Atmospheric bulk deposition of trace metals to the Seine river Basin, France: concentrations, sources and evolution from 1988 to 2001 in Paris

Concentrations of Cd, Cu, Ni, Pb and Zn were determined in bulk atmospheric deposition collected at five stations in the Seine River basin (France), to evaluate sources and fluxes of atmospheric trace metals. Bulk deposition (wet + dry) was sampled weekly from March 2001 to February 2002 for 4 sites and from March to December 2001 for the last one. The concentrations of the elements in bulk deposition (dissolved + particulate form) followed the order: Zn > Pb > Cu > Ni > Cd. Concentrations of Zn, Pb and Ni were highly correlated with one another, suggesting a common source, related to the combustion of coal and heavy fuel. Metal concentrations in bulk deposition did not exhibit a high degree of temporal variability over the annual cycle and were not obviously related to meteorological parameters (rainfall, wind). Estimates of the total annual direct atmospheric deposition of metals to the Seine Estuary ranged from 16 kg yr^{? 1} for Cd to 5600 kg yr^{? 1} for Zn. Loadings of Cd, Cu and Ni from direct atmospheric inputs were less than 1% of those contributed by the Seine River and loadings of Pb and Zn represented 1.27% and 1.56% of the Seine contribution. Direct atmospheric inputs are negligible compared to fluvial inputs, but the indirect atmospheric deposition to the estuary was not estimated. Based on these results, trace metal concentrations in Paris have decreased by a factor of 4.6 for Zn and by a factor of 50 for Ni from 1988 to 2001. Of particular interest is the continued decrease in bulk deposition of Pb during this period, underlining the impact of policy initiatives concerning the reduction of lead on emissions in France.     

Atmospheric input of trace metals to Lake Michigan

Atmospheric bulk deposition was collected on a monthly basis in the Lake Michigan basin from September 1975 through December 1976 to determine the atmospheric loading of trace elements to Lake Michigan. The sampling network consisted of bulk collectors located at 21 locations in the northern and southern basin. Atmospheric loading rates to Lake Michigan were estimated as (in units of 10⁵ kg yr^?1): Al-50; Fe-28; Mn-6.4; Zn-11; Cu-1.2; Pb-6.4; Cd-0.11; Co- <0.25; Ca-798; Mg-155; Na-110; K-64. Atmospheric deposition of all elements measured was greater in the southern basin than in the northern basin as a result of intense urban/industrial activity in the former. The percentage of total atmospheric deposition falling in the southern basin was: Fe-74%, Al-71%; Mn-75%; Zn-67%; Cu-62%; Pb-78%; Cd-74%; Co- ti 56%; Ca-79%; Mg-62%; Na-65%; K-61 %. Atmospheric loading rates reported are in general agreement with estimates made by others from emission inventories and aerosol concentrations. Atmospheric loadings were estimated to represent 10% or more of the total loadings to Lake Michigan from tributary and erosion sources for the trace elements Mn, Zn, Cu, Cd and Pb. Also, atmospheric deposition may account for recent accumulations of Zn, Cu, Cd, Pb and Co in southern Lake Michigan surficial sediments. The atmospheric Ph flux to southern Lake Michigan was estimated as ～1.7 μg sm^?2 yr^?1 for 1975–1976 which compares favorably with the 1972 anthropogenic Pb flux of 1.3 μg cm^?2 yr^?1 (total ? ～1.5 μg cm^?2 yr^?1) as determined from Pb-210 dating (Edgington and Robbins, 1976). The geographical distribution of trace element loading implicates the southern periphery of Lake Michigan as the principal emission source area.     

The flux of Cd,Cu, Pb and Zn in mining polluted soils

The monitoring of heavy metal deposition onto soils surrounding old Pb-Zn mines in two locations in the UK has shown that relatively large amounts of Cd, Pb, Zn and, in one case, Cu are entering the soil annually. Small particles of ore minerals in windblown mine tailings were found to be contributing up to 1.46 g m^?2 yr^?1 of Pb, 1.41 g m^?2 yr^?1 of Zn and 0.027 g m^?2 yr^?1 of Cd. However, when these inputs from bulk deposition are compared with the concentrations of the same metals within the soil profiles it is apparent that relatively little long-term accumulation is occurring. Metals are being lost from the soil profiles, probably through leaching. A calculated relative retention parameter gave values that ranged from 0.01 to 0.17 for Cd, 0.11 to 0.19 for Zn, 0.32 to 0.63 for Cu and over 1 for Pb. These relative retention values were found to follow the order of electronegativity of the elements concerned: Pb>Cu>Zn>Cd. Distribution coefficient (Kd) values quantifying the adsorptive capacity of the mine soils for Cd and Pb showed marked differences for the two metals (12 to 69 cm³ g^?1 for Cd and 14 to 126 cm³ g^?1 for Pb) and may, in part, account for the two to one hundred-fold variation in the relative retention parameter for the different metals within these soils.     

Bulk deposition of metals in Tulsa,Oklahoma

Samples of bulk precipitation were collected at six sites adjacent to the Arkansas River in Tulsa, Oklahoma for a period of 11 mo (June 1980 to April 1981). Collected samples were analyzed by flameless atomic absorbtion spectrophotometry for Cd, Cr, Ni, Pb, and Zn. The data were reported as volume-weighted metal concentrations (μg L¹) and metal deposition (mg m^?2 yr^?1). Metal deposition was fairly constant from site to site and appeared to be proportional to the amount of precipitation collected. Zinc was by far the largest contributing metal, 497 mg m^?2 yr^?1 followed by Pb. Cr, Ni, and Cd with depositions of 25.5, 25.7, 7.02, and 0.95 mg m^?2 yr^?1 respectively. Concentration data varied greatly over the collection period. Compared to data previously reported in the literature, all of the metal concentrations obtained in this study fall within the ranges observed by other investigators with the exception of Zn which was slightly higher. The average volume-weighted concentrations in μg L^?1 were Cd-2.1, Cr-57.0, Ni-15.6, Pb-56.6, and Zn-1100.     

东亚季风与城市活动影响下南京市大气沉降多元特征研究

Atmospheric deposition, a major pathway of metals entering into soils, plays an important role in soil environment, especially in urban regions where a large amount of pollutants are emitted into atmosphere through various sources. In order to understand the characteristics of atmospheric deposition in urban area and its relation with natural and anthropogenic sources, a three-year study of atmospheric deposition at three typical sites, industrial zone (IN), urban residential area (RZ) and suburban forested scenic area (FA), was carried out in Nanjing, a metropolitan city in eastern China from 2005 to 2007. The bulk deposition rate and element composition of atmospheric deposition varied spatio-temporally in the urban zones of Nanjing. The concentrations of Cu, Zn, Pb and Ca in the atmospheric deposits were strongly enriched in the whole Nanjing region; however, anthropogenic pollutants in atmospheric deposits were diluted by the input of external mineral dust transported from northwestern China. Source apportionment through principal component analysis (PCA) showed that the background atmospheric deposition at the FA site was the combination of external aerosol and local emission sources. The input of long-range transported Asian dust had an important influence on the urban background deposition, especially in spring when the continental dust from the northwestern China prevailed. Marine aerosol source was observed in summer and autumn, the seasons dominated by summer monsoon in Nanjing. In contrast, the contribution of local anthropogenic emission source was constant regardless of seasons. At the RZ and IN sites, the atmospheric deposition was more significantly affected by the nearby human activities than at the FA site. In addition, different urban activities and both the winter and summer Asian monsoons had substantial impacts on the characteristics of dust deposition in urban Nanjing.     

100 Years of Pb Deposition and Transport in Soils in Champaign,Illinois, U.S.A.

In Illinois, atmospheric deposition is one major source of heavy metal inputs to agricultural land. The atmospheric Pb deposition and transport record in agricultural soils in Champaign, Illinois, was established by studying surface and subsurface soil samples collectedduring the past 100 years from the Morrow Plots on the campus of the University of Illinois at Urbana-Champaign. The Pb content in the soilsamples was measured and the Pb deposition fluxes were calculated. ThePb content in surface soils increased sharply in the first half of the20th century, and stayed invariant since. The maximum Pb flux from theatmosphere was estimated to be 27 (±14) μg cm^-2 yr^-1around 1940. The major pollution source for this increase probably was residential coal burning. It was estimated that in 50 yr, morethan 50% of the Pb input had been lost from the surface soils.     

Atmospheric deposition to grassland canopies: Lysimeter budgets discriminating between interception deposition,mineral weathering and mineralization

Lysimeter experiments were used to determine atmospheric input to grassland canopies. The combined effect of interception deposition + mineral weathering + mineralization was calculated from input/output budgets. Four types of lysimeters were used, either filled with very pure quartz sand or chalk grassland soil, and either without vegetation or planted with Brachypodium pinnatum (L.) Beauv., Combination of budgets for these four types of lysimeters yielded separate estimates of interception deposition and mineral weathering + mineralization. Ratios between total deposition and bulk deposition were 1.74 and 1.93 for N and S, respectively. Sources and sinks of H⁺ for lysimeters with chalk grassland soil and planted with Brachypodium (abbrev. CP-lysimeters) were about 10 times larger than for lysimeters without plants and filled with quartz sand. The contribution of atmospheric input to total H⁺-sources was 80% for bare lysimeters filled with quartz sand, and only 12% for CP-lysimeters. Bulk deposition and total atmospheric deposition of N was 1.25 and 2.18 kmol ha^?1 yr^?1, respectively, whereas N mineralization of chalk grassland soil yielded 1.62 kmol ha^?1 yr^?1, ‘Acid rain’ has only a minor influence on H⁺-transformations within a chalk grassland ecosystem, but N cycling is seriously affected by atmospheric input.     

The effect of heavy metals and other pollutants on the sediments of Onondaga Lake

Physical and chemical characterization of the recent sediments of Onondaga Lake indicate significant pollution based alterations to the system.²¹⁰Pb data depict an extremely high sedimentation rate within the consolidated layers (5 to 9 cm yr^?1), that has resulted largely from the loading of the Lake with industrially derived Ca. A further alteration of the sedimentary system is the very extensive flocculent layer (up to 2.5 m deep) between the overlaying water and the consolidated sediments. The chemistry of the sediments, though not unusual in dominant component makeup for a hardwater lake, is characterized by very severe heavy metal and Fe contamination that has resulted from culturally derived loadings. Heavy metals and P are concentrated within the upper flocculent strata. Indirect evidence is presented for the upward vertical migration of heavy metals within the sedimentary system.     

Biogeochemistry of a forested watershed in the central Adirondack Mountains: Temporal changes and mass balances

Information on atmospheric inputs, water chemistry and hydrology were combined to evaluate elemental mass balances and assess temporal changes in elemental transport from 1983 through 1992 for the Arbutus Lake watershed. This watershed is located within a northern hardwood ecosystem at the Huntington Forest within the central Adirondack Mountains of New York (USA). Changes in water chemistry, including increasing NO₃ ^? concentrations (1.1 μmol _c , L^?1 yr-1), have been detected during this study period. Starting in 1991 hydrological flow has been measured from Arbutus Lake and these measurements were compared with predicted flow using the BROOK2 hydrological simulation model. The model adequately (r²=0.79) simulated flow from this catchment and was used to estimate drainage for earlier periods when direct hydrological measurements were not available. Modeled drainage water losses coupled with estimates of wet and dry atmospheric deposition were used to calculate solute budgets. Export of SO₄ ^2? (831 mol _c ha^?1 yr^?1) from the greater Arbutus Lake watershed exceeded estimates of atmospheric deposition in an adjacent hardwood stand suggesting an additional source of S. These large drainage losses of SO₄ ^2? also contributed to the drainage fluxes of basic cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺). Most of the atmospheric inputs of inorganic N were retained (average of 74% of wet precipitation and 85% total deposition) in the watershed. There were differences among years (56 to 228 mol ha^?1 yr^?1) in drainage water losses of N with greatest losses occurring during a warm, wet period (1989–1991).     

Watershed vs in-lake alkalinity generation: A comparison of rates using input-output studies

As a means of assessing the relative contributions of watershed (terrestrial) and in-lake processes to overall lake/watershed alkalinity budgets, alkalinity production rates for watersheds and low alkalinity lakes were compiled from the literature and compared. Based on net alkalinity production data, derived using wet or bulk deposition data, mean and median alkalinity production for 20 watersheds in North America and Europe were 89 and 69 meq m^?2 yr^?1 (range 20 to 235 meq m^?2 yr^?1). For a subset of 10 watersheds with dry deposition data, terrestrial alkalinity production neutralized an additional 35 meq m^?2 yr^?1 of acidic deposition. For 11 lakes, mean and median in-lake alkalinity generation were 99 and 88 meq m^?2 yr^?1 (range 22 to 240 meq m^?2 yr^?1). Analysis of data indicates that for the low alkalinity systems described here, areal alkalinity production rates for watersheds and lakes are approximately equal. This relationship suggests that watershed area to lake area ratio can be used as a convenient estimator of the relative importance of watershed and in-lake sources of alkalinity for drainage lake systems. For precipitation-dominated seepage lakes and other systems where hydrology limits soil-water contact, hydrologic flow paths and residence times can be of overriding importance in determining alkalinity sources. For regions dominated by drainage lakes with high watershed area to lake area ratios (such as the Northeastern U.S.), however, alkalinity budgets are dominated by watershed processes. Omission of in-lake alkalinity consideration for most lakes in such regions would have little impact on computed alkalinity budgets or on predicted response to changes in acidic deposition loadings.     

Evaluation of Trace Metal Fluxes to Soils in Hinterland of Porto Marghera Industrial Zone: Comparisons with Direct Measurements in the Lagoon of Venice

Trace metal (As, Cd, Cr, Ni, Hg, Pb) concentrations in soil samples collected around the Porto Marghera (Italy) industrial zone (2–40 km) near the city of Venice were compared with direct measurements of atmospheric deposition measured at comparable distances from the same source. Concentrations of Cd and Pb in soils decreased exponentially with increasing distance from the source; less clear signals were detected for As, Cr and Ni. Significant differences were found among the soils, which were partially resolved when their clay contents were normalised. Preliminary comparisons of fluxes of Cd and Pb derived from soil with direct deposition measurements showed increasing values with longer integration times. Annual Cd and Pb flux values of one year of direct deposition were 5 to 10 times lower than mean annual fluxes derived from soils,integrating 50 to 100 years. Values range from ～0.1–0.4 to 1–2 mg m^-2 yr^-1 for Cd, and from 3–18 to 50–100 mg m^-2 yr^-1 for Pb. These results fit information on `historical' emission trends as recorded in sediments of the lagoon.     

Heavy metal pollutant tolerance of Azolla Pinnata

The effects of Hg, As, Pb, Cu, Cd, and Cr (1, 2, and 5 mg L^?1 each) on Azolla pinnata R. Br. were analyzed. The treatments (2 and 5 mg L^?1) of the heavy metal pollutants decreased Hill activity, chlorophyll, protein and dry wt, and increased tissue permeability over control values. The effects were most pronounced with the treatment of 5 mg L^?1. The harmful effects of the metals were, in general, found by the treatments in the order: Cd 〉 Hg 〉 Cu 〉 As 〉 Pb 〉 Cr. There was no significant change in these parameters at 1 mg L^?1 of the metals over control. Thus Azolla pinnata shows tolerance to the heavy metals tested up to 1 mg L^?1 each.     

Sulfur cycling in a dutch moorland pool under elevated atmospheric S-deposition

Atmospheric S deposition, sulfate reduction and the accumulation of reduced S components were investigated in sediments of a Dutch moorland pool. Laboratory ³⁵SO42? tracer experiments indicated that the variation in reduction rate with depth in the sediment could be described by an exponential fit, suggesting first order kinetics. Sulfate reduction rates calculated from a kinetic transport model were highest in June and July (>0.6 mmol m^?2 day^?1), and decreased towards the end of the summer (<0.2 mmol m^?2 day^?1). Winter reduction rates were low, but increased towards the beginning of the spring. Concentrations of total, organic and inorganic S decreased with depth, consistent with an increasing depositional flux of S over the last century. Increased atmospheric sulfate deposition rates and consumption in the upper sedimentary layers caused a continuous increase in subsurface S concentrations. Present day S-immobilization rates were estimated between 25 to 30 mmol S in^?2 yr^?1, in the order of the annual input of S from wet atmospheric deposition. Sulfate metabolism in anaerobic moorland pool sediments may be the most important mechanism of long-term S-accumulation.     

Atmospheric monitoring network operations and results in Canada

Atmospheric monitoring activities in Canada relevant to the long-range transport of atmospheric pollutants and the ‘acid rain’ problem are reviewed. Particular aspects examined are network objectives, station density and location, sampling protocol, and quality assurance. Results from a number of these networks are presented for the purpose of outlining the nature and extent of air and precipitation contamination by pollution released in eastern North America. Examples discussed include: the spatial distribution of acidic wet deposition, the temporal variation of acid-related substances in both air and precipitation, an episode of long-range transport, and the impact of acidic emissions on the Arctic atmosphere. Acidic wet deposition is greatest in Canada east of the Manitoba-Ontario border. In 1978, it ranged from 18 to 46 mmol H⁺ m^?2 yr^?1 in the southern half of eastern Canada, with maxima in southern Ontario (44 mmol H⁺ m^?2 yr^?1) and southwestern Quebec (46 mmol H⁺ m^?2 yr^?1). Western Canada receives less acidity in precipitation, but areas of some concern are the Pacific Coast (10 mmol H⁺ m^?2 yr^?1) and to a lesser extent northern Alberta and Saskatchewan (3 to 5 mmol H⁺ m^?2 yr^?1). Acidic emissions from mid-latitude sources which reach the Arctic in winter cause an increase in the acidity of snow from a pH of approximately 5.6 in the summer to values of 4.9 to 5.1 in January through March.     

Regional Atmospheric Budgets of Reduced Nitrogen Over the British Isles Assessed Using a Multi-Layer Atmospheric Transport Model

Atmospheric budgets of reduced nitrogen for the major political regions of the British Isles are investigated with a multi-layer atmospheric transport model. The model is validated against measurements of NH₃ concentration and is developed to provide atmospheric budgets for defined subdomains of the British Isles. The study shows that NH₃ emissions, transport and deposition in a specific region can have profound effects on the composition of the atmosphere over other regions. An important feature is the high export of reduced nitrogen from Republic of Ireland and Northern Ireland to England and Scotland. England is also a net exporter of reduced nitrogen. By contrast, Scotland and Wales are approximately “ammonia neutral” as import of reduced nitrogen roughly balances export. Overall, only 7% of reduced nitrogen in the British Isles is derived from non-British Isles sources (29 kt N yr^?1), compared with emissions of 387 kt N yr^?1. Most of the reduced nitrogen is deposited in the British Isles (64%), while 36% is exported (148 kt N yr^?1).     

Influence of pH on the release and chemical fractionation of heavy metals in sediment from a suburban drainage stream in an arid mine-based oasis

Purpose

The objectives of this study were to explore the influences of pH on the release of Cu, Zn, Cd, Pb, Ni, and Cr in sediments derived from the upstream, middle, and downstream reaches of Dongdagou stream in Gansu Province, Northwest China, and to examine the fractionation changes of heavy metals in the sediments after reaching their release equilibrium under different pH conditions.

Materials and methods

Sediment samples were obtained using a stainless steel grab sampler to collect the uppermost 10 cm of sediment from the channel bed. The pH-dependent release experiment was conducted in the solid-to-liquid ratio of 1:20 at different pH values (2, 4, 6, 8, 10, and 12) at room temperature. The total Cu, Zn, Cd, Pb, Ni, and Cr concentrations in the sediments were digested using an acid digestion mixture (HNO₃ + HF + HClO₄) in an open system. Metal fractionation of selected sediments was obtained using the Tessier sequential extraction procedure. Heavy metal concentrations in the samples were determined using atomic absorption spectrophotometry.

Results and discussion

The mean concentrations of heavy metals in sediments decreased in the following order: Zn (1676.67 mg kg^?1) > Pb (528.65 mg kg^?1) > Cu (391.34 mg kg^?1) > Cr (53.48 mg kg^?1) > Ni (34.27 mg kg^?1) > Cd (11.53 mg kg^?1). Overall, the solubility of Cu, Zn, Cd, Pb, and Ni decreased with increasing pH, and they were strongly released at pH 2. Moreover, the solubility of Cr increased with increasing pH, and its release was highest at pH 12. After reaching the release equilibrium of heavy metals under different pH conditions, the percentages of organic Cu, Zn, Cd, and Fe-Mn oxyhydroxide Pb decreased, compared to their initial fractions. The residual fractions of Ni and Cr were dominant, regardless of pH.

Conclusions

The average concentrations of Cu, Zn, Cd, and Pb in sediments were highly elevated compared with the soil background values in Gansu Province, China. The results of this pH-dependent release experiment showed that the release behaviors of Cu, Zn, Pb, and Cr followed an asymmetric V-shaped pattern, whereas Cd and Ni followed an irregular L-shaped pattern. The changes in the release of heavy metals in sediments were related to their redistribution between chemical fractionations.

     

Seasonal Variations of Ten Metals in Highway Runoff and their Partition between Dissolved and Particulate Matter

Knowledge of differentiation of pollutants in urban runoff between dissolved and particulate matter is of great concern for a successful design of a water treatment process. Seasonal variations in pollutant load are of equal importance. Ten metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn), as dissolved and particulate bound, was studied in the runoff from a major urban highway during a winter season and its following summer. Studded tyres and winter salting were expected to have an impact on the runoff water quality. The dissolved part of Al, Cd, Co, Cr, Mn and Ni was significantly higher in winter in comparison with summer (p?<?0.01). For Fe, however, the dissolved part was lower during winter. No significant difference was found for Cu, Pb and Zn between the two seasons. The mass concentration (mg kg^?1) for all metals was significantly higher over the summer except for Al and Co, which showed a higher mass concentration during the winter. The concentration of selected metals vs. total suspended solids (TSS) showed a linear relationship (r ²?>?0.95) during winter runoff events except for Cd. A good correlation (r ²?>?0.90) was also found for the summer period for Al, Cu, Fe, Mn, Ni and Zn. It is suggested that the metal pollutant load during winter could be assessed indirectly by measurement of TSS.     

Potential hotspots of persistent organic pollutants in alluvial sediments of the meandering Wurm River,Germany

Purpose

Fluvial sediments can act as archives for lipophilic pollutants. However, their distribution within the highly dynamic regime of the river corridor is scarcely investigated. Herein, a novel approach combining geochemical investigations of sediment bodies in the river corridor of the Wurm River (catchment < 400 km²) and aerial photograph evaluation provide information about the history of river course change and the distribution of pollution by selected persistent organic compounds (POPs) and selected heavy metals.

Materials and methods

The study is based on nine sediment cores and a total number of 45 subsamples. The sediment samples were analyzed for trace element inventory (X-ray fluorescence), grain size composition (laser diffraction particle size analyzer), and organic compounds (chromatography-mass spectrometry). On the basis of quantitative data of persistent organic substances as well as three heavy metals (Cu, Pb, and Zn) and morphological changes from 1953 until 2016 of the area of investigation provided by eight aerial photographs, analyzed sediments were assigned to different decades, and lateral migration rates as well as deposition rates were calculated.

Results and discussion

High morphodynamics within the river corridor limits the explanatory power of single approaches (for example, geochronology and radiometric dating). However, a combination enables further insight into floodplains such as the pollution history, spatial pollutant dispersal, hotspot localization, meander migration rates (0.2–0.5 m year^?1), sedimentation rates (0.5–5.2 cm year^?1) and estimation of hotspot remobilization. Quantitative data for the analyzed heavy metals (Cu, Pb, and Zn) show a decreasing trend for locations with younger sediment bodies, whereas quantitative data for the synthetic organic pollutants reflect the corresponding history of emissions with increasing concentrations until a climax followed by decreasing concentrations due to restrictions regarding their application.

Conclusions

Results reveal hotspot areas for POPs and their degree of remobilization. This study demonstrates that by knowing the history of emissions of a lipophilic substance, potential hotspots can be localized solely based on a sufficient number of aerial photographs documenting the river channel migration and sediment body formation in the corresponding period of time.

     

Long-term changes in the Cu,Pb, and Zn content of forest soil organic horizons from North-East Scotland

Forest soil organic horizons from old and young plantations in the Alltcailleach Forest, N.E. Scotland were first sampled in 1949/50 and resampled in 1987. Copper, Pb and Zn in the soils were determined simultaneously on the original (stored) and the resampled soils. Overall mean Cu and Pb concentrations increased from 12.7 to 15.3 and 49.5 to 60.8 mg kg^?1 between 1949/50 and 1987. Zinc concentrations decreased from 76.4 to 60.7 mg kg^?1. Amounts of all 3 heavy metals increased because of increases in the thickness of organic horizons. Mean accumulation rates for Cu, Pb and Zn were 39.1, 186 and 114 g ha^?1 yr^?1, respectively. The rate of accumulation of Pb was significantly related to the rate of accumulation of organic matter. Copper and Zn concentrations were directly correlated with pH and inversely correlated with C/N ratio, whereas Pb was inversely correlated with pH and directly correlated with % C and C/N ratio. The more acidic soil organic horizons therefore contained higher concentrations of Pb and lower concentrations of Cu and Zn.     

汉江上游汉中段河流表层沉积物重金属污染风险评价

通过监测汉江上游汉中段河流表层沉积物重金属Pb,Cu,Zn,Cd,Cr的浓度,分析了各元素的含量分布特征,并选用Hakanson生态风险指数法对研究区进行了环境风险评价。结果表明,汉江上游汉中段各监测点重金属富集顺序为:Cd >Zn >Pb >Cr >Cu。单个重金属的污染指数C_fⁱ显示,汉江上游汉中段监测点仅有Cu的含量均值为0.83,小于1,为轻微污染;Pb,Zn,Cd,Cr的均值分别为1.06,1.25,1.33,1.02,略大于等于1,处于轻微污染以上水平,达到中度污染水平。综合分析多项重金属污染系数C_d,单项重金属的潜在生态风险系数E_rⁱ和多种重金属的生态系统的潜在生态风险指数I_R可知,汉江上游汉中段各监测点沉积物重金属污染属于轻微生态危害。