X-ray Spectroscopic Quantification of Phosphorus Transformation in Saharan Dust during Trans-Atlantic Dust Transport

Abstract

Saharan dust is an important phosphorus (P) supply to remote and oligotrophic parts of the oceans and American lowland tropical rainforests. Phosphorus speciation in aeolian dust ultimately controls the release and bioavailability of P after dust deposition, but the speciation in Saharan dust and its change during the trans-Atlantic transport remains unclear. Using P K-edge X-ray absorption near edge structure (XANES) spectroscopy, we showed that with increasing dust traveling distance from the Sahara Desert to Cape Verde and to Puerto Rico, about 570 and 4000 km, respectively, the proportion of Ca-bound P (Ca-P), including both apatite and non-apatite forms, decreased from 68–73% to 50–71% and to 21–37%. The changes were accompanied by increased iron/aluminum-bound P proportion from 14–25% to 23–46% and to 44–73%, correspondingly. Laboratory simulation experiments suggest that the changes in P speciation can be ascribed to increasing degrees of particle sorting and atmospheric acidification during dust transport. The presence of relatively soluble non-apatite Ca-P in the Cape Verde dust but not in the Puerto Rico dust is consistent with the higher P water solubility of the former than the latter. Our findings provide insights into the controls of atmospheric processes on P speciation, solubility, and stability in Saharan dust.

Chemical processes in receiving soils accelerate solubilisation of phosphorus from desert dust and fire ash

“…The increase in P bioavailability was significant at every pH unit drop, starting from 7 to 6, 6 to 5, or 5 to 4, which is the natural pH range of most soils around the world and on the surface of plant leaves (Batjes, 1995; Gross et al, 2021). Our results agree well with previous studies which reported increased P solubility when desert dust spends times in the atmosphere and goes through atmospheric acidification processes which dissolve Ca‐P minerals, even under moderate acidic conditions (Dam et al, 2021; Herbert et al, 2018; Shi et al, 2019; Stockdale et al, 2016; Zhang et al, 2018). Overall, our data shows that a moderate drop in pH, which is common in natural soils, is sufficient to promote the dissolution of Ca‐P minerals.…”

“…For example, modification of rhizospheric pH promotes the dissolution of P bearing minerals and the exudation of organic acids such as malic acid and oxalic acid which desorb mineral bound P via exchange reactions with Ca, Fe and Al minerals (Devau et al, 2010; Hinsinger, 2001; Hinsinger et al, 2009; Lambers et al, 2019; Penn & Camberato, 2019). These processes can affect P bioavailability of desert dust since most of its P is bound to pH sensitive Ca minerals such as apatite (the major P bearing mineral in desert dust) or Fe and Al oxides (Dam et al, 2021; Gross et al, 2015; Gu et al, 2019; Hudson‐Edwards et al, 2014; Longo et al, 2014; Nenes et al, 2011; Stockdale et al, 2016; Zhang et al, 2018). Controlled laboratory studies with synthetic minerals have shown that the dissolution of Ca‐P minerals increases at pH lower than 8 while desorption of P from Fe and Al oxides will occur at moderately acidic conditions (Devau et al, 2010; Herbert et al, 2018; Penn & Camberato, 2019; Smith et al, 1977).…”

Speciation Evolution of Phosphorus and Sulfur Derived from Sewage Sludge Biochar in Soil: Ageing Effects

“…Total P, S, and typical metal­(loid)­s including arsenic (As), cadmium (Cd), copper (Cu), and Fe in the samples were determined after being digested with HNO 3 –HClO 4 . Organic P was determined using the ashing method . Available As and P were extracted with 0.5 mol/L NaHCO 3 (pH 8.5), available S was extracted with 0.016 mol/L KH 2 PO 4 , and available Cd, Cu, and Fe were extracted with a DTPA complexing solution .…”

“…Organic P was determined using the ashing method. 34 Available As and P were extracted with 0.5 mol/L NaHCO 3 (pH 8.5), 31 available S was extracted with 0.016 mol/L KH 2 PO 4 , 9 and available Cd, Cu, and Fe were extracted with a DTPA complexing solution. 21 The chemical speciation distribution of Cu and Fe in the samples was quantified with a sequential extraction procedure (Text S2).…”

Lake Chemodiversity Driven by Natural and Anthropogenic Factors

“…The above results demonstrated that a strong connection existed between DOM in lakes and air pollution closely related to human activities. For instance, dust as a vector for the transport of nutrients and pollutants at the global scale could cause a shift in DOM in alpine lakes. , …”