Atmospheric iodine, selenium and caesium depositions in France: II. Influence of forest canopies

• Published in: Chemosphere (Oxford) 2021-06, Vol.273, p.128952, Article 128952
• Main Authors: Roulier, Marine, Bueno, Maïté, Coppin, Frédéric, Nicolas, Manuel, Thiry, Yves, Rigal, François, Pannier, Florence, Le Hécho, Isabelle
• Format: Article
• Language: English
• Subjects: Caesium; Cesium; Ecosystem; Environmental Monitoring; Forest tree species; Forests; France; Iodine; Selenium; Speciation; Throughfall; Trees
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2020.128952

Estimation of the canopy influence on atmospheric inputs of iodine (I), selenium (Se) and caesium (Cs) in terrestrial ecosystems is an essential condition for appropriate biogeochemical models. However, the processes involved in rain composition modifications after its passage through forest canopy have been barely studied for these elements. We monitored I, Se and Cs concentrations in both rainfall and throughfall of fourteen French forested sites throughout one year, and estimated dry deposition and canopy exchange fluxes for these elements, as well as speciation of I and Se. Comparison of rainfall and throughfall elemental composition highlighted an important impact of forest canopy on both (i) concentrations and fluxes of I, Se and Cs, and (ii) I and Se species. For the three elements, most of their throughfall concentrations were higher than corresponding rainfall. The increase of throughfall elemental fluxes was mostly due to dry deposition for I and Se although the canopy exchange model revealed some sorption within the canopy in most cases; for Cs, foliage leaching was most influencing. Regarding speciation, iodine species in rainfall were highly modified by forest canopy with an important increase of unidentified I proportion in throughfall (on average 49 and 82% in rainfall and throughfall, respectively), possibly due to washoff of dry deposition and/or to transformation into organic forms. Similarly, while rainfall was composed of 26–54% of inorganic Se, inorganic species were undetectable in throughfall. This dataset represents key information to improve modelling of I, Se and Cs cycling within forest ecosystems. [Display omitted] •Higher annual I, Se and Cs concentrations and fluxes in throughfall relative to rain.•Dry deposition contribution led to increased throughfall flux of I and Se.•Canopy budget model involved I and Se sorption by canopies.•Increase of annual flux of Cs in throughfall resulted mainly from canopy leaching.•Loss of inorganic I and Se species caused by forest canopy.