Cesium and strontium exchange properties of marsh soils

The cesium and strontium exchange properties of some typical marsh soils of the estuary and lower river Weser region were described. Soil samples were taken according to the existing soil maps 1:25000 of Lower Saxony e.g. a "sea marsh soil". a "brackish marsh soil", and a "river marsh soil". The exchange properties were determined by Cs/Ca and Sr/Ca exchange curves (Q/I relations) as generally used in soil potassium research. In addition to the Q/I relations the following investigations were carried out: - Cs and Sr desorption experiments (one time equilibration with Ca++ solutions) - Cs and Sr reexchange experiments (eight times equilibration with water, Ca++, Ba++, and K+ solutions) - the naturally-occuring Cs and Sr contents of the soils including amounts caused by imissions or fallout, respectively - clay mineral composition and swelling of layer silicates due to saturation with Ca++, Sr++, Cs+, and K+ ions. Q/I relations as well as desorption and reexchange experiments indicated strong cesium and low strontium fixation by the soils investigated. This was considered the reason for the stronger transfer of Sr from soil to plants as compared with Cs. Furthermore, the reexchange experiment revealed nearly complete reversibility of the Sr sorption reactions by equilibration with the divalent cations Ca++ and Ba++ and some Sr fixation after treatment with K+ solutions. However, cesium was much better reexchanged by K+ than by Ca++ and Ba++ ions. This led to the conclusion that Cs fixed in interlayer positions of clay minerals could be remobilized by potassium and ammonium fertilization. The naturally-occuring Cs contents of the soils were found to be below the detection limit of the analytical methods used. The contents of naturally-occuring exchangeable Sr, however, was in agreement with the amounts of "labile Sr" as derived from the Sr/Ca exchange curves. Concerning the cesium exchange properties a clear distinction between "sea and river marsh soils" on the one hand and "brackish marsh soils" on the other hand was established due to differences in clay mineral composition and swelling state of 1:2 layer silicates. The different cesium exchange properties of the two soil groups could also be verified by more or less pronounced hysteresis effects of sorption (Q/I relation) and desorption curves