Long-Term Patterns of Dust Deposition in High-Elevation Ecosystems Downwind of Aridic Dust Sources: The Influence of Dust Accumulation on Terrestrial and Aquatic Biogeochemistry

Recent evidence from the San Juan Mountains in southwestern Colorado suggests the accumulation of eolian dust has increased 5-7 fold over historical levels during the past two centuries. This increase in dust accumulation is evident from changes in lake sediment accumulation rates as well as the Nd and Sr isotopic composition of sediments. Soils from the San Juan Range also exhibit indications that dust deposition has been an important process during soil formation; including the accumulation of dust-derived elements in surface soils. Based on the chemical composition of contemporary dust deposited in the San Juans, the legacy of dust inputs represent a substantial increase in the flux of ecologically essential elements as well as several trace metals. The increases in dust deposition has resulted in >400% increases in Al, Ba, Be, Ca, Cd, Co, Cr, Cs, Cu loading and >400% increases in Mn, Mo, and K loading. P and N sedimentation rates also increase by >500% in the modern period alongside apparent changes in lake productivity and organic matter deposition. These inputs have implications for both aquatic and terrestrial alkalinity, productivity, and nutrient cycling of the San Juan Mountains. The observed increases in dust accumulation rates recorded in lake sediments are coincident with the expansion of settlement throughout the American Southwest, suggesting the importance of regional scale land use changes for dust processes.