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1.
Published information, both theoretical and experimental, on As chemical behavior in soils is reviewed. Because of many emission sources, As is ubiquitous. Thermodynamic calculations revealed that As(V) species (HAsO 4 2- >H2AsO 4 - at pH 7) are more abundant in soil solutions that are oxidized more than pe+pH>9. Arsenic is expected to be in As(III) form (HAsO 2 0 =H3AsO 3 0 >AsO 2 - =H2AsO 3 - at pH 7) in relatively anoxic soil solutions with pe+pH<7. Adsorption on soil colloids is an important As scavenging mechanism. The adsorption capacity and behavior of these colloids (clay, oxides or hydroxides surfaces of Al, Fe and Mn, calcium carbonates, and/or organic matter) are dependent on ever-changing factors, such as hydration, soil pH, specific adsorption, changes in cation coordination, isomorphous replacement, crystallinity, etc. Because of the altering tendencies of soil colloids properties, adsorption of As has become a complex, empirical, ambiguous, and often a self contradicting process in soils. In general, Fe oxides/hydroxides are the most commonly involved in the adsorption of As in both acidic and alkaline soils. The surfaces of Al oxides/hydroxides and clay may play a role in As adsorption, but only in acidic soils. The carbonate minerals are expected to adsorb As in calcareous soils. The role of Mn oxides and biogenic particles in the As adsorption in soils appears to be limited to acidic soils. Kinetically, As adsorption may reach over 90% completion in terms of hours. Precipitation of a solid phase is another mechanism of As removal from soil solutions. Thermodynamic calculations showed that in the acidic oxic and suboxic soils, Fe-arsenate (Fe3(AsO4)4)2) may control As solubility, whereas in the anoxic soils, sulfides of As(III) may control the concentrations of the dissolved As in soil solutions. In alkaline acidic oxic and suboxic soils, precipitation of both Fe- and Ca-arsenate may limit As concentrations in soil solutions. Field observations suggest that direct precipitation of discrete As solid phases may not occur, except in contaminated soils. Chemisorption of As oxyanions on soil colloid surfaces, especially those of Fe oxide/hydroxides and carbonates, is believed to a common mechanisms for As solid phase formation in soils. It is suggested that As oxyanions gradually concentrate on colloid surfaces to a level high enough to precipitate a discrete or mixed As solid phase. Arsenic volatilization is another As scavenging mechanism operating in soils. Many soil organisms are capable of converting arsenate and arsenite to several reduced forms, largely methylated arsines which are volatile. These organisms may generate different or similar biochemical products. Methylation and volatilization of As can be affected by several biotic (such as type of organisms, ability of organism for methylation, etc.) and abiotic factors (soil pH, temperature, redox conditions, methyl donor, presence of other ions, etc.) factors. Information on the rate of As biotransformations in soils is limited. In comparison to the biologically assisted volatilization, the chemical volatilization of As in soils is negligible.  相似文献   

2.
Zou  Juan  Guo  Xuesong  Han  Yunping  Liu  Junxin  Liang  Hanwen 《Water, air, and soil pollution》2012,223(2):889-900
Constructed wetlands are recognized as a reliable technology for rural wastewater treatment. However, conventional constructed wetlands face problems with low pollutant removal efficiency and limited oxygen transfer capability. Therefore, a novel vertical flow constructed wetland (VFCW) system with drop aeration was developed in this study. Two pilot-scale vertical flow constructed wetlands of 0.75 m2 each were constructed with the same dimensions and configuration but different media, one of which (named as CW1) was filled with a 1:1 mixture (by weight) of zeolite and dolomite and the other (named as CW2) with the same zeolite only. The oxygen transfer capability of a multilevel two-layer drop aeration device, organics and nitrogen removal of CW1 and CW2, and pollutant distribution along the depths of CW1 and CW2 in different operational phases were studied. The results demonstrated that compared with the direct drop aeration process, the multilevel, two-layer drop aeration device supplied 2–6 mg/L higher dissolved oxygen per meter of drop height, and after installation of the six-level, two-layer drop aeration devices, the 5-day biochemical oxygen demand removal load was improved from 8.1 to 14.2 g m−2 day−1 for CW1. With regard to the different filter media, nitrogen removal was improved by the adsorption of zeolite in the first year, with 5–36% higher NH4+–N removal efficiency of CW2 compared with that in CW1. Since it did not have a significant positive effect on phosphate removal, dolomite can be replaced by zeolite. The chemical oxygen demand removal mainly took place in the upper 15-cm filter layer in different operational phases, while nitrogen distribution along the depths of the VFCWs was different in different operational phases. In addition, as no operational problems occurred, the vertical flow constructed wetland system with drop aeration is an appropriate alternative for rural wastewater treatment, with numerous advantages of low capital and operation costs, no energy consumption, easy maintenance, high hydraulic loading rate, high pollutant removal efficiency, and no clogging.  相似文献   

3.
Coastal areas in the southeastern USA are prone to hurricanes and strong storms that may cause salt-water influx to freshwater aquatic sediments. These changes in environmental conditions may impact sediment processes including nitrogen (N) cycling. The relative abilities of sediment microbial communities from two freshwater golf course retention ponds that drain into the adjacent wetlands, and two proximal saline wetland ponds, to remove nitrate (NO3−) were compared to assess whether low concentrations of sulfide changed N-transformation processes. Microcosms were incubated with NO3-N (300 μg g dw−1) alone, and with NO3-N and sulfide (H2S) (100 and 200 μg g dw−1). Nitrous oxide (N2O), nitrite (NO2−), NO3−, ammonium (NH4+), SO42− and acid volatile sulfides were analyzed over time. The acetylene block technique was used to measure denitrification in sediment microcosms with no added H2S. Denitrification was measured without acetylene (C2H2) addition in microcosms with added H2S. With no added H2S, denitrification was greater in the freshwater retention ponds than in the wetland ponds. Although low H2S concentrations generally increased NO3-N removal rates at all sites, lag periods were increased and denitrification was inhibited by low sulfide in the freshwater sediments, as evidenced by the greater concentrations of N2O that accumulated compared to those in the wetland sediments. In addition to the inability of the freshwater sediments to convert N2O to N2 in the absence of C2H2, anomalously high transient NO2-N concentrations accumulated in the retention pond samples. NH4-N formation generally decreased due to H2S addition at the freshwater sites; NH4-N formation increased initially at the wetland sites, but was greater when no H2S was added. Storm events that allow influx of SO42−-containing seawater into freshwater systems may change the dominant N species produced from nitrate reduction. Even low concentrations of sulfide produced incomplete denitrification and decreased formation of NH4+ in these coastal freshwater sediments.  相似文献   

4.
PONETTE  Q.  DUFEY  J. E.  WEISSEN  F. 《Water, air, and soil pollution》1997,95(1-4):353-379
Liming and fertilization are important tools for improving the chemical status of acid, base poor forest soils. The downward movement of dolomite, kieserite and a mixture of CaCO3 and kieserite was investigated by monitoring the leachates and exchangeable cation composition from single and combined horizon columns, reconstructed from an acid brown forest soil profile (0–15 cm). Upon entering the soil, Mg ions from kieserite displaced base cations and acidity (H and Al ions) from exchange sites, which subsequently moved down with the mobile SO4 2- anions. Total leaching during the initial SO4 2- pulse was similar with the CaCO3 + kieserite mixture. Compared to the single kieserite treatment, the joint application of CaCO3 greatly increased the proportion of Ca in the leachates from all horizons. It also decreased the leaching of acidity from the surface Oe horizon and prevented pH from dropping under this layer. With both treatments, the redistribution of magnesium with SO4 2- anions resulted in a rapid increase in exchangeable Mg contents throughout the studied columns. Due to the important charge increase in the Oe horizon and to kinetic restraints imposed on dissolution, downward movement of Ca and Mg ions from dolomite was very limited. Mg was however much more mobile than Ca. In the CaCO3 + kieserite and dolomite treatments, the migration of alkalinity and base cations with time was associated with a decrease in exchangeable acidity and an increase in ECEC in the two upper soil layers. By the end of the monitoring period, overall net Mg retention in the 0–15 cm columns increased in the order kieserite < CaCO3 + kieserite << dolomite with respectively 20, 35 and 85% of cumulated inputs remaining in the columns. The corresponding net Ca retention amounted to 82 and 96% of cumulated inputs for the CaCO3 + kieserite and dolomite treatments, respectively. Results from this study complement those obtained in the field by clearly demonstrating the mechanisms involved in the downward movement of some fertilizers commonly used to increase the base saturation of acid forest soils.  相似文献   

5.
Abstract

Crystalline minerals in anaerobically digested sewage sludges were determined by x‐ray diffraction analysis. Sludge samples were prepared for x‐ray analysis by either washing with H2O to remove soluble salts or oxidizing organic matter with H2O. A limited number of minerals are present as crystalline materials in sludge. Even though the sludges contained appreciable concentrations of Cu, Zn, Cd, Pb and Ni, no crystalline metal sulfides, phosphates, hydroxides, oxides or carbonates were found with the exception of a possible Cu, Zn carbonate hydroxide. All other crystalline components detected are common minerals such as quartz, feldspar, montmorillonite, chlorite, mica, dolomite and calcite.  相似文献   

6.
Dolomite (CaMg(CO3)2) constitutes half of the global carbonates. Thus, many calcareous soils have been developing rather from dolomitic rocks than from calcite (CaCO3)‐dominated limestone. We developed a physical fractionation procedure based on three fractionation steps, using sonication with subsequent density fractionation to separate soil organic matter (SOM) from dolomite‐derived soil constituents. The method avoids acidic pretreatment for destruction of carbonates but aims at separating out carbonate minerals according to density. The fractionation was tested on three soils developed on dolostone parent material (alluvial gravel and solid rock), differing in organic‐C (OC) and inorganic‐C (IC) concentrations and degree of carbonate weathering. Soil samples were suspended and centrifuged in Na‐polytungstate (SPT) solutions of increasing density, resulting in five different fractions: two light fractions < 1.8 g cm–3 (> 20 μm and < 20 μm), rich in OC and free of carbonate, and two organomineral fractions (1.8–2.4 g cm–3 and 2.4–2.6 g cm–3), containing 66–145 mg g–1 and 16–29 mg g–1 OC. The organomineral fractions consist of residual clay from carbonate weathering such as clay minerals and iron oxides associated with SOM. The fifth fraction (> 2.6 g cm–3) was dominated by dolomite (85%–95%). The density separation yielded fractions differing in mineral compositions, as well as in SOM, indicated by soil‐type‐specific OC distributions and decreasing OC : N ratios with increasing density of fractions. The presented method is applicable to a wide range of dolomitic and most likely to all other calcareous soils.  相似文献   

7.
Purpose

Several interactions between Al and the solid phase of soil influence Al buffering in soil solution. This work evaluated soils cultivated with Pinus taeda L. to determine Al forms in organic and mineral horizons using various extraction methods and to relate acidity with clay mineralogy.

Materials and methods

Organic and mineral horizons of 10 soil profiles (up to 2.1 m deep) in southern Brazil were sampled. Organic horizons were separated into fresh, aged, and fermented/humified litter. The following Al extraction methods were utilized: 0.5 mol L?1 pH 2.8 CuCl2–Al complexed in organic matter; 1.0 mol L?1 KCl–exchangeable Al; water–Al soluble in soil solution; HF concentrated?+?HNO3 concentrated?+?H2O2 30% (v/v)–total Al. Six sequential extractions were carried out to isolate different forms of amorphous minerals that can buffer Al on soil solution: 0.05 and 0.1 mol L?1 sodium pyrophosphate; 0.1 and 0.2 mol L?1 ammonium oxalate; 0.25 and 0.5 mol L?1 NaOH. Samples of clay were also analyzed by XRD.

Results and discussion

There was a clear effect of litter age on increasing total Al concentration. In the aged litter and fermented and/or humified litter, levels of total Al were 1.4 to 3.8 and 1.5 to 7.8 times greater than in fresh litter, respectively. The CuCl2 method had higher Al extraction capacity than the KCl method for litter. The lowest Al–pyrophosphate values were observed in the Oxisol, which also had a predominance of gibbsite and the lowest levels of Al–KCl and Al–CuCl2. There was an inverse relationship between degree of soil weathering and soluble and exchangeable Al in soils. Available Al increased with higher Si proportion in minerals of the clay fraction (2:1?>?1:1?>?0:1).

Conclusions

The worst scenario was soils with the combination of high soluble and exchangeable Al levels and high concentrations of amorphous forms of Al minerals. The best predictors of Al accumulation in the youngest litter horizon were extractions of amorphous minerals with pyrophosphate and NaOH. These extractors are normally used to predict the level of Al buffering in soils. Organic matter had less influence on Al dynamics in soils.

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8.
The Al species in the soid and liquid phases were studied in eight soils developed from slates in a watershed subjected to acid deposition. From soil solution data the mechanisms possibly controlling Al solubility are also discussed. The soils are acidic, organic matter rich and with an exchange complex saturated with Al. In the solid phase, more than 75% of non-crystalline Al was organo-Al complexes, mostly highly stable. In the soil solutions, monomeric inorganic. Al forms were predominant and fluoro-Al complexes were the most abundant species, except in soil solutions of pH<4.8 and Al L/F ratio >3, in which Al3+ predominated and sulphato-Al complexes were relatively abundant. The most stable phases were kaolinite, gibbsite and non-crystalline Al hydroxides. In most samples, Al solubility was controlled by Al-hydroxides. Only in a few cases (solutions of pH 4-5, Al3+ activity >40 µmol L-1 and SO4 content >200 µmol L-1), Al-sulphates such as jurbanite also could exert some control over Al solubility. In adition to these minerals, a possible role of organo-Al complexes or the influence of adsorption reactions of sulphate is considered, especially for samples with very low Al3+ content (<0.5 µmol L-1).  相似文献   

9.
A clearcut stand of Pinus sylvestris in Flanders (Belgium) was limed with 3 ton/ha dolomite and reforested with Acer pseudoplatanus and Fagus sylvatica. Soil water monitoring revealed an overall decrease of ion concentrations and an annual peak in September due to seasonal nitrification. Liming reduced concentrations of NO3 - and Al3+ and raised concentrations of K+ and Mg2+ and the molar ratio of (Ca+Mg)/Al. Liming also stimulated release of SO4 2-, which prevented a rise of pH, except during nitrification peaks. Liming had no effect on height increment of Fagus but stimulated Acer, which suffered from severe deficiencies of calcium (Ca), magnesium (Mg), potassium (K), and phosphorus (P) without treatment. Nitrogen (N) was not growth-limiting for Fagus or Acer and liming had no effect on N concentrations in leaves of both species. Liming had a strong impact on ground vegetation. Nutrient-demanding species expanded while species that tolerate nutrient-poor conditions decreased. It is argued that changes in ground vegetation had a greater impact on reduction of NO3 - concentration in soil water than increased tree growth.  相似文献   

10.
Titanium dioxide (TiO2)–silicon dioxide (SiO2) thin films were synthesized using the peroxo titanic acid approach (PTA) combined with the sol–gel method at low temperature around 100°C. The effects of type and amount of dopants of ferric (Fe3+) or thiourea (N-S) and co-dopants of Fe3+ and N-S on the films physicochemical properties and on the photocatalytic degradation of the methylene blue and formaldehyde under UV and visible light irradiation were investigated. Physicochemical properties of photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, wavelength-dispersive X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and UV–Vis spectroscopy. The results showed that the TiO2 crystal phases obtained from this method were exclusively anatase and the needle-like crystals have an average diameter of 10–25 nm. Compared with the single dopant of 1.0 wt.% Fe3+ or 0.125 wt.% N-S that was the optimal concentration for photocatalytic degradation of methylene blue and formaldehyde, the co-dopants of 0.125 wt.% N-S + 1.0 wt.% Fe3+ furthermore increased the degradation efficiency. Co-dopants of 0.125 wt.% N-S + 1.0 wt.% Fe3+ in TiO2–SiO2 films were considered to play synergistic roles in narrowing TiO2 band gap resulting in the higher methylene blue and formaldehyde degradation efficiency. Since the crystal grain size of TiO2–SiO2 films synthesized by the PTA method is small, in the visible light region, the high transmittance was attainable to 80% with no-doped and dropped to 50–60% with doped thin films.  相似文献   

11.
福建菜田氮磷积累状况及其淋失潜力研究   总被引：8，自引：1，他引：8  
本文通过采集460个福建菜田代表性耕层土样,采用土壤测试和土柱渗漏水模拟试验的方法研究菜田土壤硝态氮和Olsen P含量状况和淋失临界指标及其淋失潜力。结果表明,耕层土壤硝态氮含量为47.455.5 mg/kg,Olsen-P含量则为61.743.2 mg/kg, 其中瓜果类蔬菜种植地土壤硝态氮和Olsen-P含量明显高于叶菜类和根茎类蔬菜种植地。 应用双速率转折点建模法,得到氮、 磷淋失临界指标X0分别为土壤硝态氮76.3 mg/kg和Olsen-P 42.8 mg/kg。 淋失临界值相当于或略高于满足蔬菜营养的农学指标。当土壤硝态氮或Olsen-P含量低于X0时,随着其含量增加,渗漏水硝态氮或总磷浓度以线性方式缓慢增加,反之,则以非线性形式急剧增大。土壤硝态氮和Olsen-P含量高于其X0的土样数分别占17.9%和81.3%, 表明这些样点具有较高的氮、 磷淋失潜力,是氮、 磷污染控制的关键地块。 瓜果类菜田土壤硝态氮和Olsen-P含量高于其X0的土样数分别占到32.3%和96.3%,淋失潜力明显高于叶菜类和根茎类菜田,是氮、 磷污染控制的优先区域。  相似文献   

12.
Chemical Composition of Precipitation in Beijing Area, Northern China   总被引：1，自引：0，他引：1  
Variations of anions (SO4 2-, NO3 -,NO2 -, Cl- and F-),cations (K+,Na+, Ca2+, Mg2+ and +) and pH values in precipitation, througfall and stemflow samples collected overa four-year period (1995–1998) in Beijing (two sitesZhongguancun and Mangshan) are presented. The annualvolume-weighted range of pH values were 6.57–7.11 inprecipitation, 5.46–6.86 in thoughfall and 5.32–6.41 instemflow. The fominant anion was , while Ca+and NH4 + were the main cations in precipitation,throughfall and stemflow. Most of ion concentrations with precipitation, throughfall and stemflow volume showed negative correlation, except for some ones. Significant correlationvalues were also found between ions (SO4 2-,NO3 -, Cl-, F-, Ca2+,Mg2+ andNa+) in precipitation, throughfall and stemflow indicatedthe common sources of these ions such as coal combustion,automobile emission and fertilizers application. Compared toprecipitation, there was an increased ion concentration inthroughfall or in stemflow. Changes of ion concentrations werein Quercus liatungensis Koiz. and Pinus tabulaefornisCarr. throughfall (or stemflow) because of different crown andbark qualities of tree species.  相似文献   

13.
Exchangeable and soluble soil aluminum (Al) is limiting plant growth in many soils worldwide. This study evaluated the effects of increasing rates of dolomite and magnesium carbonate (MgCO3) on Al3+, pH, dissolved organic carbon, cations, anions, and Al speciation on oil palm Deli dura × AVROS pisifera root growth. Dolomite and MgCO3 additions significantly raised linearly soil solution pH, magnesium (Mg2+), nitrate (NO3 ?) and chlorine (Cl?) concentrations; exponentially decreased the activity of phytotoxic Al species [aluminum (Al3+), aluminum sulfate (Al2SO4), and aluminum fluoride (AlF3)]; and reduced manganese (Mn) concentration and activity. High activity of those species exponentially reduced root dry weight. Optimum oil palm growth was achieved at: <50 μM monomeric Al, < 30 μM Mn, and <0.20 unit of the ratio Al+Mn to calcium (Ca)+Mg. High activity of Al species and Mn in acidic soil solution cause significant reduction of the root growth. Soil acidity alleviation either with dolomite or MgCO3 mitigates the toxic effect of Al and Mn.  相似文献   

14.
The adsorption and binding of plasmid p34S DNA on four different colloidal fractions from a Brown soil and clay minerals in the presence of various Ca2+ concentrations, the ability of bound DNA to transform competent cells of CaCl2-treated Escherichia coli, and the resistance of bound DNA to degradation by DNase I were studied. DNA adsorption on soil colloids and clay minerals was promoted in the presence of Ca2+. Kaolinite exhibited the highest adsorption affinity for DNA among the examined soil colloids and clay minerals. In comparison with organo-mineral complexes (organic clays) and fine clays (<0.2 μm), DNA was tightly adsorbed by H2O2-treated clays (inorganic clays) and coarse clays (0.2-2 μm). The transformation efficiency of bound DNA increased with increasing concentrations of Ca2+ at which soil colloid or clay mineral-DNA complexes were formed. DNA bound by kaolinite showed the lowest transformation efficiency, and especially no transformants were observed with kaolinite-DNA complex prepared at 5-100 mM Ca2+. Compared to organic clays and fine clays, DNA bound on inorganic clays and coarse clays showed a lower capacity to transform E. coli at different Ca2+ concentrations. The presence of soil colloids and minerals provided protection to DNA against degradation by DNase I. Montmorillonite, organic clays and fine clays showed stronger protective effects for DNA than inorganic clays and coarse clays. The protection mechanisms as well as the differences in transforming efficiency of plasmid DNA molecules bound on various soil colloidal particles are discussed. The information obtained in this study is of fundamental significance for the understanding of the horizontal dissemination of recombinant DNA and the fate of extracellular DNA in soil environments.  相似文献   

15.
Soil cover and rainfall intensity (RI) are recognized to have severe impacts on soil erosion and an interaction exists between them. This study investigates the effect of rainfall intensity (RI) and soil surface cover on losses of sediment and the selective enrichment of soil organic carbon (SOC) in the sediment by surface runoff. A field rainfall simulator was used in the laboratory to produce 90 min rainfall events of three rainfall intensities (65, 85 and 105 mm h− 1) and four cover percentages (0%, 25%, 50% and 75%) on soil material at 9% slope. A strong negative exponential relation was observed between cover percentage and RI on sediment loss under 85 and 105 mm h− 1 of rain, while under RI of 65 mm h− 1, the highest sediment loss was observed under 25% cover. Overall, higher RI and lower cover produced higher sediment and consequently higher nutrient loss, but resulted in a lower SOC enrichment ratio (ERSOC) in the sediment. The amount of runoff sediment rather than the ERSOC in the sediment was the determinant factor for the amount of nutrients lost. The values of ERSOC were high and positively correlated with the ER values of particles smaller than 20 µm (p < 0.01). Although the sediment contained substantially more fine fractions (fine silt and clay, < 20 µm), the original soil and runoff sediment were still of the same texture class, i.e. silt clay loam.  相似文献   

16.
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17.

Purpose

Wastes from a former Portuguese steel plant were deposited between 1961 and 2001 on the riverbank of a tributary of the Tagus River creating a landfill connected to the river, posing a potential contamination risk to the Tagus estuary ecosystem. This study aims to assess the transfer of chemical elements from contaminated sediments to the estuarine water from cycles of sediment leaching so as to evaluate the ecotoxicity of the leachates, and to analyze the solid phases crystallized from those leachates.

Materials and methods

Landfill sediment and estuarine water samples were collected during low tide. Sediment samples were analyzed for pH, electric conductivity (EC), Corg, NPK, and iron oxides. Leaching assays (four replicates) were done using estuarine water (200 cm3/replicate) and 1.5 kg of sediment per reactor. Each reactor was submitted to four leaching processes (0, 28, 49, and 77 days). The sediment was kept moist between leaching processes. Sediment (total (acid digestion) and available fraction (diluted organic acid extraction-Rhizo)) elemental concentrations were determined by inductively coupled plasma–instrumental neutron activation analysis (ICP/INAA). Leachates, and estuarine and sediment pore waters were analyzed for metals/metalloids by ICP/mass spectrometry (MS) and carbonates/sulfate/chloride by standard methodologies. Ecotoxicity assays were performed in leachates and estuarine and pore waters using Artemia franciscana and Brachionus plicatillis. Aliquots of the leachates were evaporated to complete dryness (23–25 °C) and crystals analyzed by X-ray powder diffraction (XRD).

Results and discussion

Sediment with pH?=?8 and high EC and Corg was contaminated with As, Cd, Cr, Cu, Pb, and Zn. The element concentrations in the available fraction of the sediment were low compared to the sediment total concentrations (<1 % for Rhizo extraction). The concentrations of potentially hazardous elements in the estuarine water were relatively low, except for Cd. Concentrations of hazardous elements in the leachates were very low. Calcium, K, Mg, Na, and chloride concentrations were high but did not vary significantly among the four leaching experiments. Total concentrations of carbonate were much higher in leachates than in estuarine water. Both estuarine water and leachates showed negligible toxicity. Crystals identified in the solids obtained from the leachates by evaporation were halite, anhydrite, epsomite, dolomite, and polyhalite.

Conclusions

The sediment showed the capacity to retain the majority of the potentially hazardous chemical elements. Remobilization of chemical elements from sediment by leaching was essentially negligible. The variation of total concentrations of Ca, carbonate, and sulfate in leachates indicates that the sediment contained reactive sulfides. Due to its composition, the sediment seems to be a dynamic system of pollution control, which should not be disturbed.
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18.
Seasonal variations in pore water and solid phase geochemistry were investigated in urbanized minerotrophic peat sediments located in southwestern Michigan, USA. Sediment pore waters were collected anaerobically, using pore water equilibrators with dialysis membranes (“peepers”) and analyzed for pH, alkalinity, dissolved ΣPO4 ?3, ΣNH4 +, ΣS?2, SO4 ?2, Fe+3, Fe+2, and Mn+2 at 1-2 cm intervals to a depth of 50 cm. Cores collected adjacent to the peepers during all four seasons were analyzed for reactive solid phase Fe according to extraction methods proposed by Kostka and Luther (1994). The association of Fe and trace metals (Mn, Pb, Zn, Cu, Cr, Co, Cd, U) with operationally defined solid phase fractions (carbonates, iron and manganese oxides, sulfides/organics and residual) was assessed for cores extracted during winter and spring using extraction methods proposed by Tessier et al. (1979, 1982). Pore water Fe and S data demonstrate a clear seasonal variation in redox stratification of these sediments. The redox stratification becomes more compressed in spring and summer, with relatively more reducing conditions closer to the sediment water interface (SWI), and less reducing conditions near the SWI in fall and winter. In the upper 10–15 cm of sediment, the pool of ascorbate extractable Fe, thought to be indicative of reactive Fe(III) oxides, diminishes during spring and summer, in agreement with seasonal changes in redox stratification indicated by the pore water data. Tessier extractions indicate that the total extractable quantity of all metals analyzed in this study decrease with depth, and that the majority of the non-residual Fe, Pb, Zn, Cu, Cr, Co, Cd, and U is typically associated with the sulfide/organic fraction of the sediments at all depths. Non-residual Mn, in contrast, is significantly associated with carbonates in the upper 15–25 cm of the sediment, and predominantly associated with the sulfide/organic fraction only in deeper sediments.  相似文献   

19.
潘宏  陈邦本  方明 《土壤学报》1993,30(4):416-422
江苏滨海盐土向潮土演化过程中，水溶性Ｆ＾－含量经历了由少变多，再由多变少的过程。水溶性氟含量变化受控于水溶性Ｃａ＾＋＋变化（Ｆ＾－＝ａ＋ｂＣａ＾＋＋－１／２），同时，由于土壤胶体和溶液中ＯＨ＾－与Ｆ＾－含量可能ＣａＦ２的活度积起控制作用，而ｐＨ值的变化起叠加作用。江苏沿海土壤中影响水溶性氟含量的矿物主要是ＣａＦ２。  相似文献   

20.
有机无机肥配施对酸性菜地土壤硝化作用的影响   总被引：5，自引：0，他引：5  
通过室内培养和田间试验, 研究了有机无机肥配施对酸性菜地土硝化作用的影响。培养试验条件为60%土壤最大持水量和25 ℃。 结果表明,土壤硝化作用模式为指数方程,延滞期10天。与纯化肥处理（NPK）相比,鲜猪粪配施无机肥（FPM+NPK）和猪粪堆肥配施无机肥（CPM+NPK）均能降低土壤硝化势和氨氧化潜势,猪粪堆肥配施无机肥还能增加土壤微生物量碳、 氮。鲜猪粪配施无机肥和猪粪堆肥配施无机肥处理在硝化培养和田间试验期间N2O释放量均没有差异,但硝化培养期间鲜猪粪配施无机肥的N2O释放量显著低于纯化肥处理,田间试验期间猪粪堆肥配施无机肥的N2O释放量显著低于纯化肥处理。培养试验结束后的土壤pH值与土壤硝化势间,以及硝化培养期间N2O累积释放量与土壤硝化势间均存在显著正相关关系。本研究表明, 有机无机肥配施显著影响土壤硝化作用以及硝化培养期间和田间N2O释放。  相似文献   

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