Influence of the pH and redox potential on phosphate activity in the Parana Medio system

The effect of redox potential and pH on the phosphate mobility in two sediments were investigated using both consolidated and suspended sediments from the area where the Parana Medio long reservoir (Atgentina) is to be built (Smirnov, 1984). In addition to direct chemical sediment analysis, extraction techniques were carried out with a stepwise NH₄Cl-NaOH-HCl shaking method, the latter supposedly separating the weakly bound, the Fe- and Al- bound and the Ca- bound phosphates in the sediments.Phosphate released into water depends upon redox potential and pH, which both were modified in an experimental setup. The source of the phosphate was the fraction of Fe and/or Al bound phosphate present both in the sediment and in the suspended solids.Abbreviations cm centimeter - km kilometer - gg gram - l liter - ¬m micrometer - °C grade centigrades - km² square kilometer - m.s^–1 meter per second - m³.s^–1 cubic meter per second - mg.1¹ miligram per liter     

Potential influence of midgut pH and redox potential on protein utilization in insect herbivores

Early insect physiologists recognized the importance of gut physicochemistry, primarily pH, redox potential, and ionic strength, on digestive processes, but studies to date have been primarily restricted to keratin- and wood-feeding insects. Recent investigations show that herbivorous insects have a broad range of gut redox conditions, with pHs ranging from 6.0 to 11.8 and measured redox potentials from −200 to +240 mV. The redox state of the gut is largely dependent on pH, which is well regulated, and the redox activity of ingested material, including plant chemicals, at that pH. Inter- and intraspecific variation in midgut redox conditions appears to be substantial enough to affect digestion via effects on the structure and function of dietary proteins and proteolytic enzymes. The impact of reducing conditions on proteins probably depends on characteristics such as tertiary structure and the number and arrangement of disulfide linkages. In addition to the effects of reducing conditions in dietary proteins, there can be effects on the activities of digestive enzymes, depending on their structure and the nature of their catalytic site. We speculate that phylogenetic and environmental determinants of gut physicochemistry may place constraints on the efficacy of different digestive processes, and may thus influence the evolution of digestive strategies in insects. © 1996 Wiley-Liss, Inc.     

High resolution vertical profiles of pH in recent sediments

High resolution (0.1 cm sampling interval) profiles of pH were obtained from some recent estuarine (Long Island Sound, Chesapeake Bay) and freshwater (Lake Erie) sediments and from laboratory microcosms containing homogenized Lake Erie sediment (both with and without tubificid oligochaetes) by incrementally precessing a micro-pH electrode downward through the sediment. These profiles revealed that hydrogen ion undergoes chemical reactions on a scale smaller than can be resolved using classic 1 cm sampling intervals, and that the vertical distribution of hydrogen ion is affected by bioturbation. In all sediments examined, a local pH minimum occurred immediately below the oxidized zone. In estuarine sediments, a second deeper pH minimum was observed. The presence of tubificids prevented profound pH changes from developing in microcosm sediments treated with a layer of activated sewage sludge and resulted in more modest alterations of pH profile in microcosm sediments lacking such a layer. The technique used in this study is by no means limited to pH. In principal, any chemical species that can be directly determined by electrodes (e.g. O₂, S^-2) may be studied. Microelectrode techniques could be especially useful in the study of chemical gradients around animal burrows and in time series studies of whole core diagenesis.     

The rates of sediment-water exchange of oxygen and sediment bioturbation in Lough Neagh,Northern Ireland

Oxygen is transported 30 mm into the sediment at an 8 m depth site in eutrophic Lough Neagh by the irrigational activities of the benthic fauna. Faunal activity also mixes the upper 20 mm of sediment. Sediment oxygen uptake rate, redox potential-depth profile and the chlorophylla concentration were measured in the upper sediment layers from February to November 1979. Chlorophylla input to the sediment, following the Spring phytoplankton maximum, remained in the 0–1 cm sediment layer but did cause the redox potential profile to change from one with potentials around 400 mV in the upper 50 mm to one with a strong gradient over the 0–30 mm region. The start of benthic faunal activity in May caused the chlorophylla to be mixed into the 1–2 cm layer and also caused oxygen to be transported into the sediment at a rate sufficient to change the redox potential back to its initial state. The biodiffusion coefficient for solids in the upper 20 mm was estimated to be 6 × 10⁻⁸ cm² s⁻¹. Oxygen transport in the pore, waters of the upper sediment layers was considered to be best described as advection, caused by the irrigational activities of the benthic fauna.     

The impact of sediment reworking by opportunistic chironomids on specialised mayflies

1. Bioturbation, by definition, changes the structure and properties of sediments, thereby altering the environment of the bioturbator and other benthic species. In addition to the indirect effects of sediment reworking (e.g. changes in water quality), bioturbating species may also directly interfere with other species via competition. This study aims, therefore, to examine both the direct and indirect effects of sediment reworking by an opportunistic detritivore on survival and growth of a specialised mayfly species. 2. Bioturbation was imposed by adding different densities of the midge Chironomus riparius to clean and polluted sediments. Changes in water quality and sediment properties, and survival and growth of the mayfly Ephoron virgo were assessed. 3. Chironomid density had a strong negative effect on the concentrations of metals, nutrients and particles in the overlying water, but increased the penetration of oxygen into the sediment. Survival and growth of E. virgo were strongly reduced in the presence of chironomids. In the polluted sediment, the activity of chironomids enhanced the negative effects of pollution on E. virgo. In the clean sediment, inhibition of the mayfly was even more pronounced. 4. This suggests that direct disturbance by C. riparius was more important than indirect changes in water quality, and over‐ruled the potential positive effects of improved oxygen penetration. The results indicated that the distribution of small insects, such as E. virgo, can be limited by bioturbating benthic invertebrates.     

The interaction between water movement,sediment dynamics and submersed macrophytes

Water movement in freshwater and marine environments affects submersed macrophytes, which also mediate water movement. The result of this complex interaction also affects sediment dynamics in and around submersed macrophyte beds. This review defines known relationships and identifies areas that need additional research on the complex interactions among submersed macrophytes, water movement, and sediment dynamics. Four areas are addressed: (1) the effects of water movement on macrophytes, (2) the effects of macrophyte stands on water movement, (3) the effects of macrophyte beds on sedimentation within vegetated areas, and (4) the relationship between sediment resuspension and macrophytes. Water movement has a significant effect on macrophyte growth, typically stimulating both abundance and diversity of macrophytes at low to moderate velocities, but reducing growth at higher velocities. In turn, macrophyte beds reduce current velocities both within and adjacent to the beds, resulting in increased sedimentation and reduced turbidity. Reduced turbidity increases light availability to macrophytes, increasing their growth. Additionally, macrophytes affect the distribution, composition and particle size of sediments in both freshwater and marine environments. Therefore, establishment and persistence of macrophytes in both marine and freshwater environments provide important ecosystem services, including: (1) improving water quality; and (2) stabilizing sediments, reducing sediment resuspension, erosion and turbidity.     

The influence of catchment characteristics on suspended sediment properties

In order to investigate the influence of catchment characteristics on suspended sediment properties, suspended sediment samples were collected from the outlets of 60 small catchments located throughout Southwest England over a 14-month period. The catchments were selected to provide a representative range of topographic, land use, soil and geological characteristics. The suspended sediment samples were collected using time-integrating trap samplers, emptied at monthly intervals. Laboratory analysis focused on a selection of suspended sediment properties, including particle size composition, cation exchange capacity, and organic carbon, nitrogen, metal, radionuclide and phosphorus content. The results presented show that despite the substantial variability of catchment characteristics associated with the 60 sampling sites, the suspended sediment properties generally fell within a relatively limited range. However, statistical analysis identified significant spatial variability of suspended sediment within Southwest England, which in turn can be linked to catchment characteristics.     

Effects of the burrowing mayfly,Hexagenia, on nitrogen and sulfur fractions in lake sediment microcosms

Effects of the burrowing mayfly, Hexagenia, on nitrogen and sulfur fractions of sediment, and overlying water were determined. Laboratory microcosms were used to reproduce the benthic environment. The activities of Hexagenia increased sediment Eh (1.98 ± 0.486 (22) mV · day ⁻¹), and decreased pH in sediment (−0.007 ± 0.001 (22) day ⁻¹) and overlying water(-0.024 ± 0.004 (10) day⁻¹). In the control, Eh decreased and pH did not change. The presence of Hexagenia also markedly increased ammonia in sediment (5.46 ± 0.14 (22) ppm N · day⁻¹) and overlying water (0.792 ± 0.154 (10) ppm N · day⁻¹), while the control did not change. In addition, the sulfate fraction of sediment (0.177 ± 0.006 (17)% dry mass) and water (50.0 ± 4.9 (5) mg · I⁻¹) in microcosms with Hexagenia was greater than that of the control (0.151 ± 0.005 (16)% dry mass; 14.7 ± 1.71 (3) mg · 1⁻¹) at the termination of the experiment. Hexagenia may also stimulate the mineralization of carbon-bonded sulfur. The general role of Hexagenia in altering sediment chemistry is discussed.     

The relative importance of biological and chemical processes in the release of phosphorus from a highly organic sediment

Bacteria can play an important role in the process of anaerobic phosphorus release: they can act as a direct source of orthophosphates, or as a catalyst of iron hydroxyde reduction. We studied their influence on phosphorus release from highly organic sediments of a Canadian shield lake. Phosphorus and iron release were measured under aerobic and anaerobic conditions, with or without sterilization, and at different pH. We measured also the abundance and activity of bacteria in sediments. The increased P release after sterilization can be explained by cell lysis. Compared to sterilization, changing oxygen concentrations or acidification had little or no effect on P release. In these sediments, phosphorus and iron movements were independent. Most of the total dissolved iron seemed to be linked to humic acids, but not phosphorus.A contribution to the GRIL (Groupe de Recherche Interuniversitaire de Limnologie)     

The impact of pH and calcium on the uptake of fluoride by tea plants (Camellia sinensis L.)

BACKGROUND AND AIMS: Tea plants (Camellia sinensis L.) accumulate large amounts of fluoride (F) from soils containing normal F concentrations. The present experiments examined the effects of pH and Ca on F uptake by this accumulating plant species. METHODS: The effect of pH was assessed in two experiments, one using uptake solutions with different pHs, and the other using lime, as CaO, applied to the soil. The effect of Ca was examined by analysing F concentrations in plants supplied with varying amounts of Ca, as Ca(NO3)2, either in uptake solutions or through the soil. KEY RESULTS: F uptake was highest at solution pH 5.5, and significantly lower at pH 4.0. In the soil experiment, leaf F decreased linearly with the amounts of lime, which raised the soil pH progressively from 4.32 to 4.91, 5.43, 5.89 and, finally, 6.55. Liming increased the water-soluble F content of the soil. Including Ca in the uptake solution or adding Ca to soil significantly decreased leaf F concentrations. The distribution pattern of F in tea plants was not altered by Ca treatment, with most F being allocated to leaves. The activity of F- in the uptake solution was unaffected and water-soluble F in the soil was sometimes increased by added Ca. CONCLUSIONS: F uptake by tea plants, which are inherently able to accumulate large quantities of F, was affected both by pH and by Ca levels in the medium. The reduced F uptake following Ca application appeared not to be due simply to the precipitation of CaF2 in solution and soil or to the complexing of Ca and F in roots, although these factors cannot be dismissed. It was more likely due to the effect of Ca on the properties of cell wall or membrane permeability in the solution experiments, and to alteration of F speciations and their quantities in soil solutions following Ca application.     

Effect of pH and Salinity on Sorption of Antimony (III and V) on Mangrove Sediment,Sundarban, India

The extent of toxic metalloid retention and bioavailability and mobility in the sediment is of interest for understanding their biogeochemical cycling and for accurate risk assessment in an ecosystem. Intensification of monsoon and rainfall, believed to be related to global warming, could drive future changes of temperature, salinity, and pH distribution pattern affecting antimony cycling in the Sundarbans. This study investigated sorption kinetics of antimony (Sb) (III and V) as a function of temperature, salinity, and pH following the Langmuir model, and demonstrated that clayey silt type mangrove sediment was an effective adsorbent with higher efficiency for Sb (V) than Sb (III). Background level of Sb in the sediment was 0.35–0.78% of the maximum adsorption capacity (Γ_m). Out of the two distinct type of sorption sites governing mobility and bioavailability of Sb in the sediment, site 1 (Humic acid) showed higher affinity for Sb than the site II (oxyhydroxide). Sb adsorption was strongly influenced by temperature, salinity, and pH, which may be altered by long-term changes in climate and rainfall pattern.     

The relationship between surface sediment diatom assemblages and pH in 33 Galloway lakes: Some regression models for reconstructing pH and their application to sediment cores

The species composition of surface sediment diatom assemblages in 33 Galloway lakes, pH range c. 4.5 to 7.4, is related in a statistically significant manner to water acidity (or to factors closely associated with pH). Predictive models of summer mean pH, using simple regression equations of Index B (Renberg & Hellberg, 1982) with both Scandinavian and Galloway data sets, and multiple regression equations using diatom pH preference groups and individual species, are described and applied to fossil diatoms in six sediment cores. Although multiple regression of individual species gives the highest correlation coefficient (r²=0.87) in the modern data set this method is least appropriate for reconstructing pH values from fossil material where predictor species are often absent. Of the four methods examined here it is suggested that multiple regression of diatom preference groups is probably the most suitable for pH reconstructions from sediment cores.     

The influence of pH on sulphite formation by yeasts

The influence of the initial pH of the substrate on the sulphite formation of three low-sulphite-and five high-sulphite-forming yeasts is described. Four distinctly different groups become apparent. The need for better evaluation of pure culture wine yeasts is stressed.     

Growth profile of ectomycorrhizal fungal mycelium: emphasis on substrate pH influence

A knowledge of behaviour of ectomycorrhizal fungal isolates to substrate pH would help in identifying candidate fungi for plantation programs. Ectomycorrhizal fungus isolates were studied to determine the pH optima for growth, substrate acidification by the culture and the effect of substrate acidification on culture growth. Of the isolates tested, the members of Agaricales (except Laccaria laccata) and Aphyllophorales favored neutral to near neutral pH, while members of the order Sclerodermatales strictly favored acidic pH. The change in substrate pH (ΔpH) was maximum at the optimum growth pH for acidophilic isolates but minimum for neutro/basophilic isolates. The experiments indicate that the substrate pH would not only determine the growth rate of the fungus but also limits further proliferation of the fungus in medium. This gives vital information for determining the subculture frequency and for designing substrate parameters for nursery/plantation programs. This revised version was published online in June 2006 with corrections to the Cover Date.     

Modelling the effect of the redox potential and pH of heating media on Listeria monocytogenes heat resistance

Aims:  Study the effect of redox potential and pH of the heating media on Listeria monocytogenes heat resistance and model its action at fixed temperature.
Methods and Results:  The heat resistance of Listeria monocytogenes at 58°C was studied in Brain Heart Infusion broth as a function of pH (from 5·0 to 7·0) and redox potential ( E _h7). The media redox was adjusted with nitrogen gas, potassium ferricyanide and dithiothreitol. A Weibull model was used to fit survival curves. The heat resistance parameter (δ_58°C) was estimated from each inactivation curve. A major effect of pH was observed. Bigelow model was used to describe the effect of redox potential on the apparent L. monocytogenes heat resistance. The highest δ_58°C values have been obtained at pH 7·0 and oxidizing conditions.
Conclusions:  The developed model indicates that the E _h7 has a significant effect and varied depending on the pH of the heating media. The z _redox values, calculated from δ_58°C allowed quantifying the influence of heating media redox potential on L. monocytogenes thermal inactivation.
Significance and Impact of the Study:  The obtained model shows the action of redox potential on L. monocytogenes thermal destruction and might be useful to take into account in food thermal processes.     

The effects of nematodes on bacterial activity and abundance in a freshwater sediment

The effects of natural nematode communities on bacterial activity and abundance were investigated in a microcosm study. Nematodes were added at different densities to a freshwater sediment and bacterial parameters were measured after 1, 5, 9, and 17 days. Significant effects of nematode density on bacterial activity were noted on day 5. No long-term changes in bacterial activity were recorded. Bacterial abundance displayed an overall decrease in both treatments and controls. In a second experiment, the effect of nematode feeding-type on bacterial activity was studied. Microcosms were incubated with 100 individuals of a fungus-feeding (Aphelenchus avenae) or a bacteria-feeding nematode species (Caenorhabditis elegans) respectively, and bacterial activity was determined after 0, 1, 2, 4, and 7 days. Significant time and feeding-type effects were found, with consistently higher bacterial activity estimates in treatments with bacteria-feeding nematodes. These results suggest that grazing affects bacterial activity, and indicate that grazing by nematodes may be more important in stimulating bacterial activity than bioturbation or excretion. Combining these results, we conclude that natural nematode communities may have an impact on bacterial activity, and that the magnitude of this impact depends on the proportion of actively feeding bactivores within the community. Received: 2 September 1996 / Accepted: 20 May 1997     

Correlation of surface sediment diatoms with the present lake water pH in 28 Algoma lakes,Ontario, Canada

The surface sediment diatom analysis of 28 Algoma lakes (pH 4.40–8.13) indicates that even though each lake has a widely different aquatic environment and characteristic diatom assemblage, a definite relationship exists between the lake water pH and their diatom assemblages. In the acidic lakes acidobiontic and acidophilous diatom species predominate whereas in circumneutral and alkaline lakes circumneutral and alkaliphilous diatoms were most common. Cluster analysis of the pH indicator diatom assemblages grouped the study lakes into three distinct cluster groups. These groups also closely corresponded to lake water pH. On the basis of published ecological information as well as their presence in our study lakes, the pH indicator status of a number of diatom taxa have been discussed. A detailed listing of the diatom taxa identified and their pH indicator status is provided in order to facilitate their use in future diatom-inferred pH studies.     

The gut microenvironment of sediment-dwelling Chironomus plumosus larvae as characterised with O2, pH, and redox microsensors

We devised a set-up in which microsensors can be used for characterising the gut microenvironment of aquatic macrofauna. In a small flow cell, we measured microscale gradients through dissected guts (O₂, pH, redox potential [E _h ]), in the haemolymph (O₂), and towards the body surface (O₂) of Chironomus plumosus larvae. The gut microenvironment was compared with the chemical conditions in the lake sediment in which the animals reside and feed. When the dissected guts were incubated at the same nominal O₂ concentration as in haemolymph, the gut content was completely anoxic and had pH and E _h values slightly lower than in the ambient sediment. When the dissected guts were artificially oxygenated, the volumetric O₂-consumption rates of the gut content were at least 10× higher than in the sediment. Using these potential O₂-consumption rates in a cylindrical diffusion–reaction model, it was predicted that diffusion of O₂ from the haemolymph to the gut could not oxygenate the gut content under in vivo conditions. Additionally, the potential O₂-consumption rates were so high that the intake of dissolved O₂ along with feeding could be ruled out to oxygenate the gut content. We conclude that microorganisms present in the gut of C. plumosus cannot exhibit an aerobic metabolism. The presented microsensor technique and the data analysis are applicable to guts of other macrofauna species with cutaneous respiration.     

Effect of bioturbation on denitrification in a marine sediment from the West Mediterranean littoral

Thein vitro effect ofNereis diversicolor on denitrification has been studied in PVC tubes filled with a coastal marine sediment defaunated by sieving. The first aim of the experiment was to determine the effect of sediment defaunation on denitrification (denitrifying population and Denitrifying Enzyme Assays). Sieving induced a loss of 70% of the initial DEA. The number of denitrifying bacteria was 10 times lower than inin situ sediment. In the top two centimetres, the DEA rose by 75% of its initial value, after 82 days. Polychaetes were only added after a return to near pre-disturbance levels to ensure that our data on the effects of their addition would not be disturbed by changes in the sediment. Introduction of Polychaetes increased the denitrifying population and DEA in the first layer (0–2 cm) of the sediment after 15 days. After 45 days, the surface of the polychaete burrows in sediment was 1.3 to 1.5 times higher than after 15 days, resulting in an increase in solute exchange between seawater and the top layer of sediment. An inhibitory effect of oxygen on denitrification was detected in the uppermost layer only.