Historical rates of atmospheric Pb deposition using210Pb dated peat cores: Corroboration,computation, and interpretation

Lead-210 dating of peat cores is one approach that has been used to arrive at historical rates of heavy metal deposition. Despite concerns regarding the validity of²¹⁰Pb dating due to Pb mobility,²¹⁰Pb dating can be used if the dates are corroborated with some other independent dating technique. In this study, based on analyses of²¹⁰Pb dated, pollen corroborated peat cores from two sites in the Czech Republic (Jezerní sla and Bo?í Dar Bog), we illustrate a previously unexplored problem concerning the computation of metal deposition, using Pb as an example. When peat cores are collected, sectioned into depth intervals,²¹⁰Pb dated and analyzed for metal contents, the²¹⁰Pb dates most appropriately correspond to the midpoint depth for each interval, whereas the metal contents correspond to the interval between the top and bottom of each section. Thus the²¹⁰Pb dates and metal content values throughout the core are offset by half the distance of each depth interval. In calculating historical rates of heavy metal deposition two approaches are available for correcting for the depth interval offsets, the traditional approach of date interpolation and our newly proposed metal content interpolation. We see noa priori reason for choosing one approach over the other, and suggest simultaneous use of both date and metal content interpolation. Additionally, acid-insoluble ash (AIA), which has been proposed as a dating technique in and of itself, may be more useful as an interpretive tool which may provide insights into the nature or sources of atmospherically deposited Pb. For example, plots of Pb content per core section versus AIA content per core section for Jezerní slat, located in a relatively pristine area, reveal increased Pb content without increased AIA contents in depths shallower than 6 cm, indicating deposition of gasoline-derived Pb after its introduction in 1922. Similar plots for Bo?í Dar Bog, located in a polluted industrialized region, indicate greater inputs of Pb than would be predicted from AIA, based on the Jezerní sla analyses. We interpret the apparent excess Pb deposition at Bo?í Dar Bog as being contributed by soil-derived dust from local metal mining. Elevated rates in Pb deposition at Bo?í Dar Bog are consistent with the history of local mining known to have occurred in the vicinity. Finally, magnetic susceptibility measurements identify combustion of fossil fuels as a source of atmospheric Pb deposition at Bo?í Dar Bog, but not at Jezerní sla      

土壤中铅锰复合污染对烟草生长及其吸收铅和锰的影响

采用盆栽试验方法研究Pb与Mn复合污染对烟草生长及其吸收积累Pb、Mn的影响,以便弄清在Pb与Mn复合污染条件下烟草的生长情况.试验结果表明:Pb与Mn复合污染可影响烟草的生长发育,在土壤中Pb浓度(500 mg/kg)不变的情况下,随着土壤中Mn浓度的提高,烟草株高、根长、根系和茎叶的干重不断减少,当土壤中Mn浓度达到2500 mg/kg时,烟草的株高、根长和烟草的产量减少分别达到极显著水平(p＜0.01).Pb与Mn复合污染也影响烟草对Pb和Mn的吸收与积累,当土壤中Pb浓度不变时,随着土壤中Mn浓度的增加,烟草各部分中Pb含量和Mn含量都在不断的提高.此外,Mn可促进烟草对Pb的吸收与积累.     

Study of wet and dry atmospheric deposition at two altitudes in central Switzerland

The analysis of various ions in atmospheric deposition at two altitudes (515 m and 950 m a.s.l.) in Switzerland during 1983/84 revealed that dry deposition depends more on altitude than wet deposition. During autumn and winter, when vertical air exchange is limited, dry deposition of substances from anthropogenic sources (e.g. SO₄-S) was higher at the lower site. In the course of the year, the pattern of wet deposition was independent of altitude and showed highest rates for S, N and Ca in summertime. A comparison between rates of wet, particulate and gaseous S and N deposition suggested that during the growing season wet deposition is the dominant flux. Total (wet + dry) deposition of S, N and Cl was lower than in other parts of Europe, but a substantial increase of NO₃-N deposition during the past 25 years must have occured.     

Wet deposition of mercury and ambient mercury concentrations at a site in the Lake Champlain basin

The “Great Waters” program, established in the 1990 Clean Air Act Amendments, mandated that atmospheric deposition of hazardous air pollutants to Lake Champlain (including Hg) be assessed. An assessment of the magnitude and seasonal variation of atmospheric Hg deposition in the Lake Champlain basin was initiated in December 1992 with one year of event precipitation collection, as well as collection of vapor and particle phase Hg in ambient air. Samples were collected at the Vermont Monitoring Cooperative air monitoring site at the Proctor Maple Research Center in Underhill Center, VT. The average volume-weighted concentration for Hg in precipitation was 8.3 ng/L for the sampling year and the average amount of Hg deposited with each precipitation event was 0.069 μg/m². The total amount of Hg deposited through precipitation during 1993 was 9.26 μg/m²/yr. A seasonal pattern for Hg in precipitation was evident, with increased concentrations and deposition during spring and summer months. Meteorological analysis indicated the highest levels of Hg in precipitation were associated with regional transport from the south regardless of season, and with transport from the west, southwest and northwest during spring and summer months. Concentrations of ambient vapor phase Hg were typical of rural locations and consistent across seasons. Ambient particulate Hg concentrations averaged 11 pg/m³ with highest concentrations during the winter months.     

An exploratory study of potential As and Pb contamination by atmospheric deposition in two urban vegetable gardens in Rome,Italy

Purpose

A preliminary study was carried out in Rome (Italy) to assess the potential role of atmospheric deposition in trace element contamination in urban vegetable gardens relative to human health risk from crop consumption.

Materials and methods

Two sites were selected on the basis of previously known contamination issues. Atmospheric deposition, parent material, soils properties affecting trace element mobility, and various anthropogenic inputs were considered. Soil samples were taken at depth from two points in each garden, within 5 cm of sampled crops. Inputs and crops were sampled and analysed for As and Pb content. A rain and dust gauge was set up in each garden for the duration of 93 days (late spring to late summer) for atmospheric deposition sampling.

Results and discussion

Atmospheric deposition influx was high at both sites (2.22 and 2.32 As and 2.67 and 3.42 Pb μg m^?3 day^?1). Soil pH was between 6.70 and 7.57 and texture varied from loamy sand to clay loam (3.4 to 31.9 % clay content). CEC ranged between 21.6 and 54.2 meq/100 g within rooting depth, rising almost commensurately with soil organic carbon (SOC) content (1.87–8.37 %). Somewhat high total soil Pb content (80.8–522.7 ppm) contrasted with negligible exchangeability and crop content (<0.01 ppm). Total soil As (17.0–32.0 ppm) corresponded with exchangeable and crop As for one site in one of the gardens. Leaves evinced high As accumulation levels (16.0–41.2 ppm) in all crops. High amounts of atmospheric Pb combined with negligible amounts of extractable Pb and Pb plant tissue content point to particulate inhalation and ingestion as a main health threat in the case of Pb. In contrast, food intake seems to be of greater concern relative to high As contamination. Greater soil As solubility may be explanatory, but the mostly low amounts of extractable As and the high atmospheric As suggest an airborne route being playing an important role.

Conclusions

Preliminary results suggest that research on trace element contamination in urban gardens should consider atmospheric deposition as a major contributing source.

     

Bulk and wet atmospheric deposition chemistry at pallanza (N. Italy)

The chemistry of wet only and bulk depositions collected weekly at Pallanza from May, 1984 to December, 1986 is compared and discussed in relation to the composition of dust fall. The comparison shows a very good agreement between pH values (volume weighted mean values of 4.35 and 4.36, respectively, for wet only and bulk samples) and differences between 6 and 12% for ammonium, sulphate, nitrate, and Na. For Ca, Mg, and K the difference range is 30 to 50%. The amount of precipitation over Pallanza (mean value 1951–1985,1709 mm), together with the solute concentrations in atmospheric deposition, mean that there is high bulk deposition of acidifing substances. The values found during the study period were 76, 93, 143, and 81 meq m² yr^?1 for H⁺, ammonium, sulphate, and nitrate, respectively.     

Forest canopy transformation of atmospheric deposition

Solute fluxes to the ground in open plots and under the forest canopy of different species were investigated in a number of long-term ecosystem studies in West Germany. From the canopy flux balance, rates of interception deposition and canopy/deposition interactions were assessed. Chemically, both open precipitation and throughfall are dilute solutions of H₂SO₄ and HNO₃ and their salts. For the sites investigated, mean pH in bulk precipitation ranged from 4.1 to 4.6, and in throughfall from 3.4 to 4.7. The increase in acidity after canopy passage at most sites indicates considerable interception deposition of strong acids to the forest stands, exceeding the rate of H+ buffering in the canopy. Evidence for buffering processes can be directly deduced from the fact that on sites with high soil alkalinity and high foliage base status, throughfall pH is usually higher than precipitation pH. Furthermore, the same idea can be concluded from changes in solution composition after canopy passage: the H⁺/SO _inf4 ^sup2? ratio is decreasing at most sites, while alkali earth cations from exchange processes occur in throughfall (Ca²⁺/SO _inf4 ^sup2? ratio increases). Solution composition and element flux data are presented for each of the sites, and the regional, orographical and site specific (species composition, ecosystem state) differentiations are discussed. A method for the assessment of total deposition and of canopy interactions such as H⁺-buffering and cation leaching is described, and results of calculations are shown. From these calculations it is concluded that forest ecosystems in Germany receive mean H⁺ loads of ca. 1 to 4 keq H⁺ · ha^?1 · a^?1 from atmospheric deposition. Acidity deposition rates seem to be related to a few key factors such as regional characteristics and ecosystem characteristics.     

大气氮素沉降研究进展

人为干扰下的大气氮素沉降已成为全球氮素生物化学循环的一个重要组成部分。作为营养源和酸源, 大气氮沉降数量的急剧增加将严重影响陆地及水生生态系统的生产力和稳定性。本文从大气氮沉降对土壤和水体环境、农业和森林生态系统以及生物多样性等方面综述了近年来国内外大气氮素沉降的研究现状及其对生态系统的影响, 并总结探讨了前人采用的大气沉降氮测定方法, 展望了我国大气氮沉降的研究前景。     

Input of pesticides by atmospheric deposition

Sampling and analytical methods were developed to examine the input of various pesticides on noncultivated areas of the FAM (Research Network on Agroecosystems) Research Station Scheyern. Off-target drift from pesticide application on nearby cultivated land, as well as input due to long-range atmospheric transport, were measured. The wet deposition was determined by a cooled wet-only sampler. Bulk samplers and specially designed samplers with glass-fiber surface were used for total deposition measurements. Analysis of pesticides was carried out using liquid/liquid or solid-phase extraction and high performance liquid chromatography-UV (HPLC-UV) or gas chromatography-nitrogen/phosphorus-sensitive detector/MS (GC-NPD/MS) detection. Obtained results demonstrated that for several compounds, total deposition, i.e. the sum of wet and dry deposition, was marginally higher than wet deposition alone. In contrast, total deposition data of pesticides having been applied near the sampling site exceeded wet deposition values by orders of magnitude. In addition to direct drift, determined as droplets depositing near pesticide application areas, an indirect drift represented by particle-associated or gaseous transport was observed, both of which contributed considerably to total deposition. Therefore, to determine the input of pesticides to nontarget areas in the close vicinity of pesticide application, direct and indirect drift, and background deposition must be considered.     

The effects of lead shot deposition on soils and crops at a clay pigeon shooting site in northern England

Abstract. The impact of lead shot on soils and crops was examined at a clay pigeon shooting site in northern England. Topsoil cores were collected along a 300 m transect from the shooting range, and the numbers of lead shot pellets per soil core, total and 'plant-available'(0.5 m acetic acid extractable) lead concentrations, organic matter content, pH and cation exchange capacity were determined. The number of oilseed rape plants and their stem diameters were recorded in 1 m² quadrats placed at the soil sampling locations. Total and 'plant-available' lead concentrations in the soil were most but plant numbers per m² and mean stem diameters were least in the area of greatest lead shot deposition. Total lead concentrations in the soil commonly exceeded 5000 mg/kg; these are considerably greater than threshold 'trigger' concentrations proposed by the Department of the Environment, above which soils are considered to be contaminated and warrant further investigation. Concentrations of lead in the oilseed rape plants themselves were also largest in the area of most intense lead shot deposition; in root samples the lead concentration exceeded 400 mg/kg. The management and remediation of contaminated soils at the clay pigeon shooting site are discussed.     

The acidifying potential of atmospheric deposition in Canada

It is proposed that the value of ([SO₄ ^??] - [Ca⁺⁺ + Mg⁺⁺]) in precipitation is a suitable way to describe the acidifying potential (AP) of the wet desposition. In eastern North America, the AP of precipitation varies from 20 to 85% of the total sulphate, the remainder of the sulphate being neutralized H₂SO₄, sulphate from salts in dust or from sea salt. The AP ranges from 20 to 80% of the H⁺ in the wet deposition. The rest of the H⁺ is contributed by the net effect of N compounds. Ammonium and nitrate ions from ammonia and NO_Xemissions do not represent a net acidic loading to the terrestrial ecosystem if they are taken up by vegetation. However, when N leaches from watersheds in the form nitrate, it constitutes an acidifying demand on the ecosystem. Therefore, the overall net acidifying potential (NAP) applied to the terrestrial ecosystem is defined by the value of ([SO₄ ^??] - [Ca⁺⁺ + Mg⁺⁺]) in precipitation plus [NO₃ ^??] in runoff from the watershed.     

Long-term changes in concentration and deposition of atmospheric mercury over Scandinavia

Samples for measurements of total gaseous mercury (Hg) in air have been collected since 1980 in south-western part of Scandinavia. A collection program for precipitation samples used to determine changes in depositional fluxes of total Hg has been in operation since 1987. A comparison of today's total gaseous Hg levels in air and the total Hg concentrations in precipitation with the ones found earlier, shows a clear decrease with time. At the Swedish west-coast, yearly average air concentrations and median levels of 3.3 and 3.1 (1980–1984), 3.2 and 2.8 (1985–1989), and 2.7 and 2.6 ng Hg/m³ (1990–1992), respectively, were found. Increased average and median winter concentrations were always found, with levels at 3.7 and 3.4, 3.7 and 3.3, and 3.0 and 2.7 ng Hg/m³ for the respective time period. Higher winter values were expected due to increased anthropogenic emissions and changes in the mixing height of the atmosphere. The corresponding total wet deposition rates decreased from 27 (1987–1989) to 10 μg Hg/m² yr. (1990–1992). A finding of special interest was the decreased number of episodic events of high total gaseous Hg levels in air, from 1990 and further on. In addition, the frequency distribution of the concentrations of Hg in air seems to be different for these years compared to the other two time periods. A frequency distribution of air concentrations of Hg more resembling a normal distribution was found for the years 1990 to 1992. The decrease of the atmospheric burden of total gaseous Hg and deposition of total Hg are most probably connected to lower emissions in source areas on the European continent. It seems logical to state that the problem of high Hg depositional fluxes to Scandinavia, is best solved by abatement strategies on the regional scale.     

Identifying indicators of atmospheric nitrogen deposition impacts in acid grasslands

Atmospheric deposition of nitrogen has become a serious concern for nature conservation managers and policy makers. It has the potential to reduce species richness, increase the graminoid component of the sward, encourage species typical of more fertile conditions and alter the soil biogeochemistry of grasslands. Calcifugous grasslands (grasslands found on acid soils) are among the most sensitive to N deposition due to their poorly buffered soils and species typical of nutrient poor environments.Indicators have an important role to play in detecting the impact of nitrogen deposition on sites of conservation importance and assessing conservation status. This study investigates potential indicators of nitrogen deposition impacts that could be incorporated into site condition monitoring programmes such as the UK Common Standards Monitoring.Using two national surveys of calcifugous grasslands we examined the potential for using: the presence or absence of indicator species, the cover of indicator species, the species richness and richness of functional groups, and the cover of functional groups as indicators of N deposition impacts. Of all the potential indicators investigated, graminoid:forb ratio was found to be the best indicator of N deposition impacts. It showed a significant relationship to N deposition in both data sets and is quick and easy to assess in the field. Vegetation indicators must be used with caution as there is potential for vegetation management regime and nutrients from other sources to cause similar changes in species composition. Consideration must be given to these before attributing changes to nitrogen deposition.     

A comparison between wet and bulk deposition at an urban site in the U.K.

As a part of an ongoing investigation into urban acidic deposition in Greater Manchester, a wet-only collector was collocated with a bulk collector in the city centre of Manchester, one of 18 sites of an urban precipitation monitoring network. A comparison of data from these collocated bulk and wet-only collectors allowed estimates of the contribution of dry deposition to the bulk collector to be made. Dry deposition was found to contribute between 15 and 17% to elevated deposition and concentrations of non marine sulphate, nitrate and ammonium in the bulk collector. By a statistical analysis between ion concentrations with gas concentrations and an evaluation of the available literature, the form of the dry deposited material was inferred. The contribution of dry deposited Ca²⁺ to concentration and deposition in the bulk collector was found to be 46%. Calcium species are suggested as being those which reduce acidity most. Statistical analyses revealed significant differences between concentrations of ions found in the bulk and wet-only collectors. An evaluation of the data from the collocated collectors has identified possible sampling artifacts introduced by the use of bulk collectors in urban areas.     

中国南方典型地区阔叶林大气氮沉降通量研究

A one-year study in a typical red soil region of southern China was conducted to determine atmospheric nitrogen （N） fluxes of typical N compounds （NH3, NH4-N, NO3-N, and NO2） and contribution of three sources （gas, rainwater, and particles） to N deposition. From July 2003 to June 2004, the total atmospheric N deposition was 70.7 kg N ha^-1, with dry deposition accounting for 75% of the total deposition. Dry NH3 deposition accounted for 73% of the dry deposition and 55% of the total deposition. Moreover, NO2 contributed 11% of the dry deposition and 8% of the total deposition. Reduced N compounds （NH4^＋ and NH3） were the predominate contributors, accounting for 66% of the total deposition. Therefore, atmospheric N deposition should be considered when soil acidification and critical loads of atmospheric deposition on soils are estimated.     

Measurements of atmospheric deposition and internal circulation of base cations to a forested catchment area

The dry deposition of base cations to a Norway spruce stand was estimated by multiplying the ratio of the ion deposition to the sodium deposition on a surrogate surface with the dry deposition of sodium on the forest stand. The method can in principle only be applied to species that are present only in particles, but the method gives reasonable results when tested on ions that are also dry deposited in other forms (SO ₄ ^2– . NO ₃ ^– and NH ₄ ⁺ ). The atmospheric input and especially the dry deposition of base cations is an important replacement for the loss of base cations from the soil by run-off. The calculated internal circulation of K⁺ and Ca²⁺ showed maxima synchronously with rainfall maxima and constitute 71% and 53%, respectively, of the net throughfall deposition. The internal circulation of Ca²⁺ was almost equal to the SO₂ uptake.     

Bioavailability of heavy metals and abundance of arbuscular mycorrhiza in a soil polluted by atmospheric deposition from a smelter

The bioavailability of heavy metals (Cd, Zn, Pb, Cu) and the abundance of arbuscular mycorrhiza (AM) were studied in two agricultural fields close to a Pb-Zn smelter and three fields outside the pollution zone all cultivated with maize (Zea mays L.). Metal extractability with ethylenediaminetetraacetic acid (EDTA)-NH₄OAc and Ca(NO₃)₂, plant metal uptake, and mycorrhizal parameters (spore number, root colonization) were assessed at two growth stages (six-leaf and maturity). Despite regular liming, the availability of Cd, Zn, and Pb was markedly higher in the two metal-polluted fields than in the three uncontaminated fields. However, the AM abundance was not correlated with metal availability. Root colonization and spore numbers in the metal polluted fields were relatively high, though at plant maturity the former was significantly lower than in one of the uncontaminated fields. The very low AM abundance in the two other unpolluted fields was related to other factors, particular soil and plant P status and soil pH. AM root colonization did not substantially prevent plant metal accumulation, since the metal concentrations in maize grown on the polluted fields strongly exceeded normal values, and for Cd and Pb reached the limits of toxicity for animal feed.     

Procedures for estimating atmospheric deposition properties of organic chemicals

A rationale for procedures to estimate the climatological mean dry deposition velocity and precipitation scavenging ratio of organic chemicals is developed. Both deposition parameters depend strongly on vapor pressure, as it affects the partitioning between vapor and sorbed phases. Separate formulae are presented for vapor and sorbed fractions using their mass-weighted average to describe the deposition parameters for the total airborne concentration. Deposition of sorbed fractions is controlled solely by particle size, and methods for estimating the particle size are presented. Dry deposition velocity for the vapor fraction is derived by semiempirical analysis, and is found to depend on Henry's Law constant, molecular diffusion coefficients in air and water, and the chemical's reaction rate in water. Estimates of the dry deposition velocity for 5 chlorinated hydrocarbons are made and compared with observations. Estimates of the precipitation scavenging ratio are compared with observational data for 11 chlorinated or aromatic hydrocarbons. The estimates generally are within an order of magnitude of the measured values.     

Detectability of step trends in the rate of atmospheric sulphate deposition

Step trend analyses are performed on acid deposition rates using a combination of monitored sulphate deposition data and a long-range transport of acid precipitation (LRTAP) model. The step trend analyses consider Sudbury's emissions and eastern North America's emissions to explore strategies for reducing SO₂ emissions such that a decrease in sulphate deposition is detected in a specified time period. Results indicate Sudbury's emissions could be reduced with significant detectable reductions in sulphate deposition occurring at the Muskoka region. Significant detectable reductions do not occur elsewhere due to the variability of monitoring data ‘masking’ the small change in sulphate depositions associated with abatement. Reductions in eastern North America's emissions would result in widespread evidence of significant detectable reductions.     

Historical atmospheric deposition in a Swedish mining area traced by S isotope ratios in soils

Mining activities for almost thousand years have caused large S emissions in the Falun area, central Sweden. Since the beginning of the 20th century, the S deposition has decreased considerably. The soil S concentrations and S isotope compositions were analyzed for ΣS and adsorbed SO42- for three soil profiles close to the mining area in order to identify the soil S sources. The δ34S values were found to be different for ΣS and adsorbed SO42- and ranged from –3.7‰ to +2.6‰. In the B-horizon, the observed ΣS δ34S values (and hence calculated δ34S values for organic S) were mostly lower than those of the adsorbed SO42-. In the O-horizon, ΣS showed similar δ34S values as the adsorbed SO42- in the mineral soil. The adsorbed SO42- showed nearly constant δ34S values with depth. The δ34S values in the soils are interpreted to reflect a mixture of historical and modern deposition due to soil S circulation with no or negligible fractionation. The lower δ34S values of organic S in the B-horizon suggests preservation of acid deposition originating from mining activities back in time. The adsorbed SO42- in the mineral soil and the organic S in the O-horizon reflect a response to a new δ34S composition in the atmosphere due to fossil fuel burning during the 20th century.