|Van Biersel, Thomas|
Submitted to: United States Geological Survey Hydrology of Washington State
Publication Type: Abstract Only
Publication Acceptance Date: 9/1/2000
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: The goal of this project is to determine the contributions of subsurface and surface runoff at the field-scale and to use these to understand basin-scale loading to aquifers and rivers. The study looks at the migration of triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate] and other environmental tracers (NO3, O18 and Si) through hydrologic pathways under a semi-arid dryland agricultural setting near Pullman, WA. This paper will report on the results of triallate sample collection from an array of capillary wick lysimeters located at the hydrologic outlet of a topographically-confined and actively farmed field. Triallate is the active ingredient in FarGor herbicide (Monsanto), which was incorporated in the soil in the fall 1999 in a granular form. The triallate concentration in surface water was >20 g/L in early fall and declined steadily through the winter and spring (3 g/L in April) until the ephemeral stream ceased to flow. Triallate was detected in pore water from lysimeters at all three depths sampled. The irregular concentration patterns suggest that preferential flow pathways were active and contributed to transport. Peak triallate concentrations can be observed after the first ground thaw and directly after no-till wheat planting. Triallate was present in the surface runoff and shallow (18 cm deep) lysimeters at concentrations above a surface water quality standard.