Random and systematic spatial variability of 137Cs inventories at reference sites in South-Central Brazil

Abstract

The precision of the 137 Cs fallout redistribution technique for the evaluation of soil erosion rates is strongly dependent on the quality of an average inventory taken at a representative reference site. The knowledge of the sources and of the degree of variation of the 137 Cs fallout spatial distribution plays an important role on its use. Four reference sites were selected in the South-Central region of Brazil which were characterized in terms of soil chemical, physical and mineralogical aspects as well as the spatial variability of 137 Cs inventories. Some important differences in the patterns of 137 Cs depth distribution in the soil profiles of the different sites were found. They are probably associated to chemical, physical, mineralogical and biological differences of the soils but many questions still remain open for future investigation, mainly those regarding the adsorption and dynamics of the 137 Cs ions in soil profiles under tropical conditions. The random spatial variability (inside each reference site) was higher than the systematic spatial variability (between reference sites) but their causes were not clearly identified as possible consequences of chemical, physical, mineralogical variability, and/or precipitation. Key words: cesium-137, spatial distribution, radioisotope, sediment, radioactive tracer VARIABILIDADE ESPACIAL RANDÔMICA E SISTEMÁTICA DOS INVENTÁRIOS DE 137 Cs DE ÁREAS DE REFERÊNCIA NO SUDESTE DO BRASILRESUMO: A precisão da técnica de análise da redistribuição do "fallout" do 137 Cs nas avaliações das taxas de erosão são fortemente dependentes da qualidade de um inventário médio tomado em uma área de referência representativa. O conhecimento das fontes e do grau de variação da distribuição do "fallout" do 137 Cs desempenham um importante papel na aplicação desta técnica. Quatro áreas de referência foram selecionadas na região Sudeste do Brasil, sendo estas caracterizadas quanto aos aspectos físicos, químicos, mineralógicos do solo, assim como a variabilidade espacial dos inventários de 137 Cs. Houve algumas diferenças importantes no padrão da distribuição do 137 Cs em profundidade nos perfis de solo dos diferentes locais que, provavelmente, estão associadas às diferenças químicas, físicas, mineralógicas e biológicas dos solos estudados. Mas muitas questões ainda permanecem abertas para futuras investigações, principalmente em relação à adsorção e à dinâmica do 137 Cs no perfil dos solos tropicais. A variabilidade espacial randômica (dentro de cada local de referência) foi maior do que a variabilidade espacial sistemática (entre áreas de referência), porém as causas disto não foram claramente identificadas, talvez em conseqüência da variabilidade química, física e/ou mineralógica bem como da precipitação.

Riparian forest potential to retain sediment and carbon evaluated by the 137Cs fallout and carbon isotopic ratio techniques

“…According to Correchel et al (2005), the inventories at the reference site varied from 277 to 367 Bq. The band widths were obtained taking average values of soil erosion or sediment deposition rates (E) for each band.…”

Inventories and concentration profiles of 137Cs in undisturbed soils in the northeast of Buenos Aires Province, Argentina

“…The inventories determined in La Plata region are compared in Fig. 3a to those determined in central region of Argentina (Juri Ayub et al, 2007, 2008Bujan et al, 2000Bujan et al, , 2003, Chile (Schuller et al, 1997(Schuller et al, , 2004 and from Brazil presented as open squares (Correchel et al, 2005;Handl et al, 2008) are also included. The circles correspond to data from Argentina (solid symbols: present work, open ones: Juri Ayub et al, 2007Ayub et al, , 2008Bujan et al, 2000Bujan et al, , 2003.…”

“…In the figure, c) the dashed vertical line represents the Cordillera de los Andes location. (Schuller et al, 1997(Schuller et al, , 2004 and Brazil (Correchel et al, 2005;Handl et al, 2008) , 2000, 2008), are also included (solid line). This comparison allows us to conclude that the experimental and the predicted data match quite well, with the exception of the Chilean inventory values, reported by Schuller et al (1997), 2004, which are systematically higher.…”

Radiological Survey in Soil of South America

“…6, differences in the patterns of 137 Cs depth distribution in the soil profiles of the different regions were found in the four studied sites of the South-Central region of Brazil (BS2-BS5), ascribed to chemical, physical, mineralogical and biological differences of the soils [Correchel et al, 2005]. The variability of the soil characteristics was not able to explain the spatial variability of the profiles.…”

“…Beside the natural chains values, the profiles of 137 Cs in the region of Buenos Aires Province have been settled [Montes et al 2010a[Montes et al , 2010b. Some studies have been performed in Brazil, dealing with the determination of the activity of the 137 Cs globally presented on the soil because of nuclear weapon tests [Correchel et al, 2005;Handl et al, 2008]. Total inventories and depth distributions of 137 Cs were established in agricultural and sheep-farming regions of Chile [Schuller et al, 1997[Schuller et al, , 2002[Schuller et al, , 2004.…”