scholarly journals Temporal variability in detrital <sup>10</sup>Be concentrations in a large Himalayan catchment

2018 ◽  
Vol 6 (3) ◽  
pp. 611-635 ◽  
Author(s):  
Elizabeth H. Dingle ◽  
Hugh D. Sinclair ◽  
Mikaël Attal ◽  
Ángel Rodés ◽  
Vimal Singh
Keyword(s):  
River Sediments ◽  
Sediment Flux ◽  
Ganga River ◽  
Sediment Delivery ◽  
Sediment Fluxes ◽  
Sediment Deposits ◽  
Tectonically Active ◽  
Mountain Front ◽  
Floodplain Deposits ◽  
Cosmogenic 10Be

Abstract. Accurately quantifying sediment fluxes in large rivers draining tectonically active landscapes is complicated by the stochastic nature of sediment inputs. Cosmogenic 10Be concentrations measured in modern river sands have been used to estimate 102- to 104-year sediment fluxes in these types of catchments, where upstream drainage areas are often in excess of 10 000 km2. It is commonly assumed that within large catchments, the effects of stochastic sediment inputs are buffered such that 10Be concentrations at the catchment outlet are relatively stable in time. We present 18 new 10Be concentrations of modern river and dated Holocene terrace and floodplain deposits from the Ganga River near to the Himalayan mountain front (or outlet). We demonstrate that 10Be concentrations measured in modern Ganga River sediments display a notable degree of variability, with concentrations ranging between ∼9000 and 19 000 atoms g−1. We propose that this observed variability is driven by two factors. Firstly, by the nature of stochastic inputs of sediment (e.g. the dominant erosional process, surface production rates, depth of landsliding, degree of mixing) and, secondly, by the evacuation timescale of individual sediment deposits which buffer their impact on catchment-averaged concentrations. Despite intensification of the Indian Summer Monsoon and subsequent doubling of sediment delivery to the Bay of Bengal between ∼11 and 7 ka, we also find that Holocene sediment 10Be concentrations documented at the Ganga outlet have remained within the variability of modern river concentrations. We demonstrate that, in certain systems, sediment flux cannot be simply approximated by converting detrital concentration into mean erosion rates and multiplying by catchment area as it is possible to generate larger volumetric sediment fluxes whilst maintaining comparable average 10Be concentrations.

scholarly journals Temporal variability in detrital <sup>10</sup>Be concentrations in large Himalayan catchments

2018 ◽  
Author(s):  
Elizabeth H. Dingle ◽  
Hugh D. Sinclair ◽  
Mikael Attal ◽  
Ángel Rodés ◽  
Vimal Singh
Keyword(s):  
River Sediments ◽  
Sediment Flux ◽  
Ganga River ◽  
Sediment Delivery ◽  
Sediment Fluxes ◽  
Sediment Deposits ◽  
Tectonically Active ◽  
Mountain Front ◽  
Floodplain Deposits ◽  
Cosmogenic 10Be

Abstract. Accurately quantifying sediment fluxes in large rivers draining tectonically active landscapes is complicated by the stochastic nature of sediment inputs. Cosmogenic 10Be concentrations measured in modern river sands have been used to estimate 102–104 year sediment fluxes in these types of catchments, where upstream drainage areas are often in excess of 10,000 km2. It is commonly assumed that within large catchments, the effects of stochastic sediment inputs are buffered such that 10Be concentrations at the catchment outlet are relatively stable in time. We present eighteen new 10Be concentrations of modern river and dated Holocene terrace and floodplain deposits from the Ganga River near to the Himalayan mountain front. We demonstrate that 10Be concentrations measured in modern Ganga River sediments display a notable degree of variability, with concentrations ranging between ~ 9,000–19,000 atoms g−1. We propose that this observed variability is driven by two factors. Firstly, by the nature of stochastic inputs of sediment (e.g. the dominant erosional process, surface production rates, depth of landsliding, degree of mixing) and, secondly, by the evacuation timescale of individual sediment deposits which buffer their impact on catchment-averaged concentrations. Despite intensification of the Indian Summer Monsoon and subsequent doubling of sediment delivery to the Bay of Bengal at ~ 11–7 ka, we also find that Holocene sediment 10Be concentrations documented at the Ganga outlet have remained within the error of modern river concentrations. We demonstrate that in these systems, sediment flux cannot be simply approximated by converting detrital concentration into mean erosion rates and multiplying by catchment area as it is possible to generate considerably larger volumetric sediment fluxes whilst maintaining comparable average 10Be concentrations.

Heavy Metals Fractionation in Ganga River Sediments, India

2007 ◽  
Vol 132 (1-3) ◽  
pp. 475-489 ◽  
Author(s):  
P. Purushothaman ◽  
G. J. Chakrapani
Keyword(s):  
Heavy Metals ◽  
River Sediments ◽  
Ganga River

Fluvial sediment fluxes response to modern climate change and human activities in the Tibetan Plateau and its margins

2021 ◽  
Author(s):  
Dongfeng Li ◽  
Xixi Lu ◽  
Ting Zhang
Keyword(s):  
Climate Change ◽  
Water Resources ◽  
Tibetan Plateau ◽  
Air Temperature ◽  
Human Activities ◽  
Sediment Flux ◽  
The Tibetan Plateau ◽  
Fluvial Sediment ◽  
Sediment Fluxes ◽  
Cold Environments

&lt;p&gt;Sediment flux in cold environments is a crucial proxy to link glacial, periglacial, and fluvial systems and highly relevant to hydropower operation, water quality, and the riverine carbon cycle. However, the long-term impacts of climate change and multiple human activities on sediment flux changes in cold environments remain insufficiently investigated due to the lack of monitoring and the complexity of the sediment cascade. Here we examine the multi-decadal changes in the in-situ observed fluvial sediment fluxes from two types of basins, namely, pristine basins and disturbed basins, in the Tibetan Plateau and its margins. The results show that the fluvial sediment fluxes in the pristine Tuotuohe headwater have substantially increased over the past three decades (i.e., a net increase of 135% from 1985&amp;#8211;1997 to 1998&amp;#8211;2017) due to the warming and wetting climate. We also quantify the relative impacts of air temperature and precipitation on the increases in the sediment fluxes with a novel attribution approach and finds that climate warming and intensified glacier-snow-permafrost melting is the primary cause of the increased sediment fluxes in the pristine cold environment (Tuotuohe headwater), with precipitation increase and its associated pluvial processes being the secondary driver. By contrast, the sediment fluxes in the downstream disturbed Jinsha River (southeastern margin of the Tibetan Plateau) exhibit a net increase of 42% from 1966-1984 to 1985-2010 mainly due to human activities such as deforestation and mineral extraction (contribution of 82%) and secondly because of climate change (contribution of 18%). Then the sediment fluxes dropped by 76% during the period of 2011-2015 because of the operations of six cascade reservoirs since 2010. In an expected warming and wetting climate for the region, we predict that the sediment fluxes in the pristine headwaters of the Tibetan Plateau will continue to increase throughout the 21st century, but the rising sediment fluxes from the Tibetan Plateau would be mostly trapped in its marginal reservoirs.&lt;/p&gt;&lt;p&gt;Overall, this work has provided the sedimentary evidence of modern climate change through robust observational sediment flux data over multiple decades. It demonstrates that sediment fluxes in pristine cold environments are more sensitive to air temperature and thermal-driven geomorphic processes than to precipitation and pluvial-driven processes. It also provides a guide to assess the relative impacts of human activities and climate change on fluvial sediment flux changes and has significant implications for water resources stakeholders to better design and manage the hydropower dams in a changing climate. Such findings may also have implications for other cold environments such as the Arctic, Antarctic, and other high mountainous basins.&lt;/p&gt;&lt;p&gt;Furthermore, this research is under the project of &quot;Water and Sediment Fluxes Response to Climate Change in the Headwater Rivers of Asian Highlands&quot; (supported by the IPCC and the Cuomo Foundation) and the project of &quot;Sediment Load Responses to Climate Change in High Mountain Asia&quot; (supported by the Ministry of Education of Singapore). Part of the results are also published in Li et al., 2018 Geomorphology, Li et al., 2020 Geophysical Research Letters, and Li et al., 2021 Water Resources Research.&lt;/p&gt;

Sediment Budgets and Sediment Delivery Ratios in River Systems

2016 ◽  
Author(s):  
Gary Brierly ◽  
Jon Tunnicliffe
Keyword(s):  
Landscape Connectivity ◽  
Sediment Accumulation ◽  
River Management ◽  
Sediment Flux ◽  
River Systems ◽  
Catchment Scale ◽  
Sediment Delivery ◽  
Sediment Movement ◽  
Sediment Budgets ◽  
Continental Scale

The term sediment flux refers to sediment movement through landscapes. Analogous to “flux” in physics, i.e., the rate of flow of a property per unit area, sediment flux is the amount of sediment that flows through a cross-section of river per unit time. The magnitude of sediment flux is moderated by catchment processes such as sediment production (erosion), sediment accumulation (deposition) and intervening processes of sediment storage and reworking (transfer). Patterns and rates of sediment flux vary over a wide range of spatial and temporal scales, from grain to grain and landform scale analyses over near instantaneous timeframes through reach and catchment-scale analyses that are typically performed over decadal to millennial timescales to continental-scale appraisals over millions of years. Sediment movement is a key physical driver of natural environments. It exerts a critical influence upon the morphology, process regime, and evolutionary traits of landscapes. For example, as sediment budgets quantify sediment transport pathways, they can be used to analyze the critical factors that affect landscape development. Sediment flux exerts a critical influence upon the physical template (habitat distribution) of river systems. As such, it is a key consideration in river management and restoration. Analysis of source-to-sink relationships at the catchment scale (and associated sediment budgets) highlights controls upon sediment delivery and the influence of landscape connectivity. Emphasis here is placed upon valley floor processes, giving only partial attention to hillslope forms and processes or consideration of lakes, deltas, and nearshore marine environments. Textbooks and journals that present overviews of sediment flux in river systems are considered first. A brief overview of global scale sediment flux summarizes the movement of sediment from terrestrial areas to the ocean and the imprint of human activities. Most of this contribution focuses on catchment-scale sediment budgets, emphasizing variability in sediment sources (hillslope inputs and reworking on valley floors), the thorny question of scale relations, controls upon the sediment delivery ratio, and the influence of landscape connectivity. In many instances, disturbance events disrupt the sediment regime of a river, creating distinct pulses (or waves) that are transferred downstream by dispersion or migration processes. This is followed by an analysis of approaches to measurement of sediment flux, differentiated in relation to conventional field techniques, use of sediment fingerprinting, and the emergence of a range of remotely sensed technologies. The final sections of this article outline implications of human-induced alterations to sediment flux for river management. Appraisal of sediment disasters (impacts of dams, fine-grained sediment accumulation, and mining activities) is followed by an assessment of implications for river restoration.

Dating lacustrine carbonate strata with detrital zircon U-Pb geochronology

Geology ◽  
2020 ◽  
Author(s):  
Emily S. Finzel ◽  
Justin A. Rosenblume
Keyword(s):  
Detrital Zircon ◽  
Relative Proportion ◽  
Foreland Basin ◽  
Depositional Environments ◽  
Detrital Zircons ◽  
Sediment Flux ◽  
Coarse Grained ◽  
Southwestern Montana ◽  
Tectonically Active ◽  
Lacustrine Carbonate

Carbonate lacustrine strata in nonmarine systems hold great potential for refining depositional ages through U-Pb dating of detrital zircons. The low clastic sediment flux in carbonate depositional environments may increase the relative proportion of zircons deposited by volcanic air fall, potentially increasing the chances of observing detrital ages near the true depositional age. We present U-Pb geochronology of detrital zircons from lacustrine carbonate strata that provides proof of concept for the effectiveness of both acid-digestion recovery and resolving depositional ages of nonmarine strata. Samples were collected from Early Cretaceous foreland basin fluvial sandstone and lacustrine carbonate in southwestern Montana (USA). Late Aptian–early Albian (ca. 115–110 Ma) maximum depositional ages young upsection and agree with biostratigraphic ages. Lacustrine carbonate is an important component in many types of tectonic basins, and application of detrital zircon U-Pb geochronology holds considerable potential for dating critical chemical and climatic events recorded in their stratigraphy. It could also reveal new information for the persistent question about whether the stratigraphic record is dominated by longer periods of background fine-grained sedimentation versus short-duration coarse-grained events. In tectonically active basins, lacustrine carbonates may be valuable for dating the beginning of tectonic subsidence, especially during periods of finer-grained deposition dominated by mudrocks and carbonates.

Revised sediment transport model for estimation of suspended sediment flux and chemical composition of the Irrawaddy and Salween rivers

2020 ◽  
Author(s):  
J. Jotautas Baronas ◽  
Edward T. Tipper ◽  
Michael J. Bickle ◽  
Robert G. Hilton ◽  
Emily I. Stevenson ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Organic Carbon ◽  
Suspended Sediment ◽  
Transport Model ◽  
Sediment Concentration ◽  
Sediment Flux ◽  
Sediment Discharge ◽  
Anthropogenic Pressures ◽  
Modeling Framework ◽  
Sediment Delivery

&lt;p&gt;A large portion of freshwater and sediment is exported to the ocean by just several of the world's major rivers. Many of these mega-rivers are under significant anthropogenic pressures, such as damming and sand mining, which are having a significant impact on water and sediment delivery to deltaic ecosystems. However, accurately measuring the total sediment flux and its mean physicochemical composition is difficult in large rivers due to hydrodynamic sorting of sediments. To account for this, we developed an updated semi-empirical Rouse modeling framework, which synoptically predicts sediment concentration, grain size distribution, and mean chemical composition (organic carbon wt%, Al/Si ratio) with depth and across the river channel.&lt;/p&gt;&lt;p&gt;We applied this model to derive new sediment flux estimates for the Irrawaddy and the Salween, the last two free-flowing mega-rivers in Southeast Asia, using a newly collected set of suspended sediment depth samples, coupled to ADCP-measured flow velocity data. Constructing sediment-discharge rating curves, we calculated an annual sediment flux of 326 (68% confidence interval of 256-417) Mt/yr for the Irrawaddy and 159 (109-237) Mt/yr for the Salween, together accounting for 2-3% of total global riverine sediment discharge. The mean flux-weighted sediment exported by the Irrawaddy is significantly coarser (D&lt;sub&gt;84&lt;/sub&gt; = 193 &amp;#177; 13 &amp;#181;m) and OC-poorer (0.29 &amp;#177; 0.08 wt%) compared to the Salween (112 &amp;#177; 27 &amp;#181;m and 0.59 &amp;#177; 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of 1.9 (1.0-3.3) Mt C/yr, contributing ~1% of the total riverine POC export to the ocean. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment fluxes, given the increasing anthropogenic pressures on these river basins.&lt;/p&gt;

Fluvial transport dynamics in the Rangitikei River (New Zealand) unravelled through single-grain feldspar luminescence

2020 ◽  
Author(s):  
Anne Guyez ◽  
Stephane Bonnet ◽  
Tony Reimann ◽  
Jakob Wallinga
Keyword(s):  
New Zealand ◽  
Light Exposure ◽  
River Sediments ◽  
High Ratio ◽  
Sediment Flux ◽  
Fluvial Terraces ◽  
The Past ◽  
Transport Distance ◽  
Fluvial Transport ◽  
Single Grain

&lt;p&gt;Over the past decades, luminescence has been widely used for dating sedimentary deposits. Several recent publications suggest luminescence signals can also be used to investigate fluvial transport. Here we explore what information luminescence signals yield in past and present sediment dynamics in the Rangitikei River (RR), New Zealand (Bonnet et al., 2019).&lt;/p&gt;&lt;p&gt;We present a dataset of 30 samples from fluvial terraces and modern river sediments of the RR. For each of the samples, we measured pIRIR luminescence signals of 300 individual sand-sized grains of feldspar (Reimann et al., 2012). We interpret results to evaluate differences between past and modern transport conditions, and to infer information on lateral input of bedrock particles in different river sections.&lt;/p&gt;&lt;p&gt;The information obtained from the single-grain analysis is incredibly rich, and requires new metrics for interpretation. To quantify the percentage of grains that were eroded from bedrock (or very old deposits) and re-deposited with minimal light-exposure, we identified grains for which the pIRIR signal is above 85% of full saturation (Wintle, 2006). For grains below this saturation threshold, we used the bootstrapped minimum age model (Galbraith et al.,1999; Cunningham and Wallinga, 2012) to determine the palaeodose, the best estimate of the natural radiation dose received by grains since their last deposition and burial event. For the modern deposits, we interpret the palaeodose to indicate the light-exposure of the best-bleached grains. Thereby, it provides a proxy of fluvial transport distance of the sediment grains.&lt;/p&gt;&lt;p&gt;For the modern river sediments we obtain palaeodoses between 2 and 6 Gy. A decreasing trend in palaeodose downstream suggests that part of the grains are transported through the entire system and are gradually bleached through light exposure during this process. The downstream trend in palaeodose of the RR is influenced by the connection of a major tributary, the Kawhatau River (KR), characterized by higher palaeodoses. Based on the observed trends, we estimate that the KR contributes three times more to modern sediment flux down the confluence than the upstream RR. Moreover, we observe that downstream of the confluence the percentage of saturated grains increase, which implies significant local input of bedrock particles from valley sides.&lt;/p&gt;&lt;p&gt;Data from recent (Holocene) autogenic fluvial terraces were acquired downstream the RR/KR confluence. They show a high to very high ratio of saturated grains (30-70%). We also document a downstream increasing trend of the percentage of saturated grains in these fluvial terraces, much stronger than for modern deposits. The maximum is observed for terraces at elevation of +28/+34 m, with an input of saturated grains that doubles over a distance of 100 km. As a consequence, saturated grains represent up to 70 % of the grain population in the most downstream sample. This implies a stronger lateral input of bedrock particles in the past, during recent incision of the river and a significant contribution of valley walls to the sediment flux of the RR, probably through landslides and/or lateral fluvial erosion.&lt;/p&gt;

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