The role of discharge variability in determining alluvial stratigraphy

We illustrate the potential for using physics-based modeling to link alluvial stratigraphy to large river morphology and dynamics. Model simulations, validated using ground penetrating radar data from the Río Paraná, Argentina, demonstrate a strong relationship between bar-scale set thickness and channel depth, which applies across a wide range of river patterns and bar types. We show that hydrologic regime, indexed by discharge variability and flood duration, exerts a first-order influence on morphodynamics and hence bar set thickness, and that planform morphology alone may be a misleading variable for interpreting deposits. Indeed, our results illustrate that rivers evolving under contrasting hydrologic regimes may have very similar morphology, yet be characterized by marked differences in stratigraphy. This realization represents an important limitation on the application of established theory that links river topography to alluvial deposits, and highlights the need to obtain field evidence of discharge variability when developing paleoenvironmental reconstructions. Model simulations demonstrate the potential for deriving such evidence using metrics of paleocurrent variance

Fluvial organic carbon composition regulated by seasonal variability in lowland river migration and water discharge

Identifying drivers of seasonal variations in fluvial particulate organic carbon (POC) composition can aid sediment provenance and biogeochemical cycling studies. We evaluate seasonal changes in POC composition in the Río Bermejo, Argentina, a lowland river running ∼1,270 km without tributaries. Weekly POC concentration and isotopic composition from 2016 to 2018 show that during the wet season, increased lateral channel migration generates an influx of 13C-enriched and 14C-enriched floodplain-sourced material, overprinting the 13C-depleted and 14C-depleted headwater signature that is observed during the dry season. These findings demonstrate how channel morphodynamics can drive variability of POC composition in lowland rivers, and may modulate the composition of POC preserved in sedimentary archives

Multi-frequency acoustics for suspended sediment studies: an application in the Parana River

A method of using two acoustic Doppler current profilers operating at different frequencies and employed at the same measuring vertical to sample a profile of suspended sediment concentration has been previously applied in the Parana River (Argentina) but has not been validated by direct sediment samples. The present work fills this gap by reporting new field data and comparing them with acoustically inferred sediment concentrations. The agreement between directly measured sediment concentrations and grain sizes with corresponding estimates from an employed backscatter model was found to be good (squared correlation coefficients are 0.9 and 0.8, and mean deviations are 14 and 6%, respectively). The interrelations between flow velocity and suspended sediment concentration at fixed locations and in a moving mode along a river cross-section have been also investigated. Observed events of bed sediment re-suspension were found to be highly correlated with fluctuations of the vertical flow velocity, with a 100\u2013150s quasi-periodicity. The size of re-suspension plumes was increasing from the channel thalweg to the low-submerged bar areas

Characterisation of the suspended particulate matter in a stratified estuarine environment employing complementary techniques

The ability to predict the sediment and nutrient circulation within estuarine waters is of significant economic and ecological importance. In these complex systems, flocculation is a dynamically active process that is directly affected by the prevalent environmental conditions. Consequently, the floc properties continuously change, which greatly complicates the characterisation of the suspended particle matter (SPM). In the present study, three different techniques are combined in a stratified estuary under quiet weather conditions and with a low river discharge to search for a solution to this problem. The challenge is to obtain the concentration, size and flux of suspended elements through selected cross-sections using the method based on the simultaneous backscatter records of 1200 and 600 kHz ADCPs, isokinetic sampling data and LISST-25X measurements. The two-ADCP method is highly effective for determining the SPM size distributions in a non-intrusive way. The isokinetic sampling and the LISST-25X diffractometer offer point measurements at specific depths, which are especially useful for calibrating the ADCP backscatter intensity as a function of the SPM concentration and size, and providing complementary information on the sites where acoustic records are not available. Limitations and potentials of the techniques applied are discussed.Fil: Thomas, Luis Pablo. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Marino, Beatriz Maria. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Szupiany, Ricardo Nicolas. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gallo, Marcos N.. Universidade Federal do Rio de Janeiro; Brasi

Meteoric 10Be concentrations and OSL depositional ages of Rio Bermejo floodplain sediment

To determine the depositional age and the long-term delivery of meteoric 10Be (10Bem) to the Rio Bermejo floodplain (northern Argentina), we collected floodplain sediment samples at four locations identified as point bars of abandoned Rio Bermejo channels. We used a stainless-steel hand auger to collect sediment down to a maximum depth of ~5 m, or until refusal. For 10Bem and 9Bereac analysis, we extracted samples that integrated material from 0-20 cm below the surface, 20-50 cm, and regularly spaced 40 cm intervals for lower depths. We homogenized the material prior to packing into clean plastic bags. Sediment particle size distributions were measured on ~10 mg aliquots using a laser diffraction particle size analyzer (Horiba LA-950). The total reactive phase, including amorphous oxyhydroxides and crystalline oxide grain coatings, was extracted from the sediment samples using a procedure adapted from Wittmann et al. (2012, doi:10.1016/j.chemgeo.2012.04.031). 10Be was purified from the extracted material, spiked with a 9Be carrier solution containing 150 µg of 9Be, and packed into targets for AMS measurement at the University of Cologne Centre for Accelerator Mass Spectrometry (Cologne, Germany). 10Be/9Be measurements were normalized to the KN01-6-2 and KN01-5-3 standards (Dewald et al., 2013, doi:10.1016/j.nimb.2012.04.030) that are consistent with a 10Be half-life of 1.36 ± 0.07 x10 yrˉ¹ (Nishiizumi et al., 2007, doi:10.1016/j.nimb.2007.01.297). 10Bem was calculated from the normalized and blank-corrected 10Be/9Be ratios. The reported 1σ uncertainties include counting statistics and the uncertainties of both standard normalization and blank correction. Stable 9Be concentrations were measured on a separate aliquot of the sample solution using inductively coupled plasma optical emission spectroscopy (ICP-OES). Uncertainty of ICP-OES measurements was 5%. We used coarse quartz grain OSL analysis to determine depositional ages for each floodplain core. For OSL analysis, we collected light-sealed samples by driving an opaque tube into our floodplain cores at two select depths in each core. OSL measurements were performed using a Risø DA 15 OSL/TL reader equipped with a 90Sr beta irradiator (4.9 Gy/min). OSL signals were stimulated with blue LEDs (470 nm, 50 s, 125 ºC) and detected through an optical filter (U 340 Hoya). For each sample, 40 aliquots were measured using the single-aliquot regenerative dose (SAR) protocol (Murray and Wintle, 2000, doi:10.1016/S1350-4487(03)00053-2) for equivalent dose determination

Meteoric 10Be, grain size, surface area data for Rio Bermejo suspended sediment depth profile samples

To test the potential of meteoric 10Be (10Bem) as a river sediment transit time proxy, we measured 10Bem concentrations in river suspended sediment of the Rio Bermejo (northern Argentina), which is a river with a ~1300 km lowland flowpath void of tributaries. We collected fluvial suspended sediment in vertical depth profiles at five sampling locations along the length of the Rio Bermejo (northern Argentina) during near-bankfull conditions, when discharge varied between 675 and 1080 m**3/s and banks were actively eroding. Additionally, we collected one depth profile from Rio San Francisco (RSF) and one from the Rio Bermejo 10 km upstream of the RSF confluence. Combining these profiles and weighting them by the relative proportions of their total sediment load input to the mainstem Bermejo serves as an integrated headwater depth profile. In the thalweg, we collected water and suspended sediment from a boat using a weighted 8-liter horizontal sampling bottle (Wildco Beta Plus bottle) with an attached pressure transducer to measure sampling depth. We separated sediment from the water using a custom-built 5-liter pressurized filtration unit with a 293 mm diameter, 0.2 µm polyethersulfone filter. In the laboratory, we rinsed sediment off the filters directly into an evaporating dish with ultrapure 18.2 MΩ water (pH~7; when needed, we added NH3 solution to the water to maintain pH~7). Samples were dried in an oven at 40ºC, and subsequently homogenized. Sediment particle size distributions were measured on ~10 mg aliquots using a laser diffraction particle size analyzer (Horiba LA-950). Specific surface area (SSA) of bulk sediment samples was measured on ~4 g aliquots using a Quantachrome NOVAtouch LX gas sorption analyzer and the Brunauer, Emmett, and Teller (BET) theory (Brunauer et al., 1938). The total reactive phase, including amorphous oxyhydroxides and crystalline oxide grain coatings, was extracted from the sediment samples using a procedure adapted from Wittmann et al. (2012, doi:10.1016/j.chemgeo.2012.04.031). 10Bem was purified from the extracted material, spiked with a 9Be carrier solution containing 150 µg of 9Be, and packed into targets for AMS measurement at the University of Cologne Centre for Accelerator Mass Spectrometry (Cologne, Germany). 10Be /9Be measurements were normalized to the KN01-6-2 and KN01-5-3 standards (Dewald et al., 2013, doi:10.1016/j.nimb.2012.04.030) that are consistent with a 10Be half-life of 1.36 ± 0.07 x10^6 yrˉ¹ (Nishiizumi et al., 2007, doi:10.1016/j.nimb.2007.01.297). [10Be]m was calculated from the normalized and blank-corrected 10Be/9Be ratios. The reported 1σ uncertainties include counting statistics and the uncertainties of both standard normalization and blank correction. Stable 9Be concentrations were measured on a separate aliquot of the sample solution using inductively coupled plasma optical emission spectroscopy (ICP-OES). Uncertainty of ICP-OES measurements was 5%

Suspended sediment collected from Puente La Valle (PLV, -25.655°S, -60.130°W) between 2016 - 2018

These data were collected from the Río Bermejo in northern Argentina. To determine the seasonal variability in the particulate organic carbon composition of exported river sediment, we collected weekly suspended sediment samples (March 2016 to March 2018) at the Puente Lavalle (PLV) monitoring site, ~870 river km downstream of the mountain front (-25.655°S, -60.130°W). Surface water samples were collected from a bridge using a river-rinsed bucket and were filtered through a 0.22 µm polyethersulfone membrane. Samples were stored on site at ambient temperatures for up to one year, transferred to Germany and subsequently stored at ~4°C until processing. Suspended sediment was rinsed from filters into pre-combusted glass evaporating dishes using ultra-pure (18.2 M) water, oven-dried at 40°C for >48 hr, and homogenized in an agate mortar without crushing. Geochemical and grain size analyses required 0.8 g sediment; for samples 0.8 g (Table S1). We split sediment samples into aliquots for grain size analysis via laser diffraction and geochemical analyses. Sediment particle size distributions were measured on ~0.2 g aliquots using a laser diffraction particle size analyzer (Retsch/Horiba LA-950V2). Aliquots for geochemical analyses were ground to <63 µm. The homogenized suspended sediment, bedrock, soil and leaf litter aliquots were further split for total nitrogen measurement (TN, wt%) and organic carbon analyses including total organic carbon (TOC, wt%), stable carbon isotope composition (δ13COC), and radiocarbon fraction modern (Fm). We decarbonated the aliquots for POC measurements using a liquid HCl leach following Galy et al., (2007). TOC and TN measurements were split between facilities at the German Research Centre for Geosciences (GFZ), Durham University, and University of Nevada Reno (UNR) using an elemental analyzer (EA). δ13COC was measured with a coupled EA-isotope ratio mass spectrometer (EA-IRMS). All isotopic compositions are reported using standard delta (δ) notation in per mil (‰) relative to Vienna PeeDee Belemnite (VPDB). Calibration and accuracy were monitored through analyses of in-house standards (Glutamic Acid, 40.82% C, 9.52% N at Durham; Boden3, HEKATECH at GFZ), which were calibrated against international standards (e.g., USGS 40, USGS 24, IAEA 600, IAEA CH3, IAEA CH7, IAEA N1, IAEA N2). Radiocarbon content was measured for a subset of 29 samples at ETH Zürich using a combined EA and accelerator mass spectrometer (EA-AMS) (Ruff et al. 2010; McIntyre et al., 2017). All 14C /12C ratios are reported as fraction modern (Fm, equivalent to F14C as defined by Reimer et al. (2004)) relative to 95% of the 14C activity of NBS Oxalic Acid II in 1950 (δ13COC = -17.8‰) and normalized to δ13COC = -25‰ of VPDB.\n\nThis geochemical dataset is supported by hydrologic measurements of daily water discharge at the El Colorado gauging station (river km 1086, SNIH, https://snih.hidricosargentina.gob.ar/) collected between 2016 and 2018

Seasonal variability of fluvial organic carbon composition between 2016-2018 in the Río Bermejo, Argentina

These data were collected from the Río Bermejo in northern Argentina. To determine the seasonal variability in the particulate organic carbon composition of exported river sediment, we collected weekly suspended sediment samples (March 2016 to March 2018) at the Puente Lavalle (PLV) monitoring site, ~870 river km downstream of the mountain front (-25.655°S, -60.130°W). Surface water samples were collected from a bridge using a river-rinsed bucket and were filtered through a 0.22 µm polyethersulfone membrane. Samples were stored on site at ambient temperatures for up to one year, transferred to Germany and subsequently stored at ~4°C until processing. To document distinct sources of particulate organic carbon (POC) to the Río Bermejo, we collected 15 soil and 13 leaf litter samples from the local floodplain, and 10 bedrock (predominantly outcroppings of fine-grained sedimentary bedrock) and 2 soil samples from the Río Bermejo headwaters. Suspended sediment was rinsed from filters into pre-combusted glass evaporating dishes using ultra-pure (18.2 M) water, oven-dried at 40°C for >48 hr, and homogenized in an agate mortar without crushing. Leaf litter and soil were oven-dried at 40°C for >48 hours. We shredded leaf litter in an industrial blender, homogenized soil samples in an agate mortar and manually removed root and plant debris >1 cm, and pulverized bedrock samples to 0.8 g (Table S1). We split sediment samples into aliquots for grain size analysis via laser diffraction and geochemical analyses. Sediment particle size distributions were measured on ~0.2 g aliquots using a laser diffraction particle size analyzer (Retsch/Horiba LA-950V2). Aliquots for geochemical analyses were ground to <63 µm. The homogenized suspended sediment, bedrock, soil and leaf litter aliquots were further split for total nitrogen measurement (TN, wt%) and organic carbon analyses including total organic carbon (TOC, wt%), stable carbon isotope composition (δ13COC), and radiocarbon fraction modern (Fm). We decarbonated the aliquots for POC measurements using a liquid HCl leach following Galy et al. (2007, doi:10.1111/j.1751-908X.2007.00864.x)). TOC and TN measurements were split between facilities at the German Research Centre for Geosciences (GFZ), Durham University, and University of Nevada Reno (UNR) using an elemental analyzer (EA). δ13COC was measured with a coupled EA-isotope ratio mass spectrometer (EA-IRMS). All isotopic compositions are reported using standard delta (δ) notation in per mil (‰) relative to Vienna PeeDee Belemnite (VPDB). Calibration and accuracy were monitored through analyses of in-house standards (Glutamic Acid, 40.82% C, 9.52% N at Durham; Boden3, HEKATECH at GFZ), which were calibrated against international standards (e.g., USGS 40, USGS 24, IAEA 600, IAEA CH3, IAEA CH7, IAEA N1, IAEA N2). Radiocarbon content was measured for a subset of 29 samples at ETH Zürich using a combined EA and accelerator mass spectrometer (EA-AMS) (Ruff et al. (2010, doi:10.1017/S003382220005637X); McIntyre et al. (2017, doi:10.1017/RDC.2016.68)). All 14C /12C ratios are reported as fraction modern (Fm, equivalent to F14C as defined by Reimer et al. (2004)) relative to 95% of the 14C activity of NBS Oxalic Acid II in 1950 (δ13COC = -17.8‰) and normalized to δ13COC = -25‰ of VPDB. This geochemical dataset is supported by hydrologic measurements of daily water discharge at the El Colorado gauging station (river km 1086, SNIH, https://snih.hidricosargentina.gob.ar/) collected between 2016 and 2018