|Van Biersal, T|
Submitted to: Annual Goldschmidt Conference
Publication Type: Abstract Only
Publication Acceptance Date: 2/16/2001
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: The goal of this project is to observe and quantify the contributions of subsurface and surface patterns of agricultural chemical loss at the field-scale and to use these to understand basin-scale loading to aquifers and rivers. The initial project phase, presented here, analyzed triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate], nitrate and environmental tracer concentrations (18O and SiO2) in surface runoff and soil solution for a single, topographically-constrained agricultural field (7.5 ha). A multiple tracer approach was applied to discern temporally varying chemical transport pathways within the semi-arid dryland agricultural watershed near Pullman, WA. Detections of triallate were sporadic and occurred in lysimeters from all three sampled depths during December and January [18, 84 and 112-cm below ground surface (bgs)] (Fig. 1a). Following the early spring ground thaw at the beginning of February, consistently low triallate concentrations (<~0.01 ?g/L) were observed in middle and deep lysimeter water while elevated concentrations (~0.1-1.0 ?g/L) occurred in pore water from shallow lysimeters (exceeding the Canadian water quality standard of 0.2 ?g/L). The pattern of pore water triallate occurrence suggests a change from non-equilibrium preferential vertical transport (before February) to saturated, predominantly horizontal transport along soil horizons.