An oxygen model for Lake Haukivesi

A simple water quality model for Lake Haukivesi, heavily loaded by pulp and paper mill effluents, has been developed. The main purpose of the model is to predict the concentration of dissolved oxygen in the hypolimnion. The lake is divided into seven sub-basins, and also into epilimnion and hypolimnion. Transfers between sub-basins are calculated using water balance equations. The state variables of the model are dissolved oxygen concentration, biochemical oxygen demand, phytoplankton biomass, and total phosphorus concentration. The effect of temperature on reaction rate coefficients has been taken into account. Temperature is calculated in the model using a second degree polynomial function. The processes affecting hypolimnetic oxygen consumption are BOD decay, decomposition of phytoplankton, benthic oxygen demand, and decomposition of slowly decaying organic matter.     

Oxygen dependent habitat selection in surface and hyporheic environments by Gammarus roeseli Gervais (Crustacea, Amphipoda): experimental evidence

Field distributions of benthic and hyporheic invertebrates are dynamic and are influenced by many physical and chemical factors. A laboratory flume containing natural gravel substrates was used to test the hypothesis that the amphipod Gammarus roeseli Gervais actively selects habitat based on two important environmental variables, dissolved oxygen concentration and direction of water flow. Under homogeneous oxygen concentrations throughout the flume, amphipods accumulated downstream. During trials with uniformly hypoxic conditions throughout the flume, G. roeseli moved to stones and screens at the water surface and above, into the zone normally saturated with humidity. This behavior, termed aquatic surface respiration, may enhance survival during periods of oxygen deficiency. Oxygen gradients were created in the flume by injecting water of differing oxygen concentrations into the head and the center of the channel. A statistically significant response to these gradients by G. roeseli demonstrates active selection of regions with more favorable oxygen concentrations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temporal and spatial variations of chemical oxygen demand in Lake Taihu,China, from 2005 to 2009

We undertook a study in Lake Taihu, China, from 2005 to 2009 including a total of 639 samples to determine: (i) the seasonal dynamics and spatial distribution of the chemical oxygen demand (COD) and (ii) the relationships between the COD concentration and the biochemical oxygen demand (BOD), phytoplankton pigment, total dissolved nitrogen (TDN), and total dissolved phosphorus (TDP) concentrations, as well as the chromophoric dissolved organic matter (CDOM) absorption coefficient. There were significant spatial differences in the COD concentration, which gradually decreased from Zhushan Bay in the northwest, to the north, the lake center, and the southeast of the lake. The COD concentration was significantly higher at near-shore sites than that at open water sites. The mean COD concentrations were significantly higher in the spring and summer than in the winter and autumn. The lowest annual mean COD concentration appeared in 2009, which could be attributed to improvements in water quality management and high rainfall. The COD concentrations in all four seasons were strongly correlated with phytoplankton pigment, suggesting that extracellular release of COD from phytoplankton was an important COD source. The correlation coefficients between the COD and phytoplankton pigment concentrations were higher in the spring, summer, and autumn than in the winter, showing a more important contribution of phytoplankton degradation to COD in the algal bloom season than in the non-algal bloom season. These new data on the temporal and spatial characteristics of the COD in Lake Taihu will be crucial for developing future strategies for water quality management.     

Basic Aspects of Electrode Potential Change in Submerged Fermentation

The platinum electrode potentials relative to the standard half cell depended on a pH value, dissolved oxygen concentration, equilibrium constant and oxidation reduction potentials of the liquid The overall potential change in submerged fermentation gave no independent information on these individual factors A thermostatic and pH-static apparatus excluded influences of temperatures and pH values on the electrode pontentials If the determination was completed for short time duration, potentials were governed by the dissolved oxygen tension. While the oxygen concentration was maintained at a same level, redox potential changes became a dominant. This measurement of redox potential, which gave the concentration of extremely low dissolved oxygen that could not be detected by the membrane-coated oxygen electrode, was practically useful for the control of aerobic fermentation     

Effect of dissolved oxygen control on growth and antibiotic production in Streptomyces clavuligerus fermentations.

A proportional-integral control system was used to control dissolved oxygen in a fermentor at constant shear and mass transfer conditions. Growth and antibiotic production in Streptomyces clavuligerus were studied at different dissolved oxygen levels during the fermentation. Three protocols were employed: no-oxygen control to provide a base case, oxygen controlled to a preset saturation level throughout the fermentation, and oxygen controlled at a high level only during the growth phase. The last protocol was aimed at optimizing the consumption of oxygen. Lower specific growth rates and cephamycin C yields were obtained when dissolved oxygen was controlled at 50% throughout the fermentation, compared to the base case. A 2.4-fold increase in the final cephamycin yield was observed when dissolved oxygen was controlled at saturation levels during the growth phase, compared to the experiments without dissolved oxygen control. This enhancement in yield was independent of the dissolved oxygen (DO) level after exponential growth, in the range of 50-100% saturation. The most effective control strategy, therefore, was to control DO only during active growth when the biosynthetic enzymes were probably synthesized.     

Dissolved oxygen content in microbiological nutrient media

The modification of a highly sensitive method for the determination of the concentration of dissolved oxygen in liquid culture media and in water is described. This modification permits the easy conversion of the relative readings of electrode membrane transducers for measuring the partial pressure of oxygen into the readings characterizing the absolute concentration of oxygen in the medium (mg/cu. dm). The content of dissolved oxygen in microbiological media and in water depends on the amount of dissolved mineral salts, amino acids and peptides (the products in incomplete proteolysis), as well as on temperature. The maximum level of oxygen saturation in liquid culture media at 37 degrees C is different for various types of media and constitutes their peculiar characteristic, determined in the process of aeration under experimental conditions.     

Availability of dissolved oxygen in interstitial waters of a sandy creek

Dissolved oxygen, pH, conductivity and alkalinity of surface and subsurface interstitial waters were investigated at Mill Creek (a small, rural, predominantly sandy stream in east Texas).Dissolved oxygen concentration tended to decrease with sediment depth, while conductivity and alkalinity did not significantly change with substrate depth. Surface water pH was significantly higher than interstitial water (p = 0.05).Chemical analyses of subsurface water from a pre- to post-storm event showed a depression in dissolved oxygen concentration in moderate and deep interstitial waters, immediately following the return of stream base flow, with the deeper strata returning to pre-storm oxygen levels four days later.A thermal convective current mechanism is proposed which would serve to transport surface water downward into these deeper interstices.     

The impact of phytoplankton on spectral water transparency in the Southern Ocean: implications for primary productivity

Spectral water transparency in the Northern Weddell Sea was studied during Austral spring. The depth of the 1-% surface irradiance level (euphotic depth) varied between 35 and 109 m and was strongly influenced by phytoplankton biomass. Secchi depths were non-linearly related to euphotic depth. In phytoplankton-poor water, the most penetrating spectral region was restricted to a relatively narrow waveband in the blue (488 nm), but the range was broader, between 488 and 525 nm when phytoplankton were abundant. Water transparency in the red spectral range was always low and only to a small extent affected by phytoplankton. Two independent procedures were used to quantify the impact of phytoplankton on spectral water transparency: (1) Regression analysis of spectral in situ vertical light attenuation coefficients in the sea, against coincident chlorophyll concentrations. This method gave chlorophyll-specific light attenuation coefficients; the y-intercept could be interpreted as a measure of light attenuation by pure water plus non-algal material. (2) Spectra of in vivo light absorption derived by spectroscopy, using phytoplankton enriched to varying degrees onto filters. Thus chlorophyll-specific absorption cross-sections were determined. Estimates obtained by both procedures were in close agreement. By integrating over the spectrum of underwater irradiance, in situ chlorophyll-specific absorption cross sections of phytoplankton suspensions, related to all photosynthetically active radiation, were calculated. Light absorption by phytoplankton for photosynthesis is accomplished mainly in the blue spectral range. Also dissolved and particulate organic matter contributed to the attenuation of blue light. Because in water poor in phytoplankton, underwater irradiance was progressively restricted to blue light, chlorophyll-specific absorption cross-sections of phytoplankton, averaged over the spectrum of photosynthetically active irradiance, increased with water depth. In water with elevated phytoplankton biomass, overall light attenuation was generally enhanced. However, because the spectral composition of underwater light changed relatively little with depth, except immediately below the water surface, light absorption cross-sections of phytoplankton changed little below 10 m depth. Vertical differences in the proportions of underwater light absorbed by the phytoplankton community here were mainly dependent on biomass variations. Because of the comparatively small attenuation of blue light by non-algal matter, the efficiency of light harvesting by phytoplankton at any given concentration of chlorophyll in Antractic waters is greater than in other marine regions. At the highest phytoplankton biomass observed by us, as much as 70% of underwater light was available for phytoplankton photosynthesis. When phytoplankton were scarce, <10% of underwater light was harvested by phytoplankton.Contribution within the European Polarstern Study (EPOS), supported by the Deutsche Forschungsgemeinschaft, Grant Ti 115/16-1 to MMT, the European Science Foundation, and by the Alfred Wegener Institut für Polar-und Meeresforschung, Bremerhaven     

Effects of dissolved oxygen tension and mechanical forces on fungal morphology in submerged fermentation

The effects of dissolved oxygen tension and mechanical forces on fungal morphology were both studied in the submerged fermentation of Aspergillus awamori. Pellet size, the hairy length of pellets, and the free filamentous mycelial fraction in the total biomass were found to be a function of the mechanical force intensity and to be independent of the dissolved oxygen tension provided that the dissolved oxygen tension was neither too low (5%) nor too high (330%). When the dissolved oxygen concentration was close to the saturation concentration corresponding to pure oxygen gas, A. awamori formed denser pellets and the free filamentous mycelial fraction was almost zero for a power input of about 1 W/kg. In the case of very low dissolved oxygen tension, the pellets were rather weak and fluffy so that they showed a very different appearance. The amount of biomass per pellet surface area appeared to be affected only by the dissolved oxygen tension and was proportional to the average dissolved oxygen tension to the power of 0.33. From this it was concluded that molecular diffusion was the dominant mechanism for oxygen transfer in the pellets and that convection and turbulent flow in the pellets were negligible in submerged fermentations. The biomass per wet pellet volume increased with the dissolved oxygen tension and decreased with the size of the pellets. This means that the smaller pellets formed under a higher dissolved oxygen tension had a higher intrinsic strength. Correspondingly, the porosity of the pellets was a function of the dissolved oxygen tension and the size of pellets. Within the studied range, the void fraction in the pellets was high and always much more than 50%.     

THE TOXICITY OF ZINC SULPHATE TO RAINBOW TROUT

The toxicity of zinc sulphate to rainbow trout ( Salmo gairdnerii Richardson) has been investigated in waters of different chemical and physical properties.
Zinc sulphate was less toxic to rainbow trout in hard water than in soft water; when the log concentration of zinc was plotted against log median period of survival of the fish the dose response curve was linear in a very soft water, and curvilinear in a hard water, approaching an apparent threshold concentration. Solutions of zinc sulphate containing calcium chloride were less toxic than those containing an equivalent concentration of calcium as bicarbonate.
An increase in temperature decreased the survival time of rainbow trout in solutions of zinc sulphate in a hard water, but the threshold concentration was not appreciably affected by changes in temperature.
A reduction in the dissolved oxygen concentration of the water increased the toxicity of zinc sulphate, but the effect was reduced when the fish were previously acclimatized to the lower oxygen concentration of the test.
The cause of death of fish in solutions of zinc sulphate was not by the precipitation of mucus on the gills but probably by damage to the gill epithelium.     

Oxygen and/or glucose limitation in a chemostat culture of Candida utilis mathematical model identification

The glucose and/or dissolved oxygen limited continuous culture of yeast Candida utilis was studied. Six different mathematical models were designed to describe and analyze the experiments. The model considering the production of surface active compounds at autoanaerobic conditions and dissolved oxygen consumption for nongrowth associated exogeneous respiration yields the best fit. The results may be applied for aerobic waste water treatment plants, process analysis and simulation.     

Simulation of oxygen transfer in microbial slimes

A model based on diffusion mechanisms accounts for oxygen transfer from flowing nutrient medium into a film of organisms in slime. Profiles of dissolved oxygen concentration are generated at distances downstream from the start of the slime. In these studies, the nutrient medium was assumed rich, thus the rate of oxygen transport limited microbial respiration. Parameter sensitivity tests were performed for flow rate, oxygen concentration in the medium, and mass transfer coefficients.     

Effect of low dissolved oxygen on simultaneous nitrification and denitrification in a membrane bioreactor treating black water

Effect of low dissolved oxygen on simultaneous nitrification and denitrification was evaluated in a membrane bioreactor treating black water. A fully aerobic membrane bioreactor was operated at a sludge age of 60 days under three low dissolved oxygen (DO) levels below 0.5mg/L. It sustained effective simultaneous nitrification/denitrification for the entire observation period. Nitrification was incomplete due to adverse effects of a number of factors such as low DO level, SMPs inhibition, alkalinity limitation, etc. DO impact was more significant on denitrification: Nitrate was fully removed at low DO level but the removal was gradually reduced as DO was increased to 0.5mg/L. Nitrogen removal remained optimal within the DO range of 0.15-0.35 mg/L. Experimental results were calibrated and simulated by model evaluation with the same model coefficients. The model defined improved mass transfer with lower affinity coefficients for oxygen and nitrate as compared to conventional activated sludge.     

An analytical solution for percutaneous drug absorption: application and removal of the vehicle

The methods of Laplace transform were used to solve a mathematical model developed for percutaneous drug absorption. This model includes application and removal of the vehicle from the skin. A system of two linear partial differential equations was solved for the application period. The concentration of the medicinal agent in the skin at the end of the application period was used as the initial condition to determine the distribution of the drug in the skin following instantaneous removal of the vehicle. The influences of the diffusion and partition coefficients, clearance factor and vehicle layer thickness on the amount of drug in the vehicle and the skin were discussed.     

Environmental factors influencing survival of threespine stickleback (Gasterosteus aculeatus) in a multipurpose constructed treatment wetland in southern California.

Survival of the threespine stickleback, Gasterosteus aculeatus, differed among marshes in a demonstration 9.9-ha multipurpose constructed treatment wetland designed to improve the quality of secondary-treated municipal wastewater in southern California. At a mean loading rate of 3.3 kg NH4-N ha(-1) d(-1) (6 kg total N ha(-1) d(-1)), the suitability of the wetland to support a population of sticklebacks was estimated to be low. The development of potentially toxic levels of un-ionized ammonia, particularly during periods when pH increased concomitantly with oxygen generation by phytoplankton biomass > 300 mg chlorophyll a liter(-1), and disinfection by-products were associated with lowered survivorship of sentinel fish. Moreover, the high oxygen demand from nitrification of NH4-N created daily periods of low dissolved oxygen concentration (6-16 h at < 2 mg liter(-1)) in the open water areas of the shallow marshes. Low dissolved oxygen concentration in open water zones of the seven marshes during a part of each day and persistent anaerobic conditions in the emergent vegetation rendered the majority of the wetland's substrate surface unavailable for successful reproduction by sticklebacks. The potential sites for Gasterosteus to replace mosquitofish, Gambusia affinis and G. holbrooki, as a biological control agent against mosquitoes are probably limited to comparatively cool-water habitats with high water quality, such as riverine wetlands.     

Ichthyophthiriasis in the mirror carp Cyprinus carpio (L.) IV. Physiological dysfunction*

Changes in blood ion concentration, oxygen absorption, blood haemoglobin concentration and blood urea-ammonia nitrogen level were measured in a group of mirror carp, Cyprinus carpio (L.) infected with measured numbers of Ichthyophthirius multifiliis under standardized conditions. The disease was characterized by a drop in serum sodium and magnesium and increase in serum potassium. The ability of infected fish to absorb oxygen was reduced as was their ability to tolerate dissolved oxygen concentrations under 5 ppm. Blood ureaammonia level was elevated during the disease but blood haemoglobin level remained unchanged.     

Agitator speed and dissolved oxygen effects in xanthan fermentations

Agitation speed affects both the extent of motion in Xanthan fermentation broths because of their rheological complexity and the rate of oxygen transfer. The combination of these two effects causes the dissolved oxygen concentration and its spatial uniformity also to change with agitator speed. Separating these complex interactions has been achieved in this study in the following way. First, the influence of agitation speeds of 500 and 1000 rpm has been investigated at a constant nonlimiting dissolved oxygen concentration of 20% of air saturation using gas blending. Under these controlled dissolved oxygen conditions, the results demonstrate that the biological performance of the culture was independent of agitation speed as long as broth homogeneity could be ensured. With the development of increasing rheological complexity lending to stagnant regions at Xanthan concentrations >20 g/L, it is shown that the superior bulk mixing achieved at 1000 rpm, compared with 500 rpm, leading to an increased proportion of the cells in the fermentor to be metabolically active and hence higher microbial oxygen uptake rates, was responsible for the enhanced performance. Second, the effects of varying dissolved oxygen are compared with a control in each case with an agitator speed of 1000 rpm to ensure full motion, but with a fixed, nonlimiting dissolved oxygen of 20% air saturation. The specific oxygen uptake rate of the culture in the exponential phase, determined using steady-state gas analysis data, was found to be independent of dissolved oxygen above 6% air saturation, whereas the specific growth rate of the culture was not influenced by dissolved oxygen, even at levels as low as 3%, although a decrease in Xanthan production rate could be measured. In the production phase, the critical oxygen level was determined to be 6% to 10%, so that, below this value, both specific Xanthan production rate as well as specific oxygen uptake rate decreased significantly. In addition, it is shown that the dynamic method of oxygen uptake determination is unsuitable even for moderately viscous Xanthan broths. Copyright 1998 John Wiley & Sons, Inc.     

The Effects of a Developing Biofilm on Chemical Changes across the Sediment-Water Interface in a Freshwater Environment

The development of a diatom biofilm on a river sediment was studied using a fluvarium channel with intensive investigations over a total duration of 16 days. The overlying solution was monitored for dissolved calcium, silicon and soluble reactive phosphorus, pH, dissolved oxygen and temperature. The surface of the sediment was sampled for chlorophyll a, algal cell density and porewater profile measurements of calcium concentration, pH and dissolved oxygen were made using microelectrodes. At the end of the experiment the sediment was longitudinally sectioned and porewaters isolated and analysed. A diatom biofilm developed within approximately 5 days leading to a decrease in the concentrations of dissolved silicon and phosphorus in the overlying solution. After approximately 270 hours, the dissolved silicon concentration remained low (average of 6.7 μM). As the diatom numbers increased, photosynthetic activity was evident from increases in dissolved oxygen and pH at the interface. By the end of the experiment diurnal changes in the overlying solution of dissolved calcium, alkalinity and soluble reactive phosphorus were evident. Vertical concentration gradients in dissolved calcium, phosphorus and silicon in the sediment porewater were found at the end of the experiment. The results are consistent with the development of a photosynthetically active diatom biofilm that acted as a barrier to the diffusion of silicon from the porewater. It also induced precipitation and dissolution of calcite and co-precipitation of phosphate with calcite. Chemical fluxes of silicon, calcium and phosphorus were estimated from concentration gradients in the sediment and found to be much smaller than fluxes measured from changes in the bulk solution indicating that processes at the sediment-water interface and biofilm mainly control the flux to the overlying solution.     

Dissolved oxygen concentration in river sediment of the Lake Biwa tributaries, Japan

The dissolved oxygen concentration in the sediment pore water downstream of rivers in the Lake Biwa basin was measured, and the factors affecting the dissolved oxygen concentration were analyzed. In August 2003, nine rivers (Sakai, Nakanoi, Hebisuna, Anziki, Yasu, Echi, Ane, Oh, and Ohura) were surveyed. The dissolved oxygen was depleted in the sediment pore water of the rivers with a high proportion of particles less than 250 μm in size. For these rivers, the difference between the dissolved oxygen concentrations of the river surface water and the pore water was large, ranging from −9.54 to −5.26 mg L⁻¹. It was found that the proportion of land turned to paddy fields has an effect on the percentage of the particles below 250 μm (standard partial regression coefficient = 0.807, p = 0.023). These results suggest that, in the Lake Biwa basin, the sedimentation of the fine particles released from paddy fields results in poor dissolved oxygen in the river sediment downstream. In addition, the water flow conditions in small- and medium-scale rivers without headwaters also affect the sedimentation of suspended particles.     

Control of photosynthetic carbon dioxide fixation by the boundary layer, stomata and ribulose 1,5-biphosphate carboxylase/oxygenase

Abstract Coefficients describing the sensitivity of the rate of photosynthetic carbon dioxide fixation to small changes in the stomatal conductance and boundary layer conductance are derived. These sensitivity or ‘control’ coefficients, together with those for the carboxylase and oxygenase activities of ribulose 1,5-bisphosphate carboxylase/oxygenase, are calculated from standard gas exchange data and apply under conditions where leaf temperature and water vapour concentration at the leaf surface remain largely constant. It is shown that the magnitude of the control coefficients depends on conditions such as photon flux density, ambient CO₂ concentration and relative humidity at the leaf surface. The extension of this analysis to encompass the sensitivity of the photosynthetic fluxes to changes in enzyme concentrations and kinetic properties is also discussed.