Human-caused increases in dust deposition in a western US mountain range

The arid landscapes of the Southwestern US have changed dramatically over the past two hundred years.  Intensive grazing, recreation and urbanization have impacted much of the Western US and increased the potential wind erosion of soils. Despite this potential change, there are very few records of anthropogenic vs. natural variation in dust deposition.  To develop such a record, we cored a series of relatively undisturbed alpine tarns in the San Juan Mountains of Colorado.   The sedimentation records from these tarns combined with Sr and Nd isotopic analysis of sediments indicate that dust deposition has increased 5-7 fold over historical rates during the past 100-300 years.  The records of sediment loading, which cover ~ 5000 years indicate that, despite widespread and severe droughts over the past 2000 years, dust deposition is now at its historical peak.  This apparent human-caused increase in dust deposition is accompanied by dramatic changes in element loading to this high elevation ecosystem including >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.  Collectively, these changes indicate that regional changes in land use and human activities have caused a widespread and significant increase in the deposition of mineral aerosols and raise a number of questions about the long-term implications of this deposition for downwind terrestrial ecosystems.