Floodplains of large rivers: Weathering reactors or simple silos?

Bouchez, Julien; Gaillardet, Jérôme; Lupker, Maarten; Louvat, Pascale; France‐Lanord, Christian; Maurice, Laurence; Armijos, Elisa; Moquet, Jean-Sébastien

doi:10.1016/j.chemgeo.2012.09.032

Cited by 114 publications

(89 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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.…”

mentioning

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.

View full text Add to dashboard Cite

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.

show abstract

mentioning

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.

View full text Add to dashboard Cite

show abstract

“…As a result, the debate on the locus of weathering in mountains is still open and different weathering reservoirs from the hillslopes to plains may dominate at different stages of the mountain evolution. Until now, four main weathering reservoirs have been identified: soils (Dixon et al, 2009b), fractured bedrock (Calmels et al,40 2011), basins (Bouchez et al, 2012), which also trap a considerable amount of organic carbon (Galy et al, 2015), and oceans (Oelkers et al, 2011). In this paper, we address the particular question of the relative contributions of in situ produced regolith and colluvial deposits in the weathering outflux of an uplifting mountain under a cooling climate.…”

Section: Introductionmentioning

confidence: 99%

“…In such regions, landslides constitute a significant weathering reservoir (Emberson et al, 2016a, b). Downstream from 35 the Andes and Himalaya, transported minerals may continue to weather significantly in the floodplain Bouchez et al, 2012;Moquet et al, 2016). As a result, the debate on the locus of weathering in mountains is still open and different weathering reservoirs from the hillslopes to plains may dominate at different stages of the mountain evolution.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Colluvial deposits as a possible weathering reservoir in uplifting mountains

Carretier¹,

Goddéris²,

Martı́nez³

et al. 2017

Preprint

View full text Add to dashboard Cite

Abstract. The role of mountain uplift in the global climate over geological times is controversial.At the heart of this debate is the capacity of rapid denudation to drive silicate weathering, a CO 2 consumer. Here we present the results of a 3D model that couples erosion and weathering during mountain uplift, in which the weathered material is traced during its stochastic transport from the hillslopes to the mountain outlet. During mountain uplift, the erosion rate increases and the climate 5 cools, which thins the regolith and produces a hump in the weathering rate evolution. Nevertheless, lateral river erosion drives mass wasting and the temporary storage of colluvial deposits on the valley borders. This new reservoir is comprised of fresh material which has a residence time ranging from several years up to several thousand years. During this period, the weathering of colluvium sustains the mountain weathering flux at a significant level. The relative weathering contribution 10 of colluvium depends on the area covered by regolith on the hillslopes. For mountains sparsely covered by regolith during cold periods, colluvium produce most of the simulated weathering flux for a large range of erosion parameters and precipitation rate patterns. In addition to other reservoirs such as deep fractured bedrock, colluvial deposits may help to maintain a substantial and constant weathering flux in rapidly uplifting mountains during cooling periods.

show abstract

“…Nevertheless, large scale uncertainties with reference to distinction of silicate weathering flux from total flux, as well as sensitivity to tectonic, lithological, and climate controls remain and the geomorphological environment in which chemical weathering takes place [7,8].…”

Section: Introductionmentioning

confidence: 99%

Silica Enrichment in a Volcanic Setting Using Petrographic Analyses and Mass Balance Calculations Using Trace Element Zircon

Wadia

2016

JGRE

View full text Add to dashboard Cite

Formulating the original composition of weathered tephra can be a challenging task. A previous study by Wadia (1998 and 2007) demonstrated the enrichment of silica according to the hypothesis that the percentage of aluminum oxide remains constant within the unweathered parent material and its weathered counterpart (Faure, 1991), which indicated the average enrichment of silica to be 6.5%. This study demonstrates the enrichment of microcrystalline-cryptocrystalline quartz in the Reid's Mistake Formation of the Newcastle Coal measures of Sydney Basin, Australia, incorporating petrographic analyses and MBC (mass balance calculations) using trace element zircon as the immobile element. For MBC, zircon is more favorable, as it is a trace element that tends to be immobile during the process of chemical weathering. The composition of the unweathered reference samples was collected from the Tertiary volcanic complexes of Northeastern New South Wales and Southeastern Queensland. ICP-AES (inductively coupled plasma-atomic emission spectroscopy) was used to determine the chemical composition of the weathered samples. The quantitative enrichment of silica was provided by performing MBC using zircon as the immobile trace element. The petrographic analyses results indicated that the tephra was subjected to chemical weathering in a meteoric regime, as represented by minerals observed in the weathered tephra. The silica enrichment by MBC involving zircon resulted in 40.11%, which is indicative of chemical weathering, and was additionally supported by the presence of chert lenses in the volcanic horizon, indicating the enrichment of silica as a result of chemical weathering.

show abstract

Floodplains of large rivers: Weathering reactors or simple silos?

Cited by 114 publications

References 55 publications

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

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

Colluvial deposits as a possible weathering reservoir in uplifting mountains

Silica Enrichment in a Volcanic Setting Using Petrographic Analyses and Mass Balance Calculations Using Trace Element Zircon

Contact Info

Product

Resources

About