ABSTRACT Although Selenium (Se) plays a role as a micronutrient for humans through vegetable consumption, it is also recognized as toxic when present in excessive quantities. Therefore, quantifying Se contents in soils can prevent diseases influenced by crop Se deficiency or excess. We aimed to measure background contents, establish quality reference values (QRV) for Se in soils from two Brazilian biomes (Cerrado and Caatinga), and assess how geopedological factors affect Se content and spatial variability. Two hundred and eight composite topsoil samples were analyzed for Se content, covering an area of about 251,578 km². Sampling sites were under the minimal anthropogenic influence to represent Se background contents. Selenium contents were determined by hydride generation atomic absorption spectroscopy (HGAAS), ranging from 0.002 to 4.78 mg kg-1. Most soils had contents below the world average of 0.44 mg kg-1 but still above the soil content that causes human Se deficiency (0.125 mg kg-1). Soils from Cerrado and Caatinga biomes showed similar average contents of Se, 0.41 and 0.47 mg kg-1, respectively. Organic carbon content and soil particle size (clay fraction) were the main factors governing Se content in the soils. Our results contribute to understanding the Se content and spatial distribution in tropical soils and the factors governing them. They also provide a tool for agriculture and environmental decision-makers to plan public policies regarding the management of Se levels in these and similar tropical soils in the world. (Se consumption quantities Therefore excess QRV (QRV Caatinga, , Caatinga) variability 251578 251 578 251,57 km² km HGAAS, HGAAS (HGAAS) 0002 0 002 0.00 478 4 78 4.7 kg1. kg1 kg 1. 1 044 44 0.4 kg- 0.125 0125 125 (0.12 . kg-1) 041 41 047 47 kg1, 1, respectively clay fraction them decisionmakers decision makers 25157 25 57 251,5 (HGAAS 000 00 0.0 7 4. 04 0. 0.12 012 12 (0.1 2515 2 5 251, 0.1 01 (0. (0 (

ABSTRACT Identifying sediment sources is fundamental for protecting and improving soil and water quality. Conventional fingerprinting studies have often collected sediments at the overall watershed outlet only, resulting in an important spatial scale dependency. This study aimed to identify and to assess the delivery patterns of sediment sources within three priority sub-catchments (Sapocaji, Piedade and Minas) located in the downstream portion of the Ipojuca River watershed in Brazil. This research would build on understanding sediment sources in the studied watershed by elucidating source type contributions on a sub-catchment basis. Both bed and suspended sediment samples were collected in these sub-catchments, and two types of sources were sampled: surface and subsurface sources. A total of 21 geochemical tracers were measured. The tracers were evaluated for their conservation and discriminatory ability (Kruskal-Wallis test and linear discriminant analysis), and the best set of tracers was selected for source apportionment modeling using MixSIAR. Surface (i.e., sugarcane croplands) sources contributed the highest to suspended sediments in the Piedade and Minas sub-catchments. There was a difference in the quality of riverbank management, which helped explain contrasts in the importance of this source. Overall, sub-catchment-specific sediment control management measures, such as the revegetation of riparian forests, need to be implemented, mainly in the Sapocaji sub-catchment. These results underscore the importance of connectivity for surface source contributions. only dependency subcatchments sub catchments Sapocaji, (Sapocaji Brazil subcatchment catchment basis subcatchments, catchments, sampled 2 measured KruskalWallis Kruskal Wallis analysis, analysis , analysis) MixSIAR i.e., ie i e (i.e. croplands subcatchments. catchments. Overall subcatchmentspecific specific measures forests implemented subcatchment. catchment. i.e. (i.e i.e

Cultivation can substantially change soil quality through improvement or degradation of the physical and chemical characteristics. Vineyard soils are sensitive to soil changes due to the intensive chemical input. This study assesses the soil fertility changes in vineyard soils of the São Francisco valley in Northeastern Brazil during different cultivation time spans (5, 6, 8, 10, 12, 15, and 16 years). An area with natural vegetation (Caatinga) was used as a reference area. We analyzed pH, exchangeable contents of Ca, Mg, Na, K, and Al, potential acidity (H+Al), available P, total organic matter, sum of bases, CEC, Al saturation, and base saturation at depths of 0-20 and 20-40 cm. Univariate and multivariate analyses were used for data evaluation. The results showed that soil fertility changes were closely related to cultivation time spans. Contents of organic matter, Ca, Mg, and K were increased in most of the vineyard soils. The management of P fertilization deserves attention as the very high concentrations in soil are prone to leach and can contribute to triggering eutrophication. Discriminant and factor analyses proved to be useful tools for distinguishing the effects of management in the cultivated areas and helping to achieve sustainable land use in such fragile agro-ecosystems.