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The annual tree rings are used to reconstruct the history of the past climate and the impact of climatic and environmental changes on tree growth. Several conifer and broad leaf tree species (e,g. Abies densa, Larix griffithiana, Pinus merkusii, P. kesiya, P. wallichiana, Quercus serrata, Toona ciliata, and Tectona grandis) have been used for diverse dendrochrological studies in Northeast India (NEI). Tree rings act as bio-indicator of changes in soil chemistry due to anthropogenic activities in urban and peri-urban areas because of rapid population growth, agricultural intensification, and industrialization. Most of the earlier studies in NEI are available with respect to the climate-tree growth relationship, however, aspects like tree ring relations with pollution history have not been attempted so far. Considering this gap, the present study has been carried out to investigate the concentration of toxic elements in tree rings. Particularly in this study, we used Magnolia champaca (Champak) tree rings to reconstruct the temporal distribution of 7 elements (Zn, Pb, Fe, Cu, Ni, Ca, and Mn) at the Tuirial dumping site in Aizawl, Mizoram. A total of 20 trees were sampled by taking two cores from each, and the dated samples covered a period of two decades from 1999 to 2019. We used an Atomic Absorption Spectrometer (AAS) to quantify concentrations of toxic elements in the tree-rings over different years. The findings indicated a rising pattern of elements in conjunction with increasing tree age, for example, the largest concentration of harmful elements was located in recent year ring growths. The range of element accumulations was: 20.46 to 30.10 mg/kg for Fe, 16.19 to 28.24 mg/kg for Mn, 13.86 to 27.4 mg/kg for Zn, 9.02 to 17.08 mg/kg for Ni, 6.08 to 14.69 mg/kg for Cu, 7.33 to 14.35 mg/kg for Ca, and 6.92 to 14.26 mg/kg for Pb. The present study indicated that Pb, Fe, Ni, and Cu exceeded the acceptable thresholds set by the World Health Organization (WHO) for harmful components in the plant. Based on the findings, we recommend Magnolia champaca as a suitable species for plantation in degraded/polluted areas as an efficient biocontrol agent for the removal of toxic elements. [ABSTRACT FROM AUTHOR]

Metal mining and processing in the central Czech Republic has led to the contamination of surrounding soils and vegetation. In this study, Hg concentrations were measured in spruce ( Picea abies L.) and beech ( Fagus sylvatica L.) tree rings to monitor historical Hg deposition in the area. The highest Hg concentrations were found in spruce at an HgS smelting contaminated site (up to 15 ng g), probably reflecting smelting activities at the end of the nineteenth century. In the vicinity of a Pb smelter, Hg concentrations increased from the 1950s to maxima (up to 8.4 ng g) in the 1970s, corresponding with a peak of metallurgical production and smelter emissions in the mid 1970s. A decreasing trend in Hg concentrations since the 1980s was probably related to improvements in flue gas cleaning technologies. The beech trees, which grow at a site between two smelters and range in age from 150 to 220 years, seem to reflect deposition from both point sources. Mercury levels in beech trees were lower, that resulting from their greater distance from pollution sources, but the concentration trend was strongly correlated with metal production. Analysis of nutrient elements (Ca, Mg, K and Mn) in wood revealed environmental changes related to acid deposition, but a relation between concentration trends of nutrients and Hg was not found. This study shows that tree rings may be a good record of Hg deposition in areas affected by ore mining and smelting. Nevertheless, further investigation of Hg cycling in trees is necessary to satisfactorily interpret this particular historical Hg record. [ABSTRACT FROM AUTHOR]

Metal processing at a Cu-Cd refinery at Prescot in N.W. England has led to severe contamination of the surrounding soils and vegetation, although Cu and Cd in bulk deposition declined dramatically between 1975 and 1990. Despite high spatial and temporal variability in metal deposition, mean Cd concentrations in annual tree rings of sycamore (Acer pseudoplatanus L.), lime (Tilia europaea L.) and beech (Fagus sylvatica L.) at Prescot were correlated with annual bulk Cd deposition. In contrast, mean Cd concentrations in ash (Fraxinus excelsior L.) were unrelated to Cd deposition and there was no significant relationship between mean Cu concentrations in tree rings and Cu deposition in any species. Mean Pb concentrations in sycamore, lime and beech at Prescot and the reference site also decreased over time. At Prescot however, Cd concentrations in tree rings formed in the mid 1990s were up to 10-fold higher than the reference site despite Cd deposition values during this period that were typical of levels expected for urban areas in the UK. The high Cd concentrations in wood during this period indicate that the majority of Cd in tree rings at Prescot is derived from soil, limiting the usefulness of dendrochemistry for monitoring temporal changes in metal deposition. It appears that trees are not simply passive recorders of metal deposition and other possibilities, in addition to decreasing atmospheric deposition, may explain the patterns of Cd and Pb found in sycamore, lime and beech. More research on the physiology of metal cycling in trees is required before dendrochemical techniques can be applied with confidence in environmental monitoring programs. [ABSTRACT FROM AUTHOR]

A dendrochemical survey of sugar maple (Acer saccharum Marsh) was conducted in south-central Ontario, which encompassed twenty-two sites in areas that both exceeded or were below the published Critical Loads with respect to acid deposition. Areas that exceeded the Critical Load were located remote from point emission sources, but were also characterized by thin, nutrient-poor soils overlying the Precambrian Shield. The pHaq of surface soils (A-horizon) was lower at sites on the Precambrian Shield and water-extractable concentrations of Ca decreased exponentially with decreasing soil pH. Significant polynomial relationships between soil pH and soil Ca and sugar maple growth, assessed as cumulative tree-ring growth between 1949 and 1998, explained 40% and 37% of the variation in sugar maple growth respectively, with lowest growth associated with low soil pH and low soil Ca. Furthermore, there was a significant linear relationship between wood Ca concentrations (averaged between 1949 and 1998) and soil pH and concentrations of several trace elements in wood (Mn, Pb, Zn, Cd, Sr and Rb) were greater at low soil pH. Poor sugar maple growth was associated with low wood Ca concentrations and high wood Al levels, which together accounted for 43% of the variation in sugar maple growth in a multiple regression model. None of the other wood chemistry variables contributed significantly to the model. These data suggest that sugar maple grows poorly on acidic soils with low Ca and high Al levels. Although such acidic podzols occur naturally in some areas overlying the Precambrian Shield, if Ca losses due to acid deposition and/or harvesting exceed inputs through weathering and deposition (i.e. exceed Critical Load), sugar maple growth may be adversely affected and ultimately lead to increased incidence of sugar maple decline. [ABSTRACT FROM AUTHOR]

Lead is very toxic and if ingested can cause severe health problems to both animals and humans. To determine if lead accumulation in trees could provide a direct pathway to enter the food chain, oaks (Q. nigra or Q. velutina) growing near two lead smelting facilities in Alabama, U.S.A., were analyzed for lead in acorns, leaves and tree cores. A relatively pristine site was used as a control. Lead was not detected in acorns collected at any site, and was only found in tree cores from the sites near smelters. Significant increases in tree core lead from 1975–1995 were detected at the active smelter site. Results were different from the inactive smelter site; lead increased in tree cores until the smelter ceased operation, then decreased after closing. Soil lead decreased linearly with distance from both smelters. In addition, a significant positive relationship was observed between leaf and soil lead at the site with the active smelter, and may be the result of both translocation via tree roots, and foliar absorption of deposited lead ions into the leaf structure. [ABSTRACT FROM AUTHOR]

Our goal was to reconstruct soil recovery from Acid Rain based upon removal of stemflow at beech (Fagus sylvatica) stands of known historic and recent soil status. Fourteen beech stands in the Vienna Woods were selected in 1984 and again in 2012 to study changes in soil and foliar chemistry over time. A part of those stands had been strip cut, and to assess reversibility of soil acidification, we analyzed soils around beech stumps from different years of felling, representing the years when acidic stemflow ceased to affect the soil. Furthermore, it was hypothesized that changes of soil chemistry are reflected in the stemwood of beech. Half-decadal samples of tree cores were analyzed for Ca, Mg, K, Mn, Fe, and Al. Soil analyses indicated recovery in the top soil of the stemflow area but recovery was delayed in the between trees areas and deeper soil horizons. Differences in soil pH between proximal and distal area from beech stumps were still detectable after 30 years indicating that soils may not recover fully from acidification or do so at a rather slow rate. Stemwood contents indicated mobilization of base cations during the early 80s followed by a steady decrease thereafter. Backward reconstructions of soil pH and soil nutrients, building on regressions between recent stemwood and soil chemistry, could not be verified by measured soil data in 1984, but matched with declining cation foliar contents from 1984 to 2012. Dendrochemical reconstructions showed highest values in the 1980s, but measured soil exchangeable cation contents were clearly lower in 1984. Hence, we conclude that our reconstructions mimicked soil solution rather than soil exchanger chemistry. [ABSTRACT FROM AUTHOR]

The impact of simulated acid rain on soil leachate and xylem chemistry in a young Jack pine (Pinus banksiana Lamb.) stand in the boreal forest of northern Ontario was evaluated. Permanent plots (5 x 2 m) were established in 1981 which were sprayed twice monthly with simulated acid rain, adjusted to pH 5.6, 4.0, 3.5, 3.0 or 2.5 with a 2:1 molar ratio of sulphuric (H2SO4) to nitric acid (HNO3) in addition to ambient rainfall. Sprays were applied between Juneand September for 5 yr. Unsprayed plots were also monitored. The pH of soil leachate collected between 1981-1985 was reduced significantly by the acid sprays and concentrations of sulphate (SO42-), nitrate (NO3-), calcium (Ca), magnesium (Mg), aluminium (Al), manganese (Mn), and zinc (Zn) increased in the A, B and C horizons. The soil recovered rapidly from the spraytreatments, although residual effects were found in soil leachate samples collected during 1986-1987, particularly in the C horizon. Trees receiving spray acidified to pH 2.5 had higher concentrations of Ca, Mn, Cd and Rb in tree-rings formed between 1981-1985 compared to trees receiving spray acidified to pH 4.0 or to trees receiving ambientrainfall alone. Some of the changes in soil chemistry resulting fromthe application of acidic sprays are reflected in the chemistry of Jack pine tree rings and these chemical signals in tree rings may be used as indicators of soil acidification. [ABSTRACT FROM AUTHOR]