Reservoir Sedimentation Research Articles

A semi-analytical model for predicting outflow concentration of vented turbidity currents with application in the Xiaolangdi reservoir

Turbidity current venting is an important way to reduce reservoir sedimentation. Existing methods to predict the outflow concentration of vented turbidity currents either depend on three-dimensional (3D) modelling with high computational cost or semi-empirical equation with a simple assumption of uniform velocity distribution. This study presents a semi-analytical model for predicting outflow concentration in turbidity current venting events, which accounts for the non-uniform and asymmetric velocity distribution in the withdrawal layer. Firstly, a 3D numerical model is established to facilitate the determination of withdrawal layer thickness and extraction of flow velocity within it, which is validated by simulating a group of venting experiments in the literature. Then, a velocity distribution equation for turbidity currents insusceptible to downstream disturbance is found to be applicable in the withdrawal layer, after relating the parameter controlling the velocity profile shape with the ratio of the outlet height to the layer thickness. Finally, the equation is derived for the relative concentration of outflow to the turbidity current concentration before the dam, whose solution is dependent on the proposed velocity distribution. Field measured data in the Xiaolangdi Reservoir and operation records of sediment release structures were collected and used to validate the model. A concept of nominal outlet width is proposed in order to apply the model in reservoirs with complex water releasing structures, which is calibrated along with the dimensionless parameter in the withdrawal layer thickness equation. The proposed model can help to optimize the design of sediment release structures and improve the venting operation.

Advances in Monitoring and Understanding the Dynamics of Suspended-Sediment Transport in the River Drava, Slovenia: An Analysis More than a Decade-Long

Managing sediment transport in streams is crucial to the surface water resource development strategy and has several implications for flood risk and water management, hydropower use, and balancing river morphology. This paper summarises the movement and behaviour of suspended sediment within the Slovenian portion of the River Drava, covering a span of thirteen years from 2005 to 2018. An analysis of relevant data collected during this period is also presented. Suspended-sediment dynamics strongly depend on flow velocity, seasonal variations in sediment sources, and human interventions in the riverbed. The transportation of material in the River Drava results in the accumulation of sediments in reservoirs and riverbeds, consequently impeding the natural hydrological cycle by reducing the outflow into aquifers. The 2018 high-water event is analysed in terms of the dependence of concentration of suspended sediments on discharge, where counterclockwise hysteresis was observed, providing an essential clue to the origin of sediment. Sediments from the River Drava in Slovenia are managed with some conventional processes and are mainly deposited or reintegrated into rivers and aquatic ecosystems. Some additional sediment management strategies with long-term solutions for efficient and comprehensive water management, hydropower, and ecological problems are proposed.

Development of multiphase solver for the modeling of turbidity currents (the case study of Dez Dam)

Dams in semi-arid regions, like Iran's Dez dam, are losing their capacity by sedimentation. Settling sediments reduces clear water, and hydropower plants' efficiency. Reservoir sedimentation relies on turbidity currents (TC). TC head velocity, and sediment content both affect particle tracking, and the removal from reservoirs. To comprehend the TC properties of Dez dam reservoir, large-scale TC modeling is required. To represent large-scale TC, a novel solver is developed. This solver couples a modified OpenFOAM® interFoam solver with the particle concentration transport equation. Two experimental tests, and Dez dam field data were verified and calibrated. The novel solution modeled these instances utilizing a two-dimensional vertical model (width averaged) with RANS turbulence closure, despite the fact that the Dez dam reservoir has a considerable size for numerical modeling. The solver simulated four Dez Dam reservoir scenarios with different water levels. Consequently, when the inlet water depth rose four times, the TC head velocity, and distance traveled by TC doubled. TC in Dez dam is a supercritical flow with the interface instabilities based on its local Richardson number, and gradient Richardson number. Furthermore, Kelvin-Helmholtz instabilities and recirculation vortex combine clear water with TC to reduce the particle concentration.

СОДЕРЖАНИЕ И РАСПРЕДЕЛЕНИЕ ТЯЖЁЛЫХ МЕТАЛЛОВ В ДОННЫХ ОТЛОЖЕНИЯХ ПЛЁСОВ ИВАНЬКОВСКОГО ВОДОХРАНИЛИЩА

Currently, the state of water bodies under the influence of technogenic factors is changing, as a rule, for the worse. Studies of the sediments of reservoirs make it possible to identify unfavorable areas and determine the sources of pollution. From the point of view of technogenic pressure, the most dangerous pollutants are trace elements Hg, Cd, Zn, Pb, Cu, Cr, Co, Ni, Fe, Mn, As. The paper presents an assessment of sediments in various areas of the Ivan’kovo reservoir. The content of mobile forms of existence of the following microelements was determined: Cd, Cu, Pb, Zn, Cr, Ni and As. The results of studies of the contamination of bottom sediments by the total concentrations of mobile forms of microelements, estimated by geo-classes - by the contamination of the sorbing fraction (less than 0.02 mm) are presented. The main contaminants are cadmium and lead, which are estimated to be slightly to moderately polluted. A picture is presented of both contamination of the bottom sediments of the Ivan’kovo reservoir with microelements, and the distribution and correlation of their mobile forms of existence in the desired sediments. From the data obtained, it can be concluded that, despite a significant number of pollution sources, at present there is no need to talk about a dangerous load on the studied objects.

DEVELOPMENT OF PORTABLE CONCRETE 3D PRINTER TO USE LOCALLY MANUFACTURED ADDITIVE

In this study, a portable concrete 3D printer is designed, and its additive is developed from local materials to address the advancement in digital fabrication for the construction industry. The authors investigate different additive materials in preparing four mixes using Ordinary Portland Cement, white cement, reservoir sediments, dune sand, commercial sand, fine marble waste, and bentonite for a portable concrete 3D printer. The two mixes showed the best compressive strength results, containing fine marble waste and reservoir sediments. The mix WSS (30% white cement, 50% sand, 20% sediment) has resulted in a compressive strength ranging from 18 to 21 kPa after 28 days of curing. The mix WSM (30% white cement, 50% dune sand and 20% fine marble waste) recorded a compressive strength range from 15 to 17 kPa after 28 days of curing. The mixes were successfully employed as an additive for crafting 28 layers in a single attempt using a newly developed portable concrete 3D printer and additive.

Experimental Investigation on Reservoir Sediment Flushing through a Bottom Tunnel with an Initially Covered Intake

Reservoir sedimentation is of worldwide concern, involving not only reservoir benefits, but environmental and ecological issues. Sediment flushing is one of the most common and effective methods for alleviating sedimentation and its negative impacts. To date, however, it has remained unknown whether sediment flushing can be accomplished through a bottom tunnel once its intake has been covered by sediment deposits. Here, a total of 65 runs of flume experiments were conducted to investigate the threshold conditions for occurrence of sediment flushing. The results demonstrate that higher water level, smaller cover layer thickness, shorter tunnel length, and steeper tunnel slope favor the occurrence of sediment flushing. Physically, as the gate located at the tunnel intake is opened, the sediment deposits immediately upstream of the intake collapse and enter the tunnel, entraining water. A mass of hyperconcentrated water-sediment mixture is generated, in which the amount of sediment depends on the cover layer thickness. If the water level is sufficiently high, the cover layer thickness is low, the tunnel slope is steep, or the tunnel is short, the pressure difference between the inlet and outlet of the tunnel suffices to drive the water-sediment mixture to move down to the outlet, overcoming the resistance due to the tunnel boundary. This way, sediment flushing is accomplished. Based on dimensional analysis of the observed data, a threshold condition is proposed for the occurrence of sediment flushing. It is also shown that an equilibrium scour hole is formed immediately upstream of the tunnel intake, and an empirical model for the scour hole geometry is proposed. The present findings can be exploited to improve sediment-rich reservoir planning, design, and operation for benefit maximization and eco-environmental wellbeing.

Evolution of the main channel of the Yangtze River

AbstractThe construction and operation of the Three Gorges Reservoir and the cascade reservoirs upstream have significantly altered the processes of flow and sediment in the main and tributary channels of the Yangtze River. This has led to substantial adjustments in the riverbed through erosion and deposition, thereby impacting flood protection, water resource utilization, navigation, and the aquatic environment in the Yangtze River basin. In this study, prototype measurements were used to analyze the variations in runoff and sediment load in the main channel of the Yangtze River, as well as the changes and evolution of the riverbed. Mathematical modeling was done to predict the trends in reservoir sedimentation and riverbed adjustments. The results indicate that, apart from the significantly increased runoff and sediment load in the river source region (Zhimenda station) over the past two decades, there is no clear unidirectional trend of increasing or decreasing in the main and tributary annual runoff of the Yangtze River. However, the release of reservoir outflows undergoes significant changes throughout the year due to reservoir regulation. Suspended sediment load in the upper Yangtze River has been decreasing since the 1990s, especially after the operation of the Three Gorges Reservoir and the four cascade reservoirs in the lower reach of the Jinsha River. The factors influencing flow and sediment variations include mainly climate change and human activities such as reservoir operation and soil and water conservation. The significant changes in flow and sediment conditions have disrupted the original relative equilibrium state of the main channel of the Yangtze River, leading to riverbed adjustments. The river sections in the upper reach, located within reservoir areas, have shifted from erosional state under natural conditions to accumulative state, while the middle and lower reaches have transitioned from a relatively equilibrium state to a process dominated by erosion and reconstruction. Overall, the river regime in the reservoir area and downstream of the Three Gorges Dam remains relatively stable, but there have been adjustments in some local river sections, for example, in the curved sections, particularly in the sharply curved sections downstream of the Three Gorges Dam, where gradual or abrupt chute cutoff has occurred. In the foreseeable future, the river channel downstream of the Three Gorges Dam will remain in an unsaturated state regarding sediment transport. The process of river channel erosion will persist for a long time and have far‐reaching consequences. Some long straight sections, multiple bifurcation sections, and sections with large curvature are expected to undergo certain adjustments in the river regime, necessitating continuous observation, long‐term monitoring, and timely river management and channel governance.

Distribution, evolution and structural properties of Wushenqi paleo-uplift in Ordos Basin, NW China

This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny (Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55–94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170–196 m and 11 298 kmbrespectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle–Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma4 Member–pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.

Application of geospatial technique and hydrological modelling in evaluating reservoir sedimentation in Chhattisgarh state of India

ABSTRACT Soil erosion and sediment deposition in the reservoirs are both consequences of the change in precipitation pattern that has been observed over the past decade. For the purpose of storing water in reservoirs built before the 1980s, the Indian state of Chhattisgarh has a few irrigation projects. As the state has grown, agricultural land has increased while the proportion of forest area has decreased. Due to this development, runoff is introducing more sediment into the reservoirs, resulting in a reduction in intended storage. The effects of sediment deposition in the Kodar reservoir, located in the Mahasamund district of Chhattisgarh State, are evaluated in present study. Prior to five years, the reservoir reported a 30% deficit in actual irrigation. To quantify the sediment load, Remote Sensing (RS), Geographic Information System (GIS), and the Hydrologic Engineering Centre – Hydrologic Modelling System (HEC-HMS) were effectively employed. From 2012 to 2014, the reservoir received an average sediment load of 1.11 million tonnes. In order to preserve soil in the watershed’s erosion-prone area, a treatment plan is developed. It includes numerous thematic maps that are overlaid in order to provide preventive measures against reservoir sedimentation and is further proposed in the form of best management practices.

Reservoirs as high-efficacy sentinels of regional atmospheric pollution and precipitation: magnetic and chemical evidence from a typical subtropical reservoir in South China.

While there is a general sense that reservoirs can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. Here multiple-proxy analyses including 210Pb, grain size, heavy metals, magnetic parameters, and spheroidal carbonaceous particles (SCPs) were conducted for a sediment core from a typical subtropical reservoir in South China (Huangkeng Reservoir). 210Pb dating revealed that the core spans from ~ 1964 to 2019, with the sedimentary rate increasing during recent years. The sedimentary environment was mainly influenced by natural process (especially precipitation), along with the accumulation of Cr, Ni, Cu, V, As, Sb, and Co and most magnetic particles. However, four heave metals (Cd, Pb, Tl, and Zn) were found mainly from atmospheric deposition from industrial/agricultural activities in Huizhou City, which was also indicated by SCPs, S-ratio, and χARM/SIRM. According to temporal variation of SCPs, the atmospheric pollution history ofnearby city (Huizhou Cityas the most close one) from 1964 was reconstructed. The study shows that reservoir sediments, especially in areas with few or no natural lakes, are high-efficacy and high-resolution achieves for research on environmental evolution in the Anthropocene related to global change and intensifying human activities.

Improving acidic sandy soil properties for plant growth with dam reservoir sediments in the face of soaring fertiliser prices

Recent actions aimed at creating an environmentally sustainable economy, as well as very high inorganic fertiliser prices, have begun a ‘renaissance’ of alternative fertilisation. It includes utilisation of dam reservoir (DR) sediments. The aim of our study was to evaluate the agricultural value of non-toxic material to be dredged from a dam reservoir in the face of changing mineral fertiliser prices. The quality of sediments was established based on pot experiment: four different sediment dosages (5 %, 10 %, 20 %, 40 %) and three plants in rotation (maize, mustard and grass mix) were tested. Application of DR sediments into sandy soil improved its texture (depending on dose 4–31 % less sand, 50–412 % more silt and 40–70 % more clay) and sorption properties, increased pH (the soil was acidic). The content of total organic carbon increased 1.4–4.3 times, total nitrogen (N) 1.4–4.7 times, ammonium nitrogen 1.3–5.2 times, nitrate nitrogen 1.7–11.8 times, total phosphorus (P) ∼1.4 times and available phosphorus ∼2.0; most changes were statistically significant. Yield of all three plants increased significantly correspondingly to the sediment application. It shows that DR sediments might be a good alternative to chemical fertilisers. Since the catchment of the analysed reservoir is mostly agricultural, N and P compounds accumulated in sediments originated from farming. Therefore, using DR sediments as fertilisers closes the cycle of these elements; N and P compounds can be used by plants. Additionally, this alternative fertiliser is cheap – since the analysed reservoir has to be dredged, large amounts of sediments will be obtained as a ‘side-effect’ of this process. Agricultural application of this nutrient-rich material would transform sediments from waste into a resource. Recent steep increase of mineral fertilisers prices – in Poland, the prices in 2022 were 2–3 times higher than in 2018 – showed that we have to diversify fertiliser sources. Low cost, ecological sustainability and good physical and chemical properties make DR sediments, if not a substitute, a good addition to the traditional methods of agricultural fertilization.

High-temperature modification of steel slag using composite modifier containing silicon calcium slag, fly ash, and reservoir sediment

Steel slag (SS) is a kind of industrial solid waste, and its accumulation brings certain harm to the ecological environment. In order to promote the building material utilization of SS, high-temperature modification (HTM) of SS is performed using a composite modifier (CMSFR) containing silicon calcium slag (SCS), fly ash (FA), and reservoir sediment (RS). Then, the authors investigated the effect of CMSFR on the cementitious properties and volume soundness of SS mixture after HTM (SMHTM). After that, the mineral composition and microstructure of SMHTM were investigated through X-ray fluorescence analysis (XRF), X-ray diffraction (XRD), scanning electronic microscopy (SEM), energy dispersive spectrometry (EDS), and particle size analysis. It was found that the free CaO (f-CaO) content obviously decreased, and the cementitious properties improved in SMHTM. When the CMSFR content was 20% (SCS: FA: RS = 9:7:4), and the modification temperature (MT) was 1,250°C, the mass fraction of f-CaO in SMHTM dropped from 4.81% to 1.90%, down by 60.5%; the 28-day activity index of SMHTM increased to 85.4%, 14.3% higher than that of raw SS, which meets the technical requirement of Steel slag powder used for cement and concrete (GB/T 20491-2017): the activity index of grade I SS powder must be greater than or equal to 80%. As the mass fraction of CMSFR grew from 10% to 30%, new mineral phases formed in SMHTM, including diopside (CMS2), ceylonite (MgFe2O4), gehlenite (C2AS), tricalcium aluminate (C3A), and magnetite (Fe3O4). The HTM with CMSFR promotes the decomposition of RO phase (a continuous solid solution composed of divalent metal oxides like FeO, MgO, MnO, and CaO) in raw SS, turning the FeO in that phase into Fe3O4. The above results indicate that the SMHTM mixed with CMSFR can be applied harmless in cement and concrete, making low-energy fine grinding of SS a possibility.

PERENCANAAN INSTALASI PENGOLAHAN AIR LIMBAH PADA INDUSTRI TAHU (Studi Kasus Pabrik Tahu WD Lamper Lor Semarang Selatan)

In the production process, the tofu industry produces solid and liquid waste. The waste contains organic matter with high levels of BOD, COD, and TSS and does not meet quality standards. If the waste is directly discharged into the environment, it will reduce the carrying capacity of the environment. This research was conducted at the WD Lamper Lor Tofu Factory, with the aim of planning the design and RAB for the construction of the wastewater treatment plant at the Tofu Factory. This research uses quantitative analysis methods which are presented in the form of numbers which are then explained and interpreted in the form of descriptions. The quality of BOD, COD, TSS, and pH were 144 mg/L, respectively; 380 mg/L; 98 mg/L; and 4.34. Based on the quality standards, the wastewater does not meet the requirements, so it is necessary to plan a wastewater treatment plant. Researchers plan the processing stages, namely Reservoir, Equalization, Anaerobic Digester, Gas Storage, Presettlement Tub, Anaerobic Biofilter, and Final Sedimentation Tub. The estimated effluent from the processing of BOD, COD, and TSS is 2,916 mg/L, respectively; 7.695 mg/L; 2.116 mg/L. In addition to processing it into water that is fit for reuse, the design of this wastewater treatment plant produces methane gas that can be used for the tofu-making process or can be used on a household scale. The total budget plan for the planning of the Wastewater Treatment Plant at the WD Tofu Factory is 31,106,117.05.

Spatial-temporal evolution of sediment transport in the upper Yangtze River Basin considering the cumulative impacts of mega reservoirs

The intensive construction of large dams in the upper Yangtze River Basin (UYRB) has formed large-scale cascade reservoirs and obviously altered the flow regime and sediment transport of the basin. However, few studies have quantitatively described the cumulative impact of these reservoirs on sediment interception. In this study, a flow and sediment transport model that fully considers the operation processes of 24 mega reservoirs in the UYRB was established, and the spatial and temporal variations in sedimentation from 2011 to 2080 were elucidated, assuming repeated series of daily input flow discharge and sediment concentration during 2011–2020 and monthly water operation levels of 24 reservoirs during 2018–2021 as boundary conditions. The results showed an annual average sedimentation of more than 300 Mt in the UYRB during 2011–2060, which falls to 270 Mt in the period 2061–2080, and more than 80% of the sedimentation occurs in the flood season. Nearly 80% of the total sedimentation during 2010–2080 was observed in the mainstream reservoirs, especially the four mega reservoirs in the lower Jinsha River and the Three Gorges Reservoir (TGR), which accounted for 31.9% and 22.7% of the total sedimentation, respectively. The proportion of sedimentation in mainstream reservoirs will further increase with increasing operation periods. Most reservoirs in the UYRB will not reach sedimentation equilibrium by 2080, except for reservoirs in the Min River Basin. The ratio of siltation capacity to average annual sediment yield determines the percentage of residual siltation capacity of each reservoir. The operation of the cascade reservoirs in 2013–2020 had no more immediate impact on the middle and lower Yangtze River than that in 2003–2012, when the TGR started impoundment. However, the joint operation of these cascade reservoirs has changed the spatial distribution of sedimentation in the UYRB, and will lead to prolonged impacts on downstream channel erosion.

Assessment of reservoir trapping efficiency and hydropower production under future projections of sedimentation in Lancang–Mekong River Basin

Sedimentation poses a significant threat to the long-term sustainability of hydropower generation. However, there is a lack of studies examining the relationship between sediment trapping efficiency and electricity generation on a basin-wide scale over time. This study aims to assess the efficiency of hydropower production in terms of reservoir sediment trapping. Modified Brune's method examined the relationship between trapped sediments in reservoirs and hydropower production, considering sediment projections for the near future. We divided the cases of existing and planned reservoirs in the mainstream river and subbasins to assess cumulative sediment trapping. Using the Lancang-Mekong River Basin as a case study, the following main findings were observed. Firstly, the existing reservoirs, under baseline conditions (2018), had the potential to trap approximately 60.9% or 82 Mt/yr of the total sediment load. Secondly, around 69% or 110 Mt/yr of the total sediments could be significantly trapped when considering the existing reservoirs and those planned according to the development plan of riparian countries. Thirdly, the hydropower production efficiency of most reservoirs in 2030 and 2040 experienced a significant decline of approximately 10%–20% and more than 30%, respectively. Therefore, sediment management is crucial for maintaining efficient hydropower production and achieving sustainable hydropower development through effective planning strategies.

Investigation of the film-forming flooding mechanism of molecular deposition in tight oil reservoirs

Most of the oil fields in China have entered the stage of high-water-content development, which has become the primary means to improve the recovery rate of high-water-content oil fields by changing the injection agent. MDFFA membrane oil drive technology is a new type of tertiary oil recovery technology that uses an aqueous solution as the transfer medium; however, it is rarely applied in the field of tight oil reservoirs in China. In this study, molecular film-wall microgravity and water-wall microgravity were compared for tight reservoirs in the Shengli oilfield. It was concluded that the MDFFA dominates in competitive adsorption, breaks through and removes the hydrated layer, and finally adsorbs firmly on the pore wall to form a nanoscale ultrathin film. The application conditions of the MDFFA were also explored, and its wetting angle was tested. Further, the variation law of MDFFA adsorption was studied, and the mechanism of MDFFA drag reduction was explained in terms of reducing the boundary layer effect and water injection friction resistance. The natural cores procured from the Shengli tight oil field were analyzed for MDFFA membrane drive cores, and a reasonable injection concentration was selected. Through a series of mechanistic and experimental studies, we provided theoretical and technical references for the development of increased tight oil production.

The impacts of dam construction on elemental deposition in a reservoir receiving mountaintop coal mining materials

Waters MN, Bernhardt ES, Gerson JR. 2023. The impacts of dam construction on elemental deposition in a reservoir receiving mountaintop coal mining materials. Lake Reserv Manage. 39:246–258. Dam construction and associated reservoirs can become depositional basins capable of concentrating material inputs from human-altered landscapes. Landscape disturbances such as agriculture and urban expansion have been shown to impact erosional processes into reservoirs, whereas less is known of material originating from intense mining operations. Mountaintop mining (MTM), a prevalent form of surface coal mining in the Central Appalachian ecoregion of the United States, can impact stream ecosystems by altering flows, conductivity, and associated elements. We applied paleolimnological techniques to determine depositional impacts in the Mud River Reservoir downstream of the Hobet Mine, West Virginia, the largest surface mine complex in the United States. Paleolimnological measurements included carbon (C), selenium (Se), sulfur (S), magnesium (Mg), phosphorus (P), nitrogen (N), calcium (Ca), and photosynthetic pigments. Our study focused on 3 primary objectives: (1) determine the materials associated with MTM that are stored in the sediment, (2) calculate the storage rate of Se, a known contaminant from this area, following dam construction (1995 CE), and (3) identify physical, environmental, and biological mechanisms associated with dam construction and how they influence elemental deposition in reservoirs. Results from sediment cores show increases in the storage of inorganic carbon (IC), Se, and Ca for both core sites throughout the period of reservoir existence, with Se deposition related to physical and environmental conditions that are associated with reservoir genesis. These data show that dam construction altered environmental processes on MTM elements, which could have lasting impacts on reservoir biota and downstream environments long after reclamation efforts are applied.

Mercury isotopes trace historical mercury pollution from Pb[sbnd]Zn smelter in China

Lead–zinc (PbZn) smelting is one of the largest anthropogenic emission sources of mercury (Hg) in China and the world. In the last few decades, Hg emission control devices have been employed in PbZn smelters to reduce Hg emissions. To evaluate the effectiveness of Hg emission control, this study uses Hg isotopes to trace the sources of Hg in soils and reservoir sediments near the Zhuzhou smelter, the largest Zn production facility in China. The results showed that Hg concentrations in reservoir sediments were higher than those in soils at the three study sites, suggesting that reservoir sediments accumulate more Hg than soils do under the same conditions. Hg concentrations and deposition fluxes in reservoir sediments have dramatically decreased since the year 2000, suggesting the effectiveness of Hg emission control in the Zhuzhou smelter. Mercury isotope compositions in soil suggest binary mixing of Hg from the Zhuzhou smelter and the local background, and the contribution of Hg from the Zhuzhou smelter to soils and sediment is mainly a function of location and distance from the source. The model output suggested that approximately 61–75% of Hg in reservoir sediments was sourced from the Zhuzhou smelter. This study demonstrates that legacy Hg will continue to be a source to local ecosystems, even after Hg emission control has been implemented for decades.

Impact of reservoir operation policies on nitrogen cycling processes and water quality dynamics in a large water supply reservoir

Reservoir operation policies affect reservoir nitrogen (N) cycling and budgets through complex influences on physical and biogeochemical processes in water and sediment. However, the underlying influencing mechanisms, especially the impact of operations on sediment processes, remain unclear. This study combines a coupled hydrodynamic-eutrophication-sediment model and a reservoir operation model to clarify reservoir operation impact on N cycling processes in water and sediment as well as impact on stored and discharged water quality. Three typical reservoir operation policies (i.e., standard, hedging, and eco-friendly) were selected to create operation scenarios. The hydrodynamic-eutrophication-sediment model was used to simulate N cycling processes and N concentrations in stored and discharged water under each scenario. Using China's Danjiangkou Reservoir as a case study, results revealed that reservoir operation policies significantly affected spatiotemporal dynamics of N cycling processes and water quality. Specifically, reservoir sediment acted as a N source, contributing to annual net release of 9.5–16.1 Gg N. Higher water levels promoted sediment ammonium release through effects on reservoir submerged area and sediment temperature. Moreover, denitrification processes in water and sediment collectively contributed to annual N removal of 14.0–16.9 Gg N. Annual N removal was greater in the higher water level scenario despite its lower denitrification rate per unit area. Additionally, these processes and hydrodynamic conditions combine to affect N forms and concentrations. The N concentration in the lower water level scenario was generally higher, risking algal bloom outbreaks in the shallow-water zone. This study is intended to help guide reservoir operation policymaking to account for N management while also coordinating water quantity and quality targets.

Source apportionment of heavy metal(loid)s in sediments of a typical karst mountain drinking-water reservoir and the associated risk assessment based on chemical speciations.

As important place for water storage and supply, drinking-water reservoirs in karst mountain areas play a key role in ensuring human well-being, and its water quality safety has attracted much attention. Source apportionment and ecological risks of heavy metal(loid)s in sediments of drinking-water reservoir are important for water security, public health, and regional water resources management, especially in karst mountain areas where water resources are scarce. To expound the accumulation, potential ecological risks, and sources of heavy metal(loid)s in a drinking-water reservoir in Northwest Guizhou, China, the surface sediments were collected and analyzed based on the combined use of the geo-accumulation index (Igeo), sequential extraction (BCR), ratios of secondary phase and primary phase (RSP), risk assessment code (RAC), modified potential ecological risk index (MRI), as well as the positive matrix factorization methods. The results indicated that the accumulation of Cd in sediments was obvious, with approximately 61.9% of the samples showing moderate to high accumulation levels, followed by Pb, Cu, Ni, and Zn, whereas the As and Cr were at low levels. A large proportion of BCR-extracted acid extractable and reducible fraction were found in Cd (72.5%) and Pb (40.3%), suggesting high bioavailability. The combined results of RSP, RAC, and MRI showed that Cd was the major pollutant in sediments with high potential ecological risk, while the risk of other elements was low. Source apportionment results of heavy metal(loid)s indicated that Cd (75.76%) and Zn (23.1%) mainly originated from agricultural activities; As (69.82%), Cr (50.05%), Cu (33.47%), and Ni (31.87%) were associated with domestic sources related to residents' lives; Cu (52.36%), Ni (44.57%), Cr (34.33%), As (26.51%), Pb (24.77%), and Zn (23.80%) primarily came from natural geological sources; and Pb (47.56%), Zn (22.46%) and Cr (13.92%) might be introduced by mixed sources of traffic and domestic. The contribution ratios of the four sources were 18.41%, 36.67%, 29.48%, and 15.44%, respectively. Overall, priority control factors for pollution in relation to agricultural sources included Cd, while domestic sources are primarily associated with As. It is crucial to place special emphasis on the impacts of human activities when formulating pollution prevention and control measures. The results of this study can provide valuable reference and insights for water resources management and pollution prevention and control strategies in karst mountainous areas.