Different effect of drying on the fluxes of dissolved organic carbon and nitrogen from a Norway spruce forest floor

The forest floor represents the major source of dissolved organic carbon (DOC) and nitrogen (DON) in forest soils. The release mechanisms of DOC and DON from forest floors and their environmental controls as well as the dynamics of concentrations and fluxes are still poorly understood. We investigated the effect of drying and rewetting on the release of DOC and DON from a Norway spruce forest floor. Undisturbed soil columns of 17 cm diameter and 15—20 cm height were taken with 7 replicates from the forest floor of a mature Norway spruce (Picea abies [L.] Karst.) site and established at 10°C in the laboratory. Columns were exposed to different periods of drying (3, 5, 10, 20 days). Each drying period was followed by a rewetting for 5 days at an irrigation rate of 10 mm d^—1 with a natural throughfall solution. The percolates from the forest floor were collected daily and analyzed for DOC, total N, NH₄, NO₃, pH, electrical conductivity and major ions. Drying for 10 and 20 days decreased the water content of the Oi horizon from 280% dry weight to about 30%. The water content of the Oe and the Oa horizon only changed from about 300% to 200%. The fluxes of DOC from the forest floor were moderately effected by drying and rewetting with an increase after 3 and 5 days of drying, but a decrease after 10 and 20 days. On the contrary, the drying for 10 and 20 days resulted in a drastic increase of the DON fluxes and a subsequent decrease of the DOC/DON ratios in the forest floor percolates from about 50 to 3.3. These results suggest that the mechanisms for DOC release in forest floors differ from those for DON and that drying and rewetting cause temporal variations in the DOC/DON ratios in forest floor percolates.     

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.     

不同物料蚓粪对土壤酸度和Cu、Pb化学形态的影响

以两种常见的有机废弃物牛粪和稻秆为原料,利用Eisenia foetida生产蚓粪,采用室内培养试验,研究了蚓粪在重金属污染的酸性土壤中对有机碳含量和形态、土壤酸度及Cu、Pb形态的影响。结果表明:在2.5%~10%的蚓粪用量下,土壤总有机碳含量增加了25%~83%,除牛粪蚓粪组的可溶性有机碳显著高于稻秆蚓粪外(P0.05),其余形态两种蚓粪间土壤有机碳含量无显著差异。蚓粪使土壤pH(H2O)值提升0.38~1.13个单位,同时交换性氢和铝的含量分别降低41%~77%和57%~94%,显著降低了土壤酸度,且较对照高出0.35~4倍;牛粪蚓粪仅在10%用量下降低土壤酸度的效果高出稻秆蚓粪22%。蚓粪使土壤中水溶-交换态Cu和Pb含量分别降低22%~70%和29%~70%,使有机结合态Cu和Pb含量分别提高19%~56%和10%~40%,表明蚓粪可以显著降低土壤中Cu和Pb的活性。蚓粪降低土壤Cu、Pb活性的效果分别较对照物料高出0.58~9.6倍和0.16~3.4倍。稻秆蚓粪降低土壤Cu、Pb活性的效果分别比牛粪蚓粪高出11%~61%和1%~32%。综上所述,蚓粪降低土壤酸度和Cu、Pb活性的效果优于对照,牛粪蚓粪降低土壤酸度的效果较好,稻秆蚓粪降低土壤Cu、Pb活性的效果更佳。在降低土壤酸度和Cu、Pb活性方面,蚓粪中的总有机碳、微生物量碳、胡敏酸碳和富里酸碳均具有重要作用,并且蚓粪中有机碳的作用效率高于对照中等量的有机碳。     

Response of the sorption behavior of Cu,Cd, and Zn to different soil management

This study investigated the effect of different farming practices over long time periods on the sorption‐desorption behavior of Cu, Cd, and Zn in soils. Various amendments in a long‐term field experiment over 44 y altered the chemical and physical properties of the soil. Adsorption isotherms obtained from batch sorption experiments with Cu, Cd, and Zn were well described by Freundlich equations for adsorption and desorption. The data showed that Cu was adsorbed in high amounts, followed by Zn and Cd. In most treatments, Cd ions were more weakly sorbed than Cu or Zn. Generally, adsorption coefficients K_F increased among the investigated farming practices in the following order: sewage sludge ≤ fallow < inorganic fertilizer without N ≈ green manure < peat < Ca(NO₃)₂ < animal manure ≤ grassland/extensive pasture. The impact of different soil management on the sorption properties of agricultural soils for trace metals was quantified. Results demonstrated that the soil pH was the main factor controlling the behavior of heavy metals in soil altered through management. Furthermore, the constants K_F and n of isotherms obtained from the experiments significantly correlated with the amount of solid and water‐soluble organic carbon (WSOC) in the soils. Higher soil pH and higher contents of soil organic carbon led to higher adsorption. Carboxyl and carbonyl groups as well as WSOC significantly influenced the sorption behavior of heavy metals in soils with similar mineral soil constituents.     

洞庭湖区典型蔬菜土壤镉、铜、锌、铅含量状况及评价

采用单项污染指数和综合污染指数法对湖南洞庭湖区典型蔬菜土壤Cd,Cu,Zn,Pb含量状况进行了评价。结果表明,与湖南省潮土土壤背景值相比,土壤Cd,Cu和Zn含量明显富集,Pb含量总体不高。与国家土壤质量二级标准(GB15618-1995)相比,洞庭湖区蔬菜土壤以Cd污染为主,其次是Zn和Cu。Pb含量没有超标,其中湘阴县、沅江市、资阳区和赫山区蔬菜土壤环境质量为轻度污染,华容县处于警戒水平,需要修复治理或者改变土地利用方式。君山区和南县蔬菜土壤为清洁水平,适宜发展无公害蔬菜。污染风险高的区域土壤Cd,Cu和Zn之间存在极显著或显著正相关关系,但相关性弱。     

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.     

Chemical speciation and bioavailability of Cd,Cu, Pb and Zn in Western Balkan soils

Abstract

Three thermal power plants in Serbia, Croatia and Bosnia of the Western Balkan region were expected to be metal polluting sources, and this study was performed to investigate the bioavailability and chemical speciation of trace metals in soils and soil water extracts, respectively. Surface (0–15 cm) soil samples along with maize and grass samples were collected at a gradient from the pollution source. The chemical speciation of metals was conducted using the Windereme Humic Aqueous Model (WHAM)/Model VI for water, whereas the Diffusion Gradient in Thin Films (DGT) technique was used to estimate plant availability. The chemical speciation indicated that more than 99% of all four metals in soil water extracts were complexed to fulvic acid. This is connected to relatively high soil pH (> 6.5) and high contents of soil organic matter in these soils. The accumulation of trace metals by DGT was not correlated to plant uptake. This is connected to the very low partitioning of free ions in solution, but also to the low variation in metal solubility and metal concentration in plant tissue between sites. In spite of active thermal power plants located in the areas, hardly any differences in concentration of soil metals between sites were seen and the partition of metals in soil waters was insignificant. The latter indicates that these soils have a large metal-retaining capacity. The only significant soil chemical variable affecting the variation in metal solubility was the soil pH. In a time with large infrastructure and industrial expansion in these areas, this investigation indicates the importance of protecting these high-quality soils from industrial use and degradation. High industrial activity has so far had insignificant effect on soil quality with respect to bioavailability of trace metals in these soils.     

马尾松-麻栎混交林土壤溶解性有机碳、氮空间分布特征

以河南省驻马店西部低山丘陵区马尾松—麻栎混交林为研究对象,分析土壤有机碳(SOC)、溶解性有机碳(DOC)和溶解性有机氮(DON)储量及其对坡向、土层深度(0—10cm和10—20cm)及胸高断面积的响应规律。结果表明:坡向和胸高断面积显著影响SOC和DOC储量(p0.05),且不同坡向土壤中SOC、DOC和DON的影响因素不同。阳坡SOC储量主要限制性因素是速效钾,阴坡是全氮;阳坡与阴坡土壤DOC和DON储量主要受全氮的影响。另外,土层深度亦对SOC、DOC和DON储量有显著影响(p0.05),且随土层加深而降低,呈表层富集的现象。相关性分析表明,SOC、DOC和DON储量与土壤物理性质即土壤湿度、紧实度及土壤中颗粒组成存在显著的相关性。SOC、DOC和DON两两之间呈显著正相关关系,并均与土壤全氮、有效氮(铵态氮、硝态氮和碱解氮)、速效磷和速效钾等含量也存在显著的相关性(p0.01),表明土壤养分含量是影响马尾松—麻栎混交林土壤有机碳储量及溶解性有机碳、氮空间分布的重要因素。     

Bioavailability of DOC in leachates, soil matrix solutions and soil water extracts from beech forest floors

The biodegradability of dissolved organic carbon (DOC) in different fractions from the forest floor was studied. Soil leachate (SL, the soil solution in macropores which is freely drained from forest floor after rainfall), the soil matrix solution (SMS, the soil solution in meso-/micropores of the soil matrix), and soil water extracts (SWE) from two different beech forest floors were compared. Zero-tension and tension lysimeters were used to collect SL and SMS, respectively. Loss of DOC (during 21 days) and respiration of CO₂-C (during 7 days) were used as conventional measures of the availability of DOC. Bacterial production, measured using the leucine incorporation technique, and bacterial growth efficiency were also estimated. All methods were used to study differences in biodegradability between plots with and without ground flora (Deschampsia flexuosa or Anemone nemorosa) and different type of forest floor (with an organic (O) horizon or a mull (A) horizon). There were no differences in bioavailability of DOC from soil solutions extracted from plots with and without ground flora. The bioavailability of DOC in the different collected soil solutions varied, however. DOC in SWE was the most available, with a mean of 39% of DOC-loss in 21 days, and 18% of DOC being respired in 7 days. DOC in soil matrix solution was the least available of the soil solutions (7% respired), significantly less than DOC in soil leachate (11% respired). The methods measuring biodegradation of DOC, DOC-loss and CO₂-C respiration gave similar results and were comparable to bacterial production and bacterial growth efficiency, with the exception of SWE from the O-horizon at the D. flexuosa site, which had low bacterial production and bacterial growth efficiency, indicating a limitation of the bacterial growth. This study is one of the first to use bacterial production and bacterial growth efficiency for measuring bioavailability in terrestrial environments, giving an extra dimension for the process of biodegradation of DOC.     

Cu Cd Pb Zn对酸性耕作土壤3种酶活性的影响

采用添加外源重金属和室内培养的方法,研究了Cu、Cd、Pb、Zn对1个酸性耕作土壤中脲酶、蛋白酶和过氧化物酶活性的影响。Cu添加浓度为50、100、200、400、600mg·kg^-1,Cd添加浓度为1、5、10、15、20mg·kg^-1,Pb添加浓度为100、300、500、800、1200mg·kg^-1,Zn添加浓度为50、100、200、400、800mg·kg^-1。结果表明,Cu、Cd、Pb、Zn对脲酶以抑制作用为主,4种重金属对酶毒性大小依次为Cu〉Cd〉Zn≥Pb,但在培养末期抑制作用都趋于减弱。Ph、Cu、Cd、Zn在前17d的培养中使蛋白酶酶活性急剧降低,以后蛋白酶活性维持在此较低水平上。短时间内（3d）Zn对过氧化物酶具有强烈的抑制作用,但总体看来4种重金属对过氧化物酶活性的影响均较小。上述结果表明,脲酶对农田土壤Cu污染具有指示作用,蛋白酶对农田土壤4种重金属污染都具有指示作用,过氧化物酶仅对土壤Zn的短期污染具有指示作用。     

Effect of low‐temperature biochar derived from pig manure and poultry litter on mobile and organic matter‐bound forms of Cu,Cd, Pb and Zn in sandy soil

Numerous studies conducted so far have shown that biochar has a significant effect on physical, chemical and biological properties of soils. Biochar can be used to alleviate the effects of soil contamination with organic and inorganic compounds, for instance, to reduce the mobility of heavy metals. The aim of the research was to evaluate the effect of pig manure and poultry litter, as well as biochars produced from these materials at a temperature of 300 °C on Cu, Cd, Pb and Zn contents in mobile and organic matter‐bound forms in soil. The research was conducted under laboratory conditions. The materials were introduced into sandy acid soil in doses of 0.5, 1.0 and 2.0% w/w. The application of pig manure‐derived biochar (BPM) and poultry litter‐derived biochar (BPL), depending on the amount added, reduced the mobility of copper from 28 to 69%, from 77 to 100% in the case of cadmium, from 94 to 99% in the case of lead, and from 15 to 97% in the case of zinc. The 2% amendment of pig manure (PM) and poultry litter (PL) caused an increase in the content of Cu extracted with NH₄NO₃ in comparison with the control treatment. A similar situation was observed in the case of zinc after the application of 0.5 and 1% amendments of pig manure (PM). Cu, Cd, Pb and Zn contents extracted with 0.025 mol C₁₀H₂₂N₄O₈ were higher than contents of these elements extracted with 1 m NH₄NO₃, mainly due to different extraction force of the extractants. The obtained results indicate that, compared with the content determined in soil from the control treatment, 1 and 2% amendments of both unconverted and thermally converted materials to the soil had a greater effect on contents of Cu, Pb and Zn in the organic matter‐bound fraction than the 0.5% amendment. The organic materials applied did not affect the content of cadmium in organic matter‐bound fraction.     

低分子有机酸对土壤中重金属的解吸及影响因素

研究了柠檬酸、草酸、酒石酸和苹果酸对矿区土壤中重金属Pb、Cd、Cu和Zn的解吸行为,并探讨了介质pH值对其解吸土中重金属的影响。振荡解吸试验结果表明四种低分子有机酸对供试污染土壤中Pb、Cd、Cu和Zn都具有一定的解吸能力。由于土壤中重金属有效态含量较低,各重金属的解吸率都不高。在对Pb和Cd的解吸中,各低分子有机酸能力大小顺序为柠檬酸>酒石酸≈苹果酸>草酸;Cu的解吸顺序为柠檬酸>草酸>酒石酸≈苹果酸;Zn的解吸顺序为酒石酸>柠檬酸≈苹果酸>草酸。低分子有机酸随浓度的增加,其解吸能力提高。低分子有机酸对重金属的解吸量随pH值的降低而增加。     

Lumbricids species diversity and heavy metal amounts in lumbricids on soil monitoring sites in Saxony-Anhalt (Germany)

This paper will contribute to an evaluation of soil monitoring sites. Abundance, biomass and species diversity of lumbricids was evaluated on 68 differently used sites (fields, grassland, deciduous forest, coniferous forest, mine spoil). Eight of the 68 studied soil monitoring sites showed increased amounts of heavy metals. Apart from the assessment of the abundance, of the biomass and the species diversity, the heavy metal accumulation in lumbricids was measured and evaluated. Earthworms are ideal bioindicators for heavy metals in the soil. Additional soil properties (organic matter content, pH, heavy metals) were measured that could explain differences in the bioavailability of the metal burdens of polluted sites. Metal concentrations in lumbricids showed considerable variation between land use type and the individual lumbricid species.     

长春市城区土壤中Pb、Cu、Zn、Cd及Cr化学形态特征

为弄清长春市城市土壤中Pb、Cu、Zn、Cr及Cd的化学形态分布特征,系统采集了26件城市表层(0~20 cm)土壤样品,采用连续提取法对重金属各化学形态含量进行了测定。结果表明:Pb、Zn、Cu及Cr主要以残渣态存在,其次是铁锰氧化物结合态、腐殖酸结合态和强有机结合态占有次要地位,离子交换态和水溶态所占比例均较低;Cd则主要以碳酸盐结合态存在,同时,水溶态和离子交换态所占比例较高。残渣态Pb和Zn在城区表层土壤中所占比例较近郊土壤中略有下降,但幅度不大,除Cu外,其余各元素易迁移、高生物有效性的水溶态在城区表层土壤中所占比例略有上升。Pearson相关分析结果表明,各元素残渣态与全量均呈极显著正相关,其它各活性态与全量间的相关程度与重金属种类有关。土壤pH值和Fe、Mn含量对重金属的化学形态的影响也与重金属种类有关,而且,同一重金属的不同存在形态受土壤pH值和Fe、Mn含量的影响程度也不同。     

温州城市土壤Cu,Zn,Pb含量及其形态研究

分别采集了温州市区风景区、交通干线、住宅区、文教区、工业区土壤样品21个,郊区农田保护区土壤样品2个,测定了各土壤样品的基本理化性质和Cu,Zn,Pb,Cd含量。结果表明:各土样Cu,Zn,Pb的平均含量分别为(34.59±18.29)mg/kg,(169.40±52.97)mg/kg,(65.22±26.86)mg/kg,均超出温州土壤背景值。Cd仅在个别土样中检出,且浓度极低。各形态含量的分析结果表明,Cu,Zn,Pb均以残余态为主,分别为60.17%,50.95%,47.33%。Cu和Pb的酸提取态含量最低,Zn则是有机态含量最低。各形态含量与土壤基本理化性质的相关分析结果表明,Cu,Zn各形态与有机质含量的相关性最大,而Pb则与土壤基本理化性质之间无明显相关关系。     

Redistribution of cadmium,copper, lead,nickel, and zinc among soil fractions in a contaminated calcareous soil after application of nitrogen fertilizers

This study was conducted to evaluate the redistribution of the heavy metals Cd, Cu, Pb, Ni, and Zn among different soil fractions by N fertilizers. In a lab experiment, soil columns were leached with distilled water, KNO₃, NaNO₃, NH₄NO₃, or Ca(NO₃)₂ · 4H₂O. After leaching, soil samples were sequentially extracted for exchangeable (EXCH), carbonate (CARB), organic‐matter (OM), Mn oxide (MNO), Fe oxide (FEO), and residual (RES) fractions. Distilled water significantly increased the concentrations of Cd and Ni in EXCH fraction, while concentration of Cu and Zn did not change significantly. Application of KNO₃, NaNO₃, NH₄NO₃, or Ca(NO₃)₂ · 4H₂O significantly increased the concentrations of Cd and Zn in EXCH fraction, while concentration of Pb and Ni was decreased. Application of all fertilizers caused an increase of Cu in the OM fraction. Moreover, leaching with these solutions significantly increased Cd [except in Ca(NO₃)₂ · 4H₂O], Cu, and Zn concentrations in the CARB fraction, while Pb and Ni concentrations were decreased. With application of all leaching solutions, Zn in the EXCH, CARB, FEO, and MNO fractions was significantly increased, while Zn in the OM fraction did not change. The mobility index indicated that Ca(NO₃)₂ · 4H₂O increased the mobility of Cd, Cu, and Zn in the soil, whereas NaNO₃ decreased the mobility of Pb and Ni in the soil. The mobility index of Pb decreased by all leaching solutions. Thus, these results suggest that applying N fertilizers may change heavy‐metal fractions in contaminated calcareous soil and possibly enhance metal mobility and that N‐fertilization management therefore may need modification.     

Release of dissolved organic carbon and nitrogen from forest floors in relation to solid phase properties,respiration and N-mineralization

Dissolved organic carbon (DOC) and nitrogen (DON) are important components of the carbon and nitrogen turnover in soils. Little is known about the controls on the release of DOC and DON from forest floors, especially about the influence of solid phase properties. We investigated the spatial variation of the release of DOC and DON from Oe and Oa forest floor samples at a regional scale. Samples were taken from 12 different Norway spruce sites with varying solid phase properties, including C/N ratio, pH, different fractions of extractable carbon and exchangeable cations. Most of these solid phase properties are available for large forested areas of Europe in high spatial resolution. The samples were incubated at water holding capacity for eight weeks at 15°C and then extracted with an artificial throughfall solution to measure DOC and DON release. The rates of soil respiration and N-mineralization were determined to estimate soil microbial activity. The release of DOC and DON from Oe samples was two- to threefold higher than from Oa samples. The amounts released differed by one order of magnitude among the sites. The DOC/DON ratios in the percolates of the Oa samples were much higher as compared to the solid phase C/N, indicating different release rates of DOC and DON. In contrast, the DOC/DON ratios of the Oe percolates were in the range of the C/N ratios of the solid phase. The release of DOC and DON from Oe samples was not statistically correlated to any of the measured solid phase parameters, but to N-mineralization. The DOC and DON release from the Oa samples was positively related only to pH and soil respiration. Overall it was not possible to explain the large spatial variation of DOC and DON release by the measured solid phase properties with satisfying accuracy.     

热带土壤上连续9年施入污水污泥后重金属Zn, Cd和Pb的分离研究

A long-term field experiment was carried out in the experiment farm of the Sao Paulo State University, Brazil, to evaluate the phytoavailability of Zn, Cd and Pb in a Typic Eutrorthox soil treated with sewage sludge for nine consecutive years, using the sequential extraction and organic matter fractionation methods. During 2005-2006, maize (Zea mays L.) was used as test plants and the experimental design was in randomized complete blocks with four treatments and five replicates. The treatments consisted of four sewage sludge rates (in a dry basis) : 0.0 (control, with mineral fertilization), 45.0, 90.0 and 127.5 t ha^-1, annually for nine years. Before maize sowing, the sewage sludge was manually applied to the soil and incorporated at 10 cm depth. Soil samples (0-20 cm layer) for Zn, Cd and Pb analysis were collected 60 days after sowing. The successive applications of sewage sludge to the soil did not affect heavy metal (Cd and Pb) fractions in the soil, with exception of Zn fractions. The Zn, Cd and Pb distributions in the soil were strongly associated with humin and residual fractions, which are characterized by stable chemical bonds. Zinc, Cd and Pb in the soil showed low phytoavailability after nine-year successive applications of sewage sludge to the soil.