no clear distinction between upper and lower slope positions. Stable isotopes of water indicated that vadose zone water beneath the active zone was composed of 27% and 81% winter precipitation for the upper and lower slope positions respectively. Nitrate peaks in the depressions were present below the depth of the tritium peaks. The upper and mid slope locations did not reveal a nitrate peak. Chloride peaks were present at the same depth as the tritium peaks for the lower slope positions. EC measurements indicate that the lower slope positions have been leached of soluble salts to below 8 m, whereas the upper slope positions were leached to between 0.5 and 1.5 m. Note:Pages 67, 68, 69, and 70 were not included in the original thesis.