Biogeochemical controls on aluminum chemistry in the O horizon of a red spruce (Picea rubens Sarg.) stand in central Maine,USA

This study examined the biotic and abiotic processes controlling solution chemistry and cycling of aluminum (Al) in the organic horizons of a northern coniferous forest ecosystem. A mass balance budget indicated that aboveground inputs of Al to the O horizon averaged 0.9 kg ha^–1 1 yr^–1, with major inputs accounted for by litterfall (69%), followed by precipitation (21%), and net canopy throughfall plus stemflow (10%). Estimated leaching losses of Al from the O horizon averaged 2.1 kg Al ha^-1 yr1. We hypothesize that the difference between measured Al inputs and outputs can be accounted for by Al release from weathering of soil minerals admixed into the O horizon. Variations in O horizon solution Al chemistry were influenced by a number of factors, including pH, Al equilibria with different solid-phase organic exchange sites, and Al complexation with humic ligands in soil solution.     

Contribution of Lithologic and Anthropogenic Factors to Surface Soil Heavy Metals in Western Iran Using Multivariate Geostatistical Analyses

Heavy metals’ origin, accumulation, and distribution in soil have been the focus of much attention by many researchers. The objective of this study was to recognize the sources of heavy metals in surface soils in Hamadan Province in western Iran using multivariate geostatistical techniques. A total of 263 surface (0–10 cm) soil samples and 18 rock samples from major parent materials were collected. Cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) contents of the samples were determined. Selected soil physical and chemical characteristics were also measured. A multivariate geostatistical analysis was performed to identify the common source of heavy metals. The quantities of Co, Cr, and Ni were found to be associated with parent rocks, corresponding to the first factor termed the “lithologic component.” The second factor was mainly attributed to Cu, which also comprised the first and third factors, indicating a mixed source both from lithologic and anthropogenic inputs. Zn and Pb contents were related to the anthropogenic activities and comprised the third factor. A significant correlation was found between metals from the lithogenic sources and selected soil properties such as soil organic matter, clay, CEC, and carbonate, indicating an interaction among them. Generally, Zn and Pb showed a less significant correlation with soil properties.     

Fungal Toxicity of Mobilized Soil Aluminum and Manganese

Inhibition of Aspergillus flavus growth from spores was used as a simple bioassay for toxicity of Al and Mn mobilized by simulated acid precipitation. Al was identified as being toxic in soil leachates resulting from acid inputs of pH less than 2.7. Inhibition by Mn was not detectable. The addition of fluoride significantly reduced Al toxicity, suggesting that biotoxicity of Al is partially dependent on the anionic composition of the soil solution.     

Interannual variations of soil organic carbon fractions in unmanaged volcanic soils (Canary Islands,Spain)

The stability over time of the organic C stocked in soils under undisturbed ecosystems is poorly studied, despite being suitable for detecting changes related to climate fluctuations and global warming. Volcanic soils often show high organic C contents due to the stabilization of organic matter by short‐range ordered minerals or Al‐humus complexes. We investigated the dynamics of different organic C fractions in volcanic soils of protected natural ecosystems of the Canary Islands (Spain) to evaluate the stability of their C pools. The study was carried out in 10 plots, including both undisturbed and formerly disturbed ecosystems, over two annual periods. C inputs to (litterfall) and outputs from (respiration) the soil, root C stocks (0–30 cm), soil organic C (SOC) fractions belonging to C pools with different degrees of biogeochemical stability –total oxidisable C (TOC), microbial biomass C (MBC), water soluble C (WSC), hot‐water extractable C (HWC), humic C (HSC), – and total soil N (TN) (at 0–15 and 15–30 cm) were measured seasonally.A statistically significant interannual increase in CO₂ emissions and a decrease in the SOC, mainly at the expense of the most labile organic forms, were observed, while the root C stocks and litterfall inputs remained relatively constant over the study period. The observed changes may reflect an initial increase in SOC resulting from low soil respiration rates due to drought during the first year of study. The soils of nearly mature ecosystems were more apparently affected by C losses, while those undergoing the process of active natural regeneration exhibited disguised C loss because of the C sequestration trend that is characteristic of progressive ecological succession.     

Spatial Assessment of Heavy Metals in Surface Soil from Klang District (Malaysia): An Example from a Tropical Environment

Heavy metals (Al, Cd, Co, Cr, Cu, Fe, Pb, Zn) in surface soil of Klang district were determined and multivariate analysis was used to understand their potential sources. The total and bioavailability of concentrations were used in identifying the potential risks to the ecology and human health. The means for the total heavy metal concentrations were found to be in the order of Fe > Al > Zn > Pb > Cu > Cr > Co > Cd, while the means for the bioavailability concentrations were found to be in the order of Al > Fe > Zn > Cu > Co > Cd > Pb > Cr. Principal Component Analysis showed Principal Component 1 as being of natural origin whereas Principal Components 2, 3, and 4 were associated with mixed anthropogenic sources, such as traffic and industrial emissions, organic matter, and granulometric fractions. Potential ecological risk assessment indicated an overall low ecological risk. Spatial assessment of non-carcinogenic risks showed that the Hazard Index values were more than one in Johan Setia, due to biomass burning of peat swamps exploited for agricultural development. While for spatial assessment of carcinogenic risks, the Lifetime Cancer Risk values were in the limit (1 × 10^?5), indicating low cancer inducing risks. Nevertheless, with intense development pressure in the Klang district could overlap pollution inputs in the future.     

Concentration and Distribution of Six Trace Metals in Northern Kentucky Soils

Concentration and distribution of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) were determined in 26 soil profiles (n = 78) of northern Kentucky in response to environmental concerns about increasing anthropogenic inputs in a fast-paced urbanizing area. The selected sites represent alluvial, glacial till or residual soils that have not received any biosolid- or industrial-waste applications. Mean concentrations of Zn (53.8 mg kg^?1) and Ni (25.9 mg kg^?1) were the highest in the soil profile, whereas Cd (0.21 mg kg^?1) was present only in trace amounts. All metals were within the low to middle range of baseline concentrations reported for US soils, suggesting minimal anthropogenic inputs. The distribution of Cu, Cr, Ni, and Zn increased with soil depth, whereas Cd and Pb concentrations were unaffected throughout the soil profile. Alluvial soils had the highest overall metal accumulations, particularly in surface soil horizons, indicating potential metal enrichment through depositional processes. The presence of a fragipan horizon or depth to bedrock did not significantly affect metal retention. Single correlation and multiple regression analyses indicated OM and pH as the most influential soil parameters for metal retention, followed by cation exchange capacity (CEC) and CEC/clay. Single correlations among metals suggested strong covariance of Zn with most metals throughout the soil profile, but weaker for Pb and Ni.     

Algal Exudates and Stream Organic Matter Influence the Structure and Function of Denitrifying Bacterial Communities

Within aquatic ecosystems, periphytic biofilms can be hot spots of denitrification, and previous work has suggested that algal taxa within periphyton can influence the species composition and activity of resident denitrifying bacteria. This study tested the hypothesis that algal species composition within biofilms influences the structure and function of associated denitrifying bacterial communities through the composition of organic exudates. A mixed population of bacteria was incubated with organic carbon isolated from one of seven algal species or from one of two streams that differed in anthropogenic inputs. Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) revealed differences in the organic composition of algal exudates and stream waters, which, in turn, selected for distinct bacterial communities. Organic carbon source had a significant effect on potential denitrification rates (DNP) of the communities, with organics isolated from a stream with high anthropogenic inputs resulting in a bacterial community with the highest DNP. There was no correlation between DNP and numbers of denitrifiers (based on nirS copy numbers), but there was a strong relationship between the species composition of denitrifier communities (as indicated by tag pyrosequencing of nosZ genes) and DNP. Specifically, the relative abundance of Pseudomonas stutzeri-like nosZ sequences across treatments correlated significantly with DNP, and bacterial communities incubated with organic carbon from the stream with high anthropogenic inputs had the highest relative abundance of P. stutzeri-like nosZ sequences. These results demonstrate a significant relationship between bacterial community composition and function and provide evidence of the potential impacts of anthropogenic inputs on the structure and function of stream microbial communities.     

Variation in soil aluminium tolerance genes is associated with local adaptation to soils at the Park Grass Experiment

Studies of the wild grass Anthoxanthum odoratum at the long‐term Park Grass Experiment (PGE, Harpenden, UK) document a well‐known example of rapid plant evolution in response to environmental change. Repeated fertilizer applications have acidified the soil in some experimental plots over the past 150+ years, and Anthoxanthum subpopulations have quickly become locally adapted. Early reciprocal transplants showed subpopulation differentiation specifically in response to soil aluminium (Al) toxicity across the experiment, even at small (30 m) spatial scales. Almost 40 years after its original measurement, we reassessed the degree of local adaptation to soil Al at the PGE using updated phenotyping methods and identified genes with variation linked to the tolerance trait. Root growth assays show that plants are locally adapted to soil Al at both the seedling and adult growth stages, but to a smaller extent than previously inferred. Among a large suite of candidate loci that were previously shown to have Al‐sensitive expression differences between sensitive and tolerant plants, three loci contained SNPs that are associated with both Al tolerance and soil acidity: an Al‐sensitive malate transporter (ALMT), a tonoplast intrinsic protein (TIP) and the putative homolog of the rice cell‐wall modification gene STAR1. Natural genetic variation at these loci is likely to have contributed to the recent rapid evolution at PGE. Continued study of Al tolerance variants in Anthoxanthum will allow us to test hypotheses about the nature and source of genetic variation that enables some species to adapt to soil acidification and other types of rapid environmental change.     

Lignin biomarkers as tracers of mercury sources in lakes water column

This study presents the role of specific terrigenous organic compounds as important vectors of mercury (Hg) transported from watersheds to lakes of the Canadian boreal forest. In order to differentiate the autochthonous from the allochthonous organic matter (OM), lignin derived biomarker signatures [Lambda, S/V, C/V, P/(V + S), 3,5-Bd/V and (Ad/Al)v] were used. Since lignin is exclusively produced by terrigenous plants, this approach can give a non equivocal picture of the watershed inputs to the lakes. Moreover, it allows a characterization of the source of OM and its state of degradation. The water column of six lakes from the Canadian Shield was sampled monthly between June and September 2005. Lake total dissolved Hg concentrations and Lambda were positively correlated, meaning that Hg and ligneous inputs are linked (dissolved OM r ² = 0.62, p < 0.0001; particulate OM r ² = 0.76, p < 0.0001). Ratios of P/(V + S) and 3,5-Bd/V from both dissolved OM and particulate OM of the water column suggest an inverse relationship between the progressive state of pedogenesis and maturation of the OM in soil before entering the lake, and the Hg concentrations in the water column. No relation was found between Hg levels in the lakes and the watershed flora composition—angiosperm versus gymnosperm or woody versus non-woody compounds. This study has significant implications for watershed management of ecosystems since limiting fresh terrestrial OM inputs should reduce Hg inputs to the aquatic systems. This is particularly the case for large-scale land-use impacts, such as deforestation, agriculture and urbanization, associated to large quantities of soil OM being transferred to aquatic systems.     

Crop residue return sustains global soil ecological stoichiometry balance

Although soil ecological stoichiometry is constrained in natural ecosystems, its responses to anthropogenic perturbations are largely unknown. Inputs of inorganic fertilizer and crop residue are key cropland anthropogenic managements, with potential to alter their soil ecological stoichiometry. We conducted a global synthesis of 682 data pairs to quantify the responses of soil carbon (C), nitrogen (N), and phosphorus (P) and grain yields to combined inputs of crop residue plus inorganic fertilizer compared with only inorganic fertilizer application. Crop residue inputs enhance soil C (10.5%–12%), N (7.63%–9.2%), and P (2.62%–5.13%) contents, with an increase in C:N (2.51%–3.42%) and C:P (7.27%–8.00%) ratios, and grain yields (6.12%–8.64%), indicating that crop residue alleviated soil C limitation caused by inorganic fertilizer inputs alone and was able to sustain balanced stoichiometry. Moreover, the increase in soil C and C:N(P) ratio reached saturation in ~13–16 years after crop residue return, while grain yield increase trend discontinued. Furthermore, we identified that the increased C, N, and P contents and C:N(P) ratios were regulated by the initial pH and C content, and the increase in grain yield was not only related to soil properties, but also negatively related to the amount of inorganic N fertilizer input to a greater extent. Given that crop residual improvement varies with soil properties and N input levels, we propose a predictive model to preliminary evaluate the potential for crop residual improvement. Particularly, we suggest that part of the global budget should be used to subsidize crop residue input management strategies, achieving to a win-win situation for agricultural production, ecological protection, and climate change mitigation.     

Ecological consequences of the expansion of N2-fixing plants in cold biomes

Research in warm-climate biomes has shown that invasion by symbiotic dinitrogen (N₂)-fixing plants can transform ecosystems in ways analogous to the transformations observed as a consequence of anthropogenic, atmospheric nitrogen (N) deposition: declines in biodiversity, soil acidification, and alterations to carbon and nutrient cycling, including increased N losses through nitrate leaching and emissions of the powerful greenhouse gas nitrous oxide (N₂O). Here, we used literature review and case study approaches to assess the evidence for similar transformations in cold-climate ecosystems of the boreal, subarctic and upper montane-temperate life zones. Our assessment focuses on the plant genera Lupinus and Alnus, which have become invasive largely as a consequence of deliberate introductions and/or reduced land management. These cold biomes are commonly located in remote areas with low anthropogenic N inputs, and the environmental impacts of N₂-fixer invasion appear to be as severe as those from anthropogenic N deposition in highly N polluted areas. Hence, inputs of N from N₂ fixation can affect ecosystems as dramatically or even more strongly than N inputs from atmospheric deposition, and biomes in cold climates represent no exception with regard to the risk of being invaded by N₂-fixing species. In particular, the cold biomes studied here show both a strong potential to be transformed by N₂-fixing plants and a rapid subsequent saturation in the ecosystem’s capacity to retain N. Therefore, analogous to increases in N deposition, N₂-fixing plant invasions must be deemed significant threats to biodiversity and to environmental quality.     

Solid-Phase Chemical Fractionation of Selected Trace Metals in Some Northern Kentucky Soils

The fractionation and distribution with depth of Cd, Cr, Cu, Ni, Pb, and Zn in 26 soils of Northern Kentucky were determined through a sequential extraction procedure in response to environmental concerns about increasing anthropogenic inputs in a fast-paced, urbanizing area. The selected sites have not received any biosolid- or industrial-waste applications. Average total concentrations per metal in soil profiles derived from alluvial, glacial till, and residual materials ranged from 0.43 to 56.00 mg kg^?1 in the sequence Zn > Ni > Pb > Cr > Cu > Cd, suggesting relatively small anthropogenic inputs. The distribution of Cu, Cr, Ni, and Zn increased with soil depth, whereas Cd and Pb remained stable, indicating a strong geological or pedogenic influence. Residual forms were most important for the retention of Cu, Zn, and Ni. Cadmium and Pb exhibited a strong affinity for the Fe-Mn oxide fraction, while Cr showed the strongest association with the organic fraction. In terms of metal mobility and toxicity potential inferred from metal concentrations in labile fractions, Cd posed the greatest risk, followed by Cr ～ Pb > Ni > Zn > Cu. Soil pH, OM, and clay content were the most important parameters explaining the partitioning of metals in labile and residual fractions, emphasizing the importance of metal fractionation in soil management decisions. Alluvial soils generally contained the highest total and labile metal concentrations, suggesting potential metal enrichment through anthropogenic additions and depositional processes. These environments exhibit the highest risk for metal mobilization due to drastic changes in redox conditions, which can destabilize existing metal retention pools.     

Phosphorus loss from land to water: integrating agricultural and environmental management

Phosphorus (P), an essential nutrient for crop and animal production, can accelerate freshwater eutrophication, now one of the most ubiquitous forms of water quality impairment in the developed world. Repeated outbreaks of harmful algal blooms (e.g., Cyanobacteria and Pfiesteria) have increased society's awareness of eutrophication, and the need for solutions. Agriculture is regarded as an important source of P in the environment. Specifically, the concentration of specialized farming systems has led to a transfer of P from areas of grain production to animal production. This has created regional surpluses in P inputs (mineral fertilizer and feed) over outputs (crop and animal produce), built up soil P in excess of crop needs, and increased the loss of P from land to water. Recent research has shown that this loss of P in both surface runoff and subsurface flow originates primarily from small areas within watersheds during a few storms. These areas occur where high soil P, or P application in mineral fertilizer or manure, coincide with high runoff or erosion potential. We argue that the overall goal of efforts to reduce P loss to water should involve balancing P inputs and outputs at farm and watershed levels by optimizing animal feed rations and land application of P as mineral fertilizer and manure. Also, conservation practices should be targeted to relatively small but critical watershed areas for P export.     

Nonlinear root-derived carbon sequestration across a gradient of nitrogen and phosphorous deposition in experimental mesocosms

Enhanced sequestration of plant‐carbon (C) inputs to soil may mitigate rising atmospheric carbon dioxide (CO₂) concentrations and related climate change but how this sequestration will respond to anthropogenic nitrogen (N) and phosphorous (P) deposition is uncertain. We couple isotope, soil C fractionation and mesocosm techniques to assess the sequestration of plant‐C inputs, and their partitioning into C pools with different sink potentials, under an experimental gradient of N and P deposition (0, 10, 30, 60 and 100 kg N ha^?1 yr^?1; and 0, 2, 6, 12 and 20 kg P ha^?1 yr^?1). We hypothesized that N deposition would increase sequestration, with the majority of the C being sequestered in faster cycling soil pools because N deposition has been shown to accelerate the turnover of these pools while decelerating the turnover of slower cycling pools. In contrast to this hypothesis, sequestration into all soil C pools peaked at intermediate levels of N deposition. Given that P amendment has been shown to cause a net loss of soil C, we postulated that P deposition would decrease sequestration. This expectation was not supported by our data, with sequestration generally being greater under P deposition. When soils were amended simultaneously with N and P, neither the shape of the sequestration relationship across the deposition gradient, nor the observed sequestration at the majority of the deposition rates, was statistically predictable from the effects of N and P in isolation. The profound nonlinearities we observed, both for total sequestration responses and the partitioning of C into soil pools with different sink potentials, suggests that the rates of N and P deposition to ecosystems will be the critical determinant of whether they enhance or decrease the long‐term sequestration of fresh plant‐C inputs to soils.     

Sources of plant-derived carbon and stability of organic matter in soil: implications for global change

Alterations in forest productivity and changes in the relative proportion of above‐ and belowground biomass may have nonlinear effects on soil organic matter (SOM) storage. To study the influence of plant litter inputs on SOM accumulation, the Detritus Input Removal and Transfer (DIRT) Experiment continuously alters above‐ and belowground plant inputs to soil by a combination of trenching, screening, and litter addition. Here, we used biogeochemical indicators [i.e., cupric oxide extractable lignin‐derived phenols and suberin/cutin‐derived substituted fatty acids (SFA)] to identify the dominant sources of plant biopolymers in SOM and various measures [i.e., soil density fractionation, laboratory incubation, and radiocarbon‐based mean residence time (MRT)] to assess the stability of SOM in two contrasting forests within the DIRT Experiment: an aggrading deciduous forest and an old‐growth coniferous forest. In the deciduous forest, removal of both above‐ and belowground inputs increased the total amount of SFA over threefold compared with the control, and shifted the SFA signature towards a root‐dominated source. Concurrently, light fraction MRT increased by 101 years and C mineralization during incubation decreased compared with the control. Together, these data suggest that root‐derived aliphatic compounds are a source of SOM with greater relative stability than leaf inputs at this site. In the coniferous forest, roots were an important source of soil lignin‐derived phenols but needle‐derived, rather than root‐derived, aliphatic compounds were preferentially preserved in soil. Fresh wood additions elevated the amount of soil C recovered as light fraction material but also elevated mineralization during incubation compared with other DIRT treatments, suggesting that not all of the added soil C is directly stabilized. Aboveground needle litter additions, which are more N‐rich than wood debris, resulted in accelerated mineralization of previously stored soil carbon. In summary, our work demonstrates that the dominant plant sources of SOM differed substantially between forest types. Furthermore, inputs to and losses from soil C pools likely will not be altered uniformly by changes in litter input rates.     

Soil Organic Carbon Content Decreases in Both Surface and Subsoil Mineral Horizons by Simulated Future Increases in Labile Carbon Inputs in a Temperate Coniferous Forest

Soils represent important pools of soil organic carbon (SOC) that can be greatly influenced by labile C inputs, which are expected to increase in future due to CO₂ enrichment of atmosphere and a concomitant rise in plant primary productivity. Studying effects of variable labile C inputs on SOC pool helps to understand how soils respond to global change. However, this knowledge is missing for coniferous forest soils despite being widespread throughout the northern temperate zone. We conducted a 7-month field manipulation experiment to study the effects of variable labile C inputs (simulated by additions of C₄ sucrose) on the C content in soil fractions and on microbial abundance in the organic (O), surface mineral (A), and subsoil mineral (B) horizons of a temperate coniferous forest soil. SOC in less-protected soil fractions and total organic C were substantially decreased by labile C additions that simulated future increases in C inputs. The SOC losses were comparable between the A and B horizon (40% vs. 30%). However, because sucrose availability estimated from its incorporation into soil fractions and microbial biomass sharply decreased with soil depth, the loss of C was higher in the B than in the A horizon when related to the amount of sucrose added. Utilization of sucrose was highest by fungi in the O horizon and by bacteria in the mineral soil horizons. The results indicate that future increases in labile C inputs to coniferous forest soils will cause rapid and substantial losses of SOC in both the surface and subsoil mineral horizons.

     

Variable Responses of Lowland Tropical Forest Nutrient Status to Fertilization and Litter Manipulation

Predicting future impacts of anthropogenic change on tropical forests requires a clear understanding of nutrient constraints on productivity. We compared experimental fertilization and litter manipulation treatments in an old-growth lowland tropical forest to distinguish between the effects of inorganic nutrient amendments and changes in nutrient cycling via litterfall. We measured the changes in soil and litter nutrient pools, litterfall, and fine root biomass in plots fertilized with nitrogen (N), phosphorus (P), or potassium (K), and in litter addition and litter removal treatments during 7 years. Soil inorganic N and litter N increased in double-litter plots but not in N-fertilized plots. Conversely, litter P and soil pools of P and K increased in fertilized plots but not in the double-litter plots. Soil and litter pools of N and K decreased in the no-litter plots. Changes in litterfall with added nutrients or litter were only marginally significant, but fine root biomass decreased with both the litter and the K addition. Differences between the two experiments are mostly attributable to the coupled cycling of carbon and nutrients in litter. Increased nutrient inputs in litter may improve plant uptake of some nutrients compared to fertilization with similar amounts. The litter layer also appears to play a key role in nutrient retention. We discuss our findings in the context of possible impacts of anthropogenic change on tropical forests.     

Chemical changes in soil and soil solution after calcium silicate addition to a northern hardwood forest

Liming has been used to mitigate effects of acidic deposition in forest ecosystems. This study was designed to examine the effects of calcium (Ca) supply on the spatial patterns and the relations between soil and soil solution chemistry in a base-poor forest watershed. Watershed 1 at the Hubbard Brook Experimental Forest in New Hampshire, USA was experimentally treated with wollastonite (CaSiO₃) in October, 1999. Exchangeable Ca (Ex-Ca), soil pH_s (in 0.01 M CaCl₂), effective cation exchange capacity (CEC_e), and effective base saturation (BS_e) increased, while exchangeable acidity (Ex-Acid) decreased in organic soil horizons in 2000 and 2002. Mineral soils experienced either small increases in Ex-Ca, pH_s, CEC_e, BS_e, small decreases in Ex-Acid or no changes. Thus, most of the added Ca remained in the forest floor during the study period. Prior to the treatment the BS_e decreased with increasing elevation in organic and mineral soil horizons. This spatial pattern changed significantly in the forest floor after the treatment, suggesting that soils at higher elevations were more responsive to the chemical addition than at lower elevations. Soil solutions draining the forest floor responded to the treatment by increases in concentrations of Ca, dissolved silica, pH, and acid neutralizing capacity (ANC), and a decrease in inorganic monomeric Al (Al_i). Treatment effects diminished with increasing soil depth and decreasing elevation. Positive correlations between Ca/total monomeric Al (Al_m) in soil solution and Ex-Ca/Ex-Al ratios in soil indicated that changes in the chemistry of soils significantly influenced the chemistry of soil water, and that Ca derived from the dissolution of wollastonite mitigated the mobilization of Al within the experimental watershed.     

Preliminary study on heavy metals contamination of soil using solid phase speciation and the influence on groundwater in Bozanta–Baia Mare Area,Romania

Abstract

A preliminary study on soil contamination with heavy metals and As based on solid phase speciation according to the Tessier scheme and the influence on groundwater in an area under anthropogenic influence (Bozanta-Baia Mare, Romania) was conducted. The partitioning of Al, As, Cd, Cu, Fe, Mn, Pb and Zn in five fractions is discussed in relation to soil characteristics, pH, organic matter content, mineralogical composition and distribution of the same elements in airborne particulate matter. The airborne particulate matter contains high quantities of As, Cd, Cu, Pb and Zn as exchangeable fraction. The sequential extraction carried out on soil samples revealed the main role of Fe-Mn oxides surface in the immobilization of metals. Organic matter has a specific role in complexation of Cu, Pb, As and Al, since high contents of these metals were recovered in the oxidizable fraction. Cadmium has a high selectivity for carbonate minerals. The amendment of soil with natural fertilizer increases the exchangeable fraction of metals with the highest toxicity. The available fraction for plants (exchangeable + carbonate-bound species) exceeded the alert values in soil, therefore the continuous monitoring of the area is necessary. The soil is unsuitable for agricultural use due to high contamination on surface with toxic elements resulted from anthropogenic activities. Groundwater is contaminated with very toxic elements (As, Cd and Pb) but also with Cu, Mn and Zn and is unsuitable as supply for drinking water.     

Comparison of Al speciation and other soil characteristics between meadow, young forest and old forest stands

The aim of this paper is to describe the influence of spruce (Picea abies) afforestation on soil chemical properties, especially on soil acidity and aluminium (Al) mobilization and speciation in soil. For our study we used a unique set of three adjacent plots, including a meadow and two spruce forest stands of different age, in otherwise comparable conditions. The plots were located in the region of Giant Mountains, north-eastern Czech Republic. In general, pH values decreased and Al concentrations increased significantly after afforestation. Speciation of KCl-extractable and water-soluble Al in soil samples was done by means of HPLC/IC method. The concentrations of Al(X)¹⁺ and Al(Y)²⁺ forms (in both extracts) are higher in humic and organically enriched (Bhs) horizons. The highest concentration of Al³⁺ in both extracts is in the B horizons of old forest.Generally, in all studied stands majority of Al in aqueous extract is in the Al(X)¹⁺ form, which indicates that a large amount of mobile Al is bound in organic complexes. It suggests that actual toxicity is rather low. On the other hand, we have proved that majority of KCl-extractable Al exists in Al³⁺ form. Thus we can conclude that disturbance of existing equilibrium may cause massive release of highly toxic Al³⁺ from soil sorption complex to the soil solution, and consequently it can endanger the whole ecosystem. Moreover, continuous soil acidification accelerated by anthropogenic factors leading to Al mobilization represents a chemical time bomb.