Can stable isotope analysis reveal dietary differences among groups with distinct income levels in the city of Piracicaba (southeast region, Brazil)?

BACKGROUND: The present study aimed to determine whether the δ(13)C and δ(15)N of fingernails (δ(13)CF and δ(15)NF, respectively) would exhibit differences between groups from different income levels in the city of Piracicaba, Brazil. METHODS: In 2010, the fingernails of 273 participants belonging to six income groups were analysed to determine isotopic composition. δ(13)CF and δ(15)NF were compared with the stable isotope of a putative diet (δ(13)CD and δ(15)ND , respectively), which was estimated via an isotopic mass balance using, as a weighting factor, macronutrient intake by the main food items, as obtained by the 2008-2009 household food purchases conducted by the Brazilian Institute of Geography and Statistics. RESULTS: δ(13)CF values showed a decreasing trend towards the lower income level groups, in accordance with the δ(13)CD values that showed the same trend. This isotopic change was mainly a result of the higher consumption of beef, bread, soft drinks and dairy by the highest income group; and also as a result of the higher consumption of soybean oil, rice and sugar by the lowest income group. The δ(15)NF values failed to capture differences in groups between income levels. This outcome was not expected because individuals in a higher income group tend to consume more animal protein and, as a result of the trophic fractionation, have higher δ(15)N values. CONCLUSIONS: The combination of household purchase surveys and stable isotopic composition in modern humans is found to be a valuable tool, especially with respect to determining the role of C3 and C4 plants through the complex modern food chain.

Potential impacts of climate change on biogeochemical functioning of Cerrado ecosystems.

The Cerrado Domain comprises one of the most diverse savannas in the world and is undergoing a rapid loss of habitats due to changes in fire regimes and intense conversion of native areas to agriculture. We reviewed data on the biogeochemical functioning of Cerrado ecosystems and evaluated the potential impacts of regional climate changes. Variation in temperature extremes and in total amount of rainfall and altitude throughout the Cerrado determines marked differences in the composition of species. Cerrado ecosystems are controlled by interactions between water and nutrient availability. In general, nutrient cycles (N, P and base cations) are very conservative, while litter, microbial and plant biomass are important stocks. In terms of C cycling, root systems and especially the soil organic matter are the most important stocks. Typical cerrado ecosystems function as C sinks on an annual basis, although they work as source of C to the atmosphere close to the end of the dry season. Fire is an important factor altering stocks and fluxes of C and nutrients. Predicted changes in temperature, amount and distribution of precipitation vary according to Cerrado sub-regions with more marked changes in the northeastern part of the domain. Higher temperatures, decreases in rainfall with increase in length of the dry season could shift net ecosystem exchanges from C sink to source of C and might intensify burning, reducing nutrient stocks. Interactions between the heterogeneity in the composition and abundance of biological communities throughout the Cerrado Domain and current and future changes in land use make it difficult to project the impacts of future climate scenarios at different temporal and spatial scales and new modeling approaches are needed.

Nitrogen mass balance in the Brazilian Amazon: an update.

The main purpose of this study is to perform a nitrogen budget survey for the entire Brazilian Amazon region. The main inputs of nitrogen to the region are biological nitrogen fixation occurring in tropical forests (7.7 Tg.yr(-1)), and biological nitrogen fixation in agricultural lands mainly due to the cultivation of a large area with soybean, which is an important nitrogen-fixing crop (1.68 Tg.yr(-1)). The input due to the use of N fertilizers (0.48 Tg.yr(-1)) is still incipient compared to the other two inputs mentioned above. The major output flux is the riverine flux, equal to 2.80 Tg.yr(-1) and export related to foodstuff, mainly the transport of soybean and beef to other parts of the country. The continuous population growth and high rate of urbanization may pose new threats to the nitrogen cycle of the region through the burning of fossil fuel and dumping of raw domestic sewage in rivers and streams of the region.