Scaling up: fulfilling the promise of X-ray microprobe for biogeochemical research

Abstract

Environmental context. Although biogeochemical processes in the environment are often considered on large spatial scales, critical processes can occur at fine-spatial scales. Quantifying these processes is a challenge, but significant recent developments in microprobe X-ray absorption spectroscopy in terms of data collection and analysis greatly facilitate micro-scale observations at the sample-level. These mapping methods create datasets that can be integrated with bulk observations with the potential for widespread application to biogeochemical research.Abstract. Biogeochemists measure and model fluxes of materials among environmental compartments, often considering large spatial-scales within and among ecosystems. However, critical biogeochemical processes occur at fine-spatial scales, and quantifying these processes is a challenge. Recent developments in microprobe X-ray absorption spectroscopy (XAS) data collection and analysis allow for micro-scale observations and quantification of chemical species at the sample-level. These speciation mapping methods create datasets that can be integrated with bulk observations through empirical and theoretical modelling. Speciation mapping approaches are possible with existing instrumentation, but the widespread application to biogeochemical research is hindered by the small number of instruments currently available.

Solid-phase arsenic speciation in aquifer sediments: A micro-X-ray absorption spectroscopy approach for quantifying trace-level speciation

“…The analytical method developed here for As relies on synchrotron X-ray microprobe for detailed description of As speciation (qualitative track via point XANES spectroscopy) and quantification of As species groups (quantitative track via speciation mapping). The approach is based on similar methods devised for S (Pickering et al, 2009;Zeng et al, 2013) and Fe (Mayhew et al, 2011;Lam et al, 2012;Toner et al, 2012Toner et al, , 2014 and provides: (1) the spatial resolution needed to address natural heterogeneity in the sediments, (2) the chemical sensitivity needed for trace elements, (3) the chemical resolution needed to identify the As species present (i.e. number of different As species), and (4) the appropriate number of observations to create statistically robust data for quantifying As species groups (i.e.…”

“…An As ''speciation mapping" protocol was developed for glacial sediments (Toner et al, 2014) (EA Fig. 1 ''Quantitative Track").…”

“…The point XANES approach is necessary to ''ground-truth" the speciation maps, as well as to identify the mineral species hosting As. This two-tiered approach to data collection, as applied to Fe geochemistry, is reviewed by Toner et al (2014Toner et al ( , 2016.…”

Diffuse Hydrothermal Venting: A Hidden Source of Iron to the Oceans

“…Data was processed using the MANTiS (Lerotic et al, 2014) software for background subtraction, image normalization, image alignment and X-ray peak fitting. Results are compared to previously published spectra of Fe minerals (Toner et al, 2009(Toner et al, , 2014(Toner et al, , 2016von der Heyden et al, 2012).…”

Hard X-ray synchrotron biogeochemistry: piecing together the increasingly detailed puzzle

“…This is justified by the fact that new data intensive techniques are available (see below) and that experimental designs have grown more complex and exhaustive (e.g. Toner et al [8] ). However, this has also translated into a flood of data.…”