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1.
The soil pollution by heavy metals was characterized in the mine tailings and surrounding soils of an old Pb–Zn mine in Huize County. Three hundred and ninety-six samples of agricultural and non-agricultural soil were analyzed for the total metal concentration by acid digestion and sixty-eight selected soil samples were used to determine the chemical fractionation of heavy metals with the modified BCR sequential extraction method. The pollution index of the heavy metals indices for As, Cd, Cr, Cu,Hg, Pb and Zn of non-agricultural soil and agricultural soils in the study area indicated the spreading of heavy metal pollution. Sequential extraction showed that most of Cd existed in an exchangeable form(31.2 %). The available content of Pb, Cu and Zn was mainly distributed in acid extractable fractions and Fe/Mn oxide fractions(27.9, 30 and 27.2 %), and Hg, As and Cr were mainly associated with residual fractions(90.4, 72.9 and 76.8 %). The risks of heavy metals were also evaluated by the risk assessment code(RAC) and potential ecological risk index, respectively. The results of RAC showed a medium and high risk of Cd(45.6 and 54.4 %), medium risk of Zn(100 %), low and medium risk of Cu(41.2 and 58.8 %), largely no risk of Hg(97.1 %), and mainly low risk of As and Pb(92.6and 91.8 %). The range of the potential ecological risk of soil was 58.2–1839.3, revealing a considerably high ecological risk in the study area, most likely related to acid mine drainage and the mining complexes located in the area. The results can be used during the ecological risk screening stage, in conjunction with the total concentrations and metal fractionation values, to better estimate ecological risk.  相似文献   

2.
Lake contamination by anthropogenic activities has become a serious threat to the aquatic ecosystem due to the presence of a high concentration of toxic heavy metals.In this study,a contaminated Lake Hussain Sagar in India was assessed for toxic heavy metal pollutants at sites associated with industrial discharges and idol immersion activities.The observed high concentration of As,Cd,Pb,Zn,Cu,and Ni in the surface water was due to industrial effluent discharge.About 1.5 times the high concentration of the same elements were observed in surface sediments(0-10 cm)by both industrial discharges and idol immersion activities,compared to deep sediments(0-40 cm)associated only with industrial discharge.The depth-wise variation of heavy metal concentration in surface sediments is due to sorption and settling behavior of suspended solids;whereas in deep sediment,it is due to constant loading of effluents,over a period of time.The sorption capacity of surface sediments is in increasing order as Pb>Cd≥Ni>Cr>Zn>Cu,and the desorption revealed that Pb and Cu were retained to a greater extent due to high clay and organic content.By fractionation study,20-50%of Zn and 50-80%of Cd were associated with exchangeable and carbonate fraction of sediments.By risk assessment code,Zn and Cd are classified under high risk to a very high-risk category,and Cr,Pb,Ni,and Cu are classified under the medium risk category.The enrichment factor value of sediments for Cd(20.42-119.48),Zn(2.19-4.85),Cu(2.02-3.19),and Pb(2.85-7.72)signifies the significant pollution by anthropogenic activities.Therefore,this study evaluates the intensity and distribution of heavy metals in the lake environment for remediation and restoration of the lake ecosystem.  相似文献   

3.
The sedimentary environment change, trophic evolution and heavy metals pollution history of the northern Taihu Lake in the last 100 years are studied according to the sedimentary geo-chemical proxies of the core sediments, such as grain size, nutrients, heavy metals, diatom, etc. The nutrients in the sediments depended mainly on the lake internal circulation and the heavy metals were from natural geogenic sources before the 1920s, which were not influenced by human activities generally, and grain size was one of the key factors influencing heavy metals content in the sediments. The alternation of manner and strength of human activities in Taihu Lake catchment before and after the 1920s made the lake sediments coarser, and hence heavy metals and TP content decreased contrasted with that before the 1920s. TP content in sediments and water increased from the 1950s to late 1970s due to anthropogenic pollutants discharge, and the lake belonging to mesotrophic state. TN and TOC content and C/N ratio increased due to the increasing external pollutants into Taihu Lake by human activities, TP content also increased obviously in water and sediments, and the diatom association was dominated by eutrophic species since the late 1970s, indicating the eutrophication state of Taihu Lake in this period. Meanwhile the increasing in heavy metals content, such as Cu, Mn, Ni, Pb and Zn, and their proportion of valid fractions in the sediments indicates that they all result from human pollutants since the late 1970s. The heavy metals in the surface sediments have certain potential biological toxicity due to the higher SEM/AVS ratio.  相似文献   

4.
Dredged sediments are being chemically treated with phosphoric acid on an industrial scale.The effectiveness of the treatment was evaluated by performing the chemical reaction in a tubular reactor, followed by convective drying and maturation of the treated sediment at ambient temperature and finally thermal destruction of the organic matter by calcinations(500℃-900℃).The influence of acid concentration and calcination temperature on the specific surface area of the sediment was investigated. The stabilization of the heavy metals was evaluated by leaching tests and sequential extraction procedures.The phosphoric acid treatment is effective in reducing heavy metal mobility,a prerequisite for recycling the sediments in various construction materials.  相似文献   

5.
Suspended sediment adsorbs pollutants from flowing water in rivers and deposits onto the bed. However, the pollutants accumulated in the river bed sediment may affect the bio-community through food chain for a long period of time. To study the problem the concentration of heavy metals （Cr, Cd, Hg, Cu, Fe, Zn, Pb and As） in water, sediment, and fish/invertebrate were investigated in the middle and lower reaches of the Yangtze River during 2006-2007. The concentrations of heavy metals were 100-10,000 times higher in the sediment than in the water. Benthic invertebrates had relatively high concentrations of heavy metals in their tissues due to their proximity to contaminated sediments. Benthic invertivore fish had moderately high concentrations of heavy metals whereas phytoplanktivore fish, such as the silver carp, accumulated the lowest concentration of heavy metals. The concentrations of Cu, Zn, and Fe were higher than Hg, Pb, Cd, Cr, and As in the tissue samples. The concentration of heavy metals was lower in the river sediments than in the lake sediments. Conversely, the concentration of heavy metals was higher in river water than in lake water. While a pollution event into a water body is often transitory, the effects of the pollutants may be long-lived due to their tendency to be absorbed in the sediments and then released into the food chain. The heavy metals were concentrated in the following order： bottom material 〉 demersal fish and benthic fauna 〉 middle-lower layer fish 〉 upper-middle layer fish 〉 water.  相似文献   

6.
The study provides a baseline for the assessment of the organic and inorganic pollution specially, heavy metal contamination in the surface sediments of Pyeongchang River,South Korea.The assessment of the study areas was done with respect to metal pollution load,ecological risk and geoaccumulated risk.Based upon the used indices,a priority index(Pindex) was used to rank the utmost contaminated sites.Though the concentrations of mercury in all sediments were below the guideline, the significant enriched contamination was observed by all applied indices.As expected,the values of pollution load index（PLI）,ecological risk index（RI） and geoaccumulation risk index(Igeo) demonstrated lower heavy metal contamination in upstream areas compared to the downstream. Admittedly,sediments were unpolluted to slightly-polluted according to PLI while high to extremely high ecological risks were observed in several sediment samples.Furthermore,all the samples were uncontaminated as per Igeo.After simplification of Igeo,the Pindex,showed the utmost contaminated sediments with a value of 2.537.Notably,protective measures should be taken to the highly contaminated areas which are prioritized by Pindex Admittedly,the maximum concentrations of total organic carbon,total nitrogen,inorganic nitrogen,total phosphorous,inorganic phosphorous,calcium, magnesium,sodium and potassium were significantly observed as 7.8×104,3,185,36,1,032,3.7, 1,5163,2,881,669 and 4,076mg/kg accordingly.  相似文献   

7.
In recent times, there had been reported cases of Pb poisoning in Anka gold mining area, Northwest Nigeria.Therefore, this study was carried out to determine the extent of bioaccumulation of heavy metals in the hairs and nails of children in the area. Forty samples(twenty nails and twenty hairs) samples were collected from ten boys and ten girls of ages 5–9 residing in the area. To ascertain the sources of heavy metals in children, 15 soils samples,15 groundwater samples, 5 samples of mine tailings, and 5 plants samples were collected. Hair and nails of the subjects were collected using internationally acceptable techniques. All samples were kept in uncontaminated ziplock bags prior to laboratory preparation and analysis. The samples were cleaned using nonionic detergent(triton X-100) and deionized water. The hairs and nails were digested with 10 mL of 6:1 mixture of nitric acid and perchloric acid. The soils, mine tailings, and plants were air-dried at room temperature, sieved, and chemically digested using the aqua regia method. The concentrations of metals in all the samples were determined using highperformance liquid chromatography–inductively coupled plasma–mass spectrometry. Statistical analysis was employed to unravel potential sources of metals in the media. Results showed that heavy metals in children of the area are above results from similar studies and pathological ranges for heavy metals in hairs and nails. Also, heavy metals in environmental media are above the recommended standards. Multivariate analysis showed that the metals are mainly from mining and other anthropogenic sources.Results of correlation between heavy metals in hairs and nails with those in geological samples revealed that heavy metal that bioaccumulates in the children of this area are mostly from contaminated environmental media. It is recommended that complete remediation and effective health education be carried out in the area.  相似文献   

8.
Trace element study in Tisa River and Danube alluvial sediment in Serbia   总被引：2，自引：0，他引：2  
The contaminated sediment serves as a long-term source of toxic elements,since that mobility and transport in the environment of these elements are strongly influenced to associated solid phase.In this study,the modified Tessier sequential extraction procedure was applied for the fractionation of Cd,As,Hg,Cu,Zn,Cr,Pb,Ni and V in the sediments（Tisa River and canal sediments - Danube alluvial formation）,to obtain an overall classification of trace element pollution in these areas through its spatial distribution.Investigations of this region are important due to the widespread occurrence of metal mining activities throughout the Tisa and Danube drainage basins and possibilities of contamination with toxic elements at studies localities.Five steps of the sequential extraction procedure partitioned elements into CH3COONH4 extractable（F1）,NH2OH·HC carbonate extractable and easily reducible（F2）, H2C2O4/（NH4）2C2O4 moderately reducible（F3）,H2O2-HNO3 organic extractable（F4）,and HCl acid soluble residue （F5）.Analyses of the extracts were performed by flame atomic absorption spectrometry.To indicate the degree of risk of toxic elements,risk assessment code and contamination factor have been used.The results of partitioning study indicate that more easily mobilized forms（metals in adsorbed/exchangeable/carbonate forms or bound to amorphous Fe and Mn oxyhydroxides and Fe and Mn oxides） were predominant for copper,zinc,cadmium and lead,which can be used as indicators for input from anthropogenic source.In contrast,the largest amount of chromium and nickel were associated with the inert fraction,which reduced their solubility and rendered them immobile under natural conditions and indicative of natural origins.Most of remaining portion of metals was bound to ferromanganese oxides fraction.It is concluded that sequential extraction results proved useful to distinguish between anthropogenic and geochemical sources of elements in the sediments.  相似文献   

9.
This study determines the pollution, fractionation, and ecological risks of sediment-bound heavy metals from coastal ecosystems off the Equatorial Atlantic Ocean. Contamination Factor(CF), pollution load index(PLI), and geoaccumulation index(Igeo) were used to assess the extent of the heavy metal pollution, while the potential ecological risk was evaluated using the risks assessment code(RAC) and Hkanson potential ecological risk. The analysis revealed concentrations(mg/g, dw) of the cadmium(Cd),chromium(Cr), copper(Cu), nickel(Ni), and lead(Pb) in sediments for wet and dry seasons vary from 4.40-5.08, 14.80-21.09. 35.03-44.8, 2.14-2.28, and 172.24-196.39, respectively. The results also showed that the metal fractionation percentages in the residual, oxidizable, and reducible fractions are the most significant, while the exchangeable and carbonate bound trace metals are relatively low. The RAC values indicate no risk for Cd and Ni and low risk for other metals at all the studied sites during both seasons.Potential ecological risk analysis of the heavy metal concentrations indicates that Cd had high individual potential ecological risk, while the other metals have low risk at all investigated sites. The multi-elemental potential ecological risk indices(R_1) indicate high ecological risk in all the ecosystems.  相似文献   

10.
《国际泥沙研究》2016,(2):164-172
The ecological risk assessment for Al,Zn,Cu,Ni,V,Pb,Cd,and Hg in surface sediment collected from the Egyptian Red Sea coast was evaluated using the Geo-accumulation Index(I_(geo)).Sediment Enrichment Factor(SEF) and Potential Ecological Risk Index(PERI) methods.The predominant heavy metal,aluminum,showed high concentrations along both of Aqaba Gulf(4378.8 ± 2554.1 μg/g) and southern part of the Red Sea(2972.8 + 1527.5 μg/g).while it recorded the lowest concentration in Suez Gulf(829.7 ± 398.2 μg/g).The determined heavy metal concentrations had the order of Al Zn -Ni V Pb Cu Cd Hg.The statistical analyses showed some correlations among the heavy metals contents.Several international sediment quality guidelines were used to estimate the quality of the collected sediments.Interestingly,the recorded average heavy metals concentrations were lower than those of the permissible contents for sediment quality guidelines.The Geo-accumulation index calculations(I_(geo)) proved that the investigated region could be classified as an unpolluted area.Sediment Enrichment Factor(K_(SEF)) study showed high values in Suez Gulf region.The single pollution index analysis of heavy metals in the sediments(C~i_f) indicated that Al,Zn,V,and Pb were of natural origin,while Ni,Cd and Hg were seriously affected by human activities.Interestingly,amongst,all the determined heavy metals,Cd and Hg gave moderate ecological risk indicators.  相似文献   

11.
《国际泥沙研究》2016,(4):324-329
Transport of contaminants in Miami River (Florida, USA) sediments with river currents is a concern due to their potential impact in areas that are away from the potential sources. Accumulation profiles of five metals (As, Cd, Hg, Zn, Pb) in the surficial sediments of the Miami River were evaluated in relation to grain size (from less than 0.075 mm to 6.3 mm) and organic content. Surficial sediment samples were collected along the river basin as well as in bay waters. Fine sediments ( o 0.106 mm) contained more than 10 times the levels of Cd and Hg and more than 6 times the levels of arsenic in comparison to the sediments that are larger than 0.850 mm. Zn and Pb levels were more than 10 times in the fine sediments ( o 0.106 mm) in comparison to those that were larger than 4.750 mm. Cd, Hg, and Zn levels had sig-nificant correlation with the total organic carbon content of the sediments. This indicates that Cd, Hg, and Zn in fine sediments have the potential to be metabolized in addition to potential to be mobilized with river currents. Analysis of the Gibbs settling velocities of particles showed that particles smaller than 0.5 mm can be transported with the river currents. The levels of heavy metal in fine sediments ( o 0.425 mm) along the river bed showed that fine particles had tendency to be mobilized and accu-mulate at locations where the rivers currents are low and carried out to the bay.  相似文献   

12.
《国际泥沙研究》2016,(3):226-236
The Murucupi River belongs to the hydrographic network of the Pará River estuary, at the southern portion of the Amazon River mouth, which consists of a fluvial-marine transitional zone under strong impact of both tidal and fluvial currents. The geochemical results obtained for bottom sediments from the Murucupi River, the Arrozal Channel, and the Pará River indicate a natural variation of Pb, Cr, Cu, Zn, and Ni content among these water ways with no significant anthropogenic influence. According to the threshold effects level (TEL), the contents of trace metals do not offer risk to the local biota. By contrast, the differences in the Pb isotopic composition of sediments in the Murucupi River, the Arrozal Channel, and the Pará River are significant. These isotopic signatures indicate an anthropogenic contribution of Pb in the Murucupi River originating from the domestic effluents of urban centers; industrial waste represented by red mud is not included. These results demonstrate that the Pb isotopic signature is a prospective indicator for future contamination of bottom sediments by trace metals and is useful for identifying contaminants among the possible anthropogenic sources.  相似文献   

13.
By comparing three sequential extraction procedures, a new optimized extraction scheme for the molybdenum association in environmental samples was proposed.Five operational steps were described as exchangeable(KH_2PO_4+K_2HPO_4: including water-soluble), associated with organic matter(NaOH), Fe–Mn oxides and/or carbonates(HCl), sulfides(H_2O_2) and residue(HNO_3+HF+H_2O_2). An optimized extraction scheme was compared with Tessier's procedure and the Commission of European Communities Bureau of Reference(BCR) was applied to black shales. Results showed Tessier's procedure gave the lowest concentration values for exchangeable molybdenum and the highest values for the residual molybdenum, which could not present the efficiency of the extraction reagents. BCR's procedure showed the highest values in oxidizable molybdenum and presented four fractions of molybdenum, which did not demonstrate the fractions of molybdenum in the black shales in detail. The optimized extraction scheme demonstrated a certain improvement on extraction efficiency over Tessier's procedure for the lowest residual molybdenum, and revealed more featured fraction information of molybdenum in black shales than BCR's. Therefore, after a comparison with other two extraction procedures, the optimized extraction scheme proved suitable for the molybdenum in black shales and it also showed an accurate determination of the molybdenum in the fractions and source of bioavailable Mo.  相似文献   

14.
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15.
The valorization solutions for dredged sediment have been the subject of a great number of investigations over the previous decades.In the current present study,treatment of polluted dredged sediment fom the commercial port of Sfax,Tunisia,is proposed.An industrial byproduct(blast furnace slag)was used to bind raw sediment for a reuse in road engineering.Following standards of this field,the raw sediment first was identified and classified according to the French technical guidance.Then an environmental assessment was applied due to the presence of heavy metals.The concentrations were measured on the raw sediment particles so as to control the binding effect on heavy metals.Sediment mixtures consisted of a mix of sand and a blast furnace slag activated with quicklime.Different mixtures were tested and some were proposed for sub-layer applications.The Sfax commercial port raw sediment is considered as a sandy loam with a very low fraction of clay.The measured concentrations of heavy metals exceed the recommended thresholds for cadmium,copper,lead,and zinc.These can induce hazardous effects in the case of their dumping into the sea.On the other hand,the concentrations of the detected elements after leaching tests run on raw sediment samples are very low compared to the thresholds;such results highlight a possible recycling of the raw sediment in subgrade layers without any negative impact.Suitable formulations were deduced for road engineering tests relying on the ratio the California Bearing Ratio index and the immediate bearing index.If the obtained ratio exceeds one,the treated sediment can be recycled and used in road layers.  相似文献   

16.
The goal of the present work is to perform a geochemical assessment of High Dam Lake bottom sediments for determining the fate, dispersion and levels of trace elements causing environmental pollution, and provided an access to their probable sources. The sediment samples were analyzed using ICP-MS for 20 elements; Ag, Ba, Cr, Cu, Ga, Hf, Mn, Pb, Rb, Sc, Se, Sn, Sr, Ta Th Ti, T1, U, V and Zr, and their obtained data were treated using statistical, graphical and mapping techniques. The results showed the data set of all analyzed elements affected by outliers and extreme values that caused deviation away from normality. Kruskal-Wallis test revealed that median of some trace element levels in Lake sediments, was not significantly different and other elements rejected the Null hypothesis. Most analyzed elements had high values of median and mean in sediments of Lake Nubia rather than Lake Nasser and their normalization gave the same results of calculated environment factors. Subsequently, Lake Nubia sediments possessed high combined EF levels ofTh, Sc, Sn, Ag, Zr, Hf, Ta, Sr, U, Ti, V, Cr, and Mn, causing significant contamination, which was great potentially related to industrial, agricultural, urbanization and mining activities. Whereas, combined EF of Se, Cu, Ga, Pb, Ba, Rb, and Tl, which are highly elevated in southern Lake Nasser sediments owing to their source are great possibly derived from Lake Nubia and geogenic activities. With decreasing distance towards the High Dam body, the contaminant elements were diminished due to reduction in the environmental factors and Sudanese pollution sources leading to the northern Lake Nasser considered to be less contaminated. Overall, the present study is an environmental alert for contaminated sediments that carried contaminants and considered the secondary source of pollution impact on ecosystem, and subsequently, their environmental risk on Human health.  相似文献   

17.
Sediment samples were collected from ten selected sites of the lower Meghna River estuary,and six heavy metals were analyzed with Atomic Absorption Spectrophotometry(AAS)to assess the contamination level and the metals’association with sediment grain size.The current results revealed that the mean concentrations of the studied metals were ranked in descending order of iron(Fe)(1.29×103 mg/kg)>zinc(Zn)(42.41 mg/kg)>lead(Pb)(12.48 mg/kg)>chromium(Cr)(10.59 mg/kg)>copper(Cu)(6.22 mg/kg)>cadmium(Cd)(0.28 mg/kg).The geo-accumulation,contamination,and pollution load indexes suggested that the lower Meghna river estuary was not contaminated by Fe,Zn,Pb,Cr,and Cu.The mean size of the sediment ranged from 28.92 to 126.2 mm,and the Pearson correlation coefficient showed a significant association between Fe and Pb(coefficient of determination,r2=0.836;p<0.05),and no significant correlation was found between individual metals and grain size,indicating no or low influence on the metals distribution.  相似文献   

18.
Cohesive sediments exhibit complex rheological behaviors that are non-Newtonian and time-dependent when subjected to external loading. This paper presents the results of an investigation on the theological properties of three types of dense cohesive sediments, collected from the mouth of the Yangtze River, the shoal of the ttangzhou Bay, and the Yangcheng Lake in China. A set of rheological parameters （including viscosity, yield stress, etc.） was studied based on experiments that were conducted with a RheolabQC rheometer. Measurements of the flow curves, shear stress-time responses, and yield stresses were made. The solid-liquid transition of the dense cohesive sediments occurred both in the shear rate ramp tests and the shear stress ramp tests. This transition was not direct, but it was mediated by a transitional deformation regime or stress plateau. Both the Herschel-Bulkley model and Carreau model were able to describe the theological behavior of dense cohesive sediments, and the empirical expressions for calculating the parameters in these models were obtained by a dimensional and regression analysis. The yield stresses determined by the shear stress ramp test and by the vane method were compared and discussed. The influence of the water content on the rheological properties of dense cohesive sediments was considered.  相似文献   

19.
Forms of phosphorus in sediments from 25 lakes in the middle and lower reaches of Yangtze River were analyzed by the sequential extraction procedure. Contents and spatial distrubution of algal available phosphorus (AAP) in sediments of Lake Taihu, the third largest freshwater lake of China, were also studied. Relationships between phosphorus forms in sediment and macrophytes coverage in sample sites, as well as phosphorus forms in sediments and chlorophyal contents in lake water were discussed. Exchangeable form of phosphorus (Ex-P) in surface sediments was significantly positive correlative to total phosphorus (IP), dissolved total phosphorus (DTP) and soluble reactive phosphorus (SRP) contents in the lake water. Bioavailable phosphorus (Bio-P) contents in sediments from macrophytes dominant sites were significantly lower than that in no macrophyte sites. In Lake Taihu, Ex-P content in top 3 cm sediment was highest. However, content of ferric fraction phosphorus (Fe-P) was highest in 4 - 10 cm. Bioavalilble phosphorus (Bio-P) contents in surface sediments positively correlated to Chlorophyll a contents in water of Lake Taihu with significant difference. Therefore, contents of Bio-P and AAP could be acted as the indicators of risks of internal release of phosphorus in the shallow lakes. It was estimated that there were 268.6 ton AAP in top 1 cm sediments in Lake Taihu. Sediment suspension caused by strong wind-induced wave disturbance could carry plenty of AAP into water in large shallow lakes like Lake Taihu.  相似文献   

20.
Concentrations of suspended particle material(SPM), dissolved silicate(DSi), biogenic silica(BSi), phytoliths(plant produced siliceous microscopic structures), and other parameters were analyzed to examine the influence of both natural processes and human activities on silica delivery to the estuary of the Huanghe River(Yellow River). Our results indicate that the concentrations of DSi in the river decreased significantly since 1986. Approximately 34% of dissolved silica was trapped in the basin between 1986 and 2010 due to a reduction of soil erosion. Phytoliths comprised 67.2%–96.3% of BSi, with the smoothing bar type being the dominant form. Concentrations of BSi are significantly higher in the Huanghe River compared to other major rivers throughout the world due to its high sediment yield. We also found that the ratios of BSi/(BSi+DSi) and BSi/SPM were approximately 0.5 and 0.003 at Lijin near the river mouth, indicating that BSi carried in suspension by the Huanghe River was an important component of the rivers silica load. Significant amounts of BSi were also composed of phytoliths in Bohai Sea sediments near the Huanghe River estuary with the smoothing bar form again being the most abundant. The relatively high specific fluxes of BSi in the Huanghe River reflect its high turbidity and high erosion rates in the basin. The high sediment load originating on the Loess Plateau is likely responsible for the higher BSi flux, in agreement with a general trend of increasing BSi flux with increasing sediment flux in global river systems. This study demonstrates that BSi transported by rivers can be composed largely of phytoliths originating from the erosion of topsoils. The flux of phytoliths in river's suspended sediment load may therefore represent a significant contribution to the biogeochemical cycle of silica in coastal waters.  相似文献   

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