Evaluating macroinvertebrate responses to recovery from acidification in small lakes in Ontario,Canada

The biomonitoring program of Environment Canada examines food chains in small Ontario lakes to interpret ecological responses of waterfowl and their foods to changing acid deposition. Macroinvertebrates and fish were sampled in three acid-sensitive regions: Muskoka (1991; N=20), Algoma (1992; N=20), and Sudbury (1994; N=22). Small lakes (<11 ha;=" important=" breeding=" habitat=" for=" waterfowl)=" were=" chosen=" to=" cover=" the=" range=" of=" ph=" in=" each=" region,=" and=" include=" those=" with=" and=" without=" fish.=" in=" all=" regions,=" macroinvertebrate=" taxonomic=" richness=" (particularly=" nekton=" and=" benthos)=" was=" greater=" in=" fishless=" lakes=" compared=" to=" lakes=" with=" fish.=" among=" fishless=" lakes,=" taxonomic=" richness=" (especially=" benthos)=" was=" positively=" correlated=" with=" ph,=" although=" regional=" differences=" were=" evident.=" previous=" studies=" near=" sudbury=" have=" shown=" that=" several=" benthic=" groups=" have=" distribution=" and=" abundance=" patterns=" with=" respect=" to=" ph=" (trichoptera,=" ephemeroptera,=" hirudinea,=" amphipoda,=" and=" gastropoda).=" those=" patterns=" continue=" near=" sudbury,=" and=" were=" also=" strongly=" apparent=" in=" algoma.=" in=" all=" regions,=" the=" number=" of=" acid-sensitive=" taxa=" per=" lake=" is=" related=" to=" ph,=" and=" should=" increase=" as=" lakes=" recover=" from=" acidification.=" however,=" predicting=" macroinvertebrate=" responses=" to=" recovery=" must=" consider=" concurrent=" effects=" of=" fish,=" as=" they=" are=" a=" dominant=" factor=" structuring=" these=">     

Critical loads of acidity to surface waters in the Vosges massif (north-east of France)

Acid clearwater fishless streams have been identified in the Vosges mountains. In order to evaluate the relatipnships between acidifying factors (such as atmospheric deposition), buffering factors (such as bedrock and soil type), and surface water acidity, an exhaustive survey of streamwater acidity in the Vosges mountains (N-E France) was performed. A network of 11 measurement stations of atmospheric deposition was used to estimate and map deposition over the whole massif (total area 5000 km²). Data on bedrock, soil, superficial deposits, and vegetation were collected from published studies. Sensitive areas as well as acidifying environment factors were derived from the corresponding maps. Over the whole massif, 19% of streams showed baseflow alkalinity below 30 eq.r¹ and 7.5 % were identified as acid (pH < 5.4).=" acid=" streams=" occur=" on=" the=" north-western=" side=" of=" the=" massif=" on=" quartzrich=" sandstone=" and=" acid=" granites.=" in=" each=" of=" these=" areas,=" we=" could=" clearly=" point=" out=" on=" one=" hand,=" the=" negative=" influence=" of=" conifer=" vegetation=" and=" glacial=" soil=" abrasion=" or=" induration,=" and=" on=" the=" other=" hand=" the=" buffering=" effect=" of=" moraine=" deposits.=" a=" corresponding=" range=" of=" critical=" loads=">< 0.2=" to=" 2.0=" keq.=">¹ yr¹) for surface water was calculated using the Steady State Water, Chemistry method (SSWC).     

Snowpack quality as an indicator of air pollution in Finnish Lapland and the Kola Peninsula,NW Russia

Bulk snow samples were collected from the snowpack in open areas along two sampling lines running to the west from the Cu-Ni smelters at Nikel and Monchegorsk, NW Russia, during 1991–1993. The aim of the study was to estimate the area affected by sulphur and heavy metal deposition from the smelters. Snowpack quality was used as an indicator of deposition during winter time. The total sulphur, copper and nickel concentrations in the snowpack decreased significantly (p<0.001) with=" increasing=" distance=" from=" the=" smelters=" along=" the=" sampling=" line=" running=" directly=" to=" the=" west=" from=" monchegorsk.=" the=" deposition=" pattern=" was=" similar=" each=" winter=" during=" 1991–1993.=" the=" ph=" values=" did=" not=" correlate=" with=" the=" corresponding=" sulphur=" concentrations,=" and=" there=" was=" no=" decreasing=" ph=" gradient=" in=" the=" snowpack=" on=" moving=" towards=" monchegorsk.=" the=" effects=" of=" sulphur=" emissions=" from=" monchegorsk=" on=" snowpack=" chemistry=" were=" not=" detectable=" on=" the=" finnish=" side=" of=" the=" border.=" the=" 3-year=" mean=" of=" the=" total=" sulphur=" concentration=" was=" 0.27=" mg/kg,=" and=" of=" the=" ph=" values=" 4.92,=" along=" the=" sampling=" line=" running=" to=" the=" west=" of=" monchegorsk.=" the=" total=" sulphur=" concentrations=" near=" the=" smelters=">< 20=" km)=" varied=" between=" 0.37=" and=" 0.95=" mg/kg.=" the=" effect=" of=" the=" cu-ni=" smelters=" at=" nikel=" on=" snowpack=" quality=" was=" not=" detectable=" in=" northern=" finnish=" lapland.=" the=" 3-year=" mean=" for=" total=" sulphur=" was=" 0.20=" mg/kg=" and=" for=" ph=" 4.96=" along=" the=" sampling=" line=" running=" to=" the=" west=" of=">     

Relationship between viscosity and molecular weight in an andosol humic acid

Viscosity and molecular weight of particle size fractions obtained from an Andosol humic acid (HA) were determined. Viscosity was determined both in solutions with and without the addition of 0.1 M NaCl (Cs 0.1 and Cs 0, respectively) at pH 7.0. Polyelectrolytic character was observed in the particle size fractions based on the changes in the concentration dependence of reduced viscosity with NaCI concentrations. The use of a Cs 0.1 solution was suitable for the determination of the values of intrinsic viscosity ([η]) of the particle size fractions. The [η] value increased with increasing weight average molecular weight ( M _w) determined by gel permeation chromatography (GPC), and ranged from 4.3 to 12.9 X 10-3 (L g^-1) in the Cs 0 solution and from 3.5 to 6.6 × 10^-3 (L g^-1) in the Cs 0.1 solution. A linear relationship between [η] in the Cs 0.1 solution and M _w on a logarithmic scale, which was similar to the MarkHouwink equation, was observed. The value of the constant a calculated from the relationship, which reflected the polymer morphology, was 0.75 in the Cs 0.1 solution, and it corresponded to a polymer with flexible chains.     

Effects of pH and Ionic Strength on the Adsorption of Cs,Sr, Eu,Zn, Cd and Hg by Pseudomonas Putida

Bacterial metal accumulation may influence the mobility and chemical form (speciation) ofmetals in the environment. The passive adsorption of six metals (Cs, Sr, Eu, Zn, Cd and Hg) by asoil bacterium, Pseudomonas putida, was studied in the present work, using a radiotracerbatch-distribution technique. To replicate natural conditions, the adsorption was considered as afunction of pH (4-10) and ionic strength (0.01 M and 0.1 M KCl) at a low metal concentration(10-8 M). P. putida exhibited a total metal accumulating capacity of 200-1000 meq kg-1 bacteria(dry weight) (measured in 0.01 M KCl at pH 6.4). This capacity is comparable to that of manyorganic soil components and it is above the capacity of most inorganic constituents. The followingaffinity order of adsorption was observed: Hg>Eu>Cd,Zn,Sr>Cs. The results indicatethat the bacterial surface carries different sites that exhibit varying affinity and capacity for bindingmetal ions. It can be concluded that the overall adsorption of metals by P. putida is determined byseveral interacting processes related to the properties of both the metals and the bacterial surfaceand to the composition of the solution phase (pH as well as ionic strength).     

Biotite weathering by <Emphasis Type="Italic">Aspergillus niger</Emphasis> and its potential utilisation

Purpose

Biotite, as a type of associated mineral, is normally applied as a filling material for buildings, or is discarded as tailings. However, as a potassium-bearing phyllosilicate mineral, biotite can be easily weathered by fungi, which leads to its internal potassium being released for agricultural production (1), and the mineral residues being weathered by the fungus may be applied for adsorption of heavy metal ions (2).

Materials and methods

This work investigates the weathering of biotite by Aspergillus niger through the analysis of the differences in ion dissolution from biotite, producing of organic acids, the change of mineral morphology and composition by inductively coupled plasma optical emission spectrometry (ICP-OES), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Besides, the mineral residues were applied for adsorption of heavy metal ions.

Results and discussion

Results showed that the mycelia envelope the mineral and form fungal–mineral aggregates. The fungus can secrete a variety of organic acids including citric acid and oxalic acid; these attacked the surface and cleavage of biotite to release ions (Al³⁺, Fe³⁺, Mg²⁺, and K⁺). During incubation with A. niger, biotite weathered as shown by the relative decrease in biotite content and increase in interlayer spacing. Moreover, a certain concentration of phytic acid and tween-80 could promote the release of K⁺, and the fermentation liquid of rice bran has the same effect. Biotite residues showed a good adsorption for Cd²⁺, Pb²⁺, Zn²⁺, and Cu²⁺.

Conclusions

The results indicate that biotite can be biotransformed and release K⁺, of which the production can be acted as heavy metal ion adsorbent. It provides a reference for application of biotite in agriculture and control of heavy metal ion pollution in soil.

     

病原菌在红壤胶体上的吸附机制研究

研究了pH和KCl离子强度对猪链球菌和大肠杆菌在红壤胶体表面吸附的影响,结合表面物化性质和Derjaguin-Landau-Verwey-Overbeek(DLVO)理论分析互作机制。结果表明,细菌在红壤胶体表面的吸附等温线能较好拟合Freundlich方程(R20.97),猪链球菌在红壤胶体表面吸附的分配系数(Kf)是大肠杆菌的4.5倍～6.1倍,细菌在去有机质胶体表面吸附的Kf值为含有机质胶体的2.4倍～3.2倍。比表面积越大或zeta电位绝对值越小,细菌吸附能力越强,吸附态细菌位于距红壤胶体表面90～100 nm处的次级小能位置。随着体系pH降低(9.0～4.0)或离子强度增大(1～10 mmol L-1),细菌与红壤胶体互作能障降低,细菌吸附量增大,吸附机制符合DLVO理论;而在高离子强度下(50～100 mmol L-1),猪链球菌吸附量降低了3.4%～5.6%,表明除DLVO作用力外,非DLVO作用力如空间位阻排斥和疏水作用对吸附也有贡献。     

Modelling long-term acidification trends of forested sandstone catchments in the Black Forest (SW Germany)

An extensive database from eight Triassic (Bunter) sandstone catchments in the Black Forest, SW Germany, was used to apply the MAGIC model and simulate long-term acidification trends. Using the ion ratio (Ca+Mg)/(SO₄+NO₃) as criterium (values< 1.5=" indicate=" an=" acidified=" state),=" hindcast=" simulations=" showed=" that=" the=" brooks=" of=" three=" catchments=" have=" reached=" values="><1.5, three=" catchments=" are=" approaching=" 1.5,=" and=" two=" catchments=" (carbonate=" bearing=" upper=" bunter)=" are=" still=" well=" above=" this=" limit.=" the=" different=" acidification=" state=" of=" the=" catchments=" is=" mainly=" caused=" by=" the=" amount=" of=" acidic=" deposition=" and=" bedrock=" geology.=" other=" differences=" (shallow=" or=" deep=" groundwater=" circulation,=" sulphate=" sorption=" and=" soil=" parameters)=" are=" less=" significant.=" to=" simulate=" the=" future=" evolution,=" three=" scenarios=" were=" tested:=" a=" pessimistic,=" an=" optimistic=" and=" a=" most=" probable=" case.=" the=" latter=" leads=" to=" a=" still=" progressing=" but=" decelerated=" acidifcation=" in=" the=" next=" 100=" years.=" in=" the=" pessimistic=" case,=" acidification=" rates=" will=" be=" accelerated=" in=" two=" of=" the=" catchments.=" even=" in=" the=" optimistic=" case,=" the=" initial=" state,=" prior=" to=" acidification,=" cannot=" be=" restored=" up=" to=" the=" year=" 2130.=" however,=" the=" forecasting=" of=" the=" future=" evolution=" is=" still=" markedly=" hampered=" by=" the=" significant=" uncertainty=" in=" the=" evaluation=" of=" nitrogen-driven=" acidification,=" a=" process=" which=" today=" already=" predominates=" in=" parts=" of=" the=" black=">     

Toxicity and binding of copper,zinc, and cadmium by the blue-green alga,Chroococcus paris

The toxic effects and accumulation of the heavy metals, Cd, Cu, and Zn by the sheath forming blue-green alga Chroococcus paris were investigated. All three of the metals were bound rapidly. Approximately 90% of the total amount of the added metal was bound within 1 min. Further significant binding occurred at a slower rate. The maximum metal binding capacity, as determined by filtration studies, was determined to be 53, 120, and 65 mg g^?1 dry algal weight for Cd, Cu, and Zn, respectively. Binding curves for the metals followed the Langmuir adsorption isotherm model. The amount of metal bound increased with increasing pH. Metal binding increased significantly when pH was increased from 4 to 7. Nearly all of the metal was found to be rapidly EDTA extractable. Metals were found to be increasingly toxic to growing cultures in the order, Zn, Cd, and Cu. All of the metals studied exhibited toxic effects at concentrations greater than 1.0 mg L^?1. The lowest concentrations used which showed detectable toxicity were 0.1 mg L^?1 for Cu and >0.4 mg L^?1 for Cd and Zn.     

Cadmium bioaccumulation by clams dwelling in different salinity regimes along the Saudi coast of the Arabian gulf

The objective of this study was to investigate Cd bioaccumulation in clams living in different salinities. Several hundred clams (Maritrix maritrix) and sediment samples were collected during 1985–1986 from 12 locations on the Saudi coastal areas of the Arabian Gulf. Soft tissue from each clam was removed and digested in HNO₃. Sediments were also digested in HNO₃. Cadmium in the recently collected seawater samples was extracted using pyrrolidine carbodithioic acid-chloroform system. Cadmium in all the collected samples was determined using an inductively coupled argon plasma analyzer. Concentrations of Cd in the sediments varied insignificantly between 0.1 and 0.22 mg kg^–1. Significant geographical variations in the mean Cd concentrations in clams (P < 0.05)=" were=" found.=" intrastation=" differences=" in=" cd=" bioaccumulation=" were=" also=" significant.=" correlation=" between=" biometric=" observations=" and=" cd=" concentrations=" in=" clams=" was=" not=" significant=" (p=">< 0.05).=" seawater=" salinity=" was=" significantly=" (p=">< 0.05)=" correlated=" to=" the=" mean=" cd=" concentrations=" in=" clams=" and=" seawater.=" cadmium=" accumulation=" in=" the=" clams=" was=" supported=" by=" the=" chemical=" behavior=" of=" cd=" in=">     

In situ ATR-FTIR study on the adhesion of Pseudomonas putida to Red soil colloids

Purpose

Bacterial adhesion to soil particles is fundamentally important in mineral weathering, organic matter degradation, heavy metal transformation, and fate of pollutants. However, the adhesion mechanism between bacteria and soil colloids under continuous flow systems in the natural environments remains unknown.

Materials and methods

The kinetics of Pseudomonas putida cellular adsorption and desorption on Red soil colloid films under controlled flow systems were examined using in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Derjaguin–Landau–Verwey–Overbeek (DLVO) and non-DLVO interactions were employed to elucidate the cellular adsorption and desorption kinetics.

Results and discussion

In situ ATR-FTIR spectroscopy can be used effectively to investigate the kinetics of bacterial adhesion to a soil colloid deposit. Surface proteins may be involved in the bacterial adhesion to soil colloids. The adsorption followed pseudo-first-order kinetic equation. High adsorption rate constant and great saturation coverage of adsorbed bacteria were found at high ionic strengths in dynamic systems.

Conclusions

P. putida bacterial cellular adsorption on the soil colloid deposit was irreversible in a wide range of ionic strengths under controlled flow systems. The less reversible adhesion was probably attributed to the DLVO predicted deep secondary energy minima together with non-DLVO factors including polymer bridging, local charge heterogeneities, surface roughness, and Lewis acid–base interactions.     

Remediation of lead-, arsenic-, and cesium-contaminated soil using consecutive washing enhanced with electro-kinetic field

Purpose

Extensive deposition of Pb, As, and Cs in soils may damage ecosystems and human’s health. Soil washing is the most conventional remediation method, and its efficiency depends on metal solubility in soil. This study aims to optimize operating variables of electro-kinetic field (EKF)-enhanced soil washing procedures.

Materials and methods

Soil samples from a Mississippi River Delta rice field were homogeneously spiked with Pb, As, and Cs, and contaminated soil was aged for 3 months. The remediation involved a first stage electro-kinetic process, followed by a soil washing procedure. Soil pH changes under EKF were studied. Effects of citric acid and reversed EKF were investigated for alleviating possible alkaline precipitation. In the washing procedure, soil washing time and cycles with different extractants were examined. The overall EKF-enhanced soil washing efficiencies were discussed as well.

Results and discussion

The implement of EKF offered an acidic soil environment around the anode areas for solubilizing metal(loid)s. Combined with EKF, citric acid was more conductive to desorb metal(loid)s. In addition, the reversed EKF effectively alleviated metal(loid) precipitation caused by alkalization in the first stage cathode areas. The EKF significantly enhanced metal(loid) extractions in the anode area of soils using Na₂EDTA, CaCl₂, and citric acid at pH of 2. The most preferable removal of Pb (80–98 %), As (48–63 %), and Cs (10–13 %) was achieved with three extractants. CaCl₂ and citric acid were proved to be suitable alternatives to Na₂EDTA for Pb extraction. A washing process of 2 h extraction with double washing cycles was optimized.

Conclusions

Soil washing time and cycles were major factors governing the metal(loid) removal from soil. Washing process of 2 h extraction with double cycles was optimized for further extraction based on higher washing efficiency. The EKF effectively improved washing efficiency while some electrical parameters need further studies for cost performance consideration.

     

Copper Binding by Activated Biochar Fibres Derived from <Emphasis Type="Italic">Luffa cylindrica</Emphasis>

The adsorption of copper (Cu(II)) from aqueous solutions by activated Luffa cylindrica biochar fibres has been investigated by means of batch equilibrium experiments and FTIR spectroscopy. The effect of various physicochemical parameters, such as pH, initial metal concentration, ionic strength, mass of the adsorbent, contact time and temperature, has been evaluated by means of batch type adsorption experiments. FTIR spectroscopy, as well as acid-base titrations, was used for the characterization of the material and the surface species formed. According to the experimental results even at pH 3, the relative sorption is above 85% and the adsorption capacity of the activated biochar fibres for Cu(II) is q _max = 248 g kg^?1. Moreover, the interaction between the surface carboxylic moieties and Cu(II) results in the formation of very stable inner-sphere complexes (?G ^o = ?11.2 kJ mol^?1 at pH 3 and ?22.4 kJ mol^?1 at pH 5.5).     

KINETICS OF ION EXCHANGE IN SOIL ORGANIC MATTER. IV. ADSORPTION AND DESORPTION OF Pb2+, Cu2+, Cd2+, Zn2+ AND Ca2+ BY PEAT

The equilibria as well as the rates of adsorption and desorption of the ions Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, and Ca²⁺ by soil organic matter were determined in batch experiments as a function of the amount of metal ions added to an aqueous suspension of HCl-washed peat. Simultaneous determination of the metal ions and hydrogen ions in the solution by atomic absorption spectrophotometry and pH-measurements showed that the adsorption of one divalent metal ion by peat was coupled with the release of two hydrogen ions. Since this equivalent ion-exchange process causes a corresponding increase of the electric conductivity of the solution, the rates of the adsorption and desorption processes were determined by an immersed conductivity electrode. The distribution coefficients show that the selective order for the metal adsorption by peat is Pb²⁺ > Cu²⁺ > Cd²⁺≌ Zn²⁺ > Ca²⁺ in the pH range of 3·5 to 4·5. The slope of -2, as observed in a double logarithmic plot of the distribution coefficients versus the total solution concentration confirms the equivalence of the ion-exchange process of divalent metal ions for monovalent H₃O⁺ -ions in peat. The absolute rates of adsorption, as well as the rates for the fractional attainment of the equilibrium, increase with increasing amounts of metal ions added. This behaviour is also observed for the subsequent desorption of the metal ions by H₃O⁺-ions. At a given amount of metal ions added, the absolute rates of adsorption decrease in the order Pb²⁺ > Cu²⁺ > Cd²⁺ > Zn²⁺ > Ca²⁺, while the rates for the fractional attainment of the equilibrium decrease in the order Ca²⁺ > Zn²⁺≌ Cd²⁺ > Pb²⁺ > Cu²⁺. The half times for adsorption and desorption were in the range of 5 to 15 sec.     

Adsorption of Cesium from Aqueous Solution of Highly Concentrated Nitric Acid Using Supermolecule/Ordered Mesoporous Carbon Composite

Calix[4]arene-crown-6 compounds are promising ligands in the removal of cesium. With this aim, a macrocyclic compound, calix[4]arene-crown-6, was chemically immobilized onto inorganic ordered mesoporous carbon material. Several adsorption parameters such as nitric acid concentration, contact time, initial cesium content, operation temperature, and competing ions were studied. The results demonstrated the prepared material conserved high cesium selectivity of calix[4]arene-crown-6 and physicochemistry stability of the ordered mesoporous carbon matrix and showed the superior cesium adsorption performance. The optimum adsorption acidity determined as 3.0 M nitric acid was consistent with the actual acidity value in the back-end of the nuclear fuel cycle. The Langmuir model indicated the monolayer coverage adsorption and the highest mass adsorption capacity was calculated as 128.06 mg cesium/g. The pseudo-second-order model and D-R model proved the adsorption was a chemical process. Thermodynamics parameters showed the adsorption was spontaneous and exothermal in nature. Competing ions hardly affected cesium adsorption. Furthermore, the adsorbent showed almost intact adsorption capacity after five adsorption-elution cycles. The comprehensive performance highlights the composite material as a promising adsorbent for cesium adsorption from wastewaters.

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Graphical Abstract

     

Radio-caesium fixation dynamics: measurement in six Cumbrian soils

Five peat soils and a mineral soil were artificially contaminated with ¹³⁷Cs. Soil solution activity and radio–lability of ¹³⁷Cs were monitored over 709 days to quantify progressive ¹³⁷Cs fixation. The peat soils fixed large amounts of ¹³⁷Cs, but less than the mineral soil did. Distribution coefficients (K_d, cm³ g^?1) ranged from 30 to 5000 at the end of equilibration. A labile ¹³⁷Cs distribution coefficient, K_dt, was estimated by a method involving solid ? solution equilibration in dilute solution. In a separate study several concentrations of KCl were added to soils in increasing concentration both before and after the addition of ¹³⁷Cs. Differences in apparent adsorption strength of radiocaesium indicated that K⁺ induced the collapse of expanded mineral interlayers, thereby trapping ions. It seemed that ^I37Cs adsorbs at sites in the small micaceous clay fraction of the peat soils. The different rates of ¹³⁷Cs adsorption and fixation in the peat and mineral soils, in which the rate of access of ¹³⁷Cs to fixation sites in peat soils is less, seems to have been caused partly by lack of K, and partly by the scarcity of fixation sites.     

pH buffering capacity of acid soils from tropical and subtropical regions of China as influenced by incorporation of crop straw biochars

Purpose

The key factors influencing pH buffering capacity of acid soils from tropical and subtropical regions, and effects of soil evolution and incorporation of biochars on pH buffering capacity were investigated to develop suitable methods to increase pH buffering capacity of acid soils.

Materials and methods

A total of 24 acid soils collected from southern China were used. The pH buffering capacity was determined using acid–base titration. The values of pH buffering capacity were obtained from the slope of titration curves of acid or alkali additions plotted against pH in the pH range 4.0–7.0. Two biochars were prepared from straws of peanut and canola using a low temperature pyrolysis method. After incubation of three acid soils, pH buffering capacity was then determined.

Results and discussion

pH buffering capacity had a range of 9.1–32.1 mmol kg^–1 pH^–1 for 18 acid soils from tropical and subtropical regions of China. The pH buffering capacity was highly correlated (R ²?=?0.707) with soil cation exchange capacity (CEC) measured with ammonium acetate method at pH 7.0 and decreased with soil evolution due to the decreased CEC. Incorporation of biochars at rates equivalent to 72 and 120 t ha^?1 increased soil pH buffering capacity due to the CEC contained in the biochars. Incorporation of peanut straw char which itself contained more CEC and alkalinity induced more increase in soil CEC, and thus greater increase in pH buffering capacity compared with canola straw char. At 5% of peanut straw char added, soil CEC increased by 80.2%, 51.3%, and 82.8% for Ultisol from Liuzhou, Oxisol from Chengmai and Ultisol from Kunlun, respectively, and by 19.8%, 19.6%, and 32.8% with 5% of canola straw char added, respectively; and correspondingly for these soils, the pH buffering capacity increased by 73.6%, 92.0%, and 123.2% with peanut straw char added; and by 31.3%, 25.6%, and 52.3% with canola straw char added, respectively. Protonation/deprotonation of oxygen-containing functional groups of biochars was the main mechanism for the increase of pH buffering capacity of acid soils with the incorporation of biochars.

Conclusions

CEC was a key factor determining pH buffering capacity of acid soils from tropical and subtropical regions of China. Decreased CEC and content of 2:1-type clay minerals during evolution of tropical soils led to decreased pH buffering capacity. Incorporation of biochars generated from crop straws did not only ameliorate soil acidity, but also increased soil pH buffering capacity.

     

The role of silvicultural systems and forest types in preventing soil erosion processes in mountain forests: a methodological approach using cesium-137 measurements

Purpose

Forests play a key role in providing protection against soil erosion. Particularly, the role of vertical forest structure in increasing rainfall interception capacity is crucial for mitigating raindrop impact and reducing splash and rill erosion. For this reason, studies on the relationships between forest structures, the past management, and the observed rates of soil loss are needed. In the last few decades, importance was given to the use of cesium-137 (¹³⁷Cs) as radioactive tracer to estimate soil erosion rates. The ¹³⁷Cs technique is linked to the global fallout of bomb-derived radiocesium which occurred during a period extending from the mid 1950s to the late 1970s.

Materials and methods

The ¹³⁷Cs technique, providing long-term retrospective estimates, could be related to forest treatments applied during the last decades in different sites, also considering the tree species composition. This approach could be useful to compare the effect of different canopy cover and biomass on soil erosion rates related to different tree species. In the work proposed here, a study area dominated by pine and beech high forests located in the Aspromonte Mountains (Calabria, Italy) was selected. The measurements, related to forest structural traits, focusing on canopy cover and biomass, and also on management approaches and forest types, are compared with rates of soil erosion provided by ¹³⁷Cs.

Results and discussion

The overall results suggest that the minimum values of soil loss are documented in areas with higher canopy cover and biomass evidencing the protective effect provided by forests against soil erosion. Also, techniques based on the use of tracers like ¹³⁷Cs proved to be helpful to select the best forest management options useful to optimize the protective role of forests, with the aim to reduce erosion processes in a long-term perspective.

Conclusions

The experiment indicates that care must be taken when new silviculture treatments are planned. These findings are in agreement with what documented by other authors in similar environments but need further studies to confirm the effectiveness of using ¹³⁷Cs in different forest ecosystems.

     

Binding,fractionation, and distribution of Cs,Co, and Sr in a US coastal soil under saturated and field capacity moisture regimes

Purpose

The concerns of the public on safe handling of nuclear energy power facilities have increased due to the recent nuclear plant accidents in Japan and others. Cesium, cobalt, and strontium are a few of the major radionuclides released from nuclear power plant accidents. The objectives of this study are to investigate binding, distribution, fractionation, and transformation of cesium (Cs), cobalt (Co), and strontium (Sr) in a US coastal soil under saturated paste (SP) and field capacity (FC) moisture regimes.

Materials and methods

There are four major nuclear power plants in the coast region around the northern Gulf of Mexico where coastal soil often undergoes soil moisture change. A coastal soil was taken from the middle region of these major nuclear power plants and spiked with different concentrations of cesium, cobalt, and strontium salts. The sequential selective dissolution technique was used to investigate the transformation and fractionations of these metals in the coastal soils affected by moisture regime, a key factor in the coastal environment.

Results and discussion

The adsorption kinetics showed that both Co and Sr reached the adsorption plateau even after 5 h of adsorption, indicating a fast initial adsorption process in the coastal soil. Cesium, cobalt, and strontium were dominantly presented in the soluble and exchangeable form (EXC) (Cs?>?Co and Sr), which linearly increased with the addition levels, possessing the high bioavailability, mobility, and ecotoxicity. Saturated regime significantly reduced the soluble and exchangeable form compared to field capacity moisture regime.

Conclusions

The current study provides the fundamental understanding for designing the cost-effective remediation technology to remediate these metals in coastal soil by targeting on the soluble and exchangeable forms and better prepare the USA for future potentially nuclear power plant accidents.

     

Removal of Cu2+ and Cd2+ from Aqueous Solution by Bentonite Clay Modified with Binary Mixture of Goethite and Humic Acid

Pre-modification of bentonite clay with goethite, humic acid, and a binary mixture of goethite and humic acid reagents increased its cation exchange capacity from 95 to 105.32, 120.4, and 125.8 meq/100 g of bentonite clay, respectively. The effective pre-modification of bentonite clay with goethite, humic acid, and goethite–humic acid reagents was confirmed from their Fourier transform infrared spectra which suggested that modification was effective on the AlAlOH and Si–O sites for goethite and humic acid modification and AlAlOH for goethite–humic acid modification. The presence of 0.001 M NaNO₃ electrolyte increased the adsorption capacity of bentonite clay. Temperature was observed to favor the adsorption of Cu²⁺ and Cd²⁺ onto both the raw and modified bentonite clay samples. The goethite–humic acid-modified bentonite gave the best adsorption capacity of ≈10 and 16 mg/g at 30 and 50°C, respectively, for both metal ions. The inner sphere complexation mechanism was suggested for the adsorption of both metal ions onto the modified adsorbents. Modifying bentonite clay with a binary mixture of goethite and humic acid reduced the selectivity of bentonite clay for either Cu²⁺ or Cd²⁺. Preadsorbed goethite and humic acid on bentonite clay will further reduce the mobility of heavy metal ions in soils and in aquatic environments.