Changes In Physicochemical Conditions Research Articles

Abundance and mineralogical association of arsenic in the Suwannee Limestone (Florida): Implications for arsenic release during water–rock interaction

Arsenic (As) is being released from the Suwannee Limestone, Upper Floridan aquifer, during aquifer storage and recovery (ASR) cycle testing with concentrations of up to 130 μg/L in the recovered water. To determine the abundance and mineralogical association of As in the Suwannee Limestone matrix we have conducted a detailed mineralogical and geochemical study of 306 core samples. In addition to random sampling of core material, we also collected “targeted” samples of core material that contained organic material, hydrous ferric oxide, pyrite, phosphate minerals and clays. Bulk As concentrations were determined by acid digestion followed by hydride generation-atomic fluorescence spectrometry (HG-AFS). Specific mineral phases were analyzed using scanning electron microscopy (SEM) and electron-probe microanalyses (EPMA). The average As concentration for all 306 samples is 3.5 ppm, but only 1.7 ppm after exclusion of the “targeted” samples. The average for the “targeted” samples is 9.5 ppm. The detailed lithologic, mineralogical, and geochemical study of As in the Upper Floridan aquifer, Suwannee Limestone shows that: (1) Arsenic is present in the Suwannee Limestone in low concentrations, but is concentrated in minor mineral phases, particularly pseudo-framboidal pyrite. (2) Pyrite is generally As-rich and can contain concentrations between 100 and 11,200 ppm As (average 2300 ppm, n = 25). (3) Compared to pyrite, other trace minerals contain much less As. (4) Pyrite is ubiquitous throughout the Suwannee Limestone, but is most abundant in high porosity zones. (5) Previously suggested hydrous ferric oxide, clay minerals and apatite are not an important source of As. This study also provided some insight into the question whether the interaction (reaction) of water with an aquifer matrix that contains only a few part per million As is capable of producing high-As concentrations in groundwater. Our findings indicate that it can be relatively easy to generate a high-As groundwater despite a low bulk As concentration in the aquifer matrix. A change in physico-chemical conditions that selectively affects the stability of As-bearing minerals is sufficient to increase As concentrations by several orders of magnitude.

Ecology and Phenology of Freshwater Ostracods in Lake Gölköy (Bolu, Turkey)

Seventeen ostracod species were recorded from Lake Golkoy (Bolu, Turkey) between January 2000 and December 2001. Limnocythere inopinata is a new record for the Bolu region. Canonical Correspondence Analysis (CCA) explained 73% of the correlation between species and environmental variables, suggesting that the occurrence of many species is temporally variable, and is related to seasonal changes in physico-chemical conditions. The four most frequently occurring cosmopolitan ostracod species (Candona neglecta, Darwinula stevensoni, Physocypria kraepelini, and Cypridopsis vidua) accounted for more than 70% of the species recorded. Water temperature, dissolved oxygen (DO), and redox potential were the most affective variables on the species occurrence. Two species (C. vidua, I. bradyi) were positively correlated to redox potential, while such a correlation was negative for P. kraepelini. The most frequently occurring species C. neglecta was most closely related to the changes in redox potential, whereas C. vidua and D. stevensoni showed a positive correlation to water temperature. Negative strong correlation (p<0.01) was found between pH and I. bradyi, but correlation was positive and weak for C. vidua. Some species (e.g. L. inopinata) showed no clear relationship with any of those environmental variables. UPGMA clustering of species based on their occurrence in different ecological conditions revealed three main species assemblages. Analysis of species phenology using the ‘Ostracod Watch Model’ showed that temporal patterns of occurrence could be similar among species with similar ecological preferences. The current status of the lake is discussed based on the present study.

The fractal structure of polycation–DNA complexes

We used static light scattering to obtain new measurements on the internal structure of aggregated non-viral gene-delivery particles in colloidal suspension. The vector particles are prepared by charge neutralization of plasmid DNA either by poly-L-lysine or by a Lipofectin/integrin-targeting peptide. We use established theories of the stability of colloidal particles and fractal concepts to explain the aggregation processes and demonstrate the existence of a new property (fractal dimension) of the aggregated vector particles. Aggregation is shown to produce particles with fractal dimensions in the range between 1.8 and 2.4; the former suggests a loose three-dimensional structure and the latter characterizes an aggregation process that leads to the formation of particles with tightly packed structures. We show that the fractal dimension of the vector particles is sensitive to changes in physicochemical conditions (ionic strength) of the buffer solution and propose that fractal dimension may provide a useful means of monitoring the physical state of non-viral delivery-vector particles during preparation and storage.

Employing a novel fiber optic detection system to monitor the dynamics of in situ lux bioreporter activity in porous media: system performance update

One of the major constraints to successful implementation of in situ bioremediation is our lack of understanding of how microbial activity is influenced by the physicochemical conditions in the subsurface environment. Our laboratory has successfully developed a novel fiber optic detection system that employs a lux bioreporter organism to non-invasively monitor real-time, in situ microbial activity in porous media. An evaluation of potential system limitations indicates that the system is not adversely affected by biofilm formation on the optical fiber tips or by bioluminescence attenuation in the porous medium employed. Additionally, the detection system effectively captures the dynamics of in situ bacterial gene expression during naphthalene catabolism under changing physicochemical conditions in saturated porous media. Therefore, this system enables laboratory-based studies of how physicochemical conditions in the subsurface influence microbial activity and will assist in improving: (1) our fundamental understanding of how transformation-related non-ideality, such as non-steady-state microbial activity, affects contaminant transport and fate; and (2) our ability to predict the efficacy of in situ bioremediation in dynamic, heterogeneous subsurface environments.

The utiquity and many roles of exopolymers (EPS) in aquatic systems

Exopolymers (EPS) are produced by unicellular and multicellular organisms. They consist largely of polysaccharides that hydrate rapidly on contact with water and link to form gels. EPS have many uses: in attachment; in locomotion on substrata; as a protection against predators, pathogens and changes in physico-chemical conditions; as a means of overcoming the threat of desiccation; in preventing abrasion; and in feeding. When free of organisms, some EPS form loosely associated polymer gels that are important in the development of organic matter aggregates. These aggregates, together with mucus-bound faecal pellets, play an essential role in nutrient cycling, and in the metabolism of ecosystems.;

Sulfate Respiration in Extreme Environments: A Kinetic Study

In situ experiments were conducted in order to quantify sulfate reduction kinetics among thermophilic prokaryotes thriving in hydrothermal springs of Yellowstone National Park (USA). Selected springs were sampled based on their varied physicochemical characteristics in order to identify the effect of extreme environmental determinants over sulfate reduction. Reduction rates range from 1 to 483 nmol cm−3 d−1 in various springs with no correlation observed between sulfate reduction rate and pH or sulfate concentration of spring waters. A weak negative correlation with temperature exists though. Results from slurry incubation experiments show that both the apparent activation energy and the half-saturation constant are site specific. Activation energies of 17, 38, and 119 kJ mol−1 were determined in three different springs whereas the half-saturation constant values of 1.24 ± 0.90 and 3.17 ± 1.02 mM were calculated for two of the sampled springs. Such variations in activity and kinetic parameters may depict a change in the microbial population in different springs, or the response of microbial assemblages to changing physicochemical conditions. In the latter case the sulfate reducers must be highly adaptive to changing environmental conditions.

Li-rich zincostaurolite and its decompression-related breakdown products in a diaspore-bearing metabauxite from East Samos (Greece): An EMP and SIMS study

Li-H-rich zincostaurolite locally formed at a metabauxite-marble contact along the eastern coast of Samos during early Alpine high-P, low-T metamorphism. The staurolite, which probably grew from gahnite, cookeite, kaolinite/pyrophyllite, diaspore, and minor Fe-oxide, occurs as prismatic crystals (up to several mm long) in a calcite matrix. It has an unusual composition with 7.5-12.9 wt% ZnO, 1.0-4.9 wt% FeO, 0.66-0.82 wt% Li 2 O, up to 2.6 wt% NiO and 0.59 wt% CoO, and ≤ 0.32 wt% MgO. Calculated structural formulae point to high H 2 O contents (≥4.14 H atoms per 48 oxygen atoms). During late-Alpine uplift of the Samos rocks, the staurolite was, at greenschist-facies conditions, variably replaced by bluish cobaltoan gahnite (X Zn &gt; 0.82), white Na-Ca-Li mica, Ni-rich chlorite (X Ni = 0.42-0.59), zincohögbomite (X Zn = 0.68-0.80), diaspore, and Fe-(hydr)oxide. Detailed EMP work and determination of Li in staurolite and mica by SIMS indicates systematic Zn- Fe-Mg-Ni-Co-Li partitioning between staurolite and its decomposition products, implying local-scale chemical equilibrium. Balanced reaction equations based on mineral-chemical data indicate that the breakdown of staurolite occurred largely isochemically with only introduction of water, Na, and Ca into the reacting system. The breakdown of high-P staurolite during uplift and decompression is thought to be related to the sensitivity of its complex crystal chemistry to changes in physico-chemical conditions.

大容量タンクで観察された自然植物プランクトン群集の製鋼スラグ添加に対する増殖応答:物理化学環境とクロロフィルの変化

大容量タンクで観察された自然植物プランクトン群集の製鋼スラグ添加に対する増殖応答:物理化学環境とクロロフィルの変化

Metal distribution during diagenesis in the contaminated sediments of Dulas Bay, Anglesey, N. Wales, UK

The Tessier sequential extraction procedure was applied to discrete layers from 9 sediment cores from Dulas Bay, Anglesey. Results provide data on the chemical association of heavy metals (Fe, Mn, Cu, Zn, Cd, and As with major) sedimentary phases, and provide information on changes in metal partitioning associated with the changing physico-chemical conditions encountered during burial. Extremely high concentrations of heavy metals were recorded (e.g. Zn 3000 μg g −1, Cu 2000 μg g −1) and resulting depth profiles clearly indicate the differential behaviour of metals during diagenesis where, with increasing depth, Fe, Mn and Cu become increasingly associated with sulphide phases. Substantial changes in porewater concentrations indicate zones of preferential mobilisation due to sharp alterations in physicochemical conditions. All metals are involved in processes of post depositional diagenetic cycling driven by organic matter degradation and O 2 utilisation in thermodynamically favoured sequence, Fe and Mn oxide and oxyhydroxide dissolution act as controlling variables leading to zones of solid phase metal enrichment. Phase equilibria have been calculated to elucidate observed solid phase partitioning at the redox boundary and processes of subsurface sulphide mineral formation.

Seasonal Transformations of Manganese in a Palustrine Emergent Wetland

Naturally occurring wetlands need to be investigated to assess their role in contaminant sequestration. Accordingly, aqueous‐ and solid‐phase analyses were conducted to monitor Mn response to changing physicochemical conditions within a Palustrine Emergent Wetland. A rhodochrosite‐like phase (MnCO3) was the dominant Mn bearing phase (by mass) within the solids throughout the year. Aqueous‐phase Mn concentrations were highly variable, but only two sampling sites in the interior of the wetland had pore‐waters supersaturated with respect to rhodochrosite. Despite that a rhodochrosite‐like material was the dominant quantity of Mn in the solids through the year, the reactivity of Mn solids, as measured by selective sequential extractions, did change seasonally. In spring, Mn was preferentially associated with the hydrofluoric acid‐extractable pool, comprising ∼35% of the total extractable Mn. The sodium acetate (SA)/acetic acid (AA) fraction appears elevated from spring through fall. Amorphous sulfide phases denoted by the difference between hydrochloric‐ and oxalic‐acid extractable Mn increased during the summer months and then decreased in early fall as the site dried. Furthermore, as the site dried, Mn associations with the MnCl2 (water soluble and exchangeable) extractable phase increased significantly (P &lt; 0.05), comprising between 26 and 43% of the total extractable Mn. Manganese removed using hydroxylamine‐hydrochloride/AA (crystalline oxide) increased significantly (P &lt; 0.05) in the summer to ∼40% of total extractable Mn. It is therefore apparent that seasonal changes in temperature and water level, with associated redox status, drive changes in surficial coatings of Mn phases and thus its reactivity.

A mesocosm study of physical-biological interactions in artificial sea ice: effects of brine channel surface evolution and brine movement on algal biomass

The impact of changing physico-chemical boundary conditions in sea ice on biological processes was investigated during a 20-day-long simulated freeze-melt cycle in an 180-m3 mesocosm filled with artificial seawater and addition of a mixed Arctic sea-ice community. Ice formation started at Tair of –15°C with a growth rate of 0.7–1.2 mm h–1 for 10 days. The last 10 days (Tair of=–5°C), ice thickness remained around 20 cm. Ice temperature gradients inside the ice were linear and determined brine salinities. Brine was collected by means of centrifugation and its volume ranged from 5 to 30% of total ice volume. Surface areas of interconnected brine channels were determined with two similar techniques and maximum values ranged between 1.5 and 4.8 m2 kg–1ice. Measurements determined with a modified method varied considerably and differed by a maximal factor of 2.0–6.5. Brine channel surfaces increased during the experiment as a result of the warming of the ice. The inoculated algal community was dominated by flagellates <10 µm. The low diatom biomass increased in the ice after the air temperature rise with rates comparable to field data (µ=0.2–0.3 day–1). Comparison with brine salinities points towards the hypothesis of vertical brine stability being a controlling factor for ice algal growth. We infer from brine channel surface measurements that persistence of brine channel surfaces during spring might be an important prerequisite for the commencement of net diatom biomass accumulation. Advantages and limitations of mesoscale mesocosms as alternatives in ice biological work are discussed.

Mineral chemistry in fenites of the Kalkfeld carbonatite complex and its bearing on the composition of the fenitising fluid

Porphyry-style mineralization is characterized by superposition of multiple generations of quartz growth, punctuated by dissolution and juxtaposed within a single vein. Such superposition inevitably obscures temporal relationships between quartz formation, alteration events, and fluid inclusion assemblages (FIAs), and consequently complicates the interpretation of fluid origin and evolution. Very detailed information of these relationships recorded within hydrothermal quartz from the Taiyangshan porphyry Cu-Mo deposit (NW China) is obtained using integrated cathodoluminescence (CL) imaging, trace element analyses, and fluid inclusion petrography.The CL characteristics range from bright blue-CL quartz (Q1) associated with early high-temperature potassic alteration, to dark blue-CL quartz (Q2) broadly coinciding with metal precipitation, to post-ore dull red-CL fine-grained, anhedral, and recrystallized quartz (Q3) subgrains. Early bright blue-CL quartz (Q1) crystals, generally at the edges of stockwork veinlets close to wallrock, are characterized by oscillatory growth zoning, and exhibit alignment of primary, equant-shaped, brine-bearing FIAs along the banded growth zones. Later dark blue-CL quartz (Q2) crystals are generally euhedral in shape and grow with c-axes pointing inward to the vein center. They exhibit well-defined, but rarely preserved, growth zones truncating Q1 and crystal terminations projecting into pyrite and chalcopyrite in the vein center although they are not spatially associated with sulfides. These vein features clearly indicate that Q2 crystals grow into an open cavity or fracture during the ore precipitation. This is also evident by coexisting, secondary, irregular-shaped, liquid-rich inclusions and vapor-rich inclusions along fractures transecting Q1 oscillatory growth bands. The coexistence of hypersaline and vapor-rich inclusions moreover provides unequivocal evidence for phase separation during mineralization. Dull red-CL quartz (Q3) crystals appear to coincide with or follow sericitic alteration, and cut and encompass preexisting Q1 and Q2 crystals. They spatially associated with sulfides. The Q3 grains contain rare well-defined FIAs, but show scattered, secondary, irregular-shaped, low-salinity aqueous inclusions with small- to medium-sized vapor bubbles (10–30 vol%), as well as complex fluid inclusions that have migrated to the margins of anhedral Q3 subgrains due to quartz dissolution and recrystallization.Formation of early blue-CL Q1 and Q2 crystals at moderate temperatures are consistent with enrichment of Ti in the quartz lattice compared to neighboring younger Q3. The Q2 crystals are typified by elevated concentrations of Al and K concentrations when compared to Q1 and Q3. The substitution of Ti4+ for Si4+ in the tetrahedral sites of quartz leads to an increased CL intensity from Q1, to Q2, and then to Q3 corresponding to a decrease in quartz precipitation temperature. Ore deposition, recorded by integration of CL textures, FIAs petrography, and trace element variations in Q2, in the Taiyangshan porphyry Cu-Mo deposit must have occurred over a significant change in physicochemical conditions. This suggests that phase separation due to fluid cooling/pressure drops during the transition from lithostatic to hydrostatic regimes is critical to porphyry mineralization. We further propose a complex hydrothermal quartz vein formation history involving multiple fluid inclusions under varying pressure and temperature conditions.

Au-Sb association and fractionation in micro-disseminated gold deposits, southwestern Guizhou—geochemistry and thermodynamics

The dual geochemical character of paragenesis and fractionation between gold, arsenic and antimony in micro-disseminated gold deposits in southwestern Guizhou is discussed in terms of spatial distribution of independent deposits, lateral and vertical enrichment, mineralization stage and factor and correlation analyses. Thermodynamic calculations of solubility and speciation of gold and antimony minerals indicate that gold is transported in hydrothermal solution as Au(HS) - 2 and antimony is mainly as Sb (OH 0 3 ) although HSb 2 S - 4 may be of increasing importance in acid environment at low temperatures during the late stage of mineralization. Changes in physicochemical conditions hold the key to the association and fractionation between gold and antimony. Gold and antimony response differently to physicochemical variations because they are distinct from each other in soluble speciation and mineral solubility, leading to precipitation at different times and localities during hydrothermal evolution.

Redistribution of Trace Elements from Contaminated Sediments of Lake Coeur d'Alene during Oxygenation

AbstractSediments of Coeur d'Alene Lake in northern Idaho are contaminated with heavy metals as a result of mining in the Coeur d'Alene River basin. Dredging and disposal operations have been suggested as a possible means of environmental remediation; thus, detailed knowledge is required as to how sediment oxygenation can result in the redistribution of trace elements. To simulate changing physicochemical soil conditions, stirred batch experiments were conducted using fresh sediment core material retrieved from the lake. Fifty grams of sediment were added to 750 mL of double deionized water and mixed while being oxygenated for 260 h. The following parameters were monitored as a function of time: pH and Eh, contaminant trace‐element release into the aqueous phase, and metal abundance within operationally defined fractions of the solid phase: magnesium chloride (exchangeable), sodium hypochlorite (organic), sodium acetate‐acetic acid (carbonate), ammonium oxalate in the dark (non‐crystalline), hydroxylamine hydrochloride (crystalline), and potassium perchlorate‐hydrochloric‐nitric acid (sulfidic) extractable sediment fractions. In all trials, levels of aqueous‐phase Zn remained high throughout the simulations (6.60 mg L−1) and were highly correlated (sigma value = 0.95) with Mn. Oxygenation and disturbance resulted in a shift in trace element partitioning from the sodium hypochlorite (organic) and potassium perchlorate‐hydrochloric‐nitric acid extractable (sulfidic) fractions into the ammonium oxalate in the dark (noncrystalline) extractable fraction. Overall, these results indicate that oxygenation and agitation of anaerobic sediment results in Zn release into solution with concomitant redistribution of trace elements in the solid‐phase.

Sources and drains: Major controls of hydrothermal fluid flow in the Kokanee Range, British Columbia, Canada

Vein fields are fractured domains of the lithosphere that have been infiltrated by hydrothermal fluids, which deposited minerals in response to changing physico-chemical conditions. Because oxygen is a major component of the infiltrating fluid and the surrounding rock matrix, the oxygen isotope composition of minerals found in veins is used to decipher ancient fluid flow within the lithosphere. We use a numerical model to simulate oxygen isotope transport in the Kokanee Range silver-lead-zinc vein field. The model considers advective, dispersive, and reactive transport in a three-dimensional porous rock matrix intersected by high-permeability planes representing fracture zones. Here we show that it is the geometrical configuration of the sources and of the drains of hydrothermal fluids, combined with the fracture pattern, that exerts the main control on the oxygen isotope distribution. Other factors that affect, to a lesser extent, the values and positions of oxygen isopleths are the fluids and rock-matrix isotopic compositions, the isotopic fractionation, the reaction rate constant, and hydraulic conductivities of the rock matrix and fracture zones.

BIOTIC AND ABIOTIC CHANGES ALONG THE RECOVERY GRADIENT OF TWO IMPOUNDED RIVERS WITH DIFFERENT IMPOUNDMENT USE

Changes in physicochemical conditions and lotic benthic macroinvertebrates along the recovery gradient of the impounded Colorado (USA) and Duraton (Spain) Rivers were examined to identify and compare major factors affecting the structure of the macrobenthic community. Although both impounded rivers were exposed to hypolimnial releases from dams, they exhibited different impoundment use; Granby Dam (Colorado River) is used for water storage whereas Burgomillodo Dam (Duraton River) is used for hydroelectric production. The major factor responsible for macroinvertebrate responses in the Colorado River appeared to be the anomalous temperature pattern caused by Granby Dam, with relatively cool temperatures during the summer and relatively warm temperatures during the winter. In contrast, the major factors responsible for macroinvertebrate responses in the Duraton River seemed to be short-term flow fluctuations and low oxygen concentrations caused by Burgomillodo Dam. Values of taxonomic richness and relative abundances of shredders (Colorado River) and scrapers (Duraton River) increased along the recovery gradient of the impounded rivers. In general, chironomids (Diptera) were tolerant to both types of impoundment use, whereas elmids (Coleoptera) and psychomyiids (Trichoptera) were very sensitive. Overall, this environmental monitoring study denotes that the downstream changes in the biotic and abiotic components of impounded rivers is a function of the particular use of impoundments.

Complex dynamics of mass-closed coupled autocatalytic systems in response to minute asymmetric perturbations

The role of kinetic coupling in catering to a remote-control mechanism for the onset and regulation of self-organization phenomena in a multicompartmental biochemical system has been examined. Using two cyclic autocatalytic reaction networks operating in two chambers separated by a membrane and coupled through a common cofactor, it has been demonstrated that (i) in response to asymmetric perturbations, the coupled reaction networks exhibit a variety of temporal self-organization phenomena such as bistability, multiple periodicity, hard excitation and coexistence of aperiodic oscillation with limit cycle even in mass-closed conditions; (ii) without disturbing a network directly, its dynamic behaviour can be regulated by perturbing some other network kinetically coupled to it and (iii) the dynamics of two coupled networks can be made to flip-flop between oscillatory and steady-states simply by modulating the time of application of external perturbations. The extreme sensitivity of this model to minute asymmetric fluctuations in the environment can predict how the impact of local changes in physico-chemical conditions can be transmitted from one compartment to another through coupled biochemical pathways in a living cell.

The constraints on the differential enrichment of au and as during hydrothermal mineralization, Southwest Guizhou, China

The differential enrichment of gold and arsenic observed in As-bearing hydrothermal gold deposits in Southwest Guizhou is induced by vapor-liquid separation in response to changing physico-chemical conditions during the hydrothermal evolution and is a reflection of the geochemical behavior of the two elements.

New and Extended Applications for USP Drug Release Apparatus 3.

The history of the development and the principles of the operation of USP 3 are described briefly. Its use for the dissolution testing of immediate release products as well as flexibility in the examination and design of controlled nlease is S1t1Itmarized. Special emphasis is given to the advantages of the instrument in mimicking the changes in physicochemical conditions and mechanical forces experienced by p1oducts in the G.l. tract.

The membrane contact seam in adhesion of erythrocytes by polymers

The influence of polymers on human erythrocyte membrane-membrane interactions has been examined. Particular attention was paid to the contact seam, i.e. whether the membranes formed spatially periodic local contact points or lay parallel to each other in a continuous seam. Exposure to the polycation poly- l-lysine resulted in a spatially periodic contact seam for all normal control cells. The lateral separation distance of contact points decreased from 1.6 μm to a lower limiting value of 0.8 μm as the concentration of 220 kDa polycation was increased threefold from the adhesion threshold value. Reduction of the glycocalyx sialic acid content by neuraminidase pretreatment decreased polycation interaction sites, reduced cell adhesion and resulted in an increased lateral separation of contact points. Normal cells agglutinated by the neutral polymer dextran showed a plane parallel contact seam, in contrast to the results with polylysine. Cells pretreated with pronase and then exposed to 72 kDa dextran in 145 mM saline showed a mode response of lateral contact separations in the range 0.8–1.2 μm. Suspensions of such pretreated cells in 120 mM saline, where electrostatic repulsion was increased, showed a change towards longer contact spacings. The experiments identify situations where either electrostatic or glycocalyx repulsion can dominate membrane interaction. The results show that changes in physicochemical conditions which increase net attraction lead to shorter lateral contact separation. The results are consistent with the interfacial instability model for the generation of local contacts.