Soil Respiration in Relation to Small-Scale Patterns of Lead and Mercury in Mor Layers of Southern Swedish Forest Sites

Pollution-related lead (Pb) andmercury (Hg) in mor layers of Southern Swedenmight have effects on soil biology, although inthe literature effect concentrations have beenidentified at much higher levels. Considerablesmall-scale spatial variability in heavy metalcontents and microbial respiration in mor layersof forest sites was used to calculatecorrelations that could reveal toxic effects.Negative correlations were always strongest atsites with high loads of Pb or Hg, which was considered to indicate metal toxicity. The highload sites were found in Southwestern Sweden,locally at a motorway and at a chlorine-alkalifactory. Other factors of possible influence,such as other pollutants, age of organic materialor climatic differences, would affect high andlow load sites alike. Negative correlations withrespiration were found for Pb at sites with 74 g g^-1 of mean Pb content in O_f-layer and for Hg at 0.25 g g^-1.     

Changing of Lead and Cadmium Pools of Swedish Forest Soils

The aims of the paper are to; i)evaluate the rate and direction of present changesin lead (Pb) and cadmium (Cd) soil pools of Swedishforests; ii) discuss processes of importance forleaching of Pb and Cd in Swedish forest soils. Thepresently ongoing changes of Pb and Cd pools ofSwedish forest soils are evaluated by compilationof data from the literature and unpublishedsources. It is concluded that Cd pools arepresently decreasing in larger areas of Sweden. Therate of decrease is mainly determined by soilacidity status; Cd leaching is regulated by ionexchange with Ca²⁺, Mg²⁺, Al³⁺ andH⁺, and is higher in acid soils. The Pb poolsare presently increasing with 0.1 to 0.3 percentannually in the soil down to 0.5 meter. Pb isredistributed from the O horizon to the B horizon,most pronounced in spruce forests; the Pb pools ofthe O horizon are presently not increasing, but isslightly decreasing by 0.1 to 0.2 percent annually. The leaching of Pb in the soil is controlled byfactors regulating the solubility of organicmatter.     

Microbial Activity in Relation to Small Scale Patterns of Heavy Metals and Substrate Quality in Spruce Mor Layers (Of) in Southern Sweden

The within-site correlations between soil respiration rates,lead (Pb), mercury (Hg) and cadmium (Cd) concentrations andorganic matter quality variables were investigated at four sites in southern Sweden. The aim was to study whether the within-site variation in heavy metal concentrations could beused to monitor biological effects of regional deposition of heavy metals. Two sites in the south-west, one in the mid-southof the country, and one in south-east were investigated. At the south-eastern, least contaminated, site there were no correlations between soil respiration rate, and either organicmatter quality variables or heavy metal concentrations. At the remaining sites, negative correlations were found between Pb andsoil respiration rate. However, at two of these three sites there was a covariation with cellulose that could account for these correlations. The within-site variation of pH and total nitrogen (N) was low, and did not show any correlative general trends with either respiration rate or heavy metals. Meta analysis showed that negative correlations between Pb or Hg, on the one hand, and cellulose or hemicellulose on the other weregenerally found in within-site investigations. However, this does not necessarily explain the correlation between Pb and soil respiration, as was shown for the southernmost site. A PLS model of soil respiration rates at this site, using allmeasured variables, including heavy metals, explained more variation than a model developed using only mor layer thickness,pH, carbohydrate, ash and nitrogen concentrations, as independent variables. Thus there is a risk of toxic effects from Pb even at the levels found in south-western Sweden today(>120 g Pb * g dw^-1). However, since the correlationsbetween heavy metals and cellulose were not significantly different at the different sites, random sampling variation could not be ruled out as an explanation of the different results for the different sites. The causes of the correlationbetween organic matter quality and heavy metals have not yet been clarified. Analysis of mor samples incubated in thelaboratory for 2 yr with 1200 g Pb * g dw^-1 or 5 gHg * g dw^-1 did not show any differences in carbohydrate composition, compared to control samples. This shows that within-site studies of correlations between respiration rate and heavy metals have to be combined with studies of metal additions to soils and analysis of organic matter quality beforeany valid conclusions can be made.     

Using Fallout Lead-210 Measurements to Estimate Soil Erosion in Three Small Catchments in Southern Italy

Soil erosion and associated off-site environmental impacts have attracted increasing attention in recent decades, and there is a growing need for reliable information on rates of soil loss. The potential for using ¹³⁷Cs fallout to quantify rates and patterns of soil redistribution over medium-term timescales (ca. 45 years) has been successfully demonstrated in a wide range of environments around the world. The similar behaviour of fallout ²¹⁰Pb in soils offers potential for its use as an alternative to ¹³⁷Cs, in areas where ¹³⁷Cs inventories are low or are complicated by additional fallout from the Chernobyl accident. There have, however, to date been few attempts to validate the use of fallout ²¹⁰Pb measurements for assessing erosion rates. This paper reports an attempt to explore the use of fallout ²¹⁰Pb to estimate rates of water-induced soil erosion on uncultivated land. It focuses on three small forest/rangeland catchments located in Calabria, southern Italy, for which measurements of sediment output are available. Comparison of the estimates of net soil loss from the catchments derived from ²¹⁰Pb measurements with the measured sediment output, confirmed the validity of the ²¹⁰Pb approach. The soil redistribution rates estimated using ²¹⁰Pb measurements were also consistent with equivalent estimates obtained for the same study catchments using ¹³⁷Cs measurements.     

Effects of Acidification and its Mitigation with Lime and Wood Ash on Forest Soil Processes in Southern Sweden. A Joint Multidisciplinary Study

A joint multidisciplinary investigation was undertaken to studythe effects of lime and wood ash applications on two Norway spruce forest Spodosolic soils. The two sites, typical for southern Sweden, were treated in 1994 with either 3.25 t ha^-1 dolomite or 4.28 t ha^-1 wood ash (Horröd site) or in 1984 with either 3.45 or 8.75 t ha^-1 dolomite (Hasslöv site). Both sites show signs of acidification by atmospheric anthropogenic deposition and possessed low soil pH(4.3) and high concentrations of inorganic Al (35 M) in theupper illuvial soil solution. The prevailing soil conditions indicated perturbed soil processes. Following treatment with lime or wood ash, the soil conditions were dramatically altered. Cation exchange capacity (CEC) and base saturation (BS) was considerable increased after addition. Four years after application most of the added Ca and Mg was still present in the mor layer. Fifteen years after application,Mg in particular, became integrated deeper in the soil profile with a greater proportion lost by leaching incomparison to Ca. The concentrations of these ions were greatestin the mor layer soil solutions and Mg had higher mobility givinghigher concentrations also deeper in the profile. Four years after treatment, the application of wood ash and limeresulted in lower pH values and higher inorganic Al in mineral subsoil solutions compared to the untreated soil. We hypothesize that this was probably due to an increased flow of hydrogen ionsfrom the upper soil as a result of displacement by Ca and Mg ionsin the enlarged exchangeable pool. In contrast, fifteen years after lime and wood ash application, the mineral subsoil horizonspossessed a higher pH and lower soil solution Al content than theuntreated plots.Liming promoted soil microbial activity increasing soil respiration 10 to 36%. This is in the same range as net carbon exchange for forests in northern Sweden and could potentially have a climatological impact. The turnover of low molecularweight organic acids (LMWOA) by the soil microbial biomass werecalculated to contribute 6 to 20% to this CO₂ evolution.At Horröd, citrate and fumarate were the predominant LMWOAs with lowest concentrations found in the treated areas. In contrast, at the Hasslöv site, propionate and malonate were the most abundant LMWOAs. Higher microbial activity in the upper soil horizons was also theprobable cause of the considerably higher DOC concentrations observed in the soil solution of ash and lime treated areas. Thelime-induced increase in DOC levels at Hasslöv could be attributed to increases in the 3–10 kDa hydrophobic size fraction. Liming also promoted nitrification with high liming doses leading to extreme concentrations of NO₃ ^- (1 mM) in soil solution.At Hasslöv the community of mycorrhizal fungi was dramatically changed by the addition of lime, with only four of 24 species recorded being common to both control and treated areas.Many of the observed effects of lime and ash treatment can be viewed as negative in terms of forest sustainability. After fouryears of treatment, there was a decrease in the pH of the soil solution and higher concentrations of inorganic Al and DOC. Increased organic matter turnover, nitrification and NO₃ ^-leakage were found at Hasslöv. Considering that the weathering rate and the mineral nutrient uptake by trees is mostprobably governed by mycorrhizal hyphae etchingmineral grains in the soil, it is important to maintain this ability of the mycorrhizal fungi. The lime and ash-induced changed mycorrhizal community structure may significantly affect this capability. In light of this investigation and others, as reviewed by Lundström et al. (2003), the implications ofliming on forest health are multifaceted with complex relationships occurring over both space and time.     

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.     

Regional Variability of Cd,Hg, Pb and C Concentrations in Different Horizons of Swedish Forest Soils

Contents of cadmium (Cd), mercury (Hg), lead (Pb) and carbon(C) in the O, B and C horizons of podzolized forest soils inSweden were surveyed. Concentrations and storage of Cd, Hg andPb in the O and B horizons were high in southern Sweden and gradually decreased towards the north, though with considerablelocal variability. This pattern reflects the influence of anthropogenic emissions of these metals, as well as the effectsof soil-forming processes. Parent till material, as representedby the C horizon concentration of the respective metal, accountedfor little of the variation in metal concentration in the O horizon. For Cd and Pb, the correlations were not significant orslightly negative (R² = 0.12 and 0.09 respectively) depending on region, while for Hg the correlation was not significant or slightly positive (R² = 0.03 and 0.08). Furthermore, parent till material accounted for more of the variation in metal concentrations in the B horizons in the northern part of Sweden than in the middle and southernmost parts, where the concentration of total carbon had more influence. The correlation between the metal concentrationsin the B and C horizon was strongest for Pb (R² = 0.63 and 0.36 in the two northernmost regions), lower for Cd (R² = 0.19 and 0.16) and not significant for Hg. For allsoil horizons, total C concentration accounted for much of thevariation in Hg concentration in particular (O-horizon R² = 0.15–0.69, B horizon R² = 0.36–0.50, C horizon R² = 0.23–0.50 and ns in one region). Ratios of metal concentrations between the B and C horizons were highest for Hg(maximum value of 30), indicating a relatively larger addition or retention of Hg compared to Cd and Pb (maximum value of 10)in the B horizon. This study indicate that factors other than parent material account for the large scale variation in O horizon concentrationsof metals but patterns correspond well with those of atmosphericdeposition of heavy metals and acidifying substances. Furthermore, the study highlights the importance of soil organicmatter and the intensity of pedogenic processes for the content and distribution of metals throughout the soil horizons.     

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.     

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.     

Measuring Aerosol and Heavy Metal Deposition on Urban Woodland and Grass Using Inventories of 210Pb and Metal Concentrations in Soil

The deposition of aerosols to trees has proved very difficult to quantify, especially in complex landscapes. However, trees are widely quoted to be efficient scavengers of particles from the atmosphere, and a growing proportion of the pollutant burden in the atmosphere is present in the aerosol phase. In this study, the deposition of aerosols onto woodland and grass was quantified at a range of locations throughout the West Midlands of England. The sites included mature deciduous woodland in Edgbaston, and Moseley, and mixed woodland at sites within Sutton Park, a large area of semi-natural vegetation. Aerosol deposition to areas of grassland close to the woodland at each site was also measured. Detailed inventories of ²¹⁰Pb in soils within the woodland and in grassland soils, together with concentrations in the atmosphere and precipitation, provided the necessary data to calculate the long-term (about 40 years) annual deposition of sub-micron aerosols onto grassland and woodland. The soil inventories of ²¹⁰Pb under woodland exceeded those under grass, by between 22% and 60%, with dry deposition contributing 24% of the total input flux for grass and 47% for woodland. The aerosol dry deposition velocity to grassland averaged 3.3 mm s^-1 and 9 mm s^-1 for woodland. The large deposition rates of aerosols onto woodland relative to grass or other short vegetation (× 3), and accumulation of heavy metals within the surface horizons of organic soils, leads to large concentrations in soils of urban woodland. Concentrations in the top 10 cm of these woodland soils averaged 252 mg kg^-1 for Pb with peaks to 400 mg kg^-1. Concentrations of Cd averaged 1.4 mg kg^-1, Cu, 126 mg kg^-1, Ni 23 mg kg^-1 and Zn 173 mg kg^-1. The accumulated Pb in urban woodland soils is shown to be large relative to UK emissions.     

Effects of Lime and Ash Treatments on DOC Fractions and Low Molecular Weight Organic Acids in Soil Solutions of Acidified Podzolic Soils

Dissolved organic carbon (DOC) fractions and different low molecular weight organic acids (LMWOAs) were determined in soil solutions from two lime or ash treated Norway spruce sites in the south of Sweden. At Hasslöv, 3.45 t ha^-1 or 8.75 t ha^-1 dolomite were applied 15 years before sampling. Horröd was treated with 4.28 t ha^-1 ash and 3.25 t ha^-1 dolomite and sampled four years later. Propionate (7–268 M) and malonate (2–34 M) were the LMWOAsfound in the highest concentrations at Hasslöv. Two other LMWOAs dominated at Horröd, namely citrate (18–64 M)and fumarate (5–31 M). The differences in concentration of most of the determined LMWOAs at Hasslöv were significantly increased due to treatment. The LMWOAs comprised between 1.1–6.3% of the DOC at Hasslöv and 4.5–17.6% at Horröd. At Hasslöv normally 3–10% of the total acidity (TA) was due to LMWOAs and the average specific buffer capacity was 74 ± 22 mmol mol^-1C.The total DOC concentration in the mor layer solution was 16 mM for the dolomite treated plots compared to 10 mM at the untreated plot. A major part of the increase in DOC at the treated plots apparently had a hydrophobic character and was of high molecular weight corresponding to 3–10 kDa. The concentration of DOC < 1 kDa in the control and treated plots was similar.     

Stem Growth of Picea Abies in South Western Sweden in the 10 Years Following Liming and Addition of PK and N

Liming and/or application of specific nutrients have been proposed as countermeasures to the acidification of forest soils in southern Sweden. In this study the stem growth of Picea abies (L.) Karst. growing on acidic mineral soils in SW Sweden was investigated 10 years after additions of lime (Ca; 3000 kg lime ha⁻¹), lime plus P (25 kg ha⁻¹) and K (80 kg ha⁻¹), or N in low doses (2 × 10 kg ha⁻¹ yr⁻¹) (treatments: CaPK, Ca, N, CaPKN, and 2Ca2P2K, respectively). Compared with the control, stem growth was increased following all treatments involving lime additions, including liming alone. The PK addition did not seem to affect growth. The most plausible cause of the observed growth increases was that the lime additions indirectly increased the supply of plant-available N. The annual low-dose N addition did not significantly affect growth. This suggests that air-borne deposition of N, which supplies very small doses of N throughout the year, has a minor or even negligible influence on P. abies growth.     

Changes in Atmospheric Deposition Rates of Heavy Metals in Sweden A Summary of Nationwide Swedish Surveys in 1968/70 – 1995

The Swedish nationwide surveys of atmospheric heavy metal deposition in 1968/70 – 1995 using bryophytes (carpet-forming mosses) as monitors are reviewed. Considered are cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), mercury (Hg), nickel (Ni), vanadium (V), and zinc (Zn). The close agreement between data obtained with deposition (precipitation) collectors and moss carpet analysis is documented briefly, as well as measures of quality control and assessment of reproducibility. Since 1968/70, the deposition rate of the heavy metals considered has declined gradually and evenly, particularly in the southern parts of the country, reflecting an improvement of general air quality due to decreasing dust emission from mainly industry and fossil fuel combustion in northern and western Europe. By far the greatest absolute decrease in deposition rate was measured in Fe, which is a main constituent of most man-generated dust particles. However, the greatest per cent decreases in deposition rates were measured for Pb. The Pb concentration of moss carpets in Sweden as a whole in 1995 was only 11% of the value in 1968/70. Corresponding figures for Fe was 20%, Cd 24%, Ni 28%, Hg 31%, V 43%, Zn 51%, and Cu 52%. For Zn the current deposition rate seems to approach a natural baseline, whereas deposition of the other seven elements are still decreasing according to the surveys of 1990 and 1995.     

High Immobilization of NH4+ in Danish Heath Soil Related to Succession,Soil and Nutrients: Implications for Critical Loads of N

During recent decades heathlands havechanged into grasslands in regions with high atmosphericnitrogen deposition. In regions with intermediatedeposition level (e.g., Denmark) changes have been lesspronounced which may be due to delay or decrease inresponse of the ecosystem. The mor layer (O horizon) mayplay an important role for this delay due to high sinkstrength for N. In this study, the capacity for netNH₄ ⁺ immobilization and mineralization wasstudied during short- and long-term incubations (2–36 days)of mor samples from Danish dry inland heaths. High short-term capacity for net NH₄ ⁺ immobilization wasfound to be a general characteristic of Danish heath morlayers both under heather (Calluna vulgaris) andcrowberry (Empetrum nigrum ssp nigrum), the latterdominating late stages in heathland succession. The netNH₄ ⁺ immobilization was higher under youngcompared to old or dead vegetation, and higher on lessnutrient poor soils than on extremely nutrient poor soils.The addition of N, P and C stimulated CO₂ productionand net NH₄ ⁺ immobilization, but not net Nmineralization. The immobilization of ¹⁵NH₄ ⁺caused release of dissolved organic N, increased N anddecreased C/N ratio in the microbial biomass, and indicatedgrowth of microorganisms with other metabolic abilitiesthan the indigenous population. No evidence was obtained ofstabilization of immobilized ¹⁵NH₄ ⁺ intosoil organic matter during the experiment. On background ofthe results and current knowledge it was concluded that therecognition of the high capacity for net NH₄ ⁺immobilization in mor layers does not allow for a raiseof critical loads for N for northern dry inland heaths.     

Air Pollution Zones and Harmful Pollution Levels of Alkaline Dust for Plants

For characterisation of landscapes in north-eastern Estoniaaffected by alkaline oil shale fly ash and cement dust the zonation-method based on average annual (C _y) and short-termconcentrations of pollutants in the air was used, as well as on deposition loads of dust and Ca²⁺. In the overground layer of atmosphere the zones with different air pollution loads were distinguished. A comparative analysis of pollution zones characteristics and biomonitoring data revealed that for sensitive lichen the dangerous level of alkaline dust in the air, introducingthe degradation of Sphagnum sp. at the level of C _y of dust 10–20 g m^-3 and at 0.5–1 hr maximums 100–150 g m^-3. For Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) this limited concentration (decline of growth parameters) of cement dust is correspondingly following: 30–50 g m^-3 and 150–500 g m^-3, in case of fly ash the limit level of C _y amounting 100 g m^-3. Daily deposition load of Ca²⁺ should not exceed approximately 4.5–15 mg m^-2 for lichen; for conifers the harmful pollution load is higher – >22 mg m^-2.     

A Retrospective Isotopic Study of Spruce Decline in the Vosges Mountains (France)

The objective of this study was to assess the time variation of mineral and water stress levels across the life of a declining, Mg-deficient, spruce stand, in order to clarify the factors that caused the decline. Since 1985, strong soil acidification linked to a large leaching of nitrate and base cations was measured at the study site. In 1994, 5 trees were felled and tree rings were measured and analysed for Ca, Mg, K, Sr, ¹³C¹²C and ⁸⁷Sr/⁸⁶Sr isotopic ratios. Strontium pools and fluxes as well as root Sr isotope ratio in relation to depth were also measured. Wood chemical concentrations and isotope ratios were strongly related to the dominance status of each tree. On average during the study period, the ⁸⁷Sr/⁸⁶Sr ratio of spruce wood decreased. Using a mechanistic model computing long term variations of ⁸⁷Sr/⁸⁶Sr ratio in trees and soils, we reproduced the observed trend by simulating soil acidification – increasing Sr drainage from the whole profile, and particularly from the organic horizon –, and root uptake becoming more superficial with time. Between 1952 and 1976, tree ring ¹³C decreased strongly and continuously, which, in addition to other factors, might be related to an increase in water stress. Thus, a decrease in rooting depth, possibly related to soil acidification, appeared as a possible cause for the long term increase in water stress. The extreme drought event of 1976 appears to have revealed and triggered the decline.     

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.     

Air Pollution Effects on Forest Trees in Balikesir,Turkey

Air pollution has become an actual problem in Balikesir because of rapid urbanisation and increasing of the polluting sources. Air pollutionproblems occur under the unfavorable meteorological conditions which increase in frequency of occurrence in winter due to use of low quality lignite coals for heating. The `Protection of Air Quality' in Turkey dated 1986 is based on the human health criteria. But the critical limit values are lethal for the forest trees as far as SO₂ is concerned. The field observations showed that leaves of the trees have yellow spots indicating acid burns in Balikesir. This study aims at determining the relationships between the SO₂ concentrationsin the air under selected climatic conditions, and the effects of air pollution on forest trees in Balikesir. Samples of leaves were collected from the City Parks in Balikesir, Deirmenboaz forested area located 10 km far fromBalikesiron the Balikesir-Bursa highway, and from the forestation areas near the Balikesir-Edremit highway. Sulfur contents of the leaves were very high especially in the city (2650–5300 g m^-3).Samples from other areas had values lower than this range but above the usual values (850–3612 g m^-3). The diameter increments of the trees were found to be lower and these results clearly showed the adverse impacts. Negative correlations were found between these sulfur concentrations and the daily mean temperatures and wind speeds. Positive correlation was seen between these concentrations and pressures, humidities. Emission sources must be controlled in order to safeguard the forests which protects the soil, facilitate water production, assimilate carbon dioxide in air and produce oxygen. It must be considered that the problems are not only regional but have a global identity.     

The Application of Stable Isotopes for Assessing the Hydrological, Sulfur, and Iron Balances of Acidic Mining Lake ML 111 (Lusatia, Germany) as a Basis for Biotechnological Remediation

Stable isotope (¹⁸O–H₂O, ²H–H₂O ³⁴S–SO₄ ^2-) andhydrochemical data (SO₄ ^2-, Fe-concentrations) have beenused to estimate the annual groundwater inflow and outflow of mining lake ML 111 and to calculate the total amount of dissolvedsulfate and iron that is carried into the lake by groundwater. The hydrological balance suggests an annual groundwater inflow of 23 700 m³ and an annual groundwater outflow of 15 700 m³. The calculation of the sulfur and iron balances yielded an annual sulfate input of 37 800 kg and an annual iron input of 7000 kg with the groundwater inflow. Furthermore it was shown that significant fluxes of these elements go into the lake sediments which results in continuous release of acidity in the lake water.     

Lowest Effect Levels of Lead and Mercury on Decomposition of Mor Layer Samples in a Long-Term Experiment

Indications of possible negative effects of lead (Pb) and mercury(Hg) on microbial respiration in Southern Swedish forest humus layers led to experiments on dose-response relationships by additions of metal salts in the laboratory. Respiration rates andweight loss due to decomposition of organic material were measured. For relevance to field situations metal doses were low,the time span was long, 550 days including freeze storage, and microbial activity was kept up by plant litter additions. We looked for effects of Pb and Hg at levels moderately elevated above the Southern Swedish reference, as well as combined effectsof Pb + Hg. A reduction in respiration and decomposition of10% was found at about 225–245 g g^-1 of total Pb, i.e. ata Pb level elevated 3.5 times. Although small effects of Hg werefound even at the lowest dose level, 10% inhibition of microbialactivity appeared temporarily at about 2–3 g g^-1 of total Hg, i. e. at 6–8 times the reference level. There were nolong-term additive effects of Pb and Hg on decomposition. Type of anion had a strong influence on the test, chlorides of Pbbeing more toxic than nitrates. Long-term monitoring and maintenance of microbial activity during the experiment were prerequisites for the occurrence of effects at low metal levels.