| The deposition of aeolian (windblown) dust is a global phenomenon with significant implications for terrestrial ecosystems. In particular, the geochemical flux of dust can be an important factor for biogeochemical cycling in soils and, in some settings, may influence ecosystem productivity and chemical weathering. To quantify the role of exogenous dust in soils, the flux and composition of dust must be compared with local soil forming factors. In general, the magnitude, particle size, and geochemical composition of dust vary regionally and are primarily dependent on the distance from dust source area. Each winter/spring the San Juan Mountains (SJM) receive a substantial flux of exogenous dust, which most likely originates form the arid Southwestern US. In comparison to the global range of dust deposition rates, the SJM experience intermediate levels of contemporary dust deposition, typically ranging from 5 to 10 g m -2 yr-1. The majority of particles deposited in are in the range of course to fine silts, but clays are also abundant. This dust is consistently enriched in Ca, P, Cd, Cu, Li, Pb, and Zn relative to the local geologic substrates. To quantify the accretion of dust to alpine soils in the SJM, I have exploited isotopic and geochemical differences between dust and the local bedrock. Specifically, I have used Sr isotopes as a tracer of dust to determine that dust accretion contributes up to 70% of particle mass in the <250 mum soil size-fraction and that long-term accretion rates could range from 8 to 25 g m-2 yr-1. In addition, I have applied these estimates of dust accretion to quantify the influence of aeolian dust on soil geochemical development and chemical weathering. The results of my work clearly show that dust inputs are an important factor in the formation of soils in the SJM and that the accumulation of dust has resulted in soil trace element enrichments. Overall, the long-term deposition of dust in the SJM region may have a homogenizing effect soil geochemical characteristics, resulting in surface soils that are less distinct than would be expected based on the diversity of local geologic substrates. Furthermore, I have found evidence that the large flux of exogenous dust may also represent an important control of soil chemical weathering. If true, this observation has implications for our interpretations of the long-term interactions between erosion, weathering, and climate. |
