Achieving ultralow levels of phosphorus (P) concentrations to prevent eutrophication is an important goal of surface water management. Hence, a highly efficient and economical adsorbent for phosphate ...removal is urgently required to meet the increasingly stringent water quality standards. This study investigated the phosphate adsorption performance of zirconium (Zr)-modified calcium-montmorillonite (Zr-CaMs). Batch experiments were conducted to obtain the adsorption isotherms, kinetics, and the influences of dosage, solution pH, and coexisting anions. The results demonstrated that Zr was successfully introduced to the surface and interlayer of raw CaM in the presence of the SiO…HOZr hydrogen bond and that it increased the specific surface area. The adsorption isotherms obeyed the Langmuir nonlinear model. The calculated maximum phosphate adsorption capacity was 22.37 mg/g, which was more than twice that of Phoslock. The Elovich model fit the kinetics data well, which was indicative of chemical adsorption. An optimum dosage of 100/1–150/1 and wide pH range (4–8.5) are recommended for practical applications. The coexistence of HCO3− slightly inhibited the adsorption capacity, whereas Cl− and SO42− had a positive impact. The adsorption mechanism was primarily the ligand exchange between the surface hydroxyl groups and phosphate resulting from the formation of inner-sphere coordination complexes. This study demonstrated that Zr-CaMs can serve as a prospective adsorbent for phosphate removal from contaminated surface water.
•Zr-CaMs were synthesized to remove phosphate from aqueous solution.•Adsorption data followed Langmuir isotherm and Elovich kinetic models.•The maximum phosphate adsorption capacity reached 22.37 mg/g.•Adsorption mechanism was primarily the formation of inner-sphere complexes.•Zr-CaMs can serve as a promising adsorbent for P removal from polluted water.
Reservoirs in southwestern China are encountering the challenge of eutrophication, in which internal phosphorus (P) release from sediments plays an important role. Studies on the high-resolution ...profile variations and release mechanisms of P at the sediment-water interface (SWI) are rare in these reservoirs until now. In this study, monthly monitoring (Nov 2017 to Oct 2018) using a composite diffusive gradient in thin films (DGT) technique was taken to determine the temporal and vertical profile variations of the DGT-labile P (Fe) at the SWI in Hongfeng Reservoir. The results showed that the average concentrations of the DGT-labile P (Fe) in surface sediments were 0.63 ± 0.24 mg·L−1 and 4.61 ± 1.12 mg·L−1, respectively, with significantly higher concentrations during the summer anoxic period than that during the winter aerobic period. The DGT-labile P (Fe) concentrations in sediments presented a significant positive correlation (r2 > 0.70, p < 0.001), supporting the simultaneous release of reactive P and reactive Fe from the sediments and indicating that the reductive dissolution of iron-bound P dominates the P release from sediments. The release rates of P ranged from 0.01 mg·m−2·d−1 to 0.83 mg·m−2·d−1 (mean: 0.22 mg·m−2·d−1) in Hongfeng Reservoir, which are higher than that in heavily eutrophic shallow lakes in eastern China, such as Lake Taihu. There is a higher P loading, stronger P reactivity, faster P release rates, and higher pollution potential in deep reservoirs of southwestern China than that in natural shallow lakes of eastern China, highlighting the importance and urgency of treating internal P pollution in deep reservoirs. Further studies on the mechanisms and controlling factors of the coupled Fe-P-S cycle in deep reservoirs are desirable in the future, so as to provide a scientific foundation for exploring effective internal P treatment techniques adaptive to deep reservoirs in southwestern China.
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•In situ, millimeter scale investigation on monthly variation of the labile P (Fe) at the SWI was first carried out using DGT in a deepwater reservoir, southwestern China.•Significant positive correlation between DGT-labile P and DGT-labile Fe in sediments indicated that P release is controlled by the reductive dissolution of iron-bound P.•The apparent P diffusion flux at the SWI was remarkably high, with a mean value of 0.22 mg·m−2·d−1, highlighting the importance of the internal P pollution.
Human activities have greatly altered terrestrial carbon (C) dynamics associated with vegetation cover and land use changes, thereby influencing the C sink in downstream ecosystems. However, the ...transport and preservation of organic C from soils that experience serious erosion in the karst area are scarce, particularly at catchment scales. In this study, chemical characteristics of organic matter (OM) isolated from the topsoil, overlying water, and lake sediments, as well as subsequent source identification, were inferred from the molecular, spectroscopic, and carbon isotopic (δ
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C) signatures in a typical karst catchment, Southwestern China. The results indicated that the elemental compositions of the calcareous soil and paddy soil significantly differed from the yellow soil. High similarities existed in the fluorescence spectra of humic substances (HS) extracted from the front two soil types with those of lake sediments, indicating the homogeneous nature of OM molecular structure. The C/N ratios of six dissolved OM fractions and sedimentary HS along with δ
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C values consistently reflected the primary terrestrial source. It was estimated to account for 60% of total organic C in sedimentary OM by end-member mixing modeling in accordance with soil erosion intensity and large recharge coefficient of this catchment. The evolution of soil loss and lake productivity can be well deduced from sediment records of organic C content, C/N ratio, and the specific information of HS. This research highlighted that the composition, source, and fate of OM in the karst lake was mainly dominated by the terrestrial C flux, rather than in-lake production. Furthermore, soil type and erosion intensity have significant effects on the nature of eroded OM and ultimate preservation.
The influence of cascade dams on the migration of microplastics (MPs) was conducted by analyzing the spatial distribution of MPs in sediments of the Wujiang river basin (Wujiang river basin) in ...Southwest China. The results showed that the abundance of MPs in Wujiang river basin sediments ranged from 310 to 2620 items/kg dw (mean: 1354 items/kg dw, a high level compared with aquatic sediments worldwide). The main chemical components of these MPs were polypropylene and polyethylene. High abundance of MPs in tributary sediments suggested that tributary inputs contributed to the main stream and reservoirs. Statistical analysis showed that gross domestic product (GDP) and the basin area of cascade reservoirs, rather than hydraulic retention time and reservoir age, were the dominating factors in the distribution of MPs in the Wujiang river basin. The accumulation of MPs in cascade reservoirs implied the interception effect of cascade dams. The rapid development of cascade dam systems and the interception effect of dams should be taken into account when predicting the flux of MPs from rivers to the ocean. Heavy metals found on the surface of the MPs showed the compound pollution of MPs and heavy metals in dammed rivers and cascade reservoirs. Our results deepen the understanding of the migration of MPs in rivers alongside intensive cascade hydropower development.
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•Distribution and abundance of microplastics was investigated at a large watershed scale.•Tributary input is an important source of microplastics in the main stream and cascade reservoirs.•GDP and basin area, instead of HRT, dominated the distribution of microplastics.•Combined pollution of microplastics and heavy metals in dammed rivers needs to be concerned.
The oxygen isotope ratio in phosphate (δ18OP) is an effective tool for tracing the sources of phosphorus (P) and their biogeochemical cycles. The HCl-extractable inorganic phosphate (HCl-PTI) is the ...primary component of P and plays a key role in the dynamic transformation of P in sediment and soil. However, it has always been difficult to purity sample for analyzing the δ18OP composition of HCl-PTI due to the significantly interference of large amounts of Fe2+/3+, Ca2+, Cl− and other impurities in the HCl-PTI extracts. In this study, we developed a simple and promising purification method for δ18OP analysis of HCl-PTI in sediments and soils based on the superior selective enrichment and elution abilities of phosphate (PO4) and efficient synchronous removal of impurities by Zr-Oxide gel in highly acidic HCl-PTI extract. The enrichment rate and elution rate of PO4 in the HCl-PTI extract by the Zr-Oxide gel could achieve 100% respectively, and the synchronous removal rates of most anions, dissolved organic carbon (DOC), metals, and trace elements could be above 96% respectively, reducing the tedious operation of conventional methods and the difficulties in removal of impurities, such as Cl− in HCl-PTI extract. It's indicated that the purity of the Ag3PO4 solid for δ18OP composition analysis of HCl-PTI could reach 99.9%. The above results show that the new method is very simple, efficient and reliable for the δ18OP analysis of HCl-PTI in sediments and soils. This study provides new methodological support for identifying the sources of P and tracing their biogeochemical cycles in sediment or soil environment.
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•A method based on selective enrichment and elution of PO4 in HCl-PTI extracts.•It avoids the significant interference of Fe2+/3+, Ca2+, Cl− and other impurities.•A simple purification protocol for HCl-PTI δ18OP analysis in sediments and soils.•A new methodological tool to trace the P source and its biogeochemical cycle.
The phosphate oxygen isotope (δ18OP) ratio has been proven to be an effective tool to trace the sources and biogeochemical cycles of phosphorus (P) in aquatic ecosystems. However, the enrichment of ...phosphate (PO4) and the removal of impurities are quite complex and easy to cause PO4 loss in current δ18OP analytical methods. Moreover, the δ18OP value obtained by the commonly-used instantaneous sampling method is more of the instantaneous information of P, which is accidental or uncertain for accurate identification of the P source. In this study, a new method of in situ enrichment, elution, and purification of PO4 (ISEEP) was developed for δ18OP analysis in waters. This method utilized a PO4 binding phase (Zr-Oxide gel) to selectively in situ adsorb PO4 in water and exhibited an adsorption capacity per unit area of up to 789.3 μg P/cm2. The PO4 on the gel was eluted easily with a 1 M NaOH solution. More than 99.7% of the common anions, cations, and dissolved organic matter (DOM), as well as more than 90% of the trace elements were removed synchronously after adsorption and elution of PO4. The recovery rate of PO4 in the whole procedure was as high as 92.8%. The XRD and SEM examinations showed that the ISEEP can obtain high-purity Ag3PO4 solid for the δ18OP measurement. The reliability of the ISEEP method is confirmed by the measured δ18OP value and standard deviation of parallel samples from different types of natural waters obtained by both the ISEEP and the current popular McLaughlin (2004) method. It provides a good prospect of this new method for tracing the P sources and their biogeochemical cycling in aquatic ecosystems.
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•A new δ18OP analysis method based on in situ enrichment of phosphate in waters.•It avoids large-volume sampling, efficiently reduces the impurities interference.•The average information of δ18OP composition in different time scales is obtained.•A simplified tool to trace the phosphorus sources and their biogeochemical cycles.•This method is very suitable for the waters in typical phosphorus pollution areas.
Phosphorus (P) released from sediment driven by oxidation-reduction potential and enzymes can increase the concentrations of dissolved P in the overlying water, which trigger widespread algal blooms. ...Therefore, identification sediment P sources is critical for the management of P and restoration of eutrophic aquatic ecosystem. Sediment P fractions have been widely reported, whereas little is known regarding the source and pathway of different P fractions in eutrophic lake sediments. In this study, we applied chemical sequential extraction with oxygen isotopic compositions of phosphate (δ18OP) to identify the inorganic P (Pi) source in the sediments of Lake Dianchi, China. Results show that contents of organic P (Po), HCl-Pi, NaOH-Pi, and NaHCO3-Pi of sediment were the main P fractions compared with that of sediment H2O-Pi, which was attributed to the bioavailable difference of these P fractions. Significant difference on the equilibrium values of δ18OP (δ18OP-eq), δ18OP of sediment P fractions, and δ18OP of external P was observed, which reflected the complex transformation processes of these P fractions in sediments. Further, the values of sediment δ18ONaHCO3-Pi at some sites (17.2–22.5‰) deviated from δ18OP-eq (14.7–19.0‰), and these values fell into the values of δ18OP for external P (7.7–23.8‰), suggesting that sediment NaHCO3-Pi at these sites derived from external P. Comparison the values of sediment δ18ONaOH-Pi (14.5–24.9‰) with δ18OP-eq and δ18O of external P sources suggested that sediment NaOH-Pi was not only from external P, but also from sedimentary Po remineralization. Pi released from sediment NaOH-Pi may be responsible for the higher values of sediment δ18OHCl-Pi (15.2–20.8‰) than that of soils (13.1–15.3‰) and phosphate rock (8.9–12.6‰). Results gained from this study provided critical insights for the source and biogeochemical cycling of P across the sediment-water interface in the eutrophic lake.
•The δ18OP was employed to identify the sediment P source of a large eutrophic lake.•NaOH-Pi and HCl-Pi were from external P and sediment P fractions redistribution.•The δ18OP is an effective tool to identify the source and pathway of sediment P.
•Liuzhou is the largest industrial city in Guangxi and a key city in southwest China.•CCA and PCA analysis of HMs in soil of a Coking plant in Liuzhou are applied.•The pollution is related to the ...production process and transportation of roads.•Ni, As and Cd have health risk to workers in the plant.•Provide reference for the prevention of HMs of other coking enterprises in China and in the world.
In response to the detailed investigation in the production enterprise by the Ministry of Ecology and Environment of the People's Republic of China, The investigation of soil pollution potential risk in a coking welfare plant in Liuzhou was carried out. Meanwhile, the key facilities and regions were identified. The monitoring factors in the soil of the plant were evaluated to judge the ecological risk and health risk caused by heavy metals (HMs) in the soil. At the same time, the application of ArcGIS was used for concentration interpolation analysis. The correlation analysis and principal component analysis of HMs in soil were applied to identify the characteristic pollutants. It was found that all HMs detected were probably the characteristic contaminant from the plant. The results showed that nickel (Ni) and arsenic (As) exceeded the screening values of the second class of using-land in standard GB36600-2018. It was found that Ni and As in the soil of the plant had different degrees of pollution. The hydrargyrum (Hg) was considered as high ecological hazards at all sites. The areas with high ecological hazard were close to the furnace ash storage area and its treatment area. Though within an acceptable range, it was found that As and Ni in the plant had a health risk to workers of the plant. The results of this study can provide experience and example for other enterprises with heavy metal pollution. This study applied the standard GB 36600-2018 promulgated in recent years to assess health risks from pollution soil, verifying the feasibility of the implementation of this standard in China. It also makes a contribution to encourage more environmental management and investigations in production enterprises of potential pollution hazards of land information in the world.
Enrichment of arsenic (As) in sediment (12–227 mg/kg) in the upstream tributaries of the Indus and Brahmaputra Rivers originating from the Tibetan Plateau where hot springs were abundant has been ...found. Sandy sediment samples from the Nu-Salween River, Lantsang-Mekong River and Jinsha-Yangtze River also originating from the Tibetan Plateau were collected in July, 2012 and were found to contain 6.8 mg/kg to 30.5 mg/kg As (average17.3 ± 6.5 mg/kg, n = 12). Deposits collected within 1 m of two hot springs in Changdu, Tibet displayed significantly higher As levels: 263.7 mg/kg in LD-2 with 65% quartz and 101.8 mg/kg in NuD-1 with 82% calcite. To evaluate the valence states of As and also the phases responsible for sorption, X-Ray Absorption Spectroscopy (XAS) was employed to analyze the two hot spring deposits and three river sediment samples: coarse sand NuD-6 (As 14.6 mg/kg), fine sand NuD-4 (As 17.8 mg/kg), and silty sand LD-1 (As 30.5 mg/kg). The X-ray absorption near edge spectrum (XANES) data indicate that 70% of As from 3 samples in the Nu-Salween River drainage (NuD-1, NuD-4 and NuD-6) is As(V) or arsenate, with the rest being As(0) or As–Fe sulfides. The proportion of As(V) is 90% for 2 samples in the Lantsang-Mekong River drainage (LD-1 and LD-2). Linear combination fit of the iron extended X-ray fine structure spectrum (EXAFS) show that 3 samples from the Nu-Salween River contain 20% ferrihydrite and 10% goethite without any hematite being detected but 2 samples from the Lantsang-Mekong River contain <10% ferrihydrite, 20% goethite and with 30–60% of hematite. Concentrations of reductively leached As and Fe are correlated (Pearson correlation coefficient 0.673), with an average value of extracted As being 1.7 ± 0.6 mg/kg (n = 8) and 4.3 ± 2.0 mg/kg (n = 3) for the Nu-Salween and Lantsang-Mekong river, respectively. Parameters from the Langmuir isotherm fit to sorption experiments of As(III) and As(V) onto three river sediment samples were used to estimate “sorbed” As concentrations in river sediment in equilibrium with the average river water As concentrations. The “sorbed” As concentrations were 0.8 mg/kg and 2.8 mg/kg for the Nu-Salween and Lantsang-Mekong drainage, respectively. Taken together, the data suggest that this pool of “sorbed” As in river sand, likely to have a geothermal As component, remains largely particle-bound in the oxic and circumneutral riverine environment during transport; it is subject to mobilization once buried in the floodplain areas down gradient.
•Mean As in sandy sediment in three rivers originating from Tibet is 17 mg/kg.•As sorbed to Fe oxyhydroxides in river sediments ranged 1–4 mg/kg.•The pool of sorbed As is immobile in the rivers and is deposited downstream.•Hot spring contributes to geogenic As source for enrichment in groundwater.
Cascade dam has important effects on the magnitude and dynamics of sediment particles, heavy metals, and biogenic elements in reservoirs. However, systematic studies on the interception effect of ...cascade dam on the various elements that occur in rivers at the watershed scale are lacking. The aims of this study were to (1) assess the interception effect of a cascade dam on heavy metals and biogenic elements and (2) investigate the key factors of these effects of the cascade dam. Surface sediments were collected from 29 sites distributed in the Wujiang River Basin (WRB, a watershed scale in Southwest China), including from tributaries (7 sites), the main stream (13 sites), and cascade reservoirs (9 sites). In addition, the particle sizes, heavy metals (Fe, Mn, Zn, Cr, Cu, As, Pb, and Cd), and biogenic elements (TOC, TN, and TP) of sediments were analyzed. Compared with the tributaries, D50 (median particle size) was significantly reduced by 56.8% of cascade reservoirs. The proportion of 63–2,000 μm decreased from 13.78 to 1.34%, indicating that more coarse particles were intercepted in the cascade reservoirs. The contents of heavy metals (Fe, Zn, Cu, As, and Cd) declined significantly along the way. On the whole, the contents of TOC, TN, and TP were highest in the midstream and lower in the upstream and downstream. The hydrological condition (reservoir age, HRT, and flow) and the basin area and internal and external inputs of cascade reservoirs are important factors. The findings deepen the current understanding of the mechanisms by which cascade dam affects the river transport of heavy metals and biogenic elements at the watershed scale and provide an important reference for establishing hydropower developments along rivers and developing aquatic environment management strategies.
