Beryllium‐7 in soils and vegetation along an arid precipitation gradient in Owens Valley, California

Abstract

Beryllium‐7 is a potentially powerful tracer of atmospheric deposition and recent sediment transport, but the quantity and distribution of 7 Be on arid landscapes have not been described. We measured 7 Be in soil, vegetation, and dust in Owens Valley, California, and describe its distribution in aridisols and mollisols to evaluate its potential as a sediment tracer in desert environments. Beryllium‐7 in vegetation and the upper few cm of soil is low but detectable (>20 Becquerels [Bq] m −2 ). Surface inventories of 7 Be at sites on the valley floor vary by a factor of five between the end of the rainy season (April) and the end of the dry season (November). In mollisols, live grasses hold ∼50 Bq 7 Be m −2 , which is on the order of half of the total springtime surface inventory. We find that within‐site variability at the 5 m scale is 5 to 22% (1 relative standard error) and can be explained by localized rain shadowing and erosion, but between site variability at the km scale can be explained by differences in rainfall. Our alpine site has more than triple the inventory that is predicted from the rainfall‐ 7 Be flux relationship that we generate using our springtime soil measurements and previously reported deposition data. Dust deposition does not appear to contribute significantly to 7 Be inventories, but anomalously high 7 Be on the eastern flank of the Sierras may be explained by a higher altitude air mass source and better scavenging efficiency of snow.