Temporal variability of groundwater chemistry in shallow and deep aquifers of Araihazar, Bangladesh

Samples were collected every 2-4 weeks from a set of 37 monitoring wells over a period of 2-3 years in Araihazar, Bangladesh, to evaluate the temporal variability of groundwater composition for As and other constituents. The monitoring wells are grouped in 6 nests and span the 5-91 m depth range. Concentrations of As, Ca, Fe, K, Mg, Mn, Na, P, and S were measured by high-resolution ICPMS with a precision of 5% or better; concentrations of Cl were measured by ion chromatography. In shallow wells <30 m deep, As and P concentrations generally varied by <30%, whereas concentrations of the major ions (Na, K, Mg, Ca and Cl) and the redox-sensitive elements (Fe, Mn, and S) varied over time by up to +/-90%. In wells tapping the deeper aquifers >30 m often below clay layers concentrations of groundwater As were much lower and varied by <10%. The concentrations of major cations also varied by <10% in these deep aquifers. In contrast, the concentration of redox-sensitive constituents Fe, S, and Mn in deep aquifers varied by up to 97% over time. Thus, strong decoupling between variations in As and Fe concentrations is evident in groundwaters from shallow and deep aquifers. Comparison of the time series data with groundwater ages determined by (3)H/(3)He and (14)C dating shows that large seasonal or inter-annual variations in major cation and chloride concentrations are restricted to shallow aquifers and groundwater recharged <5 years ago. There is no corresponding change in As concentrations despite having significant variations of redox sensitive constituents in these very young waters. This is attributed to chemical buffering due to rapid equilibrium between solute and solid As. At two sites where the As content of groundwater in existing shallow wells averages 102 microg/L (range: <5 to 648 microg/L; n=118) and 272 microg/L (range: 10 to 485 microg/L; n=65), respectively, a systematic long-term decline in As concentrations lends support to the notion that flushing may slowly deplete an aquifer of As. Shallow aquifer water with >5 years (3)H/(3)He age show a constant As:P molar ratio of 9.6 over time, suggesting common mechanisms of mobilization.     

Sustainable Exploitation of Borassus aethiopum, Elaeis guineensis and Raphia hookeri for the Extraction of Palm Wine in Côte d'Ivoire

In the rural areas of developing countries palms are major sources of many products. One of these is palm wine, which has an important role for nutrition, income and social life. In the Côte d'Ivoire (West Africa), palm wine is extracted from three different species: Borassus aethiopum Mart., Raphia hookeri Mann & Wendland and Elaeis guineensis Jacq. As the extraction methods are destructive, palm stands are locally threatened by extinction. This could have serious consequences not only for the nutritional situation of the population but also for their income. Field visits were conducted in order to assess the degree of sustainability of palm wine extraction in eight villages of Côte d'Ivoire's three major agro-ecozones. Based on the annual palm wine need for consumption and commercialisation and on the availability of palms, a sustainability index was calculated for each palm species in each village. The occurrence of palm trees depends on the vegetation type. B. aethiopum is a typical savanna tree (> 20 palms per hectare) and is almost absent in other vegetation types. In 75% of the villages the exploitation of B. aethiopum is not sustainable. The preferred vegetation type for R. hookeri is the forest along the rivers (> 33 palms per hectare) compared to the other vegetation types of the forest zone (< 5 palms per hectare). Due to the high preference for the palm wine of this species its exploitation is not sustainable in any of the selected villages. The distribution of E. guineensis depends mostly on human activities, the main vegetation types being plantations (34 palms per hectare), fallow land and cultivated fields (15 palms per hectare) and the forest along the rivers (31 palms per hectare). The exploitation of this species is in general sustainable throughout all ecozones with some rare exceptions.     

Behaviour and dynamics of di-ammonium phosphate in bauxite processing residue sand in Western Australia—I. NH<Subscript>3</Subscript> volatilisation and residual nitrogen availability

Background, aim and scope

Australia is the largest producer of bauxite in the world, with an annual output of approximately 62 million metric dry tons in 2007. For every tonne of alumina, about 2 tonnes of highly alkaline and highly saline bauxite-processing residue are produced. In Western Australia, Alcoa World Alumina, Australia (Alcoa) produces approximately 15 MT of residue annually from its refineries (Kwinana, Pinjarra and Wagerup). The bauxite-processing residue sand (BRS) fraction represents the primary material for rehabilitating Alcoa’s residue disposal areas (RDAs). However, the inherently hostile characteristics (high alkalinity, high salinity and poor nutrient availability) of BRS pose severe limitations for establishing sustainable plant cover systems. Alcoa currently applies 2.7 t ha^?1 of di-ammonium phosphate ((NH₄)₂HPO₄; DAP)-based fertiliser as a part of rehabilitation of the outer residue sand embankments of its RDAs. Limited information on the behaviour of the dominant components of this inorganic fertiliser in highly alkaline BRS is currently available, despite the known effects of pH on ammonium (NH₄) and phosphorus (P) behaviour. The aim of this study was to quantify the effects of pH on NH₃ volatilisation and residual nitrogen (N) in BRS following DAP applications.

Methods

The sponge-trapping and KCl-extraction method was used for determining NH₃ volatilisation from surface-applied DAP in samples of BRS collected from each of Alcoa’s three Western Australia Refineries (Kwinana, Pinjarra, Wagerup) under various pH conditions (pH 4, 7, 9 and 11). Following cessation of volatilisation, the residual N was extracted from BRS using 2 M KCl and concentrations of NH ₄ ⁺ –N and NO ₃ ^? –N were determined by flow injection analysis.

Results

The quantities of NH₃ volatilised increased dramatically as the pH increased from 4 to 11. Much of the N lost as NH₃ (up to 95.2%) occurred within a short period (24 h to 7 days), particularly for the pH 9 and 11 treatments. Concentrations of residual NH ₄ ⁺ –N recovered in DAP-treated BRS at the end of the experiment decreased with increasing pH. This finding was consistent with increasing loss of N via volatilisation as pH increased. The concentration of NO ₃ ^? –N was very low due to no nitrification in BRS.

Discussion

The pH was a key driver for NH₃ volatilisation from DAP-treated BRS and primarily controlled N dynamics in BRS. Results indicate that NH₄ not adsorbed by BRS was highly susceptible to volatilisation. The likely lack of nitrifying bacteria did not allow conversion of ammonium to nitrate, thereby further exacerbating the potential for loss via volatilisation

Conclusions

It was demonstrated that the pH is the key factor controlling the loss of inorganic N from BRS. Although volatilisation was considerably lower at pH 4, achieving this pH reduction in the field is not possible at present. Findings from this study highlight the need to better understand which forms of N fertiliser are most suitable for use in highly alkaline BRS.

Recommendation and perspectives

Although pH reduction is the most likely means of stopping NH₃ volatilisation in BRS, it is economically and operationally unfeasible to add sufficient acidity for adequately lowering pH in the BRS for revegetation. More attention on forms of fertilisers more suitable to highly alkaline, microbially inert soil conditions appears to be warranted.

     

Analysis of C1, C2, and C10 through C33 particle-phase and semi-volatile organic compound emissions from heavy-duty diesel engines

To meet increasingly stringent regulations for diesel engines, technologies such as combustion strategies, aftertreatment components, and fuel composition have continually evolved. The emissions reduction achieved by individual aftertreatment components using the same engine and fuel has been assessed and published previously (Liu et al., 2008a, Liu et al., 2008b, Liu et al., 2008c). The present study instead adopted a systems approach to evaluate the net effect of the corresponding technologies for model-year 2004 and 2007 engines. The 2004 engine was equipped with an exhaust gas recirculation (EGR) system, while the 2007 engine had an EGR system, a crankcase emissions coalescer, and a diesel particulate filter. The test engines were operated under the transient federal test procedure and samples were collected with a source dilution sampling system designed to stimulate atmospheric cooling and dilution conditions. The samples were analyzed for elemental carbon, organic carbon, and C₁, C₂, and C₁₀ through C₃₃ particle-phase and semi-volatile organic compounds. Of the more than 150 organic species analyzed, the largest portion of the emissions from the 2004 engine consisted of formaldehyde, acetaldehyde, and naphthalene and its derivatives, which were significantly reduced by the 2007 engine and emissions technology. The systems approach in this study simulates the operation of real-world diesel engines, and may provide insight into the future development of integrated engine technology. The results supply updated information for assessing the impact of diesel engine emissions on the chemical processes, radiative properties, and toxic components of the atmosphere.     

Spatial distributions and potential risk analysis of total soil selenium in Guangdong Province, China

A total of 260 soil profiles were examined to investigate the spatial distribution of total soil selenium (Se) in Guangdong province, China. In the investigated area, the soil Se concentrations follow an approximately lognormal distribution. The soil Se geometric mean concentration of 0.23 mg kg(-1) is higher than that of Chinese soils; however, Se concentration varies over the study area. The baseline concentration of 0.13 to 0.41 mg kg(-1) indicates that the soil Se concentration is mostly in the range of deficiency to medium level for surface soils in Guangdong province. In A-, B-, and C-horizon, soil Se spatial distribution is correlated with the nature of the parent material, with high Se concentration mainly located in limestone and sandshale areas and low Se concentration associated with purple shale and granite areas. The spatial distribution pattern of soil Se concentrations suggests that potential Se deficiency may be an issue for human health in this province. Moreover, due to soil degradation and erosion, calculated soil Se exported into surrounding waters could reach approximately 23,000 kg yr(-1) in the study area.     

Carbon dioxide efflux from soil with poultry litter applications in conventional and conservation tillage systems in northern Alabama

Increased CO2 release from soils resulting from agricultural practices such as tillage has generated concerns about contributions to global warming. Maintaining current levels of soil C and/or sequestering additional C in soils are important mechanisms to reduce CO2 in the atmosphere through production agriculture. We conducted a study in northern Alabama from 2003 to 2006 to measure CO2 efflux and C storage in long-term tilled and non-tilled cotton (Gossypium hirsutum L.) plots receiving poultry litter or ammonium nitrate (AN). Treatments were established in 1996 on a Decatur silt loam (clayey, kaolinitic thermic, Typic Paleudults) and consisted of conventional-tillage (CT), mulch-tillage (MT), and no-tillage (NT) systems with winter rye [Secale cereale (L.)] cover cropping and AN and poultry litter (PL) as nitrogen sources. Cotton was planted in 2003, 2004, and 2006. Corn was planted in 2005 as a rotation crop using a no-till planter in all plots, and no fertilizer was applied. Poultry litter application resulted in higher CO2 emission from soil compared with AN application regardless of tillage system. In 2003 and 2006, CT (4.39 and 3.40 micromol m(-2) s(-1), respectively) and MT (4.17 and 3.39 micromol m(-2) s(-1), respectively) with PL at 100 kg N ha(-1) (100 PLN) recorded significantly higher CO2 efflux compared with NT with 100 PLN (2.84 and 2.47 micromol m(-2) s(-1), respectively). Total soil C at 0- to 15-cm depth was not affected by tillage but significantly increased with PL application and winter rye cover cropping. In general, cotton produced with NT conservation tillage in conjunction with PL and winter rye cover cropping reduced CO2 emissions and sequestered more soil C compared with control treatments.     

Tillage, cropping systems, and nitrogen fertilizer source effects on soil carbon sequestration and fractions

Quantification of soil carbon (C) cycling as influenced by management practices is needed for C sequestration and soil quality improvement. We evaluated the 10-yr effects of tillage, cropping system, and N source on crop residue and soil C fractions at 0- to 20-cm depth in Decatur silt loam (clayey, kaolinitic, thermic, Typic Paleudults) in northern Alabama, USA. Treatments were incomplete factorial combinations of three tillage practices (no-till [NT], mulch till [MT], and conventional till [CT]), two cropping systems (cotton [Gossypium hirsutum L.]-cotton-corn [Zea mays L.] and rye [Secale cereale L.]/cotton-rye/cotton-corn), and two N fertilization sources and rates (0 and 100 kg N ha(-1) from NH(4)NO(3) and 100 and 200 kg N ha(-1) from poultry litter). Carbon fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Crop residue varied among treatments and years and total residue from 1997 to 2005 was greater in rye/cotton-rye/cotton-corn than in cotton-cotton-corn and greater with NH(4)NO(3) than with poultry litter at 100 kg N ha(-1). The SOC content at 0 to 20 cm after 10 yr was greater with poultry litter than with NH(4)NO(3) in NT and CT, resulting in a C sequestration rate of 510 kg C ha(-1) yr(-1) with poultry litter compared with -120 to 147 kg C ha(-1) yr(-1) with NH(4)NO(3). Poultry litter also increased PCM and MBC compared with NH(4)NO(3). Cropping increased SOC, POC, and PCM compared with fallow in NT. Long-term poultry litter application or continuous cropping increased soil C storage and microbial biomass and activity compared with inorganic N fertilization or fallow, indicating that these management practices can sequester C, offset atmospheric CO(2) levels, and improve soil and environmental quality.     

Transient behavior of heavy metals in soils during electrokinetic remediation

This paper presents a systematic bench-scale laboratory study performed to assess the transient behavior of chromium, nickel, and cadmium in different soils during electrokinetic remediation. A series of laboratory electrokinetic experiments was conducted using two different clayey soils, kaolin and glacial till. For each type of soil, four electrokinetic experiments with 1, 2, 4, and 10 d of treatment time were performed. In all tests, the contaminants were Cr(VI), Ni(II), and Cd(II) combined in the soil. A geochemical assessment was performed using the geochemical model MINEQL(+) to determine the partitioning of the heavy metals in soils as precipitated, adsorbed, and aqueous forms. Results showed that in kaolin, the extent of Ni(II) and Cd(II) migration towards the cathode increased as the treatment time increased. Unlike kaolin, in glacial till treatment time had no effect on nickel and cadmium migration because of its high buffering capacity. In both kaolin and glacial till, the extent of Cr(VI) migration towards the anode increased as the treatment time increased. However, Cr(VI) migration was higher in glacial till as compared to kaolin because of the high pH conditions that existed in glacial till. In all tests, some Cr(VI) was reduced to Cr(III), and the Cr(VI) reduction rate to Cr(III) as well as the Cr(III) migration were significantly affected by the treatment time. Overall, this study showed that the electroosmotic flow as well as the direction and extent of contaminant migration and removal depend on the polarity of the contaminant, the type of soil, and the treatment duration.     

Isolation and preliminary characterization of a 3-chlorobenzoate degrading bacteria

A study was conducted to compare the diversity of 2-, 3-, and 4-chlorobenzoate degraders in two pristine soils and one contaminated sewage sludge. These samples contained strikingly different populations of mono-chlorobenzoate degraders. Although fewer cultures were isolated in the uncontaminated soils than contaminated one, the ability of microbial populations to mineralize chlorobenzoate was widespread. The 3- and 4-chlorobenzoate degraders were more diverse than the 2-chlorobenzoate degraders. One of the strains isolated from the sewage sludge was obtained. Based on its phenotype, chemotaxonomic properties and 16S rRNA gene, the organism S-7 was classified as Rhodococcus erythropolis. The strain can grow at temperature from 4 to 37℃. It can utilize several （halo）aromatic compounds. Moreover, strain S-7 can grow and use 3-chlorobenzoate as sole carbon source in a temperatures range of 10-30℃ with stoichiometric release of chloride ions. The psychrotolerant ability was significant for bioremediation in low temperature regions. Catechol and chlorocatechol 1,2-dioxygenase activities were present in cell free extracts of the strain, but no （chloro）catechol 2,3- dioxygenase activities was detected. Spectral conversion assays with extracts from R. erythropolis S-7 showed accumulation of a compound with a similar UV spectrum as chloro-cis,cis-muconate from 3-chlorobenzoate. On the basis of these results, we proposed that S-7 degraded 3-chlorobenzoate through the modified ortho-cleave pathway.     

Adsorption-desorption behavior of copper at contaminated levels in red soils from China

Adsorption-desorption of copper (Cu2+) at contaminated levels in two red soils was investigated. The red soil derived from the Quaternary red earths (clayey, kaolinitic thermic plinthite Aquult) (REQ) adsorbed more Cu2+ than the red soil developed on the Arenaceous rock (clayey, mixed siliceous thermic typic Dystrochrept) (RAR). The maximum adsorption values (M(A)) that are obtained from the simple Langmuir model were 25.90 and 20.17 mmol Cu2+ kg(-1) soil, respectively, for REQ and RAR. Adsorption of Cu2+ decreased soil pH, by 0.8 unit for the REQ soil and 0.6 unit for the RAR soil at the highest loadings. The number of protons released per Cu2+ adsorbed increased sigmoidally with increasing initial Cu2+ concentration for the RAR soil, but the relationship was almost linear for the REQ soil. The RAR soil released about 2.57 moles of proton per mole of Cu2+ adsorbed at the highest Cu2+ loading and the corresponding value for the REQ soil was 1.12. The distribution coefficient (Kd) decreased exponentially with increasing Cu2+ loading. Most of the adsorbed Cu2+ in the soils was readily desorbed in the NH4Ac. After five successive extractions with 1 mol L(-1) NH4Ac (p 5.0), 61 to 95% of the total adsorbed Cu2+ in the RAR soil was desorbed and the corresponding value for the REQ soil was 85 to 92%, indicating that the RAR soil had a greater affinity for Cu2+ than the REQ soil at low levels of adsorbed Cu2+.