Loss of soil and PM10 from agricultural fields associated with high winds on the Columbia Plateau

Winter wheat-summer fallow is the conventional cropping system employed on >1.5 million ha within the Columbia Plateau of eastern Washington and northern Oregon. Wind erosion contributes to poor air quality in the region, yet little is known concerning the magnitude of soil and PM10 (particulate matter of≤10 μm in aerodynamic diameter) loss from agricultural lands. Therefore, loss of soil and PM10 was assessed from a silt loam in eastern Washington during 2003 and 2004. Field sites were maintained in fallow using conventional tillage practices in 2003 (9 ha field) and 2004 (16 ha field) and instrumented to assess horizontal soil flux and PM10 concentrations at the windward and leeward positions in the field during high-wind events. Soil flux was measured using creep and airborne sediment collectors while PM10 concentrations were measured using high-volume PM10 samplers. Aggregate size distribution of parent soil and eroded sediment was characterized by rotary and sonic sieving. Six high-wind events occurred over the two year period, with soil loss ranging from 43 kg ha^-1 for the 12-22 September 2003 event to 2320 kg ha^-1 for the 27-29 October 2003 event. Suspension-sized particulates (<100 μ in diameter) comprised ≥90 per cent of the eroded sediment, indicating that direct suspension may be an important process by which the silt loam eroded. The corresponding loss of PM10 for these two events ranged from 5 to 210 kg ha^-1. Loss of PM10 comprised 9-12 per cent of the total soil loss for the six events. This study suggests that the relatively small loss of PM10 from eroding agricultural fields maintained in summer fallow can affect air quality in the Columbia Plateau. Therefore, alternative tillage practices or cropping systems are needed for minimizing PM10 emissions and improving air quality in the region.