Atmospheric Transfer and Deposition Mechanisms of 210Pb Aerosols onto Forest Soils

Activities of ²¹⁰Pb carrier aerosols in an age-graded Sitka spruce conifer, three deciduous (oak, lime and sycamore) foliage and in rain and throughfall samples have been measured during the period of 2001–2002. The ²¹⁰Pb concentrations in the age-graded Sitka leaf needles have shown to accumulate until a steady state between accretion and loss of particulate matter is maintained with time. Similarly, the concentrations of ²¹⁰Pb on deciduous tree leaves increased with time until the leaves began to senesce. The ²¹⁰Pb inventory in bulk precipitation was significantly (r ²?=?0.99; P?<?0.001) large compared with that in throughfall samples, as indicated by a ratio of 1 to 0.1 of ²¹⁰Pb deposition in bulk precipitation to throughfall. This suggests that ²¹⁰Pb is retained in the Sitka spruce foliage during deposition until transfer to the ground mainly through litterfall. These findings suggest that the presence of woodland is responsible for enhanced ²¹⁰Pb deposition fluxes beneath wooded areas relative to open grassland soils.     

Concentrations and Pools of Heavy Metals in Urban Soils in Stockholm,Sweden

The concentrations of heavy metals (Cd, Cr, Cu, Hg, Ni, Pb andZn) and arsenic (As) were surveyed and the metal pools estimatedin soils in Stockholm Municipality. The sampling sites were distributed all over the entire municipality with a higher sampling density in the city centre. Soils were sampled to a maximum depth of 25 to 60 cm. Soil texture, total-C content, electrical conductivity and pH were analysed. Heavy metal concentrations were determined after wet digestion with boiling7 M HNO₃.The results showed a wide range in heavy metal concentrations, as well as in other soil properties. The city centre soils constituted a rather homogeneous group whereas outside this areano geographical zones could be distinguished. These soils were grouped based on present land use, i.e. undisturbed soils, public parks, wasteland (mainly former industrial areas), and roadside soils. The city centre and wasteland soils generally hadenhanced heavy metal concentrations to at least 30 cm depth compared to park soils outside the city centre and rural (arable)soils in the region, which were used to estimate background levels. For example, the mean Hg concentration was 0.9 (max 3.3)mg kg^-1 soil at 0–5 cm and 1.0 (max 2.9) at 30 cm depth in the city centre soils, while the background level was 0,04 mg kg^-1. Corresponding values for Pb were 104 (max 444) and135 (max 339) mg kg^-1, at 0–5 and 30 cm, respectively, while the background level was 17 mg kg^-1.The average soil pools (0–30 cm depth) of Cu, Pb and Zn were 21,38 and 58 g m^-2 respectively, which for Pb was 3–4 timeshigher and for Cu and Zn 1.5–2 times higher than the backgroundlevel. The total amount of accumulated metals (down to 30 cm)in the city centre soils (4.5^*10 ⁶ m² public gardens and green areas) was estimated at 80, 1.1, 120 and 40 t for Cu, Hg, Pb and Zn, respectively. The study showed (1) thatfrom a metal contamination point of view, more homogeneous soilgroups were obtained based on present land use than on geographicdistance to the city centre, (2) the importance of establishing a background level in order to quantify the degree of contamination, and (3) soil samples has to be taken below the surface layer (and deeper than 30 cm) in order to quantify theaccumulated metal pools in urban soils.     

Deposition and Fate of Lead in a Forested Catchment, Lesni Potok, Central Czech Republic

The deposition of trace elements and their fate in a forest ecosystemhas been monitored at the experimental site, Lesni Potok catchment (LP), with granite bedrock. The catchment is located 30 km ESE from Prague. Annual bulk Pb-deposition flux F_Pb was 3.41 kg km^-2 a^-1 in 1994 and gradually decreased to 0.49 kg km^-2 a^-1 in 2001. The decrease is comparable with those observed in Germany and in the U.S.A. in the 1970s and 1980s. The total sales ban of leaded gasoline in the Czech Republic since January 2001 was accompanied by a pronounced decrease of F_Pb in a single year. The residual Pb-deposition flux is assigned to both the long-range transport of fine-grained vehicular lead aerosol (with a long residence time in the atmosphere) and to theemissions from power plant boilers burning lignite mined in the Czech northwest coal basin. The F_Pb of lead correlates stronglywith those of As, Cd, Cu, Zn and Be, the typical metals in coal fly ash, at two monitored sites. Topsoil horizons contain elevated concentrations of Pb (53–67 mg kg^-1), which are of anthropogenicorigin. Soils in the riparian areas contain increased concentrations of Pb when compared to soils on the hillslope areas. Significant amounts of Pb were found on a stream substrate and Fe-precipitate sampled from the stream. Low concentrations of Pb in bark and bole wood suggest that the uptake of Pb by vegetation is negligible. The very small surface water outputs (average of 0.002 kg km^-2 a^-1) compared to inputs (average of 1.890 kg km^-2 a^-1) from the LP catchment indicate an ongoing accumulation of Pb in a forested landscape.     

Residual Cadmium and Lead Pollution at a Former Soviet Military Airfield in Tartu, Estonia

This paper presents data on the levels and dynamics of cadmium (Cd) and lead (Pb) concentration in the plants, soil, and groundwater of the landing corridor and airfield of a former Soviet military air base in Estonia, immediately at the end of its 40-year service in 1992 and over the following 8 yr. In 1991–92 we found high Cd concentrations in the meadow plants Trifolium pratense and Dactylis glomerata (up to 56 mg kg^-1). In 1993, the Cd concentration had dropped to 0.12–0.19 mg kg^-1, and stabilized in 1997–2000 at 0.04 mg kg^-1. Cd concentration in plants decreased significantly with increasing distance from the landing strip. Elevated Cd concentration (0.012 mg L^-1) was found in the fuel of the TU-22M (Backfire) strategic bombers. In 1991 and 1993, leaded fuel influenced the mean Pb concentration in plants (1.8–4.2 mg kg^-1). Average Pb concentration in both topsoil and the 30–40 cm soil horizon decreased between 1991 and 2000 from 28 to 6.5 and from 13.5 to 4.3 mg kg^-1, respectively. Cd concentration in the topsoil of the landingcorridor showed a significant increase between 1991 and 1993 (0.07–0.3 and 0.3–1.2 mg kg^-1, respectively), but stabilized later on the level of 0.04 mg kg^-1. The concentrations of both Pb and Cd in the soil were higher closer to the fuel bunkers. Current assessment of the movement of these metals from the vegetation to the soil and to groundwater is linked to potential leaching to the surrounding environment.     

Post-Glacial Lead Dynamics in a Forest Soil

The use of alkyl-Pb additives in gasoline during the 20th century resulted in widespread Pb pollution. The objective of this study was to determine the relative importance of atmospherically deposited Pb and Pb released through weathering to soil Pb pools at the Hubbard Brook Experimental Forest, New Hampshire. We employed a selective extraction method to estimate the amount of Pb that was: water-soluble + exchangeable (EX); inorganically bound (IB); organically bound (ORG); bound to amorphous oxides (AMOX); and bound in crystalline minerals (RES). After normalizing crystalline-Pb concentrations to the immobile element Ti, we estimated that 14.1 kg ha^-1 of Pb has been weathered from Hubbard Brook soils in the 12,000–14,000 yr since deglaciation – a long-term average release of 1.0–1.2 g ha^-1 a^-1. Analysis of Ti-normalized total Pb concentrations indicated a net post-glacial decrease of 7.2 kg ha^-1 in the total Pb pool – consisting of a net accumulation of 4.9 kg ha^-1 in the O horizon, and a net loss of 12.1 kg ha^-1 from mineral soil. Atmospheric deposition of Pb between 1926 and 1989 (estimated as 8.7 kg ha^-1) was a major source of Pb in the post-glacial period. Together, long-term weathering release and 20th century atmospheric deposition could account for all of the Pb in the EX, IB, ORG, and AMOX fractions. Lead from gasoline appears to constitute a major fraction of the total Pb burden in Hubbard Brook soils. Periodic analysis of soil Pb fractions may be useful in monitoring the fate of Pb in forest soils.     

Changes in Extractability of Cr and Pb in a Polycontaminated Soil After Bioaugmentation With Microbial Producers of Biosurfactants, Organic Acids and Siderophores

Partly because of the low bioavailability of metals, the soil cleaning-up using phytoremediation is usually time-consuming. In order to enhance the amount of metals at the plant's disposal, the soil bioaugmentation coupled together with phytoextraction is an emerging technology. In this preliminary work, two agricultural soils which mainly differed in their Cr, Hg and Pb contents (LC, low-contaminated soil; HC, high-contaminated soil) were bioaugmented in laboratory conditions by either bacterial (Bacillus subtilis, Pseudomonas aeruginosa, Pseudomonas fluorescens or Ralstonia metallidurans) or fungal inocula (Aspergillus niger or Penicillium simplicissimum) and incubated during three weeks. The LC soil pots bioaugmented with A. niger and P. aeruginosa contained higher concentrations of Cr (0.08 and 0.25 mg.kg⁻¹ dw soil) and Pb (0.25 and 0.3 mg.kg⁻¹ dw soil) in the exchangeable fraction F1 (extraction with MgCl₂) by comparison with the non-bioaugmented soil where neither Cr nor Pb was detected. Conversely, immobilization of Cr and Pb in the soil were observed with the other microorganisms. The soil bioaugmentation not only modified the metal speciation for the most easily extractable fractions but also modified the distribution of metals in the other fractions, to a lesser extent nevertheless. The difference in microbial concentrations between the bioaugmented or not HC soils reached up to 1.8 log units. Thus the microorganisms that we chose for the soil bioaugmentation were competitive towards the indigenous microflora. The PCA analysis showed close positive relationships between the microorganisms which potentially produced siderophores in the soil and the amount of Cr and Pb in the fraction F1.     

Atmospheric Metal Pollutants-Archives, Methods, and History

Pollution of the atmosphere with cadmium (Cd), mercury (Hg), and lead (Pb) is a consequence of human activities. Natural archives are necessary to reconstruct the long-term history of metal deposition because accurate measurement of atmospheric deposition is a recent accomplishment. Reconstructions require: (1) accurate determination of concentrations of elements and isotopes, (2) accurate chronology of archives, and (3) archives that faithfully record atmosphere deposition. The most useful long-term archives are accumulations of ice and snow, peat, and lake sediment. Quantification of Cd deposition is uncommon because of its low concentration and substantial chemical mobility. Nonetheless, trends in peat and lake sediment are similar to those of Hg and Pb since ca. 1800 a.d. Both Hg and Pb are relatively chemically immobile and thus the peat and lake archives are believed to record historic trends of atmospheric deposition. Isotopic and concentration studies of Pb indicate a history of northern hemisphere atmospheric pollution extending back prior to 0 a.d. Although measurements of Hg concentration are now routine, isotopic measurements are in their infancy. Some Hg pollution sources have unique isotopic ratios, thereby contributing unique signals to the total Hg. Maximum accumulation rates of Hg and Pb occur up to 10 years later than for Cd (1970s versus 1960s in eastern North America, perhaps slightly later in Europe). By 2004, deposition of Cd, Hg, and Pb had declined from peak values in eastern North America more than 75, 75, and 90%, respectively.     

Impact of Atmospheric Long Range Transport of Lead,Mercury and Cadmium on the Swedish Forest Environment

Emissions of Hg, Pb, and Cd to air aretransported over wide areas in Europe and deposited far awayfrom their sources. About 80% of the atmospheric depositionof these metals in south Sweden originate from emissions inother countries. As a result of the increased anthropogenicdeposition the concentrations of Hg, Pb, and Cd in the morlayer of forest soils have increased considerably, mainlyduring the 20th century. Although the atmosphericdeposition of these elements has declined during the mostrecent decades, the reduction of the input of Hg and Pb isnot sufficient to prevent a further accumulation. Theconcentrations of Hg and Pb are still increasing by ca. 0.5and ca. 0.2% annually in the surface layer of forest soils.In contrast, the Cd concentration is currentlydecreasing in a large part of Sweden as a result of bothdeposition decreases and enhanced leaching induced by soilacidification. The accumulation factors of Hg and Pb,especially in the forest topsoils of south Sweden, arealready above those at which adverse effects on soilbiological processes and organisms have been demonstrated instudies of gradients from local emission sources andlaboratory assessment. There are also indications of sucheffects at the current regional concentrations of Hg and Pbin mor layers from south Sweden, judging from observationsin field and laboratory studies. There is an apparent riskof Pb induced reduction in microbial activity over parts ofsouth Sweden. This might cause increased accumulation oforganic matter and a reduced availability of soil nutrients.At current concentrations of Hg in Swedish forest soils,effects similar to those of Pb are likely. Increasedconcentrations of these elements in organs of mammals andbirds have also been measured, though decreases have beendemonstrated in recent years, related to changes inatmospheric deposition rates. As a result of current andpast deposition in south Sweden, concentrations of Hg infish have increased about fivefold during the 20thcentury. This implies risks for human health, when fish frominland waters are used for food. Although the concentrationof Hg in fish has decreased ca. 20% during the last decade,probably as a result of the reduced deposition, the levelstill exceeds the general limit (0.5 mg kg^-1) in about half(ca. 40 000) of the Swedish lakes. In order to reduceconcentrations in fish to the level recommended, and avoidfurther accumulation of Hg in soils, the atmosphericdeposition has to be reduced to ca. 20% of the current deposition rate. This can only be achieved by international co-operation.     

The Influence of Atmospheric N Deposition on Nitrous Oxide and Nitric Oxide Fluxes and Soil Ammonium and Nitrate Concentrations

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N₂O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N₂O emissions 1) elevated NH₃ deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO ₃ ^– and NH ₄ ⁺ aerosol. Flux measurements of NO and N₂O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N₂O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH₃ concentrations measured by passive diffusion and inference from measurements of the ²¹⁰Pb inventory of soils under tree canopies compared with open grassland. NO and N₂O emissions and KCl-extractable soil NH ₄ ⁺ and NO ₃ ^– concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH₃ downwind of intensive livestock farms or wet-deposited NH ₄ ⁺ and NO ₃ ^– in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N₂O from these soils increased with both N deposition and KCl extractable NH ₄ ⁺ , but the relationship between NH ₄ ⁺ and N deposition (ln NH ₄ ⁺ = 0.62 ln N_deposition + 0.21, r ² = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N₂O fluxes.     

The influence of atmospheric n deposition on nitrous oxide and nitric oxide fluxes and soil ammonium and nitrate concentrations

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N₂O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N₂O emissions 1) elevated NH₃ deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO^? ₃ and NH⁺ ₄ aerosol. Flux measurements of NO and N₂O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N₂O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH₃ concentrations measured by passive diffusion and inference from measurements of the ²¹⁰Pb inventory of soils under tree canopies compared with open grassland. NO and N₂O emissions and KCl-extractable soil NH⁺ ₄ and NO^? ₃ concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH₃ downwind of intensive livestock farms or wet-deposited NH⁺ ₄and NO^? ₃ in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N₂O from these soils increased with both N deposition and KCl extractable NH⁺ ₄, but the relationship between NH⁺ ₄ and N deposition (ln NH⁺ ₄ = 0.62 ln N_deposition+0.21, r ² = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N₂O fluxes.     

Total Lead and Stable Lead Isotopes in Stockholm Sediments

Lead (Pb) in the environment is derived from both naturaland anthropogenic sources. The aim of this study is to estimate the isotopic signature of anthropogenic Pb in sediments from a highly contaminated area (Stockholm), to discuss the influence of different sources on this signature, and to suggest natural Pb background concentrations. Also distribution patterns and differences between different water areas in Stockholm have been studied, both by total Pb and stable Pb isotopes. In 1993, sediment samples were collected at 24 stations in the Stockholm area and analysed for total Pb, zirconium (Zr), scandium (Sc) and stable Pb isotopes (^{204, 206-208}Pb). Total Pb data show that the Stockholm sediments are severely contaminated by Pb. The contamination seems to be rather local since the small lakes surrounding the central parts of Stockholm are much less effected than the central parts. Stockholm is clearly influenced by anthropogenic and natural sources, but in some of the small lakes also by Pb in zircons from the geological basement. The anthropogenic Pb in Stockholm has typical ²⁰⁷Pb/²⁰⁶Pb ratios of 0.85–0.89 and ²⁰⁸Pb/²⁰⁴Pb ratios of 36–38, which are distinct from natural sources. Pb/Sc ratios suggest that the natural background Pb concentration is 10–20 mg kg^-1 d.w.     

Changes in cadmium mobility during composting and after soil application

The effect of twelve weeks of composting on the mobility and bioavailability of cadmium in six composts containing sewage sludge, wood chips and grass was studied, along with the cadmium immobilization capacity of compost. Two different soils were used and Cd accumulation measured in above-ground oat biomass (Avena sativa L.). Increasing pH appears to be an important cause of the observed decreases in available cadmium through the composting process. A pot experiment was performed with two different amounts of compost (9.6 and 28.8 g per kg of soil) added into Fluvisol with total Cd 0.255 mg kg^?1, and contaminated Cambisol with total Cd 6.16 mg kg^?1. Decrease of extractable Cd (0.01 mol l^?1 CaCl₂) was found in both soils after compost application. The higher amount of compost immobilized an exchangeable portion of Cd (0.11 mol l^?1 CH₃COOH extractable) in contaminated Cambisol unlike in light Fluvisol. The addition of a low amount of compost decreased the content of Cd in associated above-ground oat biomass grown in both soils, while a high amount of compost decreased the Cd content in oats only in the Cambisol.     

Vertical Distribution of Atmospheric Pollution Lead in Swedish Boreal Forest Soils

In order to understand the fate of anthropogenic lead (Pb)pollution in boreal forest soils, and to predict future trends, it is important to know where in the soil the pollution Pb is accumulated and how large the pollution and natural Pb inventories are in different soil horizons. We combined stable Pb isotope (²⁰⁶Pb/²⁰⁷Pb ratios) and concentration analyses to study Pb in podzol profiles and mor samples from old-growth forest stands at seven sites distributed from southern to northern Sweden. Additional samples were taken from managed forests, and from an agricultural field, to give some idea of the effects of land-use. Pb concentrations are typically 60–100 g g^-1 dry mass in the mor layer in southern Sweden and about 30 g g^-1 in northern Sweden. Pb isotope analyses show that virtually all of this Pb is pollution Pb. The isotope composition also shows that pollution Pb has penetrated downwards between 20–60 cm in the forest soils. The total pollution Pb inventories vary between 0.7–3.0 g m^-2 ground surface, with larger inventories in southern compared to northern Sweden. Although the highest Pb concentrations occur in the mor layer, the largest inventories of pollution Pb are found in the Bs-horizon. The limited investigation of Pb distribution and inventories in soils from managed forests did not point to any major difference compared to the old-growth forests. The agricultural field revealed, however, a completely deviating Pb profile with all pollution Pb evenly distributed in the 20 cm thick top-soil.     

Long Term NH3 Flux Measurements above Grasslands in The Netherlands

Ammonia concentration gradients were measuredabove a grassland in an agricultural region fromJuly 1998 to July 2000 at the locationSchagerbrug in the Netherlands. They were used tocalculate the surface-atmosphere exchange ofammonia by means of the aerodynamic gradienttechnique. Measurements of the ammonia exchangewere also performed at a grass field that is partof a major wetland reserve in the centre of theNetherlands (Oostvaardersplassen), during theperiod June 1994–September 1995. At Schagerbrug,low net emissions or small depositions weremeasured during the winter months, and a netemission up to 5 kg NH₃ ha^-1 month^-1 in summer. The net annual emission was 26 kgN ha^-1, with manure application contributingabout 50% of this emission. AtOostvaardersplassen mainly deposition occurred,but large emissions were measured in autumn. Themeasured exchange fluxes are compared to modelevaluations that incorporate plant physiologicaldata, such as apoplastic NH₄ ⁺concentrations and pH. Results show a goodagreement between field observations and modelsimulations, although some improvements arenecessary during nighttime periods. Themeasurements are conducted within the GRAMINAEproject, a second tranche project of EC TERI.     

Forest Ecosystem Responses to Atmospheric Pollution: Linking Comparative With Experimental Studies

The impact on an ecosystem of an environmental stress, such as climate change or air pollution, can be studied through experimentation, through comparisons of sites across a gradient of the stress, through long-term studies at a single site, or through theoretical or modelling approaches. Although the former three techniques often are used to develop and test models, it is much rarer to explicitly link experimental, comparative or long-term studies together. Here we present a concept for combining experimental and comparative research to assess the direction and rate of change, the expected long-term state, and the rate at which the long-term state is achieved after an ecosystem is exposed to an environmental stress. We do this by comparing the response of a forest in Denmark to experimentally increased N deposition with the expected long-term response based on a European database of forests exposed to different levels of N deposition over long time periods. The analysis suggests that if N deposition were to increase by 3-fold to about 50 kg N ha^-1 a^-1 at the Danish site, and remain at this level, the N concentration in needles would respond within 2–4 yr after the onset of the enhanced N deposition, and would rapidly plateau to an expected mean value of 18.0 mg N g^-1 dry mass (95% confidence interval ± 2.5 mg g^-1). The N concentration of new litter also would respond rapidly (1–2 yr) to reach an expected value of 16.6 mg N kg^-1 dry mass (± 3). The N concentration of the organic layer in the soil would increase much more slowly, but a significant increase would be expected within 5–10 yr. Mineral soil pH would take more than 7 yr to change. Finally, the flux of dissolved inorganic N in leachate wouldbegin to increase immediately, but would take many years to reach the expected level of 22.4 kg N ha^-1 a^-1(± 4).     

Characterization of oily sludge from a wastewater treatment plant flocculation-flotation unit in a petroleum refinery and its treatment implications

Partly due to the complex and variable composition of oily sludge generated by the petroleum industry, cost-effective treatment and proper disposal pose considerable challenges worldwide. In this study, an extended component-based analysis of the oily sludge from a flocculation-flotation unit of a wastewater treatment system in a refinery in Sweden was carried out over 1 year. The heterogeneity of the oily sludge is illustrated by the wide ranges of concentrations found for different chemical components, particularly metals. Among the petroleum hydrocarbons, the most abundant compounds were nonpolar aliphatic hydrocarbons (63.7 ± 16.7 g kg⁻¹); from the benzene, toluene, ethylbenzene, and xylene group, xylenes (91–240 mg kg⁻¹) were most abundant; and among polycyclic aromatic hydrocarbons, naphthalene (25.7 ± 21.4), fluorene (27.25 ± 10.0), and phenanthrene (43.8 ± 18.4 mg kg⁻¹) were most abundant (all results in terms of dry matter). Based on the EU guidelines and the mean concentration values for metals found in the oily sludge, e.g., Pb (135.4 ± 125.8), Cu (105.2 ± 79.1), Hg (42.8 ± 31.3), Ni (320 ± 267.4), and Zn (1321.7 ± 529.9 mg kg⁻¹), disposal of oily sludge even in landfills for hazardous waste is not allowed. The organic content of the sludge can be reduced through biotreatment, but not the metal content. A multistep component-based treatment scheme is therefore needed.     

Accumulation of pollutant nitrogen in calcareous and acidic grasslands: Evidence from N flux and 15N tracer studies

Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0, +35 and +140 kg N ha^?1 year^?1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets—calculated from the N flux data—showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutant N in the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing ¹⁵N labelled ammonium nitrate (+35 kg N ha^?1 year^?1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of ¹⁵N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study.     

Sediment–Water Interactions in an Eroded and Heavy Metal Contaminated Peatland Catchment,Southern Pennines,UK

Atmospherically deposited lead in the upper layer of the heavily eroded peatlands of the Peak District, southern Pennines, UK, reaches concentrations in excess of 1,000 mg kg⁻¹. Erosion of the upper peat layer in this region is releasing lead, associated with eroded peat particles, into the fluvial system. Understanding the process mechanisms that control dissolved lead concentrations in contaminated peatland streams is vital for understanding lead cycling and transport in peatland streams. Many headwater streams of the southern Pennines recharge drinking water reservoirs. Measurements in the Upper North Grain (UNG) study catchment show that mean sediment-associated and dissolved lead concentrations are 102 ± 39.4 mg kg⁻¹ and 5.73 ± 2.16 μg l⁻¹, respectively. Experimental evidence demonstrates that lead can desorb from suspended sediments, composed of contaminated peat, into stream waters. In-stream processing could therefore account for the elevated dissolved lead concentrations in the fluvial system of UNG.     

Impact of Land Use on Soluble Organic Nitrogen in Soil

Although it has been hypothesized that soluble organic nitrogen (SON) plays a central role in regulating productivity in some terrestrial ecosystems, the factors controlling the size of the SON pool in soil remain poorly understood. Therefore our principal aim in this work was to assess the impact of seven different land use systems (rough and managed grassland, deciduous and coniferous woodland, heathland, wetland and tilled land) on the size of the SON and inorganic N (NO ₃ ^– , NH ₄ ⁺ ) pools in the surface soil layer (0–15 cm). After extraction with deionised water, we found that in most cases the size of the water extractable organic N (WEON) pool was similar in size to the inorganic N pool. In contrast, the KCl extractable organic N (KClEON) pool constituted the dominant form of soluble N in soils under all land uses, perhaps indicating that significant amounts were held on the soil exchange phase. In contrast to inorganic N, which varied significantly with land use, the size of the KClEON and WEON pool was similar for all land uses with the exception of KClEON in tilled land, where significantly lower amounts were observed. We conclude that SON constitutes an important soil N pool in a broad range of land uses, and that its role in microbial N assimilation, plant nutrition and ecosystem responses to atmospheric N deposition warrants further attention. SAFRD, University of Newcastle, Newcastle-upon-Tyne, NE1 7RU, U.K.     

Accumulation of pollutant nitrogen in calcareous and acidic grasslands: Evidence from N flux and 15N tracer studies

Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0, +35 and +140 kg N ha^–1 year^–1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets—calculated from the N flux data—showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutant N in the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing ¹⁵N labelled ammonium nitrate (+35 kg N ha^–1 year^–1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of ¹⁵N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study.