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Radioactive tracer techniques may be useful for assessing water transport and the overall effects of concurrent biogeochemical processes in river‐reservoir systems. In this study, we show that radium isotopes can assess the hydrodynamics and sediment/nutrient retention in the Xiaolangdi Reservoir, the largest impoundment along the Yellow River, China. Activity ratios of 224Ra/226Ra and 223Ra/226Ra were used for water mass age calculations in the riverine, transition, and lentic reaches of the reservoir. Water ages were combined with the length scale of three river‐reservoir zones to determine water transport rates of 3.6 ± 1.2, 1.3 ± 0.3, and 0.16 ± 0.14 km/day, respectively. Radium ages were also used to quantify the net retention of sediment and nutrients in different parts of the river‐reservoir system. Suspended sediment was removed at a rate of 1.4 ± 0.6 g/m3/day, mainly in the riverine zone. Nutrient dynamics were more complicated, with addition or removal at different rates within the three zones. Plain Language Summary: This paper should be of interest to fluvial aquatic scientists and resource managers. Typically, numerical models have been used to estimate reservoir hydrodynamics, and associated biogeochemical processes are investigated separately. Here for the first time, we explore the validity of using radium isotope tracers to assess water age distributions in the Xiaolangdi Reservoir, the largest impoundment along the Yellow River (China). Radium ages were then used to quantitatively evaluate the net retentions of suspended sediments and nutrients within the reservoir. The technique is easy to conduct at relatively low cost and allows one to assess the overall effect of synchronized biogeochemical processes. Key Points: Ra‐age technique is suitable for hydrodynamic assessments in river‐reservoir systems where model assumptions are metSediment and nutrient retentions may be quantified using Ra water agesNutrients are added and/or removed at different rates within three identified zones of the reservoir [ABSTRACT FROM AUTHOR]

The Water–Sediment Regulation Scheme (WSRS) is an important water conservancy project in the Yellow River basin, which is usually operated annually from June to July to control water and sediment release from the Xiaolangdi Reservoir in the middle reaches. As a greatly concentrated period of delivering terrigenous materials from the Yellow River to the sea, the WSRS can serve as a natural laboratory to examine the geochemical behavior of elements during their transport along the river. Uranium isotopes ( 234 U and 238 U) were measured in Yellow River waters at stations Xiaolangdi (located in the middle reaches of the Yellow River) and Lijin (the last hydrologic station near the Yellow River estuary) during the WSRS 2012. Compared with station Xiaolangdi, dissolved uranium concentration at station Lijin was markedly higher, showing a significant impact from the WSRS. Budget calculation for dissolved uranium during the WSRS indicated that two major sources of new added dissolved uranium in the section of the Yellow River between Xiaolangdi and Lijin: suspended particles (46%) and porewater of bottom sediment (45%). The flux of dissolved uranium from the Yellow River to the sea was estimated to be 2.40 × 10 7 g during the WSRS 2012. [ABSTRACT FROM AUTHOR]

Dissolved nutrient concentration in the Huanghe (Yellow) River at Lijin was monitored during a water-sediment regulation period and a subsequent rainstorm from 14 June to 19 July, 2005. This study provides detailed information on nutrient concentrations in the Huanghe River during the water-sediment regulation and rainstorm periods, and is of significance for the downstream area of the Huanghe River and the Bohai Sea. The average concentrations of nitrate, nitrite and ammonia were 304.7 μmol/L, 0.19 μmol/L, and 1.10 μmol/L, respectively, while the average concentrations of dissolved inorganic phosphorus (DIP) and dissolved silicate (DSi) were 0.23 μmol/L and 122.9 μmol/L, respectively. Nutrient concentrations during the water-sediment regulation period were mainly influenced by the dilution effect, floodplain effect and sediment resuspension while dilution and erosion effects were the main factors during the rainstorm. The fluxes of dissolved inorganic nitrogen (DIN), DIP and DSi during the water-sediment regulation and rainstorm periods accounted for 20.4%, 19.5%, 16.7% and 4.97%, 6.45%, 5.47% of the annual nutrient fluxes, respectively. Discharge was the main factor influencing the fluxes of nutrients during both the water-sediment regulation and the rainstorm periods. [ABSTRACT FROM AUTHOR]

The Huanghe River (Yellow River) had been the second largest river in the world in terms of sediment load to the sea; however, the river water discharge and sediment flux to the sea and their seasonal variability have been significantly altered by the dam activities and recent water–sediment regulation. These changes are believed to have important impacts on the flux of phosphorus that is generally transported in particulate form. In this article, the samples of suspended particulate matter (SPM) were collected at the Lijin Station during two high-discharge events in 2005 and were separated by particle size. Sequential extractions were applied to determine the forms of P in different particle size fractions and to assess the potential bio-availability of particulate phosphorus (PP). Based on the in-laboratory measurement, the impacts of different hydrological regimes on the source of PP and its bio-availability were also analyzed. The results indicate that exchangeable, organic, authigenic, and refractory P were preferentially associated with clay, very fine, and fine silt fractions. Detrital P was mainly associated with the medium and coarse silt fractions. Detrital P and authigenic P (two forms of calcium bound phosphorus) were the dominant fractions in all samples. Thus, the potential bio-available PP (exchangeable P and organic P) was mainly associated with the finer particles, such as clay. Higher content of exchangeable, organic, authigenic, and residual P and lower content of detrital P were found during the period of rainstorm compared to that of WSR. P forms and partitioning of P forms among different particle size fractions were assumed to depend on the sources of SPM. It is likely that the pathways and fates of PP forms were controlled by damming and by the related changes of hydrological regime. Therefore, anthropogenic changes of hydrological regime and particle size dominanted the amount and distribution pattern of bio-available P transportation to the estuary and the adjacent sea, which will have profound impacts on the marine ecosystems at the Huanghe River Estuary and even the Bohai Sea. [ABSTRACT FROM AUTHOR]

Abstract: Provenance discrimination of marine sediments is an important topic in marine geology. Although the catchments of the Changjiang and Huanghe Rivers are regarded as the main sources of sediments on the shelves of the China Sea, identification of detailed sediment provenance is necessary for understanding sediment transport patterns and the paleoenvironment. Magnetic properties of both bulk sediment samples and different-sized particles from the Changjiang and Huanghe Estuaries are studied to discuss the origin of the sediments. The results show that the sediments are dominated by ferrimagnetic magnetite with a minor content of anti-ferromagnetic minerals such as hematite, and a higher concentration of ferrimagnetic minerals is observed for the Changjiang Estuary sediments. The crystal grains of ferrimagnetic minerals in the Changjiang Estuary are coarser than those in the Huanghe Estuary, whereas superparamagnetic grains significantly contribute to the Huanghe sediments. Magnetic parameters of χ SIRM, SOFT and χ ARM from different-sized particles present more obvious differences than these parameters from bulk particles, and S−100 and S−300 for both bulk samples and different-sized particles show distinct differences between the sediments from the two estuaries. Therefore the latter parameters are more useful to distinguish sediment origins. A comparison of the magnetic properties of sediments in these two estuaries with those on the shelves of the adjacent China Sea also suggests that the analysis of sediment magnetic properties is effective to identify sediment provenances. [Copyright &y& Elsevier]

Abstract: Uranium isotopes were measured in waters and suspended particulate matters (SPM) of the main channel of Yellow River, China that were sampled during four field trips between August 2005 and July 2006. The results show that the concentration of dissolved U (2.04–7.83μg/l) and the activity ratio of 234U/238U (1.36–1.67) are much higher than the average U concentrations and activity ratios of global major rivers. Mass balance calculations using the results of simulated experiments and measurement data show that the section of the Yellow River between Lanzhou and Sanmenxia has its dissolved U derived from two sources: suspended sediments (68%) and groundwater/runoff from loess deposits (32%). Both sources are related to the heavy erosion of the Chinese Loess Plateau. [Copyright &y& Elsevier]

Abstract Radium isotopes are known to be excellent geochemical tracers for study of oceanographic processes. We show here that radium isotopes can also be used to assess adsorption/desorption and transport processes in rivers. The Yellow River (Huanghe), one of the longest, most turbid and heavily regulated rivers in the world, is used as an example. We first investigated the temporal and spatial behavior of radium isotopes (224Ra and 226Ra) in the lower reaches of the river, and found that this zone displayed some of the highest known riverine radium concentrations and fluxes in the world. Suspended particulate matter (SPM) is shown to be the dominant factor controlling radium activities. Laboratory simulation experiments showed that radium desorption from SPM obeys an exponential relationship in fresh water (S = 0). When salinities are >10, the increase in radium concentration follows a linear increase with respect to the amounts of SPM added. Significantly higher radium concentrations (3–5 times), especially for short-lived 224Ra, were observed during the "Water-Sediment Regulation Scheme" (WSRS), an annual management event when ∼15%–55% of the annual water discharge and ∼30%–75% of the annual sediment load are released from a reservoir to control sedimentation in the Yellow River. The radium fluxes during WSRS periods (∼2 weeks long) accounted for more than half of the entire annual load during the periods studied. Sediment erosion and pore water release are also thought to be important processes supplying radium to the river. After a WSRS, Ra desorption from SPM increases and becomes the prevailing process. Highlights • The Yellow River has the highest radium concentrations in the world. • Examination of the time and space patterns of radium isotopes in the Yellow River. • Estimated how salinity and SPM concentrations affect radium activities. • Calculated annual radium fluxes discharged by the Yellow River to the Bohai Sea. [ABSTRACT FROM AUTHOR]

Anthropogenic activities alter the natural states of large rivers and their surrounding environment. The Yellow River is a well-studied case of a large river with heavy human control. An artificial managed water and sediment release system, known as the Water-Sediment Regulation Scheme (WSRS), has been carried out annually in the Yellow River since 2002. Nutrient concentrations and composition display significant time and space variations during the WSRS period. To figure out the anthropogenic impact of nutrient changes and transport in the Yellow River, biogeochemical observations were carried out in both middle reaches and lower reaches of the Yellow River during 2014 WSRS period. WSRS has a direct impact on water oxidation-reduction environment in the middle reaches; concentrations of nitrite (NO 2 − ) and ammonium (NH 4 + ) increased, while nitrate (NO 3 − ) concentration decreased by enhanced denitrification. WSRS changed transport of water and sediment; dissolved silicate (DSi) in the middle reaches was directly controlled by sediments release during the WSRS while in the lower reaches, DSi changed with both sediments and water released from middle reaches. During the WSRS, the differences of nutrient fluxes and concentrations between lower reaches and middle reaches were significant; dissolved inorganic phosphorous (DIP) and dissolved inorganic nitrogen (DIN) were higher in low reaches because of anthropogenic inputs. Human intervention, especially WSRS, can apparently change the natural states of both the mainstream and estuarine environments of the Yellow River within a short time. [ABSTRACT FROM AUTHOR]

The high HCO 3 − concentrations in the Yellow River (China) are generally believed to originate primarily from the carbonate-rich Loess Plateau as a result of carbonate weathering reactions that consume atmospheric CO 2 . We studied chemical weathering across the entire Yellow River basin in 2007 and 2009 and found that the amounts of CO 2 consumption by carbonate and silicate weathering were 87.61 × 10 9 mol/a and 10.70 × 10 9 mol/a, respectively. As the source of water for the Yellow River, although the Qinghai–Tibet Plateau accounts for only 30% of the area of the basin, it has a strong leaching effect and contributes a majority (61%) of the atmospheric CO 2 consumption of the entire basin and a majority of the riverine DIC flux (66%) to the ocean. As a result, the dissolved inorganic carbon (DIC) concentrations in this river are among the highest of the world's major rivers. In contrast, despite the abundant carbonate mineral content in the Loess Plateau, the high ratio of evaporation to precipitation (4.2) limits the weathering processes, and the low amount of runoff restricts the transport of weathering products, which results in a relatively low contribution (38%) to the basin-wide atmospheric CO 2 consumption, which is much lower than was previously thought. The Qinghai–Tibet Plateau is the origin of the high levels of HCO 3 − in and acts as the main DIC contributor to the Yellow River. [ABSTRACT FROM AUTHOR]