Abstract

The deposition of aeolian dust alters nutrient cycles in soils across a variety of climatic and geologic settings, especially by the addition of phosphorus. In the southern Sierra Nevada, where bedrock-driven P limitation may control the spatial distribution of vegetation, aeolian dust inputs could significantly influence soil P and primary productivity. To distinguish the role of bedrockderived nutrients and dust-derived nutrients in this region, we measured radiogenic Nd isotopes in bedrock, soil, and Pinus jeffreyi trees from a sparse forest on the Bald Mountain Granite, and compared these values to measurements from dust collected in the same region. Since Nd tends to concentrate in phosphate minerals and does not fractionate biologically, measurements of 143Nd/144Nd should help distinguish sources of mineral-bound, inorganic P accessed by local vegetation. 

Our results show that soils are enriched in 143Nd relative to bedrock and depleted in 143Nd relative to dust on average (soil: εNd = -5.87±0.16; bedrock: εNd = -8.61±0.07; dust: εNd = -5.05±0.16). A twocomponent mixing model of dust and bedrock shows that 70-80% of Nd in the soil was derived from dust over the residence time of the soil. Pine needles are also enriched in 143Nd compared to bedrock (pine needles: εNd = -5.46±0.16), indicating that the trees obtain 80-90% Nd from dust and only 10-20% Nd from the bedrock substrate. The predominance of dust-derived Nd in soils and pine needles supports the hypothesis that Sierra Nevada ecosystems are strongly influenced by dust-derived P from Asian sources, which account for 50% of the modern dust flux. Our analysis highlights the potential for using radiogenic Nd isotopes to understand the cycling of exogenous and endogenous nutrients in the critical zone.

Citation

Arvin, L., Riebe, C., Aciego, S., Blakowski, M. (2016): Nd Isotopes in Soils and Pine Needles Trace Aeolian Inputs to Sierra Nevada Ecosystems.  Goldschmidt Abstracts. Yokohama, Japan. .