|VAN BIERSEL, THOMAS|
Submitted to: Geological Society of America Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 9/1/2000
Publication Date: N/A
Technical Abstract: The goal of this project is to quantify the contributions of subsurface and surface runoff to the loading of non-point pollutants to rivers at multiple scales of study (field-to basin). The study looks at the migration of triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate], nitrate and environmental tracers (O18 and SiO20) through hydrologic pathways under a semi-arid dryland agricultural setting near Pullman, WA. Samples were collected at approximately 10-day intervals from an array of capillary wick lysimeters located in the subsurface and an ephemeral stream at the hydrologic outlet of the field. Triallate was incorporated in the soil in the fall 1999 in a granular form (0.73 kg per ha). Triallate was detected in pore water collected from the lysimeters at all three sampled depths [18, 84 and 112-cm below ground surface (bgs)]. The concentration in the shallow samples (18-cm bgs) exceeded the water quality standard of 0.2 ug/L. Pulses of triallate were detected at 84 and 112-cm bgs in pore water early in the winter (Dec-Jan). This pattern of occurrence suggests preferential transport to these depths was associated with precipitation events when the soil was wet and within a few months of application. At these depths, the triallate concentration diminished to consistently low or non-detectable during the late winter to spring. The triallate concentration in the ephemeral stream declined steadily from >20ug/L in December until the stream ceased to flow in April.