Effects of heating and autoclaving on sorption and desorption of phosphorus in some forest soils

A number of biological and chemical processes may affect soil phosphorus availability when forest fires occur, partly as a result of heating. We describe here a laboratory experiment to study the effects of soil heating on changes in sorption and desorption of P. Autoclaving was also included as an additional treatment of moist heating under pressure. Five forest soils (two Podzols, one Arenosol, one Luvisol and one Alisol) were heated to 60°C, 120°C and 250°C or autoclaved for 30 min. They were repeatedly extracted with Bray I and analysed for inorganic and organic P fractions. The desorbed P data were fitted to an asymptotic exponential equation to obtain the desorption rate and capacity parameters. Podzol and Arenosol soils showed a quick P desorption after heating, while Luvisol and Alisol soils showed a slow desorption rate. The immediate increase in available P that occurred after heating or autoclaving originated mostly from solubilisation of microbial metabolites and soil organic components. Autoclaving decreased P sorption capacity in all soils, but the effects of heating on P sorption differed among soils. Except for one of the soils, the low P-fixing soils (Podzol and Arenosol) showed a decrease in P sorption when heated to high temperatures, whereas the high P-fixing soils (Luvisol and Alisol) showed little changes after heating. Fire intensity and soil characteristics are important factors determining short-term and long-term soil P dynamics.     

生物质炭对磺胺类抗生素在坡耕地紫色土中吸附-解吸及淋溶过程的影响

吸附-解吸是影响抗生素类污染物在土壤中迁移转化及生物有效性的重要过程,本文以川中丘陵区坡耕地紫色土为研究对象,通过批量平衡实验和柱实验研究生物炭施用（投加量0(B0)、39.75 (B1)t/hm2和198.75 (B2) t/hm2）及田间老化作用（夏季干湿交替）对三种典型磺胺类抗生素（磺胺嘧啶（SD）、磺胺二甲基嘧啶（SM2）及磺胺甲恶唑（SMZ））在紫色土中的吸附-解吸和淋溶行为的影响。结果表明：在几种处理中,三种磺胺类抗生素吸附强弱的顺序都表现为SD>SMZ>SM2;与B0处理相比,添加生物炭能增加土壤对三种抗生素的吸附能力,其中SM2的吸附显著增加（P<0.05）,但这种促进作用在经过老化过程后有所减弱。在解吸过程中,三种抗生素的Freundlich常数Kf大小顺序为SD>SMZ>SM2,表明SD在土壤中吸附容量最大且不易解吸,其次是SMZ和SM2;相应的迟滞系数H大小顺序为SD相似文献   

有机肥非水溶性分解产物对 铜 、镉吸附及解吸的影响

研究了稻草、紫云英和猪粪淹水培养的非水溶性分解产物、两种土壤( 红壤、潮土) 与这 3 种有机肥共同淹水培养后的非水溶性产物( 水溶性物质被除去) 对铜、镉的沉淀、吸附及解吸作 用的影响。 结果表明, 当铜初始浓度为 10-4mol/ L, pH <6 时有机残渣促进铜的沉淀;当 pH >6 时则抑制了铜的沉淀。 当铜初始浓度降为 10-5mol/ L 时, 有机残渣对铜沉淀的促进作用加强。 3 种有机残渣均促进镉的沉淀, 但促进程度比铜低。 与有机肥共同培养的红壤, 在相同的 pH 条 件下, 提高对铜、镉的吸附;在不调节 pH 条件下, 由于有机肥料有提高 pH 的作用, 进一步提高 对铜 、镉的吸附。 与有机肥共同培养的潮土, 在相同的 pH 条件下, 对铜、镉吸附的影响很小;在 不调节 pH 时, 提高了潮土对铜的吸附, 但对镉吸附的影响则较复杂。 上述结果表明, 有机肥的 非水溶性分解产物主要通过提高体系的 pH 值、与铜、镉形成不溶性的络合物而影响铜、镉的吸 附。 与有机物料共同培养的红壤所吸附的铜、镉的解吸率均不同程度降低。     

The effect of soil flooding on the transformation of Fe oxides and the adsorption/desorption behavior of phosphate

As repeatedly reported, soil flooding improves the availability of P to rice. This is in contrast with an increased P sorption in paddy soils. The effects of soil flooding on the transformation of Fe oxides and the adsorption/desorption of P of two paddy soils of Zhejiang Province in Southeast‐China were studied in anaerobic incubation experiments (submerging with water in N₂ atmosphere). Soil flooding significantly increased oxalate‐extractable Fe (Fe_ox), mainly at the expense of dithionite‐soluble Fe (Fe_DCB), as well as oxalate‐extractable P (P_ox), but decreased the ratio of P_ox/Fe_ox. Flooding largely increased both, P adsorption and the maximum P adsorption capacity. The majority of newly sorbed P in the soils was P_ox, but also more newly retained P was found to be not extractable by oxalate. Flooding also changed the characteristics of P desorption in the soils. Due to a decrease of the saturation index of the P sorption capacity, P adsorbed by flooded soils was much less desorbable than that from non‐flooded soils. There are obviously significant differences in the nature of both, the Fe_ox and P_ox fractions under non‐flooded and flooded conditions. The degree of the changes in Fe_ox, P_ox, P adsorption and P desorption by flooding depended on the contents of amorphous and total Fe oxides in non‐flooded soils. Our results confirm that the adsorption and desorption behavior of P in paddy soils is largely controlled by the transformation of the Fe oxides. The reasons of the often‐reported improved P availability to rice induced by flooding, in spite of the unfavorable effect on P desorbability, are discussed.     

黄土高原干旱半干旱区生物结皮覆盖土壤水汽吸附与凝结特征

生物结皮是一种广泛分布于干旱半干旱地区土壤表层的特殊复合体,为揭示其对土壤水汽吸附与凝结过程的影响,该研究通过室内定量水汽吸附试验和野外对水汽凝结的连续观测,对黄土高原典型生物结皮(藻结皮、藻藓混生结皮、藓结皮)与裸沙的水汽吸附和凝结特征进行对比研究。结果表明:生物结皮的覆盖显著提升了表层土壤的水汽吸附能力,其平均水汽吸附量比裸沙高66.7%。不同类型生物结皮水汽吸附能力差异显著,表现为藓结皮最高,混生结皮次之,而藻结皮最低。GAB(Guggenheim-Anderson-de Boer)吸附模型能较好的描述生物结皮土壤水汽吸附与解吸附过程,模拟结果决定系数R2>0.99、均方根误差RMSE<0.001 2 g/g及平均相对偏差百分比E<16.0%;此外,生物结皮加剧了土壤水汽吸附与解吸附曲线之间的滞后效应,其滞后指数平均是裸沙的2.0～2.9倍。水汽凝结结果显示,水汽凝结过程均受气温与相对湿度等气象因子制约,且生物结皮覆盖下表层土壤的水汽凝结和蒸发过程相较于裸沙更为迅速。同时,生物结皮的日均水汽凝结量是裸沙的1.6～1.8倍。综上,干旱和半干旱地区生物结皮覆盖显著提...     

The Remobilization of Metals from Iron Oxides and Sediments by Metal-EDTA Complexes

Synthetic chelating agents such as EDTA form strong complexes with heavy metals and therefore have the potential to remobilize metals from sediments and aquifers. In natural waters EDTA is present almost exclusively in the form of metal-complexes. Therefore, remobilization of metals is always a metal-metal-EDTA exchange reaction. We have investigated, to our knowledge for the first time, the remobilization of metals from the surface of synthetic iron oxides and from a river sediment by different metal-EDTA complexes. The metals are exchanged as follows:MeEDTA_dissolved + Me^ast _adsorbed Me^astEDTA_dissolved + Me_adsorbed The order of the remobilization rate of Zn²⁺ from goethite is CaEDTA > Fe(III)EDTA, reflecting the slow exchange reaction of Fe(III)EDTA. For the remobilization of Pb²⁺ from goethite, the rate was found to be Fe(III)EDTA > CaEDTA > ZnEDTA. Here, Fe(III)EDTA has surprisingly the fastest exchange rate. Only very limited remobilization of Pb²⁺ is possible from hydrous ferric oxide at pH 8 due to the very strong adsorption of Pb²⁺. The order of remobilization of Zn²⁺ from a natural river sediment was found to be CaEDTA > CuEDTA > Fe(III)EDTA. The remobilization rate of Zn²⁺ with Fe(III)EDTA is only 12% of the rate with CaEDTA, illustrating the importance of EDTA speciation for assessing remobilization.     

土壤有机质对疏水性有机污染物的非线性吸附及其影响因素

土壤有机质(SOM)是土壤的重要组成部分,它对疏水性有机污染物(HOCs)的吸附作用对污染物在环境中的迁移转化有着至关重要的影响。近年来的一些研究表明,HOCs在SOM上的吸附行为并不严格地符合传统的线性分配模型。本文综述了近年来一些学者提出的SOM对HOCs的非线性吸附作用的机制及其影响因素,认为SOM的组成和结构均对HOCs的吸附有着重要的影响。SOM吸附在土壤矿物表面后,其结构或各组分的比例发生了改变,从而对其本身的吸附作用产生影响。溶液的化学环境(主要是阳离子)会对SOM的结构和吸附作用产生影响,特别是当溶液中存在一些过渡金属(如,铜或银)的离子时,共吸附的金属离子可能会与多环芳烃类分子形成阳离子-π键的作用,从而促进多环芳烃类物质在SOM上的吸附。     

Physical carbon‐sequestration mechanisms under special consideration of soil wettability

The protective impact of aggregation on microbial degradation through separation has been described frequently, especially for biotically formed aggregates. However, to date little information exists on the effects of organic‐matter (OM) quantity and OM quality on physical protection, i.e., reduced degradability by microorganisms caused by physical factors. In the present paper, we hypothesize that soil wettability, which is significantly influenced by OM, may act as a key factor for OM stabilization as it controls the microbial accessibility for water, nutrients, and oxygen in three‐phase systems like soil. Based on this hypothesis, the first objective is to evaluate new findings on the organization of organo‐mineral complexes at the nanoscale as one of the processes creating water‐repellent coatings on mineral surfaces. The second objective is to quantify the degree of alteration of coated surfaces with regard to water repellence. We introduce a recently developed trial that combines FTIR spectra with contact‐angle data as the link between chemical composition of OM and the physical wetting behavior of soil particles. In addition to characterizing the wetting properties of OM coatings, we discuss the implications of water‐repellent surfaces for different physical protection mechanisms of OM. For typical minerals, the OM loading on mineral surfaces is patchy, whereas OM forms nanoscaled micro‐aggregates together with metal oxides and hydroxides and with layered clay minerals. Such small aggregates may efficiently stabilize OM against microbial decomposition. However, despite the patchy structure of OM coating, we observed a relation between the chemical composition of OM and wettability. A higher hydrophobicity of the OM appears to stabilize the organic C in soil, either caused by a specific reduced biodegradability of OM or indirectly caused by increased aggregate stability. In partly saturated nonaggregated soil, the specific distribution of the pore water appears to further affect the mineralization of OM as a function of wettability. We conclude that the wettability of OM, quantified by the contact angle, links the chemical structure of OM with a bundle of physical soil properties and that reduced wettability results in the stabilization of OM in soils.     

不同年限稻田红壤发生层土壤磷的固持容量及其释放潜能研究

以江西鹰潭孙家典型红壤小流域中期稻田(MP)、新稻田(NP)与老稻田(OP)的发生层土壤为研究对象,基于吸附-解吸实验与结构方程模型,分析了稻田红壤各发生层土壤磷的固持能力(PSI)、最大固持容量(MCSP)及释放潜能的变化差异与影响因子,明确了固定态磷的释放机制与流失风险。结果表明：随发生层深度的增加,稻田红壤PSI及MCSP逐渐增大,二者变化分别为：MP > NP > OP与NP > MP > OP;但稻田红壤发生层中电性吸附态磷(CaCl2-P)及OP剖面专性吸附态磷(EDTA-P)逐渐降低,而MP剖面和NP剖面的EDTA-P以及稻田红壤发生层的残留态磷(Red-P)则相反;OP剖面发生层CaCl2-P与EDTA-P的比值随发生层深度的增加呈逐渐升高趋势,且显著高于MP和NP剖面。结构方程模型分析结果表明,土壤有机质、全磷、pH和铁铝氧化物之间相互作用且协同调控着稻田红壤的磷吸附位点数量及其吸附-解吸能力。稻田红壤水耕层(Ap层)土壤吸磷能力弱、释磷能力强,土壤磷流失风险大;而氧化还原层(Br)和母质层(C)土壤吸磷能力强、释磷能力弱,土壤磷固持容量大。与新稻田和中期稻田剖面相比,老稻田发生层土壤中吸附态磷更难以向专性吸附态磷及残留态磷转化,土壤磷流失风险相对较大,需及时采取相应的调控措施。     

天然土壤中典型多溴联苯醚解吸过程的初步研究

选择5种有机质含量不同的天然土壤,采用批量实验方法考察典型多溴联苯醚8DE47的解吸行为,并尝试利用非线性Freundlich模型和线性模型模拟不同初试浓度条件下BDE47的土壤解吸过程。针对较为显著的器壁吸附影像,所有检测数据均进行器壁吸附定量修正。结果表明,BDE47土壤解吸过程总体分为初始的快解吸和后续的慢解吸两个阶段。在初始阶段,BDE47解吸过程表现为线性行为,但非线性特征随解吸时间延长呈现增强趋势。土壤有机质（用TOC表征）释放的溶解有机质是影响土壤中BDE47解吸行为差异的主要因素之一。