Methodological approach to assess the effect of soil ageing on selenium behaviour: first results concerning mobility and solid fractionation of selenium
Résumé
The aim of the study presented here is to determine the impact of short- and medium-term transformations (0–3 years) of the soil organic matter (SOM) on the major processes and parameters that enable or inhibit selenite, Se(+IV), transfers between the soil components (solid, liquid or gaseous). Three types of soil of similar mineralogical origin but containing diverse quantities and qualities of SOM were first contaminated with Se(+IV) and incubated at 28°C. Soils were sampled throughout the incubation period to characterise the mobility of Se (batch and soil column experiments) and also its fractionation within the soil compartments (selective extractions and size-density fractionation). The following are the main results obtained within the first month of incubation. (a) Selenium was partly volatilized during soil incubation (<0.1%), (b) Se extracted with CaCl2 (5×10−4 M) was equally small for the three soil samples (∼1–5%), suggesting that Se was strongly sorbed on the solid phase and (c) at least 10% of Se was associated to the particulate organic matter $${\left( {{\text{POM}}_{{ > {\text{50}}\mu {\text{m}}}} } \right)},$$whereas 60% of Se was extracted with soil humic substances. These results suggested that both SOM quantity and quality played a significant role in selenium retention. Furthermore, comparison between experimental and predicted variations of CO2 fluxes (due to C mineralisation) and soil biomasses are presented. By this way, we estimated the capacity of the RothC model as an experimental gauging tool in the prediction of C turnover on a laboratory scale.