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.

As part of a joint Brazilian–French project, entitled ‘Hydrology and Geochemistry of the Amazon Basin’, we carried out a seven‐year study (1994–2000) on the distribution, behaviour and flux of particulate and dissolved organic carbon in the Amazon River and its main tributaries (the Negro, Solimões, Branco, Madeira, Tapajós, Xingú and Trombetas rivers).The concentrations of particulate and dissolved organic carbon varied from one river to another and according to the season, but dissolved organic carbon (DOC) always accounted for about 70% of the total organic carbon (TOC). The mean concentration of dissolved organic carbon was 6·1 mg l−1 in the Madeira River, 5·83 mg l−1 in the Solimões River and 12·7 mg l−1 in the Negro River. The percentage in weight of the particulate organic carbon decreased as the concentration of suspended matter increased. The Solimões River contributed the most carbon to the Amazon River: about 500 kg C s−1 during the high water period and about 300 kg C s−1 during the low water period. However, the temporal variations in organic carbon in the Amazon River (i.e. downstream of Manaus) are basically controlled by inputs from the Negro River and its variations. The Negro River does not produce a simple dilution effect. During the high water period (between March and August) the TOC flux, calculated as the sum of the Solimões, Negro and Madeira tributaries, was about 5·7 × 1013 g C yr−1, whereas during the low water period (between September and February) the TOC flux was about 2·6 × 1013 g C yr−1.The mean annual flux of TOC at Óbidos (the final gauging station upstream of the estuary) was about 3·27 × 1013 g C yr−1 (i.e. 32·7 ± 3·3 Tg yr−1). Of this, the flux of DOC represents about 2·7 × 1013 g C yr−1 and the flux of particulate organic carbon (POC) represents about 0·5 × 1013 g C yr−1. The mean annual input of TOC by all tributaries (Negro, Solimões, Madeira, Trombetas, Tapajós and Xingú) was about 2·8 × 1013 g C yr−1. When we compared this input with the output recorded at Óbidos (3·27 × 1013 g C yr−1), we found that the amount of organic carbon increased (about 0·4 × 1013 g C yr−1). This shows that other important sources of organic carbon exist in the lower reaches of the Amazon River. These inputs can be attributed to the adjacent floodplain lake system, called ‘várzea’. Copyright © 2003 John Wiley & Sons, Ltd.

The floodplains of the Amazon basin influence the hydrology and fluxes of suspended solids and solutes on multiple scales. Our study focused on the floodplain of Lago Grande de Curuaí (Óbidos, Brazil), a 4000 km 2 segment of floodplain and local upland catchment representative of the lower Amazon. Based on in situ and satellite data acquired from 1997 to 2003, we calculated the exchanges of water between the floodplain and the river and determined the temporal dynamics of flooded area water derived from river flooding, rainfall, runoff, and exchange with groundwater annually for six years. The Amazon River dominated the inputs of water to the flooded area year-round, accounting about 77% of the annual total inputs; rainfall and runoff accounted for about 9% and 10%, respectively, while seepage from the groundwater system accounted for 4%. The hydrologic residence time of the lake was about three months, and the floodplain made a net contribution of water to the river. The exported volume (net balance between water input and 0022-1694/$ -see front matter ª a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l losses) varied between 4.2 and 7.3 km 3 depending on the year and represented about 0.75 times the maximal storage reached each year. ª

The two long-term sources of atmospheric carbon are CO 2 degassing from metamorphic and volcanic activity, and oxidation of organic carbon (OC) contained in sedimentary rocks, or petrogenic organic carbon (OC petro). The latter flux is still poorly constrained. In this study, we report Particulate Organic Carbon (POC) content and 14 C-activity measurements in Amazon River sediments, which allow for estimates of the OC petro content of these sediments. A large

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[1] The composition, sources, and age of particulate organic matter were determined in an Amazonian river-floodplain system during rising, high, falling, and low water periods over 7 yr (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006), and a mass balance for total organic carbon (dissolved and particulate) was estimated. The Curuai floodplain, composed of several temporally interconnected lakes, is permanently connected to the Amazon River via channels. Organic matter (OM) is imported to the floodplain from the Amazon River mainly during the rising water period and produced in the floodplain and exported to the river during high and falling water periods. No significant exchanges occurred during low water periods. The OM produced in the floodplain is characterized by low C/N ratios and by high chlorophyll a concentrations (Chl-a). The d 13 C signature has a seasonal trend, with more negative d 13 C values during the high water period than other periods. Δ 14 C results indicate that the bulk OM present in floodplain lakes is predominantly post-bomb (i.e., post-1950). Particulate organic carbon (POC) and dissolved organic carbon (DOC) fluxes exported by the Curuai floodplain represent 1.3% and 0.1%, respectively, of the POC and DOC annual fluxes in the mainstem Amazon River at Óbidos but may reach up to 3.3% and 0.8% during falling water. Based on Δ 14 C, d 13 C, Chl-a, and elemental analysis of the particulate organic matter, we demonstrate that floodplain lakes have intense phytoplankton and macrophyte primary production, which is partly exported to the main river channel. Floodplains are thus a significant source of modern and labile organic carbon to the river mainstem, where it can be rapidly degraded and recycled back to the atmosphere.Citation: Moreira-Turcq, P., M.-P. Bonnet, M. Amorim, M. Bernardes, C. Lagane, L. Maurice, M. Perez, and P. Seyler (2013), Seasonal variability in concentration, composition, age, and fluxes of particulate organic carbon exchanged between the floodplain and Amazon River, Global Biogeochem. Cycles, 27,[119][120][121][122][123][124][125][126][127][128][129][130]

The French critical zone initiative, called OZCAR (Observatoires de la Zone Critique-Application et Recherche or Critical Zone Observatories-Application and Research) is a National Research Infrastructure (RI). OZCAR-RI is a network of instrumented sites, bringing together 21 pre-existing research observatories monitoring different compartments of the zone situated between "the rock and the sky," the Earth's skin or critical zone (CZ), over the long term. These observatories are regionally based and have specific initial scientific questions, monitoring strategies, databases, and modeling activities. The diversity of OZCAR-RI observatories and sites is well representative of the heterogeneity of the CZ and of the scientific communities studying it. Despite this diversity, all OZCAR-RI sites share a main overarching mandate, which is to monitor, understand, and predict ("earthcast") the fluxes of water and matter of the Earth's near surface and how they will change in response to the "new climatic regime." The vision for OZCAR strategic development aims at designing an open infrastructure, building a national CZ community able to share a systemic representation of the CZ , and educating a new generation of scientists more apt to tackle the wicked problem of the Anthropocene. OZCAR articulates around: (i) a set of common scientific questions and cross-cutting scientific activities using the wealth of OZCAR-RI observatories, (ii) an ambitious instrumental development program, and (iii) a better interaction between data and models to integrate the different time and spatial scales. Internationally, OZCAR-RI aims at strengthening the CZ community by providing a model of organization for pre-existing observatories and by offering CZ instrumented sites. OZCAR is one of two French mirrors of the European Strategy Forum on Research Infrastructure (eLTER-ESFRI) project.

To trace the origin of branched glycerol dialkyl glycerol tetraethers (brGDGTs), their distribution in soils and suspended particulate matter (SPM) of Amazonian rivers and floodplain lakes (várzeas) was studied. Differences in distribution between river SPM and surrounding (lowland) soils suggests an additional brGDGT source to eroded soils in the lowland drainage basin. Erosion of high Andean soils (above 2500 m in altitude) has no major influence because its brGDGT distribution differs substantially from that in river SPM. Furthermore, SPM in the Tapajó s River, a tributary that does not derive from the Andes, has a virtually identical brGDGT distribution to that of the Amazon main stem. The higher proportion of phospholipid-derived brGDGTs in river SPM compared to soils indicates that in situ production in the Amazon is an additional source for riverine brGDGTs. This affects the methylation and cyclization index of brGDGTs (MBT-CBT), resulting in slightly lower MBT-CBT-derived temperatures and slightly higher CBT-derived pH values, i.e., between the pH of the basin soil and that of the river. Since the difference between MBT-CBT-derived temperatures of Amazon River SPM and the surrounding soils is relatively small (2uC) compared to other aquatic systems (for lakes a difference of , 10uC has been observed), it might still be possible to trace large climate changes in the Amazon basin with the MBT-CBT using river fan cores. However, variations in in situ production of brGDGTs in the Amazon River over time and space have to be evaluated in the future. Likewise, in situ production may affect the application of the MBT-CBT paleothermometer in other river systems. Our results also show that crenarchaeol is primarily produced in the Amazon River and that its varying production influences the branched vs. isoprenoid tetraether (BIT) index. This indicates that the BIT index not only represents the input of soil organic carbon to the river but is also affected by in situ production of brGDGTs and crenarchaeol.