Evidence for the presence of a widespread PCDD source in coastal sediments and soils from Queensland, Australia

Recent studies have demonstrated the occurrence of elevated levels of higher chlorinated PCDDs in the coastal environment of Queensland, Australia. This study presents new data for OCDD contamination and full PCDD/F profile analysis in the environment of Queensland. Marine sediments, irrigation drain sediments and topsoil were collected from sites that were expected to be influenced by specific land-use types. High OCDD concentrations were associated mainly with sediments collected near the mouth of rivers which drain into large catchments in the tropical and subtropical regions. Further, analysis of sediments from irrigation drains could be clearly differentiated on the basis of OCDD contamination, with high concentrations in samples from sugarcane drains collected from coastal regions, and low concentrations in drain sediments from drier inland cotton growing areas. PCDD/F congener-specific analysis demonstrated almost identical congener profiles in all samples collected along the coastline. This indicates the source to be widespread. Profiles were dominated by higher chlorinated PCDDs, in particular OCDD whereas 2,3,7,8-substituted PCDFs were below the limit of quantification in the majority of samples. The full PCDD/F profile analysis of samples strongly resemble those reported for lake sediments from Mississippi and kaolinite samples from Germany, Strong similarities to these samples with respect to congener profiles and isomer patterns may indicate the presence of a similar source and/or formation process that is yet unidentified. (C) 2001 Elsevier Science Ltd. All rights reserved.

The measurement of actual acidity in acid sulfate soils and the determination of sulfidic acidity in suspension after peroxide oxidation

Improvements to the routine methods for the determination of actual acidity in suspension for acid sulfate soils (ASS) are introduced. The titratable sulfidic acidity (TSA) results using an improved peroxide-based method were compared with the theoretical acidity predicted by the chromium reducible sulfur method for 9 acid sulfate soils. The regression between these 2 measures of sulfidic acidity was highly significant, the slope of the regression line not significantly different from unity (P = 0.05) and the intercept not significantly different from zero. This contrasts with results of other workers using earlier peroxide oxidation methods, where TSA substantially underestimated the theoretical acidity predicted by reduced inorganic sulfur analysis. Comparison was made between the 2 principal measurements from the improved peroxide method (TSA and S-POS), with S-POS converted to theoretical sulfidic acidity to allow comparison. The relationship between these 2 measurements was highly significant. The effects of titration in suspension, as well as raising titration end points to pH 6.5, were investigated, principally with respect to the titratable actual acidity (TAA) result. TAA results obtained by KCl extraction were compared with those obtained using BaCl2, MgCl2, and water extraction. TAA in 1 M KCl suspensions titrated to pH 6.5 agreed well with titratable actual acidity measured using the 25-h extraction approach of the Lin et al. (2000a) BaCl2 method. Both BaCl2 and KCl solutions were ineffective at fully recovering acidity from synthetic jarosite without repeated extraction and titration. The application of correction factors for the estimation of total actual acidity in ASS is not supported by the results of this investigation. Acid sulfate soils that contain substantial quantities of jarosite or other acid-producing but relatively insoluble sulfate minerals continue to prove problematic to chemically analyse; however, an approach for estimating this component is discussed.

Improvements to peroxide oxidation methods for analysing sulfur in acid sulfate soils

Improvements to peroxide oxidation methods for analysing acid sulfate soils (ASS) are introduced. The soil solution ratio has been increased to 1 : 40, titrations are performed in suspension, and the duration of the peroxide digest stage is substantially shortened. For 9 acid sulfate soils, the peroxide oxidisable sulfur value obtained using the improved method was compared with the reduced inorganic sulfur result obtained using the chromium reducible sulfur method. Their regression was highly significant, the slope of the regression line was not significantly different (P = 0.05) from unity, and the intercept not significantly different from zero. A complete sulfur budget for the improved method showed there was no loss of sulfur as has been reported for earlier peroxide oxidation techniques. When soils were very finely ground, efficient oxidation of sulfides was achieved, despite the milder digestion conditions. Highly sulfidic and organic soils were shown to be the most difficult to analyse using either the improved method or the chromium method. No single analytical method can be universally applied to all ASS, rather a suite of methods is necessary for a thorough understanding of many ASS. The improved peroxide method, in combination with the chromium method and the 4 M HCl extraction, form a sound platform for informed decision making on the management of acid sulfate soils.

Hydrofluoric acid pre-treatment for improving 13C CPMAS NMR spectral quality of forest soils in south-east Queensland, Australia

Hydrofluoric acid (HF) was used to pre-treat forest soils of south-east Queensland for assessing the effectiveness of iron (Fe) removal, carbon (C) composition using C-13 cross-polarisation (CP) with magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) before and after the HF pre-treatment, and the improvement of C-13 CPMAS NMR spectra. Soil samples were collected from 4 experimental sites of different soil types, harvest residue management or prescribed burning, and tree species. More than 86% of Fe was in all soil types removed by the HF treatment. The C-13 NMR spectral quality was improved with increased resolution, especially in the alkyl C and O-alkyl C regions, and reduced NMR run-time (1-5 h per sample compared with >20 h per sample without the pre-treatment). The C composition appeared to alter slightly after the pre-treatment, but this might be largely due to improved spectrometer conditions and increased resolution leading to more accurate NMR spectral integration. Organic C recovery after HF pre-treatment varied with soil types and forest management, and soluble soil organic matter (SOM) could be lost during the pre-treatment. The Fourier Transform-Infrared (FT-IR) spectra of HF extracts indicated the preferential removal of carboxylic C groups during the pre-treatment, but this could also be due to adsorbed water on the mineral matter. The NMR spectra revealed some changes in C composition and quality due to residue management and decomposition. Overall, the HF treatment was a useful pre-treatment for obtaining semi-quantitative C-13 CPMAS NMR spectra of subtropical Australian forest soils.

Growing Atriplex and Maireana species in saline sodic and waterlogged soils

Utilization of salt affected wasteland by growing forage shrubs has enormous economic and environmental implication for developing countries like Pakistan, where approximately 6.3 million ha of the land is salt affected. Considering the importance of Atriplex and Maireana species, research has been conducted using their different species on the salt affected soils of Faisalabad. Most of Atriplex and Maireana species survived under the environmental conditions of Faisalabad and gave the good yield in the form of forage. Some of these species are woody and can be used for fuel purposes. Sixteen genotypes of Atriplex and Maireana were tested for their tolerance to waterlogging in order to identify halophytic fodder shrubs suitable for growth on secondary salt-affected and waterlogged farmland. The physiological and morphological responses of the species tested were typical of species with a generally poor tolerance to waterlogging. Despite this, some species (e.g., A. amnicola) were surprisingly resistant, surviving up to five months of waterlogging at moderate salinity and high evapotranspirational demand. The most resistant species, A amnicola maintained higher transpiration rates, leaf water potentials and shoot extension rates than most other species during five weeks of waterlogging, and a return to control levels more quickly than other species after plots were drained. Although little morphological adaptation to waterlogged conditions was detected, a shallow and extensive lateral root system and the formation of many short aerenchymatous adventitious roots from procumbent branches appeared to advantage A. amnicola in an environment highly heterogeneous in salinity and low in oxygen concentration. Waterlogging quickly killed shallow fibrous rooted species, although the procumbent branches of some individuals survived as clones if they developed adventitious roots.

The decomposition of starch grains in soils: implications for archaeological residue analyses

Recent research involving starch grains recovered from archaeological contexts has highlighted the need for a review of the mechanisms and consequences of starch degradation specifically relevant to archaeology. This paper presents a review of the plant physiological and soil biochemical literature pertinent to the archaeological investigation of starch grains found as residues on artefacts and in archaeological sediments. Preservative and destructive factors affecting starch survival, including enzymes, clays, metals and soil properties, as well as differential degradation of starches of varying sizes and amylose content, were considered. The synthesis and character of chloroplast-formed 'transitory' starch grains, and the differentiation of these from 'storage' starches formed in tubers and seeds were also addressed. Findings of the review include the higher susceptibility of small starch grains to biotic degradation, and that protective mechanisms are provided to starch by both soil aggregates and artefact surfaces. These findings suggest that current reasoning which equates higher numbers of starch grains on an artefact than in associated sediments with the use of the artefact for processing starchy plants needs to be reconsidered. It is argued that an increased understanding of starch decomposition processes is necessary to accurately reconstruct both archaeological activities involving starchy plants and environmental change investigated through starch analysis. (C) 2004 Elsevier Ltd. All rights reserved.

Do decomposing organic matter residues reduce phosphorus sorption in highly weathered soils?

Many studies have shown a reduction in P sorption in highly weathered soils when organic matter (OM) is applied, suggesting competition between OM decomposition products and P for sorption sites. However, such studies seldom consider the P released from the added OM. To delineate the effects of OM addition on P availability through sorption competition and P addition, water leachate from incubated soybean (SB) [Glycine mar (L.) Merr.] and Rhodes grass (RG) (Chloris gayana Knuth cv. Callide) was used in competitive P sorption studies both undiluted and after acidification (i.e., the fulvic acid [FA] component). Addition of two rates (0.2 and 2 mL) of SB leachate to an Oxisol significantly increased P sorption at the higher rate, while a similar trend was observed following RG leachate addition at the same rates. Extending the range of highly weathered soils examined (two Oxisols, an Ultisol, and an acidic Vertisol) resulted in no observed decrease in P sorption following addition of OM leachate. Surprisingly, SB leachate transiently increased P sorption in the two Oxisol soils. Addition of the FA component of the leachates resulted in a transient (< 6 d) decrease in P sorption in three of the four soils examined and constituted the only evidence in this study that decomposing OM residues reduced P sorption. This research provides further evidence contradicting the long held assumption that inhibition of P sorption by dissolved organic compounds, derived from decomposing OM, is responsible for increased P phytoavailability when P fertilizer and OM are applied together.

Assessment of P availability in heavily fertilized soils using the diffusive gradient in thin films (DGT) technique

Phosphorus-availability tests typically provide an indication of quantity of P available (Colwell bicarbonate-extractable P), or of the intensity of supply (0.01 M CaCl2-extractable P). The soil's capacity to buffer P is more difficult to assess, and is generally estimated using a P-adsorption curve. The diffusive gradient in thin films (DGT) approach may provide a simpler means of assessing a soil's ability to maintain soil solution P. Optimal extraction conditions were found to be 24 h exposure of DGT samplers to saturated soil. The DGT approach was evaluated on a range of 24 soils, some of which had high Colwell- (>100 mu g g(-1)) and Bray 1- (>30 mu g g(-1)) extractable P content, but showed a tomato (Lycopersicon esculentum Mill.) yield response to the addition of P fertilizer. The DGT approach provided an excellent separation of soils on which tomato showed a yield response, from those where fertilizer P did not increase dry-matter yield. Phosphorus accumulation was strongly correlated with soil solution P concentration and anion exchange resin-extractable P, but showed poor correlation with Colwell- or Bray 1-extractable P. The DGT P accumulation rate of 3.62 x 10(-7) to 4.79 x 10(-5) mol s(-1) m(-3) for the soils tested was comparable to the uptake rate of roots of tomato plants that were adequately supplied with P (2.25 x 10(-5) mol s(-1) m(-3)).

Rhizodeposits of Trifolium pratense and Lolium perenne: Their comparative effects on 2,4-D mineralization in two contrasting soils

Rhizosphere enhanced biodegradation of organic pollutants has been reported frequently and a stimulatory role for specific components of rhizodeposits postulated. As rhizodeposit composition is a function of plant species and soil type, we compared the effect of Lolium perenne and Trifolium pratense grown in two different soils (a sandy silt loam: pH 4, 2.8% OC, no previous 2,4-D exposure and a silt loam: pH 6.5, 4.3% OC, previous 2,4-D exposure) on the mineralization of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid). We investigated the relationship of mineralization kinetics to dehydrogenase activity, most probable number of 2,4-D degraders (MPN2,4-D) and 2,4-D degrader composition (using sequence analysis of the gene encoding alpha-ketoglutarate/2,4-D dioxygenase (tfdA)). There were significant (P < 0.01) plant-soil interaction effects on MPN2,4-D and 2,4-D mineralization kinetics (e.g. T pratense rhizodeposits enhanced the maximum mineralization rate by 30% in the acid sandy silt loam soil, but not in the neutral silt loam soil). Differences in mineralization kinetics could not be ascribed to 2,4-D degrader composition as both soils had tfdA sequences which clustered with tfdAs representative of two distinct classes of 2,4-D degrader: canonical R. eutropha JMP134-like and oligotrophic alpha-proteobacterial-like. Other explanations for the differential rhizodeposit effect between soils and plants (e.g. nutrient competition effects) are discussed. Our findings stress that complexity of soil-plant-microbe interactions in the rhizosphere make the occurrence and extent of rhizosphere-enhanced xenobiotic degradation difficult to predict.

Farmers' strategies for managing acid upland soils in Southeast Asia: an evolutionary perspective

The acid soils of the uplands of Southeast Asia have resisted intensive agricultural use for centuries. In recent decades, however, due to rapid population growth, escalating market demand for agricultural produce, and govemment policies for land development and settlement, the acid uplands have become the focus of more intensive land-use systems, placing greater demands on farmers and requiring the development and dissemination of improved practices for soil management. In order to develop appropriate soil management technologies and plan effective interventions to facilitate their adoption, it is important to understand the goals and circumstances of farmers in the acid uplands, the range of farming systems they have developed, and the variety of socio-economic factors and trends influencing the evolution of these farming systems. Building on Boserup's model of agrarian change, an evolutionary framework is developed and applied to five case studies: a long-fallow (shifting) cultivation system in Sarawak, Malaysia; a short-fallow system in South Kalimantan, Indonesia; a continuous cropping system in Bukidnon, Philippines; a tree crop (with intercropping) system in Southern Thailand; a livestock grazing system in Daclac, Vietnam. The framework provides a useful tool to interpret and categorise farmers' evolving soil management strategies and to plan more effective soil management research and interventions. (c) 2004 Elsevier B.V. All rights reserved.

Hydraulic properties of layered soils influence survival of Rhodes grass (Chloris gayana Kunth.) during water stress

Survival of vegetation on soil-capped mining wastes is often impaired during dry seasons due to the limited amount of water stored in the shallow soil capping. Growth and survival of Rhodes grass (Chloris gayana) during soil drying on various layered capping sequences constructed of combinations of topsoil, subsoil, seawater-neutralised residue sand and low grade bauxite was determined in a glasshouse. The aim was to describe the survival of Rhodes grass in terms of plant and soil water relationships. The soil water characteristic curve and soil texture analysis was a good predictor of plant survival. The combination of soil with a high water holding capacity and low soil water diffusivity (e.g. subsoil with high clay contents) with soil having a high water holding capacity and high diffusivity (e.g. residue sand) gave best survival during drying down (up to 88 days without water), whereas topsoil and low grade bauxite were unsuitable (plants died within 18-39 days). Clayey soil improved plant survival by triggering a water stress response during peak evaporative water demand once residue sand dried down and its diffusivity fell below a critical range. Thus, for revegetation in seasonally dry climates, soil capping should combine one soil with low diffusivity and one or more soils with high total water holding capacity and high diffusivity.

Heterogeneity of physico-chemical properties in structured soils and its consequences

Structured soils are characterized by the presence of inter- and intra-aggregate pore systems and aggregates, which show varying chemical, physical, and biological properties depending on the aggregate type and land use system. How far these aspects also affect the ion exchange processes and to what extent the interaction between the carbon distribution and kind of organic substances affect the internal soil strength as well as hydraulic properties like wettability are still under discussion. Thus, the objective of this research was to clarify the effect of soil aggregation on physical and chemical properties of structured soils at two scales: homogenized material and single aggregates. Data obtained by sequentially peeling off soil aggregates layers revealed gradients in the chemical composition from the aggregate surface to the aggregate core. In aggregates from long term untreated forest soils we found lower amounts of carbon in the external layer, while in arable soils the differentiation was not pronounced. However, soil aggregates originating from these sites exhibited a higher concentration of microbial activity in the outer aggregate layer and declined towards the interior. Furthermore, soil depth and the vegetation type affected the wettability. Aggregate strength depended. on water suction and differences in tillage treatments.