Recharge rate estimation with environmental tracers in semi-arid environment
Abstract
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.