Influence of development stage of spring oilseed rape and spring wheat on interception of wet-deposited radiocaesium and radiostrontium

The dry and wet deposition of radionuclides released into the atmosphere can be intercepted by vegetation in terrestrial ecosystems. The aim of this study was to quantify the interception of wet deposited ¹³⁴Cs and ⁸⁵Sr by spring oilseed rape (Brassíca napus L.) and spring wheat (Tríticum aestívum L.). The dependency of the intercepted fraction (f) on total above ground plant biomass, growing stage and the Leaf Area Index (LAI) was quantified. A trial was established in Uppsala (east central Sweden), with land management in accordance to common agricultural practices. The field trial was a randomised block design of 1 × 1 m² parcels with three replicates. During the growing season of 2010, a rainfall simulator deposited ¹³⁴Cs and ⁸⁵Sr during six different growth stages. Two to 3 h after deposition, the biomass of the centre 25 × 25 cm² area of each parcel was sampled and above ground biomass and LAI were measured. The radioactivity concentration and radioactivity of samples were measured by High Purity Germanium (HPGe)-detectors. For ¹³⁴Cs, there was a correlation between f and LAI (r² = 0.55, p < 0.05) for spring wheat, but not for spring oilseed rape (r² = 0.28, p > 0.05). For ⁸⁵Sr, there was a correlation between f and LAI for both crops (r² = 0.41, p < 0.05 for spring oilseed rape and r² = 0.48 p, <0.05 for spring wheat). There was no correlation between f and above ground plant biomass in spring oilseed rape for either ¹³⁴Cs (r² = 0.01, p > 0.05) or for ⁸⁵Sr (r² = 0.11, p > 0.05). For spring wheat, there was a correlation for both ¹³⁴Cs (r² = 0.36, p < 0.05) and ⁸⁵Sr (r² = 0.32, p < 0.05). For spring oilseed rape, f was highest at growth stage ‘stem elongation’ for ¹³⁴Cs (0.32 ± 0.22) and ⁸⁵Sr (0.41 ± 0.29). For spring wheat, f was highest at growth stage ‘ripening’ for both radionuclides (¹³⁴Cs was 0.36 ± 0.14 and ⁸⁵Sr was 0.48 ± 0.18). Thus, LAI can be used to quantify interception of both radionuclides for both crops, whereas, above ground plant biomass is a weak measure of interception of wet deposited radiocaesium and radiostrontium.