The compositional evolution of dissolved and particulate organic matter along the lower Amazon River—Óbidos to the ocean

Ward, Nicholas D.; Krusche, Alex V.; Sawakuchi, Henrique O.; Brito, Daímio Chaves; Cunha, Alan Cavalcanti da; Moura, J. M. S.; Silva, Rodrigo da; Yager, Patricia L.; Keil, Richard G.; Richey, Jeffrey E.

doi:10.1016/j.marchem.2015.06.013

Cited by 86 publications

(172 citation statements)

References 102 publications

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“…9a, reflecting dominant input of in situ production, consistent with prior observations of Tapajós River POC composition (Mortillaro et al, 2011;Kim et al, 2012;Ward et al, 2015). The combination of a relatively deep euphotic zone depth and slower water velocities in the Tapajós River, especially during high water in July, encourages the growth of phytoplankton and cyanobacteria (Mortillaro et al, 2011).…”

Section: Prominent Soil-derived Poc Source To the Main Stemsupporting

confidence: 83%

“…Still, measurements at Óbidos exclude the influences of influx from the Tapajós, Trombetas, Xingu and Tocantins rivers. The omission of these downstream tributaries has bearings on interpretations of POC flux to the ocean from the Amazon River, and has encouraged more recent studies to sample along transects of the river system between Óbidos, or sites upstream, and the river plume (e.g., Ward et al, 2015). Further, interpreting point measurements at one location of the river network is limiting because large rivers systems like the Amazon are heterogeneous in space and time.…”

Section: Introductionmentioning

confidence: 99%

“…Finally, seasonality presents another challenge to measuring fluxes. Water levels in the Amazon River alone fluctuate by at least a factor of two between the rainy and dry seasons (Moreira-Turcq et al, 2013), which manifests in variability in POC flux and composition as well (Richey et al, 1990;Kim et al, 2012;Ward et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

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Novel analytical strategies for tracing the organic carbon cycle in marine and riverine particles

Rosengard¹

2017

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Particulate organic carbon (POC) in the ocean and mobilized by rivers on land transfers ~0.1% of global primary productivity to the deep ocean sediments. This small fraction regulates the long-term carbon cycle by removing carbon dioxide from the atmosphere for centuries to millennia. This thesis investigates mechanisms of POC transfer to the deep ocean by analyzing particles collected in transit through two globally significant carbon reservoirs: the Southern Ocean and the Amazon River Basin. These endeavors test the hypothesis that organic matter composition controls the recycling and transfer efficiency of POC to the deep ocean, and illustrate new applications for ramped pyrolysis/oxidation (RPO), a growing method of POC characterization by thermal stability. By coupling RPO to stable and radiocarbon isotope analyses of riverine POC, I quantify three thermally distinct soil organic carbon pools mobilized by the Amazon River, and evaluate the degradability and fate of these different pools during transport to the coastal Atlantic Ocean. More directly, RPO analyses of marine samples suggest that POC transfer in the water column is in fact selective. Observations of consistent biomolecular changes that accompany transport of phytoplankton-derived organic matter to depth across the Southern Ocean support the argument for preferential degradation of specific POC pools in the water column. Combining discussions of POC recycling and transfer across both marine and terrestrial systems offer new perspectives of thermal stability as a proxy for diagenetic stability and POC degradation state. The challenges of interpreting RPO data in these two environments set the stage for applying the technique to more controlled experiments that trace POC from source to long-term sink.

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Section: Prominent Soil-derived Poc Source To the Main Stemsupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

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Novel analytical strategies for tracing the organic carbon cycle in marine and riverine particles

Rosengard¹

2017

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“…Keywords: Amazon, Carbon Cycle, Xingu River, Tapajós River, greenhouse gases INTRODUCTION Recent research has undermined the view of rivers as passive conveyors of organic matter, and demonstrates their role in the transport, modulation, and deposition of carbon (Cole et al, 2007;Tranvik et al, 2009;Aufdenkampe et al, 2011;Ward et al, 2015). Inland waters emit at least 0.8 Pg of carbon per year (Cole et al, 2007;Tranvik et al, 2009).…”

mentioning

confidence: 99%

“…The Amazonian rivers represent about 15% of the terrestrial gross primary production and 25% of the global rivers emissions of CO 2 (Field, 1998;Richey et al, 2002). Most studies that have considered organic matter remineralization and carbon storage in the region focused on the Amazon mainstem and its floodplains (Richey et al, 2002;Bouchez et al, 2010Bouchez et al, , 2012Abril et al, 2014;Ward et al, 2015). However, the lack of geochemical data to constrain the role of major clearwater tributaries of the Amazon River as a source or sink of organic sediments limited the understanding of the carbon cycling dynamics across the terrestrial and aquatic environments of the Amazon basin.…”

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confidence: 99%

The Fate of Carbon in Sediments of the Xingu and Tapajós Clearwater Rivers, Eastern Amazon

Bertassoli

Sawakuchi

et al. 2017

Front. Mar. Sci.

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The Xingu and Tapajós rivers in the eastern Amazon are the largest clearwater systems of the Amazon basin. Both rivers have "fluvial rias" (i.e., lake-like channels) in their downstream reaches as they are naturally impounded by the Amazon mainstem. Fluvial rias are widespread in the Amazon landscape and most of the sedimentary load from the major clearwater and blackwater rivers is deposited in these channels. So far, little is known about the role of Amazon rias as a trap and reactor for organic sediments. In this study, we used organic and inorganic geochemistry, magnetic susceptibility, diatom, and pollen analyses in sediments (suspended, riverbed, and downcore) of the Xingu and Tapajós rias to investigate the effects of hydrologic variations on the carbon budget in these clearwater rivers over the Holocene. Ages of sediment deposition (∼100 to 5,500 years) were constrained by optically stimulated luminescence and radiocarbon. Major elements geochemistry and concentration of total organic carbon (TOC) indicate that seasonal hydrologic variations exert a strong influence on riverine productivity and on the input and preservation of organic matter in sediments. Stable carbon isotope data (δ 13 C from −31.04 to −27.49‰) and pollen analysis indicate that most of the carbon buried in rias is derived from forests. In the Xingu River, diatom analysis in bottom sediments revealed 65 infrageneric taxa that are mostly well-adapted to slack oligotrophic and acidic waters. TOC values in sediment cores are similar to values measured in riverbed sediments and indicate suitable conditions for organic matter preservation in sediments of the Xingu and Tapajós rias at least since the mid-Holocene, with carbon burial rates varying from about 84 g m −2 yr −1 to 169 g m −2 yr −1 . However, redox-sensitive elements in sediment core indicate alternation between anoxic/dysoxic and oxic conditions in the water-sediment interface that may be linked to abrupt changes in precipitation. The variation between anoxic/dysoxic and oxic conditions in the water-sediment interface controls organic matter mineralization and methanogenesis. Thus, such changes promoted by hydrological variations significantly affect the capacity of Amazon rias to act either as sources or sinks of carbon.

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Source to sink: Evolution of lignin composition in the Madre de Dios River system with connection to the Amazon basin and offshore

et al. 2016

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While lignin geochemistry has been extensively investigated in the Amazon River, little is known about lignin distribution and dynamics within deep, stratified river channels or its transformations within soils prior to delivery to rivers. We characterized lignin phenols in soils, river particulate organic matter (POM), and dissolved organic matter (DOM) across a 4 km elevation gradient in the Madre de Dios River system, Peru, as well as in marine sediments to investigate the source‐to‐sink evolution of lignin. In soils, we found more oxidized lignin in organic horizons relative to mineral horizons. The oxidized lignin signature was maintained during transfer into rivers, and lignin was a relatively constant fraction of bulk organic carbon in soils and riverine POM. Lignin in DOM became increasingly oxidized downstream, indicating active transformation of dissolved lignin during transport, especially in the dry season. In contrast, POM accumulated undegraded lignin downstream during the wet season, suggesting that terrestrial input exceeded in‐river degradation. We discovered high concentrations of relatively undegraded lignin in POM at depth in the lower Madre de Dios River in both seasons, revealing a woody undercurrent for its transfer within these deep rivers. Our study of lignin evolution in the soil‐river‐ocean continuum highlights important seasonal and depth variations of river carbon components and their connection to soil carbon pools, providing new insights into fluvial carbon dynamics associated with the transfer of lignin biomarkers from source to sink.

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The compositional evolution of dissolved and particulate organic matter along the lower Amazon River—Óbidos to the ocean

Cited by 86 publications

References 102 publications

Novel analytical strategies for tracing the organic carbon cycle in marine and riverine particles

Novel analytical strategies for tracing the organic carbon cycle in marine and riverine particles

The Fate of Carbon in Sediments of the Xingu and Tapajós Clearwater Rivers, Eastern Amazon

Source to sink: Evolution of lignin composition in the Madre de Dios River system with connection to the Amazon basin and offshore

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