Suspended Load Of Rivers Research Articles

Physicochemical and mineral properties of suspended sediments of the Tigris and Euphrates rivers in the Mesopotamian Plain

Most of the suspended river load from the Tigris and Euphrates rivers is deposited in the Mesopotamian Plain in Iraq. This suspended river load comprises sediments consisting of minerals and organic particles generated from weathering, erosion, transport, and sedimentation. Therefore, it is crucial to analyze, either quantitative or qualitatively, the types of minerals in the sediment particles transported by the suspended river load, in addition to the potential value they may add to the agricultural lands irrigated by the Tigris and Euphrates rivers. Herein, samples of suspended sediments were collected from both rivers for physical, chemical, and mineral assessments. The results revealed the predominance of silt particles, followed by clay, and then sand. The presence of clay particles increased while that of silt and sand decreased with further travel into the rivers. The pH values ranged from 7.39 to 7.70 and the electrical conductivity ranged from 1.39 to 2.16 ds m−1. The values of the total and active calcium carbonate minerals were 352.87–336.12 and 172.64–194.56 g kg−1 for the Tigris and Euphrates rivers, respectively. The mineral analysis identified the presence of non-clay minerals at a rate of 83 %, including calcite, quartz, albite, dolomite, and gypsum. Clay minerals, including chlorite, illite, montmorillonite, palygorskite, vermiculite, and kaolinite, were found at a rate of 17 %. Both rivers exhibited distributions of clay and non-clay minerals that vary as they move along the rivers.

Estimation of Some Heavy Elements Transported in the Suspended River Load of the Tigris and Euphrates Rivers

Estimation of Some Heavy Elements Transported in the Suspended River Load of the Tigris and Euphrates Rivers

The transformation of the runoff of the suspended load in Kamchatkan rivers due to volcanism

This paper considers the influence of volcanic eruptions on the variation in the characteristics of the runoff of the suspended river load (suspended sediment concentration, discharge, rate of runoff, and grain-size distribution) on a variety of space–time scales (daily, seasonal, and long-term). The main factors that affect the yield of suspended load in rivers that flow in volcanic areas include the water runoff, drainage area, and the abundance of unconsolidated volcanic deposits. The areas of recent volcanism in Kamchatka are characterized by the maximum values of potential scour of particles, the mean long-term suspended sediment concentration, and specific suspended sediment yield. The largest increment in the transport of suspended river load in areas of volcanic activity is observed after major eruptions. The daily variations in the transport of suspended load are controlled by the water regime of rivers on the slopes of active volcanoes, namely, periodic cessations of surface runoff because of filtering into volcanic deposits.

Seawater δ7Li: A direct proxy for global CO2 consumption by continental silicate weathering?

The fractionation of stable Li isotopes (6Li, 7Li) has become a promising proxy for assessing changes related to continental silicate weathering patterns. Recently, the first complete record of Cenozoic seawater Li isotopic composition (δ7Li) was reported (Misra and Froelich, 2012, Science 335, 818–821) showing a stepwise increase of +9‰ over the last 56Ma. This increase was attributed to a general change in continental silicate weathering behavior caused by tectonic uplift. In particular, the low global average riverine δ7Li inferred for the Paleocene–Eocene boundary was explained by congruent silicate weathering of primary silicate minerals, which is inconsistent with the stoichiometry of secondary minerals and the resultant water chemistry.In this study, we present a novel reactive transport modeling approach that explicitly includes Li isotopic fractionation to assess alternative geochemically-constrained interpretations that do not rely on congruent weathering. Simulations show that riverine δ7Li is mainly controlled by the subsurface residence time, the corresponding weathering intensity, and the concentration of a river's suspended load. Based on these factors, we suspect that the low δ7Li observed at the Paleocene–Eocene boundary was inherited from a high weathering intensity with predominant weathering of previously formed secondary mineral phases (e.g., clays, oxides) having low δ7Li values. Moreover, we conclude that the Cenozoic δ7Li increase was caused by an increasing amount of primary silicate mineral dissolution inherited from an increasing suspended river load concentration and a decreasing weathering intensity both likely induced by tectonic uplift. In contrast, Cenozoic cooling and corresponding pCO2 and precipitation variations do not seem to have a distinct control on the Cenozoic δ7Li record.Finally, our simulations revealed a close relation between δ7Li and CO2 consumption by silicate weathering implying that the Cenozoic seawater δ7Li record could be potentially used to quantify such CO2 consumption through time. However, more experimental and modeling work is required to quantify the correlation between seawater δ7Li and global CO2 consumption by silicate weathering. Key parameters are the temperature-dependent thermodynamic properties of specific Li-bearing primary and secondary minerals (e.g., crystallographic Li substitution reaction, maximum Li substitution, Li solubility, Li isotopic fractionation factor) as well as the determination of global average subsurface and river discharges through time.

Riverine particulate organic carbon from an active mountain belt: Importance of landslides

We investigate the routing and transfer of particulate organic carbon (POC) from the western Southern Alps, New Zealand, using organic carbon (Corg) and nitrogen (Norg) concentrations and stable carbon isotopes (δ13Corg). In this active mountain belt, sediment discharge is dominated by landslide‐derived material. Landsliding acts to homogenize the geochemically diverse hillslope POC, mixing POC from the standing biomass and soil with the fossil POC from bedrock. As a result, the POC in river sediment at the mountain front is a binary mixture of fossil and nonfossil carbon sourced from many landslide deposits. We calculate that nonfossil biogenic POC makes up 63 ± 7% of the total POC in the suspended load of rivers draining the western Southern Alps. The erosional flux of biogenic POC from these catchments represents a transfer of 39 tC km−2 a−1 of atmospheric CO2 averaged over the west flank of the mountain belt. If more than 10% of this POC is preserved in sediments on geological timescales, then this process is the most significant way in which the Southern Alps and similar, tectonically active mountain belts with restricted alluvial aprons consume atmospheric CO2.

Fallen between the Cracks: Conservation Linking Land and Sea

Fallen between the Cracks: Conservation Linking Land and Sea

Comment on “Heavy iron isotope composition of granites determined by high resolution MC-ICP-MS”, by F. Poitrasson and R. Freydier [Chem. Geol. 222 132–147

Scrutiny of published Fe isotope data for igneous rocks that have > 71 wt.% SiO 2 reveals that most samples have the same Fe isotope composition as mafic igneous rocks, contrary to the conclusions of Poitrasson and Freydier [Poitrasson, F. and Freydier, R., 2005. Heavy iron isotope composition of granites determined by high resolution MC-ICP-MS. Chem. Geol. 222, 132–147]. The only silicic igneous rocks that have Fe isotope compositions that are significantly different than mafic igneous rocks are 4 granitic samples that have SiO 2 > 75 wt.% analyzed by Poitrasson and Freydier [Poitrasson, F. and Freydier, R., 2005. Heavy iron isotope composition of granites determined by high resolution MC-ICP-MS. Chem. Geol. 222, 132–147]; three silicic igneous rocks analyzed by Beard et al. [Beard, B.L, Johnson, C.M., Skulan, J.L., Nealson, K.H., Cox, L., Sun, H., 2003a. Application of Fe isotopes to tracing the geochemical and biological cycling of Fe. Chem. Geol. 195 87–117] (SiO 2 > 75 wt.%) have Fe isotope compositions that are identical to mafic igneous rocks, but these samples were ignored. Moreover, the Fe isotope composition of upper continental crust as deduced from the 58 sedimentary clastic rocks (shales, loess, modern marine sediments, and suspended load of rivers), reported by Beard et al. [Beard, B.L., Johnson, C.M., von Damm, K.L. and Poulson, R.L, 2003b. Iron isotope constraints on Fe cycling and mass balance in oxygenated Earth oceans. Geology 31 629–632], is the same as the average of igneous rocks. These data suggest that granitic rocks which deviate from the igneous average may be rare.

Contribution of phytoliths to the suspended load of biogenic silica in the Nyong basin rivers (Cameroon)

Particulate biogenic silica (BSi) carried by rivers to estuaries and marine sediments is generally assumed to be primarily composed of diatoms. Phytoliths – biogenic opal formed in plants – are found in some marine sediments where they are interpreted to be the result of atmospheric and river inputs. In this study, we evaluate the contribution of phytoliths to the suspended load of rivers of the Nyong basin (Cameroon). BSi (2 μm to 2 mm fraction) in the soils and the rivers range respectively, from 0.9 to 3.9 wt% and from 1.3 to 4 wt%. About 90% of the BSi pool in both soils and river suspended load are composed of phytoliths. Thecamoebians and fresh water diatoms are minor components. The concentrations of BSi and the phytolith assemblages show great similarities between the waters and the soil samples. This result implies that the erosion of top soils is the major source of the suspended load, in good agreement with the transport-limited weathering regime of the study basin.

Late Cenozoic phosphogenesis on the western shelf of South Africa in the vicinity of the Cape Canyon

The strontium isotope ( 87Sr/ 86Sr) composition of phosphorite (carbonate fluorapatite) cemented grains (PCG), phosphate-cemented limestone (PCL), skeletal phosphorite grains (SPG) and biogenic calcite (mollusc shell, benthic foraminifera and echinoid spines) from sediment on the outer continental shelf in the vicinity of the Cape Canyon ranges from 0.707981 to 0.709167 and corresponds to an age range of late early Oligocene to late Pleistocene. Most biogenic carbonate Sr ages agree with biostratigraphic ages, but some samples contain significantly older and reworked robust (>250 μm) benthic foraminifera. Although the Sr ages of biogenic and phosphorite grains indicate that sedimentation was fairly continuous, most sediment is reworked with only lower Miocene, upper Pliocene and upper Pleistocene successions generally preserved in the study area. The initial phosphogenic episode from the latest Oligocene to early early Miocene (21–26 Ma) was the largest, with additional phosphogenic episodes in the late early Miocene (16–19 Ma) and middle Miocene (10–15 Ma). Most phosphorite occurs as PCG that formed during marine transgressions and highstands from the late Oligocene warming event until the mid-Miocene climatic optimum, a period of episodic Antarctic glaciation and several positive marine δ 13C excursions. Upper Oligocene to lower Miocene PCG have been extensively reworked and are associated with major erosional unconformities. PCG vary from peloidal sands to gravel mollusc moulds and contain variable amounts of quartz, glauconite and pyrite inclusions. PCL formed from 9 to 17 Ma by cementation and replacement of older calcareous sediment during the middle to late Miocene marine regression. Phosphorite, as well as associated glauconite and pyrite, indicate that periods of rapid accumulation of organic-rich, terrigenous muds derived from the focusing of the suspended load of rivers and organic matter produced in areas of coastal upwelling have occurred episodically on the margin since the late Oligocene. The relative paucity of phosphorite younger than the middle Miocene may result from frequent erosional events as documented by pronounced unconformities on the shelf that reflect lowered eustatic sea level, tectonic uplift and high-frequency, high-amplitude Quaternary sea-level fluctuations.

Sediment transport in the shelf canyon “Swatch of No Ground” (Bay of Bengal)

The Swatch of No Ground is a shelf canyon that deeply incises the Bengal shelf near the Ganges–Brahmaputra river mouth, cuts the foreset beds of the subaqueous river delta and acts as temporary depocenter between river mouth and Bengal fan. Sedimentation rates in the Swatch of No Ground are highest near the canyon head at ∼50 cm a−1, decreasing to ∼15 cm a−1 in 600 m water depth. The canyon deposits consist of intercalated fine (silt–clay) and coarse (silt–sand) grained deposits. In seismic profiles, small-scale sedimentary structures and parallel-bedded layers reveal that sediment in the canyon is mainly deposited from suspension. During fair weather conditions tidal currents are the dominant mechanism that transports plumes of suspended river load towards the canyon, forming fine-grained silt–clay layers. During storm conditions, sediment is resuspended on the inner shelf and subaqueous delta east of the canyon. Storm-generated bottom currents transport the resuspended sediment alongshelf to the canyon where the particles are trapped and form graded coarse silt–sand layers. Channels and gullies in the Swatch of No Ground indicate active gravity-driven currents with an erosional character in the upper canyon and non-depositional character below ∼450 m, suggesting that persistent or ephemeral currents presently export sediment to the Bengal fan. Numerous slumps and slides observed in the canyon show small-scale acoustically transparent layers that indicate sediment liquefaction presumably initiated along the steep canyon margin. These mudflows move downslope and halt where the canyon gradient decreases. One widespread acoustically transparent layer with an age of approximately 140–160 years BP can be traced throughout much of the canyon and is probably the result of large-scale sediment remobilization triggered by a catastrophic event like an earthquake. This may represent decennial-to-centennial scale events that remove large quantities of sediment and prevent the canyon from rapid infilling.

Chemical Exchange Between Volcanic Ash in Seawater: Abiotic Versus Biotic, Warm vs Cold

Volcanic glass is probably chemically the most reactive material that is deposited in the oceans, as aerosol, as suspended river load from volcanic terrain, or as part of the extrusive layer of the oceanic crust. The total volume of this material is large, probably on the order of about 10~6g/a, providing the potential of very large chemical fluxes. Recent studies have shown that microbial activity plays an important role in the dissolution of glass in the marine environment, through mediation of the dissolution process, and, presumably, utilization of components of the glass freed up during this process (e.g. Thorseth et al., 1995; Fumes et al., 1996, Giovarmoni et al., 1996; Staudigel et al., 1995). The interaction between biota and volcanic glass is likely an influence on local ecology as well as on the chemical mass balance between biosphere, hydrosphere and lithosphere. We carried out a series of experiments to explore further the role of colonizing microorganisms on the dissolution of glass. All experiments were done with natural populations of microbes from surface sea water at two temperatures, under the ambient light intensity in the laboratory and in the dark. Open system experiments were done with a constant supply of fresh seawater. The closed system apparatus included 501 seawater reservoirs and a FEP Teflon column setup with approximately 150 g of glass (Staudigel et al., 1997). A closed system with autoclaved components and seawater served as an abiotic control. More recent continuous flow experiments include approximately 300 g of glass and a continuous flow of 20 1 of fresh sand-filtered seawater per day. We carried out an experiment at 60 ~ C and compared this to an experiment at 16~ Run products were analysed for major and trace elements and for changes in glass surface structure and in microbial colonization by SEM. Microbial populations were characterized with a variety of metabolic tests. Closed-system sterile control experiments remained sterile for periods exceeding 450 days showing that these experimental conditions do not allow for microbial contamination. Biologically active experiments display a diverse population of microbes, including a series of algae including Si utilizers (diatoms) and algae with aragonitic exosceletons (halimeda). In cold experiments we identified several chemolithotrophs including a rod-shaped motile sulphur-oxidizer, probably Thiobacillus sp., and two strains of rod-shaped non-motile ammoniaoxidizers. Photoautotrophs, all cyanobacteria, include Spirulina, Phormidium, Anacystis, and a sheathed, filamentous strain that is probably either Anabaena or Nostoc. 60~ experiments displayed no significant thermophile activity for the first two months of its duration. However, after about g months we could identify a diverse population of thermophilic microorganisms, including heterotrophs, sulphuroxidizers, nitrite-oxidizers and ammonia-oxidizers. These results suggest that surface seawater has the means to transport thermophilic microbial life, even though in our experiments it took between two to eight months for them to appear. Overall these results suggests that surface seawater contains a sufficiently diverse environmental microbial population that can adjust to a wide range of conditions, and newly developed hydrothermal systems do not remain abiotic for a long time after initiation. Such processes are expected to occur not only in the mixing zone of

The Transfer of River Load to Deep-Sea Fans: A Quantitative Approach

The size of a river-fed deep-sea fan is controlled in the long term mainly by the amount of sediment available from a terrestrial source, whereas sea level fluctuations only trigger mass transfer to the deep sea. The deposition rate (i.e., the sediment volume deposited per unit time) and fan length correlate for most fans formed on abyssal plains. Fan size is independent of depositional environment (lake or sea), time span, or geological period, which may be characterized by different amplitudes and frequencies of sea level fluctuations. In climatically stable regions such as the tropics about 25 ±10% of the suspended river load reaching the river mouth is transported to the deep sea over the long term. The type of river mouth, however, affects the amount of material transported to the deep sea: estuaries with deeply incised canyons may transfer 6-8 times more material than fluvial-dominated and lobate deltas, provided the suspended river load is equal in both cases. However, the exact difference in the transfer ratio can only be derived indirectly because the available database is too small. For most river-fed deep-sea fans, a well-defined geometry develops on unconfined abyssal plains. The width/length ratio is about 0.2 at the base of the slope, and reaches a maximum of 0.5 farther downward. This is in good agreement with flume experiments. The volume of such fans resting on a planar base is roughly 0.35 × area × maximum thickness. The quantitative relationships of fans with respect to geometry, deposition rate, and river suspended discharge may provide some basic data for basin modeling and calculation of the sediment budget of erosional-depositional systems.