Adsorption and desorption of organotin compounds in organic and mineral soils

Organotin compounds (OTC) are deposited from the atmosphere into terrestrial ecosystems and can accumulate in soils. We studied the adsorption and desorption of methyltin and butyltin compounds in organic and mineral soils in batch experiments. The adsorption and desorption isotherms for all species and soils were linear over the concentration range of 10–100 ng Sn ml^?1. The strength of OTC adsorption correlated well with the carbon content and cation exchange capacity of the soil and was in the order mono‐ > di‐ > tri‐substituted OTCs and butyltin > methyltin compounds. The OTC adsorption coefficients were much larger in organic soils (K_d > 10⁴) than in mineral soils. The adsorption and desorption showed a pronounced hysteresis. Trimethyltin adsorption was partly reversible in all soils (desorption 2–12% of the adsorbed amounts). Dimethyltin, tributyltin and dibutyltin exhibited reversible adsorption only in mineral soils (desorption 4–33% of the adsorbed amounts). Mono‐substituted OTCs adsorbed almost irreversibly in all soils (desorption < 1% of adsorbed amounts). Trimethyltin was more mobile and more bioavailable in soils than other OTCs. It might therefore be leached from soils and accumulate in aquatic ecosystems. The other OTCs are scarcely mobile and are strongly retained in soils.     

Mineralization of dissolved organic carbon in mineral soil solution of two forest soils

Dissolved organic carbon (DOC) constitutes an important carbon input flux to forested mineral soils. Seepage from mineral subsoils contains only small amounts of DOC because of mineralization, sorption or the formation of particulate organic matter (POM). However, the relation between these processes is largely unknown. Therefore, the objective of this study was to quantify the mineralization of DOC from different depths of forest soils, and to determine degradation rate constants for rapidly and slowly degradable DOC pools. Mineralization of DOC and formation of POM in mineral soil solution from two forested sites in northern Bavaria (Germany) were quantified in a 97 days laboratory incubation experiment. Furthermore, spectroscopic properties such as specific UV absorption and a humification index derived from fluorescence emission spectrometry were measured before and after incubation. DOC in all samples turned out to belong mainly to the stable DOC pool (> 95 %) with half‐lives ranging from years to decades. Spectroscopic properties were not suitable to predict the mineralization of DOC from mineral soils. However, together with data on DOC from the forest floor and long‐term data on DOC concentrations in the field they helped to identify the processes involved in C sequestration in mineral subsoils. Mineralization, formation of POM, and probably sorption seem all to be responsible for maintaining low concentrations of DOC in the upper mineral soil. DOC below the upper mineral soil is highly resistant to mineralization, and thus the further decrease of DOC concentrations in the subsoil as observed under field conditions cannot be attributed to mineralization. Our results suggest that sorption and to some minor extent the formation of POM may be responsible for C sequestration in the subsoil.     

Extraction of water‐soluble organic matter from mineral horizons of forest soils

Dissolved organic matter (DOM) is involved in many important biogeochemical processes in soil. As its collection is laborious, very often water‐soluble organic matter (WSOM) obtained by extracting organic or mineral soil horizons with a dilute salt solution has been used as a substitute of DOM. We extracted WSOM (measured as water‐soluble organic C, WSOC) from seven mineral horizons of three forest soils from North‐Rhine Westphalia, Germany, with demineralized H₂O, 0.01 M CaCl₂, and 0.5 M K₂SO₄. We investigated the quantitative and qualitative effects of the extractants on WSOM and compared it with DOM collected with ceramic suction cups from the same horizons. The amounts of WSOC extracted differed significantly between both the extractants and the horizons. With two exceptions, K₂SO₄ extracted the largest amounts of WSOC (up to 126 mg C kg^–1) followed by H₂O followed by CaCl₂. The H₂O extracts revealed by far the highest molar UV absorptivities at 254 nm (up to 5834 L mol^–1 cm^–1) compared to the salt solutions which is attributed to solubilization of highly aromatic compounds. The amounts of WSOC extracted did not depend on the amounts of Fe and Al oxides as well as on soil organic C and pH. Water‐soluble organic matter extracted by K₂SO₄ bore the largest similarity to DOM due to relatively analogue molar absorptivities. Therefore, we recommend to use this extractant when trying to obtain a substitute for DOM, but as WSOM extraction is a rate‐limited process, the suitability of extraction procedures to obtain a surrogate of DOM remains ambiguous.     

Contribution of dissolved organic matter to carbon storage in forest mineral soils

Dissolved organic matter (DOM) is often considered the most labile portion of organic matter in soil and to be negligible with respect to the accumulation of soil C. In this short review, we present recent evidence that this view is invalid. The stability of DOM from forest floor horizons, peats, and topsoils against microbial degradation increases with advanced decomposition of the parent organic matter (OM). Aromatic compounds, deriving from lignin, likely are the most stable components of DOM while plant‐derived carbohydrates seem easily degradable. Carbohydrates and N‐rich compounds of microbial origin produced during the degradation of DOM can be relatively stable. Such components contribute much to DOM in the mineral subsoil. Sorption of DOM to soil minerals and (co‐)precipitation with Al (and probably also with Fe), especially of the inherently stable aromatic moieties, result in distinct stabilization. In laboratory incubation experiments, the mean residence time of DOM from the Oa horizon of a Haplic Podzol increased from <30 y in solution to >90 y after sorption to a subsoil. We combined DOM fluxes and mineralization rate constants for DOM sorbed to minerals and a subsoil horizon, and (co‐)precipitated with Al to estimate the potential contribution of DOM to total C in the mineral soil of a Haplic Podzol in Germany. The contribution of roots to DOM was not considered because of lack of data. The DOM‐derived soil C ranges from 20 to 55 Mg ha^–1 in the mineral soil, which represents 19%–50% of the total soil C. The variation of the estimate reflects the variation in mineralization rate constants obtained for sorbed and (co‐)precipitated DOM. Nevertheless, the estimates indicate that DOM contributes significantly to the accumulation of stable OM in soil. A more precise estimation of DOM‐derived C in soils requires mineralization rate constants for DOM sorbed to all relevant minerals or (co‐)precipitated with Fe. Additionally, we need information on the contribution of sorption to distinct minerals as well as of (co‐)precipitation with Al and Fe to DOM retention.     

Vertical distribution and bioavailability of 137Cs in organic and mineral soils

The vertical distribution and bioavailability of ¹³⁷Cs in Histosols and mineral soils with different physicochemical properties from the southeast of Bavaria (Germany) more than ten years after the Chernobyl accident were the focus of this study. The vertical distribution of ¹³⁷Cs was low in the investigated soils. About 85–98 % of the total ¹³⁷Cs was located in the upper 10 cm of the mineral soils. Slightly higher ¹³⁷Cs percentages were observed in deeper soil layers of the peat soils. Although the organic matter is assumed to enhance ¹³⁷Cs mobility in soils, ¹³⁷Cs was also located in the upper 10 cm of the peat soils (73–85 %). The highest ¹³⁷Cs‐activities were found in the humus layers of forest soils, where 45–93 % of the total ¹³⁷Cs soil inventories were observed. To determine the bioavailability of radiocesium, the soil‐to‐plant transfer of ¹³⁷Cs and additionally added ¹³⁴Cs was investigated under controlled conditions. The results revealed that the ^134+137Cs soil‐to‐plant transfer factors as well as the percentages of NH₄‐exchangeable ^134+137Cs were much higher for the peat soils and humus layers than for the mineral soils. Nevertheless, the migration of ¹³⁷Cs from the humus layers to the underlying soils was low. Considering the high bioavailability and low migration of radiocesium in the humus layers, it is suggested that radiocesium is involved in a shortcut element cycle in the system humus layer‐plant uptake‐litter. Furthermore, the organic matter has to be taken into account for radiocesium immobilization.     

Evidence of dissolved trivalent manganese in acidic forest soils

Background

Evidence of trivalent manganese (Mn³⁺) in the aqueous phase of soils is unknown so far although this strong oxidant has large environmental implications.

Aims

We aimed to modify a spectrophotometric protocol (porphyrin method) and to discriminate between Mn²⁺ and Mn³⁺ in the aqueous phase of forest soils based on kinetic modeling.

Methods

We investigated manganese speciation in 12 forest floor solutions and 41 soil solutions from an acidic forest site by adjusting pH and correcting for absorbance.

Results

The solutions showed broad ranges in pH (3.4−6.3), dissolved organic carbon (DOC, 1.78−77.1 mg C L⁻¹), and total Mn (Mn_T, 23.9−908 µg L⁻¹). For acidic solutions, a pH-buffer was added to increase the pH of the solutions to 7.5−8.0, and background absorption was corrected for colored solutions, that is, solutions high in DOC. This was done to accelerate the reaction kinetics and avoid overestimation of Mn_T concentrations. After the pH and color adjustments, the comparison of Mn_T concentrations between the porphyrin method and optical emission spectrometry showed good agreement. Trivalent Mn, which is stabilized by organic ligands, constitutes significant proportions in both forest floor solutions (10−87%) and soil solutions (0.5−74%).

Conclusions

The dissolved Mn³⁺ is present in acidic forest soils. Thus, we revise the paradigm that this species is not stable and encourage to apply the revised method to other soils.     

缙云山森林土壤微生物数量与群落特征

本文以重庆市缙云山国家森林保护区的毛竹林、 马尾松针叶林、 马尾松针阔混交林为供试对象,研究了不同森林群落的土壤微生物数量、 群落特征及其与土壤养分的关系。结果表明,毛竹林土壤中的细菌、 放线菌、 真菌数量最多,混交林次之,针叶林最少,高低之间分别相差 32.3倍（细菌）、 19.2倍（放线菌）和19.3倍（真菌）。说明森林植被群落的生产力越高,枯枝落叶量越大,土壤微生物数量越多。在毛竹林土壤中,微生物的多样性指数、 均匀度指数和优势度指数显著高于针叶林和混交林,说明毛竹土壤的生态环境相对稳定良好,微生物种群丰富,密度较大,种群优势突出。此外,土壤微生物存在明显的季节变化,夏季最高,冬季最低,与土壤有效氮、 磷的季节变化基本耦合。土壤微生物数量与土壤有机质和碱解氮呈显著正相关（r有机质=0.592**~0.741**,r碱解氮=0.490*~0.581**,n=24）; 在毛竹林和混交林土壤中,土壤微生物数量与有效磷呈显著正相关（r毛竹林=0.461*,r 混交林=0.450*,n=24）,说明微生物在土壤有机质转化和氮、 磷供应过程中起重要作用,与森林植被群落的生产力密切相关。     

土壤有机复合物降解的动力学模型

A set of equations in suggested to describe the kinetics of degradation of organic ompounds applied to soils ad the kinetics of growth of the inolved microorganisms:-dx/dt=jx kxm dm/dt=-fm gxm where x is the concentration of organic compound at time t,m is the numer of microorganisms capable of degrading the organic compound at time t,while j,k,f and g are positive constants,This model can satisfactorily be used to explain the degradation curve of organic compounds and the growth curve of the involved microorganisms.     

Identification of degraded forest soils by means of a fuzzy‐logic based model

The term ”︁forest soil degradation” is frequently used in forest ecology. It is a highly integrated site property summarizing negative effects over a wide, yet undefined range of variables and a complex range of processes. In forest ecology, different, undefined, and idiosyncratic meanings of the term ’︁soil degradation’ are used. The evaluation for a particular soil is therefore not clear and may be inconsistent among experts. We integrated indicators of forest soil degradation into a fuzzy‐logic based model and predicted forest soil degradation for a set of sites by means of standard soil chemical data and easily accessible site characteristics. For validation we used expert judgements on selected sites. We also compared if the predicted soil degradation agrees with the results of a recent assessment of the ”︁naturalness” (hemeroby) of Austrian forests. The predicted results were consistent with our expectations: sites with a long history of nutrient exploitation were found to be degraded by the model. The fuzzy‐logic based model is open. Rules can be changed, additional rules can be included and others can be removed, if desired. We want to promote fuzzy‐logic based modeling as a means to support experts decisions in complex situations, where clarification can be added by crisply defining the pathway of the decision making process.     

Spatial and temporal patterns of water-extractable organic carbon (WEOC) of surface mineral soil in a cool temperate forest ecosystem

Water-extractable organic carbon (WEOC) drives the C and N cycles in forest ecosystems via microbial activity. However, few studies have considered both then spatial and temporal patterns of WEOC in forest soils. We investigated the spatial and temporal variation in WEOC along a topographic sequence in a cool temperate deciduous forest. The concentrations of WEOC, carbohydrates, total phenols, and other organics were 126±51, 40±15, 1.5±0.5 and 85±43 mg C kg dry soil⁻¹, respectively. Carbohydrates and phenols accounted for 33±11 and 1.5±1.0% of WEOC, respectively. The effect of season on the WEOC concentration was stronger than that of slope position the growing season, although most of the soil properties varied markedly with slope position. The concentration of carbohydrates in WEOC showed similar seasonal patterns across slope positions. The carbohydrate concentration peaked in May and August. The results suggest that carbohydrates are controlled by the recent production of C, rather than by organic C that has accumulated in soil.     

Chemistry of soil organic matter as related to C : N in Norway spruce forest (Picea abies(L.) Karst.) floors and mineral soils

Due to high nitrogen deposition in central Europe, the C : N ratio of litter and the forest floor has narrowed in the past. This may cause changes in the chemical composition of the soil organic matter. Here we investigate the composition of organic matter in Oh and A horizons of 15 Norway spruce soils with a wide range of C : N ratios. Samples are analyzed with solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy, along with chemolytic analyses of lignin, polysaccharides, and amino acid‐N. The data are investigated for functional relationships between C, N contents and C : N ratios by structural analysis. With increasing N content, the concentration of lignin decreases in the Oh horizons, but increases in the A horizons. A negative effect of N on lignin degradation is observed in the mineral soil, but not in the humus layer. In the A horizons non‐phenolic aromatic C compounds accumulate, especially at low N values. At high N levels, N is preferentially incorporated into the amino acid fraction and only to a smaller extent into the non‐hydrolyzable N fraction. High total N concentrations are associated with a higher relative contribution of organic matter of microbial origin.     

黄土高原南部半湿润残塬沟壑区人工纯林土壤性质极化研究

为充分认识黄土高原南部半湿润残塬沟壑区主要人工纯林土壤性质的极化趋势,采用多样地多样点混合取土法,对该区进入后期成熟生长期的油松（Pinus tabulaeformis）、侧柏（Platycladus orientalis）和刺槐（Robinia pseudoacia）等人工纯林,以及相同立地条件下植被充分覆盖、生长旺盛的天然草地（对照）土壤性质进行测定。结果表明：油松林土壤物理性质弱度恶化（极化度Pr为-9．26％）,有偏酸性发展的趋势,中度贫养化（Pr为-11．54％）,部分酶活性中度恶化（Pr为-12．88％）,微生物总数量有所增加;侧柏林土壤物理性质有恶化趋势,pH值保持基本稳定,弱度贫养化（Pr为-8．24％）,部分酶活性尚未发生明显极化,微生物总数量保持基本稳定;刺槐林土壤物理性质呈中度恶化（Pr为-12．74％）,pH值保持基本稳定,中度贫养化（Pr为-12．77％）,部分酶活性弱度恶化（Pr为-8．89％）,微生物总数量保持基本稳定;各种土壤性质的绝对综合极化程度表现为微生物数量组成最为敏感,酸碱性相对变化缓慢。可见,长期生长或多代连栽的人工纯林土壤性质存在极化和退化的危险。     

A scheme for sampling inorganic nitrogen in forest soils

Abstract

An efficient sampling scheme for evaluating seasonal changes of inorganic nitrogen in a forest soil was designed. It was based on variances of ammonium‐ and nitrate‐nitrogen estimated from core samples from each of three horizons (A1, A2, B1) taken from 8 randomly selected sites in a three‐hectare study area. The scheme adopted was: At each sampling time a single composite sample for each horizon was made using 15 cores from randomly‐selected locations; duplicate subsamples from each composite were analyzed for ammonium‐ and nitrate‐nitrogen.     

Mobilization and immobilization of dissolved organic matter in forest soils

Field and laboratory studies combined with destructive and nondestructive analytical methods were used to characterize dissolved organic matter (DOM) in acid forest soils. DOM is produced in significant amounts in the forest canopy and in the forest floor. A major part of the organic solutes are lignocellulose-degradation products being strongly microbially altered in the course of ligninolysis. The release of lignin-derived moieties into the soil solution is controlled by their degree of biooxidation. Microorganisms contribute also directly to the organic solutes through the release of microbial metabolites. DOM released from the forest floor passes the upper mineral soil almost conservatively, whereas in the subsoil most DOM is removed from solution. Immobilization of DOM is mainly due to sorption on Fe and Al oxides. The highly oxidized lignin-derived moieties are preferentially removed from the soil solution whereas the saccharides are relatively enriched. We conclude that DOM in the forest soil output to the hydrosphere is a result of (1) the release of microbially degraded lignocellulose compounds and of microbial metabolites into the forest floor solution and (2) selective sorptive removal of the lignin-derived constituents in the subsoil.     

Soil properties of drained and rewetted fen soils

The intensive agricultural use and consequently the drainage of fen soils have caused modifications in structure and nutrient dynamics. Pedogenetic processes result in the formation of typical soil horizons with distinctive soil properties. These are the basis for soil classification. In the present review, results are compiled. Modifications of abiotic and biotic parameters of fen soils due to drainage and rewetting are presented. Recommendations on the further use of fen soils are submitted.     

Correlations between element concentrations in spruce foliage and forest soils

Abstract

The relationships between foliage element concentrations in red spruce and soil chemical properties were studied to determine if standard soil measurements of individual elements in soils were well correlated with the concentrations of these elements in foliage. Significant positive correlations between O horizon and foliage concentrations existed only for K, Mn and P. Significant negative correlations between the concentrations of the major divalent cations (i.e. Ca, Mg, Mn) and K in the foliage were found suggesting a possible antagonism between the mono‐ and divalent cations for uptake from the soil. Trees with the highest foliage concentrations of Ca also were determined to be growing on soils which were producing the best growth rates. Foliage concentrations of P, and to a lesser extent K and Mg, were below values considered to be adequate for optimum growth in red spruce.     

Potential carbon stock in Japanese forest soils – simulated impact of forest management and climate change using the CENTURY model

Forest management and climate change may have a substantial impact on future soil organic carbon (SOC) stocks at the country scale. Potential SOC in Japanese forest soils was regionally estimated under nine forest managements and a climate change scenario using the CENTURY ecosystem model. Three rotations (30, 50, 100 yr) and three thinning regimes were tested: no‐thinning; 30% of the trees cut in the middle of the rotation (e.g. 15 year in a 30‐yr rotation) and thinned trees all left as litter or slash (ThinLef) and the trees from thinning removed from the forest (ThinRem). A climate change scenario was tested (ca. 3 °C increase in air temperature and 9% increase in precipitation). The model was run at 1 km resolution using climate, vegetation and soil databases. The estimated SOC stock ranged from 1600 to 1830 TgC (from 6800 to 7800 gC/m²), and the SOC stock was largest with the longest rotation and was largest under ThinLef with all three rotations. Despite an increase in net primary production, the SOC stock decreased by 5% under the climate change scenario.     

A new evaluation of carbon stocks in British forest soils

Carbon (C) stocks in forest soils were evaluated in the first comprehensive survey of Great Britain, the BioSoil soil survey, using a total of 167 plots (72 in England, 26 in Wales and 69 in Scotland). The average C stock down to 80 cm depth for seven main soil types ranged between 108 and 448 t C/ha with maximum values from 511 to 927 t C/ha. Carbon stock varied with soil depth and type, forest type, and stand age. Stocks within the upper mineral soil (0–20 cm) represented between 29 and 69% of the total 0–80 cm C stock, while those in the top 40 cm comprised 59–100% of the total. Carbon stocks decreased in the order deep peats > peaty gleys > groundwater gleys > surface‐water gleys > podzols and ironpans > brown earths > rankers and rendzinas. Litter and fermentation horizons on average contributed an additional 7.3 and 8.8 t C/ha, respectively, to the overall soil C stock. Measured soil C stocks (0–80 cm) were upscaled by area of main soil and forest types to provide national estimates. Total forest soil stocks for England, Wales and Scotland were upscaled to 163, 46 and 337 Mt C, respectively, with an additional 17, 4 and 21 Mt C within surface organic layers (litter and fermentation horizons). Carbon stocks were larger under conifers compared with broadleaves. Peaty gleys contributed most to the total C stock in Scotland, while brown earths and podzolic soils made the largest contribution in Wales, and brown earths and surface‐water gley soils in England. Estimated total carbon stocks in forest soils in Great Britain, including organic layers, are 589 Mt C in the top 80 cm and 664 Mt C in the top 1 m of soil. The BioSoil soil survey provides the most comprehensive estimate of forest soil C stocks in Great Britain to date and provides a good baseline for assessing future change even though variability in forest soil C stocks is high. However, a relatively small number of additional plots to fill existing gaps in spatial coverage and to increase representation of rendzinas and highly organic soils would significantly reduce the level of uncertainty.     

Pedotransfer function to predict density of forest soils in Switzerland

Soil density is an important soil property, but respective measurements are usually scarce. With data from 559 mineral soil horizons (134 sites) we developed a linear regression pedotransfer function (PTF) for the density of forest soils (sieved to ≤ 2 mm). The field estimate of density was the most important covariate. RMSE of 0.205 Mg m^?3 and R² of 0.67, calculated on independent data (131 horizons), were better than the statistics obtained by published, recalibrated PTF (RMSE 0.271–0.324 Mg m^?3; R² 0.28–0.42).