THE ROLE OF DUST DEPOSITION IN DRYLAND SOILS (Invited Presentation)

The importance of dust deposition in the biogeochemical cycling of nutrients, sediment redistribution, and soil formation is well-known. Anthropogenic activities can influence dust flux deposition rates, dust organic matter content, and the chemical composition of dust. We investigate seasonal and spatial variations in dust deposition rates, dust organic matter, dust inorganic matter, and dust geochemistry from passive dust traps. The Reynolds Creek Experimental Watershed (RCEW) and the Northwest Irrigation and Soils Research Lab (Snake River Plain, Idaho) are considered non-agricultural and agricultural sites respectively. Our results show high variability in monthly and annual aeolian mass flux. Notably, the annual dust flux at the agricultural site (50.2 g/m2/year) is 7.6 times higher than the annual dust flux rate at the non-agricultural site (6.6 g/m2/year). We compare measured loess accumulation rates with loess accumulation on millennial timescales inferred from loess thickness and loess ages from Optically Stimulated Luminescence (OSL). Based on the annual dust flux measured in this study, the dust accumulation rates for soils in the Snake River Plain are 4 cm ka-1. OSL ages between 50.14± 9.19 ka to 8.32 ± 1.88 ka from the Snake River Plain site indicate average accumulation rates from ~ 50 ka to 34 ka and ~ 34 ka to 18 ka are 6 ± 4 cm ka-1 and 6 ± 3 cm ka-1 respectively. However, dust accumulation rates increase to 17 ± 4 cm ka-1 in the interval between 18 ka to 8 ka. We infer that increased rates of deposition may reflect increased sediment availability following the ~18 ka Bonneville Flood on the ancestral Snake River. Over the last 8,000 years, the rate decreased to 7 ± 2 cm ka-1.

Dust organic matter analysis indicates a relatively high percentage of organic matter in dust. While aeolian deposits in both agricultural and non-agricultural areas show organic matter content of around 18 g/m2/year (~26%) and 4 g/m2/year (~38%), respectively, the soil in both locations exhibits a low organic matter percentage of 1.3% and 1.8%. Geochemical analysis shows the concentration of most elements is generally lower than the average upper continental crust concentration for both study areas; however, dust deposition is enriched in some trace elements such as Co, Cd, and Zn at both the agricultural and non-agricultural sites.