Jean Pierre Henry Balbaud Ometto

Recuperation of nitrogen cycling in Amazonian forests following agricultural abandonment.

Phosphorus (P) is generally considered the most common limiting nutrient for productivity of mature tropical lowland forests growing on highly weathered soils. It is often assumed that P limitation also applies to young tropical forests, but nitrogen (N) losses during land-use change may alter the stoichiometric balance of nutrient cycling processes. In the Amazon basin, about 16% of the original forest area has been cleared, and about 30–50% of cleared land is estimated now to be in some stage of secondary forest succession following agricultural abandonment. Here we use forest age chronosequences to demonstrate that young successional forests growing after agricultural abandonment on highly weathered lowland tropical soils exhibit conservative N-cycling properties much like those of N-limited forests on younger soils in temperate latitudes. As secondary succession progresses, N-cycling properties recover and the dominance of a conservative P cycle typical of mature lowland tropical forests re-emerges. These successional shifts in N:P cycling ratios with forest age provide a mechanistic explanation for initially lower and then gradually increasing soil emissions of the greenhouse gas nitrous oxide (N2O). The patterns of N and P cycling during secondary forest succession, demonstrated here over decadal timescales, are similar to N- and P-cycling patterns during primary succession as soils age over thousands and millions of years, thus revealing that N availability in terrestrial ecosystems is ephemeral and can be disrupted by either natural or anthropogenic disturbances at several timescales.

EFFECTS OF URBAN SEWAGE ON DISSOLVED OXYGEN, DISSOLVED INORGANIC AND ORGANIC CARBON, AND ELECTRICAL CONDUCTIVITY OF SMALL STREAMS ALONG A GRADIENT OF URBANIZATION IN THE PIRACICABA RIVER BASIN

In Brazil most of the urban sewage is dumped without treatment into rivers. Because of this, it is extremely important to evaluate the consequences of organic matter rich sewage on the structure and functioning of river ecosystems. In this study we investigated the effects of urban sewage on the dissolved oxygen (O2), dissolved inorganic (DIC) and organic carbon (DOC), and electrical conductivity (EC) in 10 small streams of the Piracicaba River basin, southeast region of Brazil. In the Piracicaba River basin, which is one of the most developed regions of the country, only 16% of the total sewage load generated is treated. These streams were classified into two groups, one with heavy influence of urban sewage and another with less influence. Both concentrations and seasonal variability were distinct between the two groups. The streams that received sewage effluent had a combination of low O2 with high DIC, DOC, and EC. In the polluted streams, concentrations of dissolved carbon forms and EC were higher and O2 concentration lower during the low water period. In the less polluted streams seasonal variations in concentrations were small. We also investigated the efficiency of a sewage treatment plant installed two years ago in the catchment of one of these streams. It was observed an increase in the O2 concentration after the beginning of the treatment, and a decrease of DIC and DOC concentrations especially during the low water period. However, no significant change was observed in the EC, suggesting that the concentrations of major ions is still unaltered, and that a secondary treatment is necessary in order to reduce ion load into the stream.

Carbon isotope discrimination in forest and pasture ecosystems of the Amazon Basin, Brazil

(1) Our objective was to measure the stable carbon isotope composition of leaf tissue and CO2 released by respiration (dr), and to use this information as an estimate of changes in ecosystem isotopic discrimination that occur in response to seasonal and interannual changes in environmental conditions, and land-use change (forest-pasture conversion). We made measurements in primary forest and pastures in the Amazon Basin of Brazil. At the Santarem forest site, dr values showed a seasonal cycle varying from less than 29% to approximately 26%. The observed seasonal change in dr was correlated with variation in the observed monthly precipitation. In contrast, there was no significant seasonal variation in dr at the Manaus forest site (average dr approximately 28%), consistent with a narrower range of variation in monthly precipitation than occurred in Santarem. Despite substantial (9%) vertical variation in leaf d 13 C, the average dr values observed for all forest sites were similar to the d 13 C values of the most exposed sun foliage of the dominant tree species. This suggested that the major portion of recently respired carbon dioxide in these forests was metabolized carbohydrate fixed by the sun leaves at the top of the forest canopy. There was no significant seasonal variation observed in the d 13 C values of leaf organic matter for the forest sites. We sampled in pastures dominated by the C4 grass, Brachiaria spp., which is planted after forest vegetation has been cleared. The carbon isotope ratio of respired CO2 in pastures was enriched in 13 C by approximately 10% compared to forest ecosystems. A significant temporal change occurred in dr after the Manaus pasture was burned. Burning removed much of the encroaching C3 shrub vegetation and so allowed an increased dominance of the C4 pasture grass, which resulted in higher dr values. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 1610 Global Change: Atmosphere (0315, 0325); 1615 Global Change: Biogeochemical processes (4805); 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); KEYWORDS: carbon cycle, global change, tropical ecosystems, atmospheric carbon dioxide

Estimating greenhouse gas emissions from cattle raising in Brazil

The study estimated, for the first time, the greenhouse gas emissions associated with cattle raising in Brazil, focusing on the period from 2003 to 2008 and the three principal sources: 1) portion of deforestation resulting in pasture establishment and subsequent burning of felled vegetation; 2) pasture burning; and 3) bovine enteric fermentation. Deforestation for pasture establishment was only considered for the Amazon and Cerrado. Emissions from pasture burning and enteric fermentation were accounted for the entire country. The consolidated emissions estimate lies between approximately 813 Mt CO2eq in 2008 (smallest value) and approximately 1,090 Mt CO2eq in 2003 (greatest value). The total emissions associated with Amazon cattle ranching ranged from 499 to 775 Mt CO2eq, that of the Cerrado from 229 to 231 Mt CO2eq, and that of the rest of the country between 84 and 87 Mt CO2eq. The full set of emissions originating from cattle raising is responsible for approximately half of all Brazilian emissions (estimated to be approximately 1,055 Mt CO2eq in 2005), even without considering cattle related sources not explicitly estimated in this study, such as energy use for transport and refrigeration along the beef and derivatives supply chain. The potential for reduction of greenhouse gas emissions offered by the Brazilian cattle industry is very high and might constitute Brazil’s most important opportunity for emissions mitigation. The study offers a series of policy recommendations for mitigation that can be implemented by public and private administrators at a low cost relative to other greenhouse gas reduction options.

Toward an integrated monitoring framework to assess the effects of tropical forest degradation and recovery on carbon stocks and biodiversity

Tropical forests harbor a significant portion of global biodiversity and are a critical component of the climate system. Reducing deforestation and forest degradation contributes to global climate-change mitigation efforts, yet emissions and removals from forest dynamics are still poorly quantified. We reviewed the main challenges to estimate changes in carbon stocks and biodiversity due to degradation and recovery of tropical forests, focusing on three main areas: (1) the combination of field surveys and remote sensing; (2) evaluation of biodiversity and carbon values under a unified strategy; and (3) research efforts needed to understand and quantify forest degradation and recovery. The improvement of models and estimates of changes of forest carbon can foster process-oriented monitoring of forest dynamics, including different variables and using spatially explicit algorithms that account for regional and local differences, such as variation in climate, soil, nutrient content, topography, biodiversity, disturbance history, recovery pathways, and socioeconomic factors. Generating the data for these models requires affordable large-scale remote-sensing tools associated with a robust network of field plots that can generate spatially explicit information on a range of variables through time. By combining ecosystem models, multiscale remote sensing, and networks of field plots, we will be able to evaluate forest degradation and recovery and their interactions with biodiversity and carbon cycling. Improving monitoring strategies will allow a better understanding of the role of forest dynamics in climate-change mitigation, adaptation, and carbon cycle feedbacks, thereby reducing uncertainties in models of the key processes in the carbon cycle, including their impacts on biodiversity, which are fundamental to support forest governance policies, such as Reducing Emissions from Deforestation and Forest Degradation.

RIVERINE ORGANIC MATTER COMPOSITION AS A FUNCTION OF LAND USE CHANGES, SOUTHWEST AMAZON

We investigated the forms and composition of dissolved and particulate organic matter in rivers of the Ji-Parana Basin, which is situated at the southern limit of the Amazon lowlands and has experienced extensive deforestation in the last three decades (∼35 000 km2). Our objective was to investigate how extensive land-use changes, from forest to cattle pasture, have affected river biogeochemistry. We measured a series of chemical, biochemical, and isotopic tracers in three size classes of organic matter within five sites along Ji-Parana River and eight more sites in six tributaries. The results were compared with C4 leaf and pasture soils end members in order to test for a pasture-derived signal in the riverine organic matter. The coarse size fraction was least degraded and derived primarily from fresh leaves in lowland forests. The fine fraction was mostly associated with a mineral soil phase, but its ultimate source appeared to be leaves from forests; this fraction was the most enriched in nitrogen. The ultrafiltered dissolved organic matter (UDOM) appeared to have the same source as the coarse fraction, but it was the most extensively degraded of the three fractions. In contrast to Amazon white-water rivers, rivers of the Ji-Parana Basin had lower concentrations of suspended solids with a higher carbon and nitrogen content in the three size fractions. However, principal component analyses showed a correlation between areas covered with pasture and the δ13C values of the three size fractions. The highest δ13C values were observed in the ultrafiltered dissolved organic matter of the Rolim-de-Moura and Jaru rivers, which have the highest areas covered with pasture. The lower the order of the streams and the higher the pasture area, the greater is the possibility that the C4-derived organic matter signal will be detected first in the faster-cycling fraction (UDOM). The large change in land use in the Ji-Parana Basin, replacement of primary forests by C4 pastures for cattle feeding, that has taken place in the last 30–40 yr, has already changed the characteristics of the composition of the riverine organic matter.

Parameterization of Canopy Structure and Leaf-Level Gas Exchange for an Eastern Amazonian Tropical Rain Forest (Tapajós National Forest, Pará, Brazil)

Abstract Carbon flux of Amazonian primary forest vegetation has been shown to vary both spatially and temporally. Process-based models are adequate tools to understand the basis of such variation and can also provide projections to future scenarios. The parameterization of such process-based models requires information from the vegetation in question simply because ecosystem-level gas exchange is a direct result of the tightly coupled interaction between local vegetation and regional climate. In this study, data are presented concerning canopy structure [leaf area index (LAI), and the ratio of leaf dry mass to leaf area (LMA)], leaf chemistry [area-based foliar nitrogen content (Narea) and carbon isotope composition (δ13C)], and photosynthetic gas exchange [maximum carbon assimilation rates (Amax), stomatal conductance (gs@Amax), maximum carboxylation capacity (Vcmax), and respiration rates (Rd)] versus relative height from an extensive survey of primary forest vegetation of the Santarem region (eastern A...

Caatinga, the Brazilian dry tropical forest: can it tolerate climate changes?

Our review focuses on the projections of climate change in the Brazilian semiarid region, the Caatinga, based on recent publications about global climate change and biology. We found several vulnerable points in the initial estimates, the main one being that the data were collected and analyzed without a multidisciplinary knowledge. This review discusses several studies that show the current knowledge in many semiarid regions around the world. Some of these studies argue for the increase in vegetation greenness responses even under severe and prolonged drought, based on the high resilience the Caatinga native species show under severe drought conditions over the years. Additionally, we include in this review recent data produced by our group on key ecophysiological variables under drought conditions. We also show successful examples of deforested areas recovery in the semiarid region of the Central America. It is critical that the recovery of semiarid areas is coupled with the implementation of socio-environmental policies, engaging the local population and providing subsidies for life wealth improvement. These are key aspects for a long-term recovery and conservation of the Brazilian dry tropical forest.

Stable isotopes of bulk organic matter to trace carbon and nitrogen dynamics in an estuarine ecosystem in Babitonga Bay (Santa Catarina, Brazil).

The biogeochemical processes affecting the transport and cycling of terrestrial organic carbon in coastal and transition areas are still not fully understood. One means of distinguishing between the sources of organic materials contributing to particulate organic matter (POM) in Babitonga Bay waters and sediments is by the direct measurement of delta(13)C of dissolved inorganic carbon (DIC) and delta(13)C and delta(15)N in the organic constituents. An isotopic survey was taken from samples collected in the Bay in late spring of 2004. The results indicate that the delta(13)C and delta(15)N compositions of OM varied from -21.7 per thousand to -26.2 per thousand and from +9.2 per thousand to -0.1 per thousand, respectively. delta(13)C from DIC ranges from +0.04 per thousand to -12.7 per thousand. The difference in the isotope compositions enables the determination of three distinct end-members: terrestrial, marine and urban. Moreover, the evaluation of source contribution to the particulate organic matter (POM) in the Bay, enables assessment of the anthropogenic impact. Comparing the depleted values of delta(13)C(DIC) and delta(13)C(POC) it is possible to further understand the carbon dynamic within Babitonga Bay.

Addressing the complexity of the Earth system

This paper discusses the development of a prediction system that integrates physical, biogeochemical, and societal processes in a unified Earth system framework. Such development requires collaborations among physical and social scientists, and should include i) the development of global Earth system analysis and prediction models that account for physical, chemical, and biological processes in a coupled atmosphere–ocean–land–ice system; ii) the development of a systematic framework that links the global climate and regionally constrained weather systems and the interactions and associated feedbacks with biogeochemistry, biology, and socioeconomic drivers (e.g., demography, global policy constraints, technological innovations) across scales and disciplines; and iii) the exploration and development of methodologies and models that account for societal drivers (e.g., governance, institutional dynamics) and their impacts and feedbacks on environmental and climate systems.