Characterization of nitrogen-fixing cyanobacteria in the Brazilian Amazon floodplain

The diversity of the free-living nitrogen-fixing cyanobacterial community in the floodplain sediments along the Solimões and Amazon Rivers and some of their tributaries (Japurá, Negro and Madeira) was investigated. Five cyanobacterial genera were morphologically identified, four of which (Nostoc, Calothrix, Cylindrospermum and Fischerella) have not previously been isolated from the Brazilian Amazon floodplain. Nostoc strains were the most commonly found heterocyst-forming cyanobacteria. Five strains (N. muscorum CENA18 and CENA61, N. piscinale CENA21, Cylindrospermum sp. CENA33 and Fischerella sp. CENA19) were selected for growth measurement, ability to fix N₂ and phylogenetic analysis, based on their widespread distribution and morphological distinction. Molecular analyses employing 16S rRNA sequences indicated that some of the isolates may represent novel cyanobacterial species. Dinitrogen fixed by these strains was measured indirectly as acetylene reduction activity and ranged from 11.5 to 22.2 nmol C₂H₄ μg Chl a⁻¹ h⁻¹. These results provide evidence of widespread and importance of nitrogen-fixing cyanobacteria as a source of N inputs in the Amazonian ecosystem.     

The role of toxicity in the carcinogenicity of Endosulfan

Two studies have been undertaken on the toxicity and carcinogenicity of endosulfan, a chlorinated cyclodiene - the NCI Endosulfan Rat Study and the NCI Endosulfan Mouse Study. Histological sections have been examined and the results of this review are based on my diagnoses.Endosulfan is highly toxic for male and female Osborne-Mendel rats, particularly for male rats. The chemical causes interstitial fibrosis or acute tubular necrosis of the kidney and death. These lesions, as well as atrophy of the testes, polyarteritis, parathyroid hyperplasia, osteitis fibrosis of bone, and abscesses of the lung, interfere with the health of the animals and with the development of neoplasms.Endosulfan, even though it is extremely toxic, is carcinogenic for male and female Osborne-Mendel rats. The chemical induced malignant neoplasms at all sites in male and female rats and in the endocrine organs in male rats. Rats of both sexes developed lymphosarcomas, and female rats had neoplasms of the reproductive system. Endosulfan is also carcinogenic for the liver of female mice.     

谷粮中硫丹及其代谢物残留的GC-MS分析

本文建立了固相萃取-气相色谱-质谱法(SPE-GC-MS)同时测定谷粮中硫丹及其代谢物的方法。样品经过正己烷提取、固相萃取柱净化,采用GC-MS检测,外标法定量。在此条件下,样品加标回收率在87.3%～110.2%之间,相对标准偏差在1.7%～3.9%之间(n=6),方法检出限(S/N=3)为0.002mg/kg～0.003mg/kg。该方法简便、快速,具有良好的灵敏度、重复性,可适用于谷粮中硫丹及其代谢物残留的检测。     

Indicators of coastal groundwater quality changes induced by seawater infiltration

The diminishing public water supply in Greater Beirut induced by various factors since the 1960's reaching its climax during the civil war (1975–1992), led to the drilling of a multitude of private wells in the Cenomanian coastal aquifer. The increasingly high extraction of the groundwater led to progressive changes in the quality of the ground‐water due to seawater infiltration. This problem stimulated some studies directed at detecting and assessing the status and magnitude of the seawater infiltration, but most of them failed to apply any reliable diagnostic indicators designed to detect and to trace any changes in the quality of the groundwater. In contrast, the present study demonstrates the application of certain diagnostic indicators (DI) devised specifically for the detection, progress and trends of seawater infiltration into an aquifer.     

A comparative study of using two numerical strategies to simulate the biochemical processes in microbially induced calcite precipitation

In this study, we carried out a comparative study of two different numerical strategies for the modeling of the biogeochemical processes in microbially induced calcite precipitation (MICP) process. A simplified MICP model was used, which is based on the mass transport theory. Two numerical strategies, namely the operator splitting (OS) and the global implicit (GI) strategies, were adopted to solve the coupled reactive mass transport problems. These two strategies were compared in the aspects of numerical accuracy, convergence property and computational efficiency by solving the presented MICP model. To look more into the details of the model, sensitivity analysis of some important modeling parameters was also carried out in this paper.     

Eco-physiological adaptations that favour freshwater cyanobacteria in a changing climate

Climate change scenarios predict that rivers, lakes, and reservoirs will experience increased temperatures, more intense and longer periods of thermal stratification, modified hydrology, and altered nutrient loading. These environmental drivers will have substantial effects on freshwater phytoplankton species composition and biomass, potentially favouring cyanobacteria over other phytoplankton. In this Review, we examine how several cyanobacterial eco-physiological traits, specifically, the ability to grow in warmer temperatures; buoyancy; high affinity for, and ability to store, phosphorus; nitrogen-fixation; akinete production; and efficient light harvesting, vary amongst cyanobacteria genera and may enable them to dominate in future climate scenarios. We predict that spatial variation in climate change will interact with physiological variation in cyanobacteria to create differences in the dominant cyanobacterial taxa among regions. Finally, we suggest that physiological traits specific to different cyanobacterial taxa may favour certain taxa over others in different regions, but overall, cyanobacteria as a group are likely to increase in most regions in the future.     

Profile deformation of a circular tunnel induced by ambient stress changes

Since profiles of a tunnel can be most easily and precisely measured using the current approaches such as the profile-image method, the measurement of profiles has become the standard process for evaluating the safety of a tunnel. The deformation of a profile yields important information on changes in the ambient stress of a tunnel. This study presents a method for distinguishing the two-dimensional, deformational displacement from the translational and rotational displacement. Based on this method, the net deformational displacements of a profile under various loading conditions are obtained. The studied loading conditions include ambient uniaxial and biaxial loadings, loading near the lining, inclined loading and sliding along a weak plan. The deformation patterns correspond to various loading conditions can be easily distinguished, that changes in ambient stress can be identified from the measured profile deformation. More sophisticated situations, elasto-plastic material, initial deformation, and profiles other than circular profiles are also examined to investigate the effectiveness of further extensions or application of the proposed method.     

Active and passive pressures with seismically induced changes in the direction of surface-friction forces

Conditions favorable to the development, and characteristic features of the accounting of the “reverse” direction of surface-friction forces at the contact between a retaining wall and soil medium with determination of the latter's lateral pressure are indicated. Basic computational relationships are presented for steep and inclined walls, and also the results of the mathematical modeling of the “structure/soil-medium” system with variation of the latter's computational parameters are presented. A general computational algorithm, which takes into account any direction of contact-friction forces, and a program that runs the algorithm on a computer, as well as tables of the range of combinations of initial parameters, including parameters that account for seismic effects, are developed. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 14–18, May–June, 1996.     

Chemically induced changes in the geotechnical response of cementing paste backfill in shaking table test

Cemented paste backfill(CPB) is extensively used for underground mine support and/or tailings management.However,CPB behavior under cyclic loadings might be affected by the chemistry of its porewater,which often contains sulphate ions.Till today,no studies have addressed the effect of sulphate on the response of CPB to cyclic loadings by using shaking table technique.This study presents new findings of assessing the effect of the sulphate in the pore water of CPB on its geotechnical response to cyclic loading by using shaking table.CPB mixtures were prepared(with and without sulphate),poured into a flexible laminar shear box,cured to 4 h,and then exposed to cyclic loading using one-dimensional(1D) shaking table.Several parameters(e.g.pore water pressure,settlement,lateral deformation,acceleration,electrical conductivity,effective stress,and liquefaction susceptibility) were monitored or determined before,during,and after shaking.Obtained results indicate that the sulphate-bearing CPB cured to 4 h can be prone to liquefaction under the studied conditions.However,sulphate-free CPB samples are resistant to liquefaction.These results are expected to contribute to a better understanding of the effect of water chemistry on the cyclic behavior of CPB,consequently enhancing the cost-effective design of CPB structures.     

Endosulfan, a global pesticide: A review of its fate in the environment and occurrence in the Arctic

This review investigates the fate and behaviour of endosulfan, a current-use organochlorine pesticide, in temperate environments and the Arctic. Usage data and patterns, physical-chemical properties, environmental partitioning and degradation, environmental levels, global distribution and temporal trends are evaluated and discussed in the context of criteria that designate a substance as a persistent organic pollutant. Endosulfan is one of the most abundant OC pesticides in the global atmosphere and is capable of undergoing long range transport to remote locations such as the Arctic. Degradation of the two isomers, α- and β-endosulfan, does occur in temperate/tropical soil and aquatic systems, both by abiotic and biotic processes, although this is highly dependent on the prevailing environmental conditions. Endosulfan sulfate is the major metabolite and this recalcitrant compound has been detected in air and is present in remote mountain lake sediments, although in comparison to α-endosulfan, data for this compound in the wider environment are lacking.Temporal trends from ice/snow cores as well as mountain lake sediments reveal a marked increase in endosulfan accumulation from the 1980s onwards. Furthermore, unlike other ‘legacy’ OC pesticides, levels of α-endosulfan do not show a decline in atmospheric monitoring data, reflecting ongoing use of this pesticide in the northern hemisphere. Endosulfan is present at low concentrations (relative to the pesticide, lindane) in surface Arctic Ocean waters, with the atmosphere likely to be the major contemporary source. Residues of endosulfan have been detected in marine biota for different geographical regions of the Arctic, with higher bioaccumulation factors (> 10³-10⁷) for zooplankton and various species of fish, compared to studies in warmer/temperate systems. Endosulfan is present in marine mammals, although there is uncertainty in the various Arctic biota datasets due to differences in analytical techniques. For some biota, biomagnification factors for α-endosulfan are > 1, notably from fish to seal, although there is a wide variability in values between the same species for different regions of the Arctic. There is little if any evidence of trophic magnification of α-endosulfan in well-defined marine foodwebs, with some evidence of bio-dilution at higher trophic levels, presumably due to increased metabolism.Endosulfan does fulfil several of the criteria under the UNEP Stockholm Convention for designation as a persistent organic pollutant. The α- and β-isomer have similar physical-chemical properties and environmental behaviour to some of the obsolete organochlorine pesticides, although an assessment of their persistence and toxicity should be viewed alongside endosulfan sulfate, as ‘Σendosulfan’. Persistence of ‘Σendosulfan’ coupled to ongoing use of endosulfan pesticides, will ensure continued long-range transport and contamination of remote environments.     

Fabric changes induced by super-absorbent polymer on cemente-lime stabilized excavated clayey soil

This paper studies the microstructure variation induced by super-absorbent polymer(SAP) to understand the mechanism of macroscopic strength improvement of stabilized soil. The fabric changes of cement elime stabilized soil were analyzed with respect to the variation of SAP content, water content, lime content and curing time, using mercury intrusion porosimetry(MIP) tests. It can be observed that the delimitation pore diameter between inter-and intra-aggregate pores was 0.2 mm for the studied soil,determined through the intrusion/extrusion cycles. Experimental results showed that fabric in both inter-and intra-aggregate pores varied significantly with SAP content, lime content, water content and curing time. Two main changes in fabric due to SAP are identified as:(1) an increase in intra-aggregate pores(0.2 mm) due to the closer soilecementelime cluster space at higher SAP content; and(2) a decrease in inter-aggregate pores represented by a reduction in small-pores(0.2-2 mm) due to the lower pore volume of soil mixture after water absorption by SAP, and a slight increase in large-pores(2 mm)due to the shrinkage of SAP particle during the freezeedry process of MIP test. Accordingly, the strength gain due to SAP for cementelime stabilized soil was mainly due to a denser fabric with less interaggregate pores. The cementitious products gradually developed over time, leading to an increase in intra-aggregate pores with an increasing proportion of micro-pores(0.006-0.2 mm). Meanwhile, the inter-aggregate pores were filled by cementitious products, resulting in a decrease in total void ratio.Hence, the strength development over time is attributable to the enhancement of cementation bonding and the refinement of fabric due to the increasing cementitious compounds.     

Transient characters of energy changes induced by blasting excavation of deep-buried tunnels

As energy release plays an important role in engineering disasters such as rockburst, seismicity induced by deep rock mass excavation via drill and blast, energy changes caused by excavation have been studied for a long time. However, previous studies ignored the time factor and took the unloading of in-situ stress on the excavation boundary as a quasi-static process. In this paper, energy changes induced by quasi-static unloading of in-situ stress (QSUIS) and transient release of in-situ stress (TRIS) were analyzed for the case of circular excavation under the condition of in-situ hydrostatic stress. Results show that, different from energy changes caused by QSUIS, the dynamic adjustment of strain energy induced by TRIS which first decreases and then increases, is a transient process. With the propagation of the unloading stress wave from the excavation boundary to the far surrounding rock masses, energy is transmitted by the way of radial stress doing work from the far surrounding rock masses to the near ones which causes the transient aggregation of strain energy. Comparison based on the effects of energy changes on the damage range indicates that higher aggregation degree of strain energy causes larger damage range induced by TRIS than that induced by QSUIS. In addition, a practical application in Jinping II hydropower project was presented as a verification.     

Fabric changes induced by super-absorbent polymer on cement–lime stabilized excavated clayey soil

This paper studies the microstructure variation induced by super-absorbent polymer (SAP) to understand the mechanism of macroscopic strength improvement of stabilized soil. The fabric changes of cement–lime stabilized soil were analyzed with respect to the variation of SAP content, water content, lime content and curing time, using mercury intrusion porosimetry (MIP) tests. It can be observed that the delimitation pore diameter between inter- and intra-aggregate pores was 0.2 μm for the studied soil, determined through the intrusion/extrusion cycles. Experimental results showed that fabric in both inter- and intra-aggregate pores varied significantly with SAP content, lime content, water content and curing time. Two main changes in fabric due to SAP are identified as: (1) an increase in intra-aggregate pores (<0.2 μm) due to the closer soil–cement–lime cluster space at higher SAP content; and (2) a decrease in inter-aggregate pores represented by a reduction in small-pores (0.2–2 μm) due to the lower pore volume of soil mixture after water absorption by SAP, and a slight increase in large-pores (>2 μm) due to the shrinkage of SAP particle during the freeze–dry process of MIP test. Accordingly, the strength gain due to SAP for cement–lime stabilized soil was mainly due to a denser fabric with less inter-aggregate pores. The cementitious products gradually developed over time, leading to an increase in intra-aggregate pores with an increasing proportion of micro-pores (0.006–0.2 μm). Meanwhile, the inter-aggregate pores were filled by cementitious products, resulting in a decrease in total void ratio. Hence, the strength development over time is attributable to the enhancement of cementation bonding and the refinement of fabric due to the increasing cementitious compounds.     

Selective suppression of harmful cyanobacteria in an entire lake with hydrogen peroxide

Although harmful cyanobacteria form a major threat to water quality, few methods exist for the rapid suppression of cyanobacterial blooms. Since laboratory studies indicated that cyanobacteria are more sensitive to hydrogen peroxide (H₂O₂) than eukaryotic phytoplankton, we tested the application of H₂O₂ in natural waters. First, we exposed water samples from a recreational lake dominated by the toxic cyanobacterium Planktothrix agardhii to dilute H₂O₂. This reduced the photosynthetic vitality by more than 70% within a few hours. Next, we installed experimental enclosures in the lake, which revealed that H₂O₂ selectively killed the cyanobacteria without major impacts on eukaryotic phytoplankton, zooplankton, or macrofauna. Based on these tests, we introduced 2 mg L⁻¹ (60 μM) of H₂O₂ homogeneously into the entire water volume of the lake with a special dispersal device, called the water harrow. The cyanobacterial population as well as the microcystin concentration collapsed by 99% within a few days. Eukaryotic phytoplankton (including green algae, cryptophytes, chrysophytes and diatoms), zooplankton and macrofauna remained largely unaffected. Following the treatment, cyanobacterial abundances remained low for 7 weeks. Based on these results, we propose the use of dilute H₂O₂ for the selective elimination of harmful cyanobacteria from recreational lakes and drinking water reservoirs, especially when immediate action is urgent and/or cyanobacterial control by reduction of eutrophication is currently not feasible. A key advantage of this method is that the added H₂O₂ degrades to water and oxygen within a few days, and thus leaves no long-term chemical traces in the environment.     

Whole lake selective withdrawal experiment to control harmful cyanobacteria in an urban impoundment

Different environmental conditions support optimal growth by Aphanizomenon and Microcystis in Ford Lake, Michigan, USA, based on weekly species biovolume and water chemistry measurements from June through October 2005-2007. Experimental withdrawal of hypolimnetic water through the outlet dam was conducted in 2006, with 2005 and 2007 acting as control years, to test theory regarding management of nuisance and toxic cyanobacteria. The dynamics of Aphanizomenon and Microcystis blooms in Ford Lake appear to be driven largely by NO₃⁻ concentrations, with higher levels shifting the advantage to Microcystis (P < 0.0001). Aphanizomenon was most successful with a mean TN:TP ratio (mol:mol) of 48.3:1, whereas Microcystis thrived with a mean ratio of 70.1:1. Withdrawal of hypolimnetic water successfully destabilized the water column and led to higher levels of NO₃⁻ and the near elimination of the Aphanizomenon bloom in 2006 (P < 0.0001). Selective withdrawal did not reduce Microcystis biovolume or microcystin toxicity. Microcystis biovolume and NO₃⁻ levels were positively correlated with microcystin toxin (P = 0.01) and jointly accounted for 30.5% of the variability in the data. Selective withdrawal may be a viable management option for improving water quality under certain circumstances. To fully address the problem of nuisance and toxic algal blooms in Ford Lake, however, an integrated approach is required that targets cyanobacteria biovolume dynamics as well as conditions suited for toxin production.     

Deviation of hydraulic fractures through poroelastic stress changes induced by fluid injection and pumping

This paper presents an analysis of the deviation of hydraulic fractures associated with the poroelastic change of the in situ stress field caused by fluid injection and pumping in the reservoir. This mechanism is studied within the confines of a simple model involving one injection and one pumping well, and a hydraulic fracture propagating along the path initially equidistant from the two wells. Analysis of the fracture deviation from its straight-ahead path and determination of the conditions leading to attraction of the fracture by the injection well are both based on a theoretical study of the stress trajectories. Comparison of the analytical prediction of the fracture path with the computed path using a numerical technique shows excellent agreement between the two methods, provided that a certain dimensionless toughness is small.The principal results of this study can be summarized as follows. First, a fracture propagating along a path, initially midway between an injection and a pumping well, will always be deviated by the injection well due to the shear stress induced by fluid injection and pumping along the initial path.Second, the injection well acts as an attractor of hydraulic fractures propagating within its “attraction basin”. Then, the fracture will propagate toward the injection well rather than simply be deviated by it. One of the features of this attraction basin is the existence of a “fracture barrier” characterized by a 90° rotation of the principal stress directions, with respect to far-field principal directions.Third, fracture deviation and attraction towards the injection well appears to be primarily controlled by only two dimensionless quantities: ., the ratio of the stress deviator at infinity over the characteristic stress σ∗ associated with injection and pumping of fluid, and π = 4ct/L², a dimensionless time (where c is the diffusivity and L is the half-distance between the two wells). The number of significant parameters is thus remarkably less than expected from a dimensional consideration. Only in the region close to the injection well is there an influence of an additional number , the ratio of the difference between the mean pressure at infinity and initial pore pressure to the characteristic stress σ∗.     

On the issue of limiting nutrient and predictions of cyanobacteria in aquatic systems

This study aims at bridging the gap between freshwater and marine eutrophication studies by presenting (1) a cross-system analysis of the relationship between chlorophyll and the total nitrogen (TN) to total phosphorus (TP) ratio (2) a general model to predict concentrations of cyanobacteria from data on TP, the TN/TP ratio, salinity and temperature, and (3) a general trophic level classification for aquatic systems based on chlorophyll classes (for oligo-, meso-, eu- and hypertrophic systems). The data compiled in this study concerns more than 500 lakes and coastal areas covering a very wide domain in terms of nutrient concentrations and salinity. There was no simple relationship between the TN/TP ratio and empirical chlorophyll concentrations or concentrations of cyanobacteria. Variations in TP rather than TN generally seem to be more important to predict variations among systems in chlorophyll-a and cyanobacteria. Different "bioavailable" forms of the nutrients (DIN, DIP, phosphate, nitrate, etc.) have been shown to have very high coefficients of variation (CV), which means that many samples are needed to obtain reliable empirical data which are necessary in models aiming for high predictive power and practical usefulness.     

Influence of salinity and mineralization on trace metal sorption to cyanobacteria in natural waters

The equilibrium distribution of Cd, Cu and Pb between the cyanobacterium Anabaena spp. and natural lake water as a function of salinity and degree of algal decomposition, was studied using batch experiments. Adsorption isotherms could be described with the Freundlich equation. Distribution coefficients (K_d) for Anabaena spp. were largest for Pb, followed by Cd and Cu. The variation in K_d values for Cd was explained by a model accounting for metal complexation to the algal surface and complexation by dissolved ligands of variable concentration. The phytoplankton/water distribution of Cd in waters of different salinity appears to be regulated by the free Cd²⁺ activity in solution. Mineralization of Anabaena spp. for 42 d resulted in a decrease of the solid to water ratio by a factor of 12, and an increase in K_d for Cd (factor four), Cu (factor eight) and Pb (factor 10–20). The increase in K_d is attributed to a higher affinity of the metals for the adsorbent. The use of constant K_d values for mineralizing phytoplankton and detritus in trace metal fate models, may result in underestimations of bound fractions. The extent to which this fraction is underestimated, depends on the time course of the distribution coefficient and the solid to water ratio during the mineralization process.     

Evaluation of extracellular products and mutagenicity in cyanobacteria cultures separated from a eutrophic reservoir

The algal extracellular products (ECPs) in three cultures of cyanobacteria species (Anabaena, Microcystis, and Oscillatoria) dominating the eutrophic reservoir populations and their toxins have been investigated in the present work. Using gas chromatography coupled with high-resolution electron-impact mass spectrometry (GC/EI-MS) and high performance anion-exchange chromatography (HPAEC) techniques, more than 20 compounds were found in the algal culture (including cells and filtrates) extracts. The main identified ECPs were classified to polysaccharides, hydrocarbons, and aldehydes. Odor causing substances such as trans-1,10-dimethyl-trans-9-decalol (geosmin) and 2-methylisoborneol (2-MIB)were also found in the algal cultures. The potential mutagenicity of the algal suspensions was also studied with the Ames test. The organic extracts of the algal suspension from the axenic cultures were mutagenicity in TA98 without S9 mix and in TA100 with and without S9 mix. The results indicate that the ECPs of three algae species dominating the eutrophic reservoir were mutagenic clearly in the bacterial test.