ARS | Publication request: FIELD SCALE TRACER AND PESTICIDE TRANSPORT THROUGH UNSATURATED CULTIVATED LOESS

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: September 1, 2000
Publication Date: N/A

Technical Abstract: The project seeks to quantify the contributions of subsurface and surface runoff to the loading of non-point pollutants to streams in a semi-arid watershed. The study looks at the migration of triallate and nitrate, in combination with environmental tracers (dissolved silica and electrical conductivity) through hydrologic pathways in a typical agricultural setting near Pullman, WA. The site is a 7.5 ha. topographically-defined field, actively farmed by the USDA under no-till conditions. Samples were collected at regular 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) and nitrate was applied in the Spring at a rate of 12.5 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 highest triallate concentrations were observed at the shallow depth following the late winter ground thaw and pulses of triallate were detected at 84 and 112-cm bgs in pore water early in the winter (Dec-Jan). The triallate concentration in the ephemeral stream declined steadily from >20ug/L in December until the stream ceased to flow in April. Nitrate concentrations were highest at shallow depth and lowest at deeper depth during the late winter ground thaw. Concentration of dissolved silica and electrical conductivity results show steadily increasing values during the Spring and Summer period. Environmental tracer and chemical patterns suggest that specific tillage and thawing events enhance fluxes and transport of pesticides and fertilizers in this setting.