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All over the world, the oceans are the final destination of sewage transported by river estuaries, rainwater and other coastal discharges. The risks to human health related to direct contact with water and consumption of contaminated fish are well known, but little is known about the potential for atmospheric exposure to pollutants and pathogens from contaminated seawater. The release of microbial particles from the sea into the atmosphere occurs mainly by the eruption of rising bubbles through the sea surface microlayer (SML) or by sea spray. We investigated the heterotrophic bacteria density and relative abundance in SML and bioaerosols originated on the seafront of Fortaleza (Atlantic coastal zone, northeastern Brazil) influenced by wastewater disposal. There was a difference in the density of total heterotrophic bacteria (THB) according to the matrix analyzed during two seasons: the bacterial count was highest in the SML during the rainy season while the highest number of bacteria in bioaerosols samples was recorded during the dry season. Twenty-nine bacterial taxonomic groups were identified with variable abundance for both environments. These were the same in both matrices, with environmental variables influencing their abundance and composition. The contribution of the marine and continental environments in shaping the microbiota of the SML and coastal bioaerosols was clear, with the constant and representative presence of Enterobacteria standing out. The aerosolization of bacteria resulting from the discharge of untreated sewage is an important issue related to coastal environmental health and ecological safety., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Per- and polyfluoroalkyl substances (PFAS), often referred to as "forever chemicals", are a class of man-made, extremely stable chemicals, which are widely used in industrial and commercial applications. Exposure to some PFAS is now known to be detrimental to human health. By virtue of PFAS long residence times, they are widely detected in the environment, including remote locations such as the Arctics, where the origin of the PFAS is poorly understood. It has been suggested that PFAS may be transported through contaminated waters, leading to accumulation in coastal areas, where they can be aerosolised via sea spray, thereby extending their geographical distribution far beyond their original source regions. The aim of this work is to investigate, for the first time, whether "forever chemicals" could be transported to areas considered to be pristine, far from coastal sites. This study was performed at the Amazonian Tall Tower Observatory (ATTO), a unique remote site situated in the middle of the Amazon rainforest, where a restricted PFAS, perfluorooctanoic acid (PFOA), was observed with concentrations reaching up to 2 pg/m 3 . A clear trend of increasing concentration with sampling height was observed and air masses from the south over Manaus had the highest concentrations. Atmospheric lifetime estimations, removal mechanisms supported by measurements at two heights (320 and 42 m above the rainforest), and concentration spikes indicated a long-range transport of PFOA to pristine Amazon rainforest. Potential sources, including industrial activities in urban areas, were explored, and historical fire management practices considered. This research presents the first measurements of PFAS in the atmosphere of Amazon rainforest. Remarkably, even in this remote natural environment, appreciable levels of PFAS can be detected. This study provides valuable insights into the long-range transport of the anthropogenic "forever chemical" into a remote natural ecosystem and should raise awareness of potential environmental implications., Competing Interests: Declaration of competing interest The authors declare they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The nitrogen isotopic composition of sedimentary rocks (δ 15 N) can trace redox-dependent biological pathways and early Earth oxygenation 1,2 . However, there is no substantial change in the sedimentary δ 15 N record across the Great Oxidation Event about 2.45 billion years ago (Ga) 3 , a prominent redox change. This argues for a temporal decoupling between the emergence of the first oxygen-based oxidative pathways of the nitrogen cycle and the accumulation of atmospheric oxygen after 2.45 Ga (ref.  3 ). The transition between both states shows strongly positive δ 15 N values (10-50‰) in rocks deposited between 2.8 Ga and 2.6 Ga, but their origin and spatial extent remain uncertain 4,5 . Here we report strongly positive δ 15 N values (>30‰) in the 2.68-Gyr-old shallow to deep marine sedimentary deposit of the Serra Sul Formation 6 , Amazonian Craton, Brazil. Our findings are best explained by regionally variable extents of ammonium oxidation to N 2 or N 2 O tied to a cryptic oxygen cycle, implying that oxygenic photosynthesis was operating at 2.7 Ga. Molecular oxygen production probably shifted the redox potential so that an intermediate N cycle based on ammonium oxidation developed before nitrate accumulation in surface waters. We propose to name this period, when strongly positive nitrogen isotopic compositions are superimposed on the usual range of Precambrian δ 15 N values, the Nitrogen Isotope Event. We suggest that it marks the earliest steps of the biogeochemical reorganizations that led to the Great Oxidation Event., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

This study examines the gasification kinetics of Brazilian municipal solid waste (MSW) and its components under air, CO 2, and air/CO 2 (70/30 vol%) atmospheres. The ignition indices of paper and plastic are 6 and 3 times that of food waste, which are 38.6 × 10 -3  %/min 3 and 19.6 × 10 -3  %/min 3 , respectively, implying a faster separation of volatile compounds from the paper and plastic. The minimum E α values of 132 kJ/mol and 140 kJ/mol have been obtained for paper waste under air and air/CO 2 , respectively. On CO 2 condition, MSW has an average E a value of 96 kJ/mol. Under an air/CO 2 atmosphere, a high synergistic ΔW of -4.7 wt% has been identified between individual components. The presence of air and CO 2 improves the oxidation and char gasification process, thus resulting in better combustion. Hence, the gasification of MSW under an air/CO 2 atmosphere would improve the waste-to-energy plant's performance and minimize the CO 2 emission., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The Amazon forest carbon sink is declining, mainly as a result of land-use and climate change 1-4 . Here we investigate how changes in law enforcement of environmental protection policies may have affected the Amazonian carbon balance between 2010 and 2018 compared with 2019 and 2020, based on atmospheric CO 2 vertical profiles 5,6 , deforestation 7 and fire data 8 , as well as infraction notices related to illegal deforestation 9 . We estimate that Amazonia carbon emissions increased from a mean of 0.24 ± 0.08 PgC year -1 in 2010-2018 to 0.44 ± 0.10 PgC year -1 in 2019 and 0.52 ± 0.10 PgC year -1 in 2020 (± uncertainty). The observed increases in deforestation were 82% and 77% (94% accuracy) and burned area were 14% and 42% in 2019 and 2020 compared with the 2010-2018 mean, respectively. We find that the numbers of notifications of infractions against flora decreased by 30% and 54% and fines paid by 74% and 89% in 2019 and 2020, respectively. Carbon losses during 2019-2020 were comparable with those of the record warm El Niño (2015-2016) without an extreme drought event. Statistical tests show that the observed differences between the 2010-2018 mean and 2019-2020 are unlikely to have arisen by chance. The changes in the carbon budget of Amazonia during 2019-2020 were mainly because of western Amazonia becoming a carbon source. Our results indicate that a decline in law enforcement led to increases in deforestation, biomass burning and forest degradation, which increased carbon emissions and enhanced drying and warming of the Amazon forests., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

An estimated 90 to 95% of Indigenous people in Amazonia died after European contact. This population collapse is postulated to have caused decreases in atmospheric carbon dioxide concentrations at around 1610 CE, as a result of a wave of land abandonment in the wake of disease, slavery, and warfare, whereby the attendant reversion to forest substantially increased terrestrial carbon sequestration. On the basis of 39 Amazonian fossil pollen records, we show that there was no synchronous reforestation event associated with such an atmospheric carbon dioxide response after European arrival in Amazonia. Instead, we find that, at most sites, land abandonment and forest regrowth began about 300 to 600 years before European arrival. Pre-European pandemics, social strife, or environmental change may have contributed to these early site abandonments and ecological shifts., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Isoprene is the dominant non-methane organic compound emitted to the atmosphere 1-3 . It drives ozone and aerosol production, modulates atmospheric oxidation and interacts with the global nitrogen cycle 4-8 . Isoprene emissions are highly uncertain 1,9 , as is the nonlinear chemistry coupling isoprene and the hydroxyl radical, OH-its primary sink 10-13 . Here we present global isoprene measurements taken from space using the Cross-track Infrared Sounder. Together with observations of formaldehyde, an isoprene oxidation product, these measurements provide constraints on isoprene emissions and atmospheric oxidation. We find that the isoprene-formaldehyde relationships measured from space are broadly consistent with the current understanding of isoprene-OH chemistry, with no indication of missing OH recycling at low nitrogen oxide concentrations. We analyse these datasets over four global isoprene hotspots in relation to model predictions, and present a quantification of isoprene emissions based directly on satellite measurements of isoprene itself. A major discrepancy emerges over Amazonia, where current underestimates of natural nitrogen oxide emissions bias modelled OH and hence isoprene. Over southern Africa, we find that a prominent isoprene hotspot is missing from bottom-up predictions. A multi-year analysis sheds light on interannual isoprene variability, and suggests the influence of the El Niño/Southern Oscillation.

As COVID-19 spread all over the world, most of the countries adopted some kind of restrictions to avoid the collapse of health systems. In Brazil, São Paulo and Rio the Janeiro, the two most populated cities in the country, were the first to determine social distancing. In this study, the impact of the social distancing measures on the concentrations of the three main primary air pollutants (PM 10 , NO 2 and CO) was analyzed. CO levels showed the most significant reductions (up to 100%) since it is related to light-duty vehicular emissions. NO 2 also showed reductions (9.1%-41.8%) while PM 10 levels were only reduced in the 1st lockdown week. The decrease of pollutants was not directly proportional to the vehicular flux reduction, because it depends on other factors such as the transport of air masses from industrial and rural areas. The differences observed can be explained considering the fleet characteristics in the two cities and the response of the population to the social distancing recommendations.

Enhanced silicate rock weathering (ERW), deployable with croplands, has potential use for atmospheric carbon dioxide (CO 2 ) removal (CDR), which is now necessary to mitigate anthropogenic climate change 1 . ERW also has possible co-benefits for improved food and soil security, and reduced ocean acidification 2-4 . Here we use an integrated performance modelling approach to make an initial techno-economic assessment for 2050, quantifying how CDR potential and costs vary among nations in relation to business-as-usual energy policies and policies consistent with limiting future warming to 2 degrees Celsius 5 . China, India, the USA and Brazil have great potential to help achieve average global CDR goals of 0.5 to 2 gigatonnes of carbon dioxide (CO 2 ) per year with extraction costs of approximately US$80-180 per tonne of CO 2 . These goals and costs are robust, regardless of future energy policies. Deployment within existing croplands offers opportunities to align agriculture and climate policy. However, success will depend upon overcoming political and social inertia to develop regulatory and incentive frameworks. We discuss the challenges and opportunities of ERW deployment, including the potential for excess industrial silicate materials (basalt mine overburden, concrete, and iron and steel slag) to obviate the need for new mining, as well as uncertainties in soil weathering rates and land-ocean transfer of weathered products.

Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions 1-3 . Climate-driven vegetation models typically predict that this tropical forest 'carbon sink' will continue for decades 4,5 . Here we assess trends in the carbon sink using 244 structurally intact African tropical forests spanning 11 countries, compare them with 321 published plots from Amazonia and investigate the underlying drivers of the trends. The carbon sink in live aboveground biomass in intact African tropical forests has been stable for the three decades to 2015, at 0.66 tonnes of carbon per hectare per year (95 per cent confidence interval 0.53-0.79), in contrast to the long-term decline in Amazonian forests 6 . Therefore the carbon sink responses of Earth's two largest expanses of tropical forest have diverged. The difference is largely driven by carbon losses from tree mortality, with no detectable multi-decadal trend in Africa and a long-term increase in Amazonia. Both continents show increasing tree growth, consistent with the expected net effect of rising atmospheric carbon dioxide and air temperature 7-9 . Despite the past stability of the African carbon sink, our most intensively monitored plots suggest a post-2010 increase in carbon losses, delayed compared to Amazonia, indicating asynchronous carbon sink saturation on the two continents. A statistical model including carbon dioxide, temperature, drought and forest dynamics accounts for the observed trends and indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly. Overall, the uptake of carbon into Earth's intact tropical forests peaked in the 1990s. Given that the global terrestrial carbon sink is increasing in size, independent observations indicating greater recent carbon uptake into the Northern Hemisphere landmass 10 reinforce our conclusion that the intact tropical forest carbon sink has already peaked. This saturation and ongoing decline of the tropical forest carbon sink has consequences for policies intended to stabilize Earth's climate.

The emissions, deposition, and chemistry of volatile organic compounds (VOCs) are thought to be influenced by underlying landscape heterogeneity at intermediate horizontal scales of several hundred meters across different forest subtypes within a tropical forest. Quantitative observations and scientific understanding at these scales, however, remain lacking, in large part due to a historical absence of canopy access and suitable observational approaches. Herein, horizontal heterogeneity in VOC concentrations in the near-canopy atmosphere was examined by sampling from an unmanned aerial vehicle (UAV) flown horizontally several hundred meters over the plateau and slope forests in central Amazonia during the morning and early afternoon periods of the wet season of 2018. Unlike terpene concentrations, the isoprene concentrations in the near-canopy atmosphere over the plateau forest were 60% greater than those over the slope forest. A gradient transport model constrained by the data suggests that isoprene emissions differed by 220 to 330% from these forest subtypes, which is in contrast to a 0% difference implemented in most present-day biosphere emissions models (i.e., homogeneous emissions). Quantifying VOC concentrations, emissions, and other processes at intermediate horizontal scales is essential for understanding the ecological and Earth system roles of VOCs and representing them in climate and air quality models., Competing Interests: The authors declare no conflict of interest.

Organosulfates are formed in the atmosphere from reactions between reactive organic compounds (such as oxidation products of isoprene) and acidic sulfate aerosol. Here we investigated speciated organosulfates in an area typically downwind of the city of Manaus situated in the Amazon forest in Brazil during "GoAmazon2014/5" in both the wet season (February-March) and dry season (August-October). We observe products consistent with the reaction of isoprene photooxidation products and sulfate aerosols, leading to formation of several types of isoprene-derived organosulfates, which contribute 3% up to 42% of total sulfate aerosol measured by aerosol mass spectrometry. During the wet season the average contribution of summed organic sulfate concentrations to total sulfate was 19 ± 10% and similarly during the dry season the contribution was 19 ± 8%. This is the highest fraction of speciated organic sulfate to total sulfate observed at any reported site. Organosulfates appeared to be dominantly formed from isoprene epoxydiols (IEPOX), averaging 104 ± 73 ng m-3 (range 15-328 ng m-3) during the wet season, with much higher abundance 610 ± 400 ng m-3 (range 86-1962 ng m-3) during the dry season. The concentration of isoprene-derived organic sulfate correlated with total inorganic sulfate (R2 = 0.35 and 0.51 during the wet and dry seasons, respectively), implying the significant influence of inorganic sulfate aerosol for the heterogeneous reactive uptake of IEPOX. Organosulfates also contributed to organic matter in aerosols (3.5 ± 1.9% during the wet season and 5.1 ± 2.5% during the dry season). The present study shows that an important fraction of sulfate in aerosols in the Amazon downwind of Manaus consists of multifunctional organic chemicals formed in the atmosphere, and that increased SO2 emissions would substantially increase SOA formation from isoprene.

Soil greenhouse gas (GHG) emissions are a significant environmental problem resulting from microbially-mediated nitrogen (N) and carbon (C) cycling. This study aimed to investigate the impact of Eucalyptus plantations on the structure and function of a soil microbial community, and how resulting alterations may be linked to GHG fluxes. We sampled and monitored two adjacent Eucalyptus plantations-a recently logged site that harbored new seedlings and an adult plantation-and compared them to a site hosting native vegetation. We used 16S rRNA gene sequencing and qPCR amplifications of key nitrogen and methane cycle genes to characterize microbial structure and functional gene abundance and compared our data with soil parameters and GHG fluxes. Both microbial community attributes were significantly affected by land use and logging of Eucalyptus plantations. The genes nosZ and archaeal amoA were significantly more abundant in native forest than in either young or old Eucalyptus plantations. Statistical analyses suggest that land use type has a greater impact on microbial community structure and functional gene abundance than Eucalyptus rotation. There was no correlation between GHG fluxes and shifts in microbial community, suggesting that microbial community structure and functional gene abundance are not the main drivers of GHG fluxes in this system.

Nonstructural carbon (NSC) reserves act as buffers to sustain tree activity during periods when carbon (C) assimilation does not meet C demand, but little is known about their age and accessibility; we designed a controlled girdling experiment in the Amazon to study tree survival on NSC reserves. We used bomb-radiocarbon ( 14 C) to monitor the time elapsed between C fixation and release ('age' of substrates). We simultaneously monitored how the mobilization of reserve C affected δ 13 CO 2 . Six ungirdled control trees relied almost exclusively on recent assimilates throughout the 17 months of measurement. The Δ 14 C of CO 2 emitted from the six girdled stems increased significantly over time after girdling, indicating substantial remobilization of storage NSC fixed up to 13-14 yr previously. This remobilization was not accompanied by a consistent change in observed δ 13 CO 2 . These trees have access to storage pools integrating C accumulated over more than a decade. Remobilization follows a very clear reverse chronological mobilization with younger reserve pools being mobilized first. The lack of a shift in the δ 13 CO 2 might indicate a constant contribution of starch hydrolysis to the soluble sugar pool even outside pronounced stress periods (regular mixing)., (© 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.)

Atmospheric carbon dioxide records indicate that the land surface has acted as a strong global carbon sink over recent decades, with a substantial fraction of this sink probably located in the tropics, particularly in the Amazon. Nevertheless, it is unclear how the terrestrial carbon sink will evolve as climate and atmospheric composition continue to change. Here we analyse the historical evolution of the biomass dynamics of the Amazon rainforest over three decades using a distributed network of 321 plots. While this analysis confirms that Amazon forests have acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation. Rates of net increase in above-ground biomass declined by one-third during the past decade compared to the 1990s. This is a consequence of growth rate increases levelling off recently, while biomass mortality persistently increased throughout, leading to a shortening of carbon residence times. Potential drivers for the mortality increase include greater climate variability, and feedbacks of faster growth on mortality, resulting in shortened tree longevity. The observed decline of the Amazon sink diverges markedly from the recent increase in terrestrial carbon uptake at the global scale, and is contrary to expectations based on models.

High concentrations of arsenic (>50μg L(-1)) have been detected for the first time in groundwater of the wave-dominated Paraiba do Sul delta, Brazil. The deltaic shallow groundwater aquifer is enriched in arsenic fixed by authigenic sulfides. A study of palynomorphs confirmed that aquifer sediments were formed in inter-dune lakes/swamps lately covered by eolian sands. The organic sediments of contemporaneous inter-dune lake/swamp contain very high concentration of As: up to 180mg kg(-1) and 163μg L(-1) in dry gyttja material and interstitial water, respectively. The As in recent lake/swamp sediments is retained by iron hydroxides in upper and probably by sulfides in lower layers. In the absence of connection of inter-dune lakes/swamps with fluvial currents, the atmospheric input of As could be considered as the principal source in sediments. The calculation demonstrates the possibility of high concentrations of As accumulation in sediments of inter-dune lakes/swamps from atmospheric precipitations within several centuries before they will be covered by eolian sands and turned into shallow aquifer. Considering the commonalities of wave-dominated delta formations, we can predict more prevalent As accumulation in delta plain groundwater., (Copyright © 2014 Elsevier B.V. All rights reserved.)

This work presents the application of a new method to facilitate the distinction between biologically produced (primary) and atmospherically produced (secondary) organic compounds in ambient aerosols based on their chirality. The compounds chosen for this analysis were the stereomers of 2-methyltetraols, (2R,3S)- and (2S,3R)-methylerythritol, (l- and d-form, respectively), and (2S,3S)- and (2R,3R)-methylthreitol (l- and d-form), shown previously to display some enantiomeric excesses in atmospheric aerosols, thus to have at least a partial biological origin. In this work PM10 aerosol fractions were collected in a remote tropical rainforest environment near Manaus, Brazil, between June 2008 and June 2009 and analysed. Both 2-methylerythritol and 2-methylthreitol displayed a net excess of one enantiomer (either the l- or the d-form) in 60 to 72% of these samples. These net enantiomeric excesses corresponded to compounds entirely biological but accounted for only about 5% of the total 2-methyltetrol mass in all the samples. Further analysis showed that, in addition, a large mass of the racemic fractions (equal mixtures of d- and l-forms) was also biological. Estimating the contribution of secondary reactions from the isomeric ratios measured in the samples (=ratios 2-methylthreitol over 2-methylerythritol), the mass fraction of secondary methyltetrols in these samples was estimated to a maximum of 31% and their primary fraction to a minimum of 69%. Such large primary fractions could have been expected in PM10 aerosols, largely influenced by biological emissions, and would now need to be investigated in finer aerosols. This work demonstrates the effectiveness of chiral and isomeric analyses as the first direct tool to assess the primary and secondary fractions of organic aerosols.

Feedbacks between land carbon pools and climate provide one of the largest sources of uncertainty in our predictions of global climate. Estimates of the sensitivity of the terrestrial carbon budget to climate anomalies in the tropics and the identification of the mechanisms responsible for feedback effects remain uncertain. The Amazon basin stores a vast amount of carbon, and has experienced increasingly higher temperatures and more frequent floods and droughts over the past two decades. Here we report seasonal and annual carbon balances across the Amazon basin, based on carbon dioxide and carbon monoxide measurements for the anomalously dry and wet years 2010 and 2011, respectively. We find that the Amazon basin lost 0.48 ± 0.18 petagrams of carbon per year (Pg C yr(-1)) during the dry year but was carbon neutral (0.06 ± 0.1 Pg C yr(-1)) during the wet year. Taking into account carbon losses from fire by using carbon monoxide measurements, we derived the basin net biome exchange (that is, the carbon flux between the non-burned forest and the atmosphere) revealing that during the dry year, vegetation was carbon neutral. During the wet year, vegetation was a net carbon sink of 0.25 ± 0.14 Pg C yr(-1), which is roughly consistent with the mean long-term intact-forest biomass sink of 0.39 ± 0.10 Pg C yr(-1) previously estimated from forest censuses. Observations from Amazonian forest plots suggest the suppression of photosynthesis during drought as the primary cause for the 2010 sink neutralization. Overall, our results suggest that moisture has an important role in determining the Amazonian carbon balance. If the recent trend of increasing precipitation extremes persists, the Amazon may become an increasing carbon source as a result of both emissions from fires and the suppression of net biome exchange by drought.

River systems connect the terrestrial biosphere, the atmosphere and the ocean in the global carbon cycle. A recent estimate suggests that up to 3 petagrams of carbon per year could be emitted as carbon dioxide (CO2) from global inland waters, offsetting the carbon uptake by terrestrial ecosystems. It is generally assumed that inland waters emit carbon that has been previously fixed upstream by land plant photosynthesis, then transferred to soils, and subsequently transported downstream in run-off. But at the scale of entire drainage basins, the lateral carbon fluxes carried by small rivers upstream do not account for all of the CO2 emitted from inundated areas downstream. Three-quarters of the world's flooded land consists of temporary wetlands, but the contribution of these productive ecosystems to the inland water carbon budget has been largely overlooked. Here we show that wetlands pump large amounts of atmospheric CO2 into river waters in the floodplains of the central Amazon. Flooded forests and floating vegetation export large amounts of carbon to river waters and the dissolved CO2 can be transported dozens to hundreds of kilometres downstream before being emitted. We estimate that Amazonian wetlands export half of their gross primary production to river waters as dissolved CO2 and organic carbon, compared with only a few per cent of gross primary production exported in upland (not flooded) ecosystems. Moreover, we suggest that wetland carbon export is potentially large enough to account for at least the 0.21 petagrams of carbon emitted per year as CO2 from the central Amazon River and its floodplains. Global carbon budgets should explicitly address temporary or vegetated flooded areas, because these ecosystems combine high aerial primary production with large, fast carbon export, potentially supporting a substantial fraction of CO2 evasion from inland waters.

Vegetation affects precipitation patterns by mediating moisture, energy and trace-gas fluxes between the surface and atmosphere. When forests are replaced by pasture or crops, evapotranspiration of moisture from soil and vegetation is often diminished, leading to reduced atmospheric humidity and potentially suppressing precipitation. Climate models predict that large-scale tropical deforestation causes reduced regional precipitation, although the magnitude of the effect is model and resolution dependent. In contrast, observational studies have linked deforestation to increased precipitation locally but have been unable to explore the impact of large-scale deforestation. Here we use satellite remote-sensing data of tropical precipitation and vegetation, combined with simulated atmospheric transport patterns, to assess the pan-tropical effect of forests on tropical rainfall. We find that for more than 60 per cent of the tropical land surface (latitudes 30 degrees south to 30 degrees north), air that has passed over extensive vegetation in the preceding few days produces at least twice as much rain as air that has passed over little vegetation. We demonstrate that this empirical correlation is consistent with evapotranspiration maintaining atmospheric moisture in air that passes over extensive vegetation. We combine these empirical relationships with current trends of Amazonian deforestation to estimate reductions of 12 and 21 per cent in wet-season and dry-season precipitation respectively across the Amazon basin by 2050, due to less-efficient moisture recycling. Our observation-based results complement similar estimates from climate models, in which the physical mechanisms and feedbacks at work could be explored in more detail.

This study aimed to verify the impact of inhalable particulate matter (PM(10)) on cancer incidence and mortality in the city of São Paulo, Brazil. Statistical techniques were used to investigate the relationship between PM(10) on cancer incidence and mortality in selected districts. For some types of cancer (skin, lung, thyroid, larynx, and bladder) and some periods, the correlation coefficients ranged from 0.60 to 0.80 for incidence. Lung cancer mortality showed more correlations during the overall period. Spatial analysis showed that districts distant from the city center showed higher than expected relative risk, depending on the type of cancer. According to the study, urban PM(10) can contribute to increased incidence of some cancers and may also contribute to increased cancer mortality. The results highlight the need to adopt measures to reduce atmospheric PM(10) levels and the importance of their continuous monitoring.

Total ²¹⁰Pb and ⁷Be fallout rates were measured on the coastal region of Niteroi, Brazil. The monthly depositional flux of ²¹⁰Pb and ⁷Be varied by a factor of 26, from 1.7 to 43.3 mBq cm⁻² year⁻¹ and ∼27, from 7.5 to 203.5 mBq cm⁻² year⁻¹, respectively. The relatively large oscillations in the depositional flux of ²¹⁰Pb at this study site were likely due to variations in air mass sources, while the ⁷Be fluctuations may be driven by a combination of weather conditions. Local geology could support the periodic high fluxes of ²¹⁰Pb from continental air masses, as shifting oceanic wind sources were affirmed by the uncorrelated ²¹⁰Pb and ⁷Be fallout activities and ⁷Be/²¹⁰Pb ratios. The ²¹⁰Pb atmospheric deposition was found to be in agreement with local sediment inventories, an important consideration in geochemical studies that estimate sedimentation processes., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Urban particulate matter (UPM) contributes to lung cancer incidence. Here, we have studied the mutagenic activity and DNA adduct-forming ability of fractionated UPM extractable organic matter (EOM). UPM was collected with a high-volume sampler in June 2004 at two sites, one at street level adjacent to a roadway and the other inside a park within the urban area of the city of São Paulo, Brazil. UPM was extracted using dichloromethane, and the resulting EOM was separated by HPLC to obtain PAH, nitro-PAH, and oxy-PAH fractions which were tested for mutagenicity with the Salmonella strains TA98 and YG1041 with and without S9 metabolic activation. The PAH fraction from both sites showed negligible mutagenic activity in both strains. The highest mutagenic activity was found for the nitro-PAH fraction using YG1041 without metabolic activation; however, results were comparable for both sites. The nitro-PAH and oxy-PAH fractions were incubated with calf thymus DNA under reductive conditions appropriate for the activation of nitro aromatic compounds, then DNA adduct patterns and levels were determined with thin-layer chromatography (TLC) 32P-postlabeling method using two enrichment procedures-nuclease P1 digestion and butanol extraction. Reductively activated fractions from both sites produced diagonal radioactive zones (DRZ) of putative aromatic DNA adducts on thin layer plates with both enrichment procedures. No such DRZ were observed in control experiments using fractions from unexposed filters or from incubations without activating system. Total adduct levels produced by the nitro-PAH fractions were similar for both sites ranging from 30 to 45 adducts per 10(8) normal nucleotides. In contrast, the DNA binding of reductively activated oxy-PAH fractions was three times higher and the adduct pattern consisted of multiple discrete spots along the diagonal line on the thin layer plates. However, DNA adduct levels were not significantly different between the sampling sites. Both samples presented the same levels of mutagenic activity. The response in the Salmonella assay was typical of nitroaromatics. Although, more mutagenic activity was related to the nitro-PAH fraction in the Salmonella assay, the oxy-PAH fractions showed the highest DNA adduct levels. More studies are needed to elucidate the nature of the genotoxicants occurring in São Paulo atmospheric samples.

Hydraulic redistribution (HR), the nocturnal vertical transfer of soil water from moister to drier regions in the soil profile by roots, has now been observed in Amazonian trees. We have incorporated HR into an atmospheric general circulation model (the National Center for Atmospheric Research Community Atmospheric Model Version 2) to estimate its impact on climate over the Amazon and other parts of the globe where plants displaying HR occur. Model results show that photosynthesis and evapotranspiration increase significantly in the Amazon during the dry season when plants are allowed to redistribute soil water. Plants draw water up and deposit it into the surface layers, and this water subsidy sustains transpiration at rates that deep roots alone cannot accomplish. The water used for dry season transpiration is from the deep storage layers in the soil, recharged during the previous wet season. We estimate that HR increases dry season (July to November) transpiration by approximately 40% over the Amazon. Our model also indicates that such an increase in transpiration over the Amazon and other drought-stressed regions affects the seasonal cycles of temperature through changes in latent heat, thereby establishing a direct link between plant root functioning and climate.

Rivers are generally supersaturated with respect to carbon dioxide, resulting in large gas evasion fluxes that can be a significant component of regional net carbon budgets. Amazonian rivers were recently shown to outgas more than ten times the amount of carbon exported to the ocean in the form of total organic carbon or dissolved inorganic carbon. High carbon dioxide concentrations in rivers originate largely from in situ respiration of organic carbon, but little agreement exists about the sources or turnover times of this carbon. Here we present results of an extensive survey of the carbon isotope composition (13C and 14C) of dissolved inorganic carbon and three size-fractions of organic carbon across the Amazonian river system. We find that respiration of contemporary organic matter (less than five years old) originating on land and near rivers is the dominant source of excess carbon dioxide that drives outgassing in medium to large rivers, although we find that bulk organic carbon fractions transported by these rivers range from tens to thousands of years in age. We therefore suggest that a small, rapidly cycling pool of organic carbon is responsible for the large carbon fluxes from land to water to atmosphere in the humid tropics.

During the last glacial period, large millennial-scale temperature oscillations--the 'Dansgaard/Oeschger' cycles--were the primary climate signal in Northern Hemisphere climate archives from the high latitudes to the tropics. But whether the influence of these abrupt climate changes extended to the tropical and subtropical Southern Hemisphere, where changes in insolation are thought to be the main direct forcing of climate, has remained unclear. Here we present a high-resolution oxygen isotope record of a U/Th-dated stalagmite from subtropical southern Brazil, covering the past 116,200 years. The oxygen isotope signature varies with shifts in the source region and amount of rainfall in the area, and hence records changes in atmospheric circulation and convective intensity over South America. We find that these variations in rainfall source and amount are primarily driven by summer solar radiation, which is controlled by the Earth's precessional cycle. The Dansgaard/Oeschger cycles can be detected in our record and therefore we confirm that they also affect the tropical hydrological cycle, but that in southern subtropical Brazil, millennial-scale climate changes are not as dominant as they are in the Northern Hemisphere.

Amazonian rainforests are some of the most species-rich tree communities on earth. Here we show that, over the past two decades, forests in a central Amazonian landscape have experienced highly nonrandom changes in dynamics and composition. Our analyses are based on a network of 18 permanent plots unaffected by any detectable disturbance. Within these plots, rates of tree mortality, recruitment and growth have increased over time. Of 115 relatively abundant tree genera, 27 changed significantly in population density or basal area--a value nearly 14 times greater than that expected by chance. An independent, eight-year study in nearby forests corroborates these shifts in composition. Contrary to recent predictions, we observed no increase in pioneer trees. However, genera of faster-growing trees, including many canopy and emergent species, are increasing in dominance or density, whereas genera of slower-growing trees, including many subcanopy species, are declining. Rising atmospheric CO2 concentrations may explain these changes, although the effects of this and other large-scale environmental alterations remain uncertain. These compositional changes could have important impacts on the carbon storage, dynamics and biota of Amazonian forests.

Terrestrial ecosystems in the humid tropics play a potentially important but presently ambiguous role in the global carbon cycle. Whereas global estimates of atmospheric CO2 exchange indicate that the tropics are near equilibrium or are a source with respect to carbon, ground-based estimates indicate that the amount of carbon that is being absorbed by mature rainforests is similar to or greater than that being released by tropical deforestation (about 1.6 Gt C yr-1). Estimates of the magnitude of carbon sequestration are uncertain, however, depending on whether they are derived from measurements of gas fluxes above forests or of biomass accumulation in vegetation and soils. It is also possible that methodological errors may overestimate rates of carbon uptake or that other loss processes have yet to be identified. Here we demonstrate that outgassing (evasion) of CO2 from rivers and wetlands of the central Amazon basin constitutes an important carbon loss process, equal to 1.2 +/- 0.3 Mg C ha-1 yr-1. This carbon probably originates from organic matter transported from upland and flooded forests, which is then respired and outgassed downstream. Extrapolated across the entire basin, this flux-at 0.5 Gt C yr-1-is an order of magnitude greater than fluvial export of organic carbon to the ocean. From these findings, we suggest that the overall carbon budget of rainforests, summed across terrestrial and aquatic environments, appears closer to being in balance than would be inferred from studies of uplands alone.