Oxygen budgets in macrophyte impacted streams

Measurements of daily dissolved oxygen variations were made throughout a calender year on three separate segments of a stream dominated by the growth of aquatic macrophytes. Mass balance budgets, quantifying respective sources and sinks of dissolved oxygen for the study segments, demonstrated the validity of incorporating an aquatic plant respiration pattern which varied in direct proportion to dissolved oxygen concentrations. The effects of oxygen consumption by the plant population on field estimates of reaeration, daily gross primary productivity, community respiration and maximum net primary productivity in the budgeting process are evaluated.     

Oxygen and pH fluctuations in rivers

A mathematical model for oxygen fluctuations in a river reach, involving photosynthesis, total community respiration, and reaeration is presented. Analogy is established between diurnal oxygen fluctuations and diurnal pH-fluctuations. Comparison is made between oxygen production and respiration, and carbon dioxide consumption and production.Twin curve analysis of diurnal oxygen fluctuations and diurnal pH-fluctuations is made of measurements on a single river reach in Denmark. The measurements were carried out about once a month for a little more than one year. The analysis has revealed seasonal variations of the river parameters: total daily gross production of oxygen, total community respiration and reaeration coefficient. These parameters are important for river modelling.     

Stream productivity analysis with dorm—I: Development of computational model

A numerical dissolved oxygen routing model (DORM) is developed to determine total stream community photosynthesis (P) and community respiration rates (R) through iterative routing of two-station diel DO measurements. The model differs from existing procedures for diel curve productivity analysis; it uses the complete stream DO transport equation, including longitudinal dispersion, dependence of respiratory rate on water temperature and dissolved oxygen and wind dependent oxygen transfer through the water surface. The model, DORM, is more accurate than the traditional graphical procedures of diel curve analysis and is simple to apply. DORM is also valuable in an analysis of the results' sensitivity to the numerous coefficient and parametric assumptions required in diel curve analysis. The model is not a predictive DO model, but is designed for the interpretation of DO measurements in a stream, channel or river.     

Atmospheric reaeration in natural streams

The available reaeration data on natural streams have been reanalyzed to determine the relationship between the dimensionless reaeration parameter and the Reynolds number. The analysis of such data indicates that the reaeration parameter is a function of the Reynolds number and the functional relationship between these two parameters follows essentially a straight line on a log—log plot.The reaeration phenomenon in a natural stream is analogous to the dispersion mechanism in the body of water, as both of these characteristics are related to the Reynolds number. The vertical dispersion parameter or the longitudinal dispersion parameter have been found to be linearly related to the reaeration parameter on a log—log plot. The applicability of the relationship so evolved is not dependent on the regional location of the stream and takes into account both the physical and flow characteristics of the stream. The availability of the new equation for reaeration coefficient opens a new approach to evaluate the effect of photosynthesis and respiration in a natural stream.     

Technique for determining the volatilization coefficients of priority pollutants in streams

The volatilization coefficients of benzene, chloroform, methylene chloride, and toluene were measured in the laboratory over a range of mixing conditions concurrently with the measurement of the oxygen absorption coefficient. Application of the constancy of the ratios between the organic solute and oxygen coefficients to the modified tracer technique for the measurement of stream reaeration coefficients permits the determination of the volatilization coefficients of these solutes for any stream or river without direct introduction of these substances into the natural waters. Volatilization coefficients expressed as the liquid-film coefficients are presented for these solutes for a number of streams and rivers of the United States.     

Variations in water quality during winter in two Yukon rivers with emphasis on dissolved oxygen concentration

Winter variations in water quality were investigated in an arctic and a sub-arctic river basin in the Yukon Territory. In both cases dissolved oxygen depressions were observed during the winter, a phenomenon which occurred at all stations where water was sampled under ice. Lowest values were measured in late winter when ice cover was most extensive and when concentrations of basic cations reached highest annual values. No direct relationship was observed between oxygen levels, ice thickness and ice type. It appears that as winter progresses the stream water consists more and more of groundwater which usually contains low oxygen levels. Because of ice cover during that period little opportunity exists for reaeration and, although river sections with open water showed slightly higher oxygen concentrations than under ice samples, such open areas were not sufficiently large for reaeration. Oxygen concentrations in groundwater thus have a profound influence on oxygen concentration in the streams, but groundwater is not the only cause as other factors such as oxygen uptake by suspended material and biota possibly contribute to the low overall values. Some of the data from this study are corroborated by similar findings in Alaska suggesting that natural oxygen depressions in late winter are a widespread phenomenon in northern environments.     

Quantification of oxygen fluxes in a long gravity sewer

Quantification of the oxygen fluxes in the sewer system is at present the optimal methodology to obtain information about the influence of sewers on transformations and mass balances in the urban drainage system. However, the relative and absolute values of these fluxes are practically unknown. In this work, the oxygen fluxes were quantified experimentally in a full-scale aerobic main sewer. The sewer biofilm respiration was determined with an in situ flow cell, a method that has not been used before in the sewer. The surface reaeration was determined with a gas tracer method based on the inert, non-radio-active and non-toxic gas tracer sulphur hexafluoride. In addition, the wastewater biomass respiration rate was measured. The validity of the applied methods was verified with redundant oxygen balances over a 2-km-long section. Measurement campaigns under different hydrodynamic conditions showed that the relative contribution of the biofilm, the wastewater, the reaeration and the in- and outflow with the water, all contributed significantly. However, the absolute contributions varied extensively and depended especially on the discharge. The COD conversion in the sewer could be estimated from the aerobic activity. The aerobic total degradation in the study reach was 3%. However, when extrapolated to the entire sewer net of the catchment area with 5000 PE, the COD conversion was estimated as high as 30% of the dissolved COD during the night. This indicates that the wastewater composition at the treatment plant will be strongly affected by the sewer system.     

Uncertainty in dissolved oxygen prediction due to variability in algal photosynthesis

The contribution of variance in river community metabolism to overall uncertainty in predictions from dissolved oxygen models is evaluated using Monte Carlo simulation. Results using a modification of the Streeter-Phelps model to include a term for mean daily net production show that uncertainty in parameters used to describe community metabolism must be considered when probability distributions of dissolved oxygen in rivers are estimated. This conclusion is shown to be valid for a range of conditions and is therefore applicable to all but heavily polluted or highly turbid streams. Use of a refined version of the oxygen balance equation that accounts for diel variation in algal productivity demonstrates that variance in dissolved oxygen in rivers is likely to be much larger than that predicted by models that use mean daily values of net production.     

The ecology of a land drainage channel—I. Oxygen balance

In shallow land drainage channels day-time solar heating during the summer produced vertical temperature and density gradients. These facilitated the development of marked gradients of dissolved oxygen, with maximum sub-surface values exceeding 300% air saturation and deoxygenated water near the sediments. Night-time cooling promoted mixing of the water column. Rates of community photosynthesis and respiration, calculated from dissolved oxygen distributions by two methods, were high.     

Evaluating eutrophication potential from river community productivity

Measurements of dissolved oxygen, temperature and solar radiation were used to estimate net community production (P-R), respiration (R), gross production (P), and the P:R ratio for six rivers during the summer of 1974. Analysis of these data and comparison with a subjective ranking of the “eutrophy” of the rivers based on nutrient and chlorophyll data showed that productivity measurements in streams can be used to evaluate eutrophication potential. No single parameter or index proved reliable, but a discriminant analysis suggested that the use of respiration and the P:R ratio in conjunction can be useful. Also, the degree of temporal variability of community metabolism was a consistently good indicator of water quality. The analyses suggest that the eutrophication potential of an “unknown” river can be determined by comparing several weeks of productivity data for summer, low-flow conditions with the data presented here.     

Modelling nitrification effects on the dissolved oxygen regime of the speed river

Field studies on nitrification in an 11 km stretch of the Speed River below Guelph are described. The data, collected during three intensive surveys in spring-summer 1976 and winter 1977, were used to calibrate and verify a steady-state dissolved oxygen (DO) model which incorporates the effects of carbonaceous and nitrogenous oxygen demand (CBOD and NOD), plant and algal respiration and photosynthesis, and reaeration. The model calibration result for one of the survey conditions includes comparisons between the corresponding observed and predicted values of CBOD, NOD and daily minimum and maximum DO. The comparisons of the first three sets of parameters were satisfactory, but the predicted maximum DO values were generally higher than the observations. The model verification results for two other survey conditions were somewhat similar to those of the calibration study. Predictions of the relative effects of various sinks on the minimum DO levels under one of the survey conditions indicate that instream nitrification alone causes a DO deficit of about 4.5 mg 1⁻¹; in contrast, the deficits due to CBOD and respiration were in the order of 1 mg 1⁻¹ only. The model was also used to predict spatial DO distributions under several streamflow and temperature regimes. For each case, computer runs were made with NOD concentrations resulting from a conventional secondary (i.e. non-nitrified) efluent and a nitrified effluent. The predictions indicate that the minimum DO level increases with an increase in streamflow and a decrease in temperature. In the case of non-nitrified effluents, anoxic conditions are predicted to occur at about 25°C when streamflow rates are lower than about 1 m³s⁻¹; whereas in-plant nitrification would result in daily minimum DO levels of 4 mg 1⁻¹ or greater. The predictions also show the occurrence of two DO sags in the study stretch, one being mainly due to a high degree of nitrification, while the other is due to the combined effect of all of the DO sinks.     

Cobalt interference in the “non-steady state clean water test” for the evaluation of aerator equipment—II. Occurrence and magnitude for various natural water systems

Water soluble and insoluble oxidizing compounds are formed during the non-steady state clean water test in certain natural water systems causing interference with Winkler dissolved oxygen determination. This results in pseudo high oxygen transfer efficiency of aerator devices. The interfering precipitate consists mainly of hydrated cobaltic oxide. Evaluation of the electrochemical-oxygen equivalent measurements made the presence of hydrated cobalt dioxide in the precipitate plausible. The presence of hydrogen peroxide in the filtrate suggested the formation of peroxodi- and peroxomono-sulfuric acid during the reaeration step. The pH along with the buffering capacity of a test water are the most critical water quality parameters directly affecting the magnitude of the cobalt interference. At pH values of 6.9 and below the cobalt and peroxide interference in the non-steady state clean water tests can be eliminated. Maximum cobalt interference was found to occur at pH values of 10–11.     

Cobalt interference in the “non-steady state clean water test” for the evaluation of aerator equipment—I. Causes and mechanisms

Water soluble and insoluble oxidizing compounds are formed during the non-steady state clean water test in certain natural water systems causing interference with Winkler dissolved oxygen determination. This results in pseudo high oxygen transfer efficiency of aerator devices. The interfering precipitate consists mainly of hydrated cobaltic oxide. Evaluation of the electrochemical-oxygen equivalent measurements made the presence of hydrated cobalt dioxide in the precipitate plausible. The presence of hydrogen peroxide in the filtrate suggested the formation of peroxodi- and peroxomono-sulfuric acid during the reaeration step. The pH along with the buffering capacity of a test water are the most critical water quality parameters directly affecting the magnitude of the cobalt interference. At pH values of 6.9 and below the cobalt and peroxide interference in the non-steady state clean water tests can be eliminated. Maximum cobalt interference was found to occur at pH values of 10–11.     

Laboratory study on the open channel flow reaeration: a dimensional approach

Results of laboratory experiments on open channel flow reaeration are presented and commented on. The tests were designed on the basis of the classical dimensional analysis. They were carried out using three 15 m long channels with different cross-sections: 1) 0.5 m wide semi-circular cross-section; 2) 0.4 m wide rectangular cross section; 3) 0.2 m wide rectangular cross-section. The longitudinal bottom slope, the roughness and the flow discharge were varied independently. The disturbed equilibrium approach was adopted within an innovative experimental procedure, i.e. comparing the dissolved oxygen measures acquired in tests without de-oxygenation agent (hereinafter ‘white tests’) with those performed in runs with de-oxygenation agent (‘reaeration tests’). A new relationship between the reaeration coefficient and the hydrodynamic characteristics of an open channel is proposed. The relationship is applicable to a wide range of values of hydraulic characteristics not previously analysed in the literature and typical of small rivers.     

Effects of impurities on oxygen transfer rates in diffused aeration systems

A series of unsteady-state reaeration tests were performed in a 500-L tank at 0.81-4.58 m3/h diffused-air flow rate and 288-302 K water temperature. Three different types of impurities: soybean oil, surfactant, and diatomaceous earth were doped to simulate the impurities in wastewaters and the effects of the impurities on the oxygen transfer rate were investigated. The ASCE and the two-zone oxygen mass-transfer models were used to analyze the unsteady-state reaeration data and the volumetric mass-transfer coefficients determined from the unsteady-state reaeration data were correlated as a function of the diffused-air flow rate, water temperature, and impurity concentration. The results showed that the alpha factors based on the ASCE model are less sensitive to the impurity concentration while the presence of the impurities significantly reduces the alpha factors in the gas bubble zone. The saturation DO concentration and volumetric oxygen mass-transfer rate can be predicted by the two-zone model along with the correlation obtained in this study.     

Influence of temperature and river discharge on water quality of the western scheldt estuary

Dissolved oxygen concentrations and information on the nitrification process collected respectively during a 14- and a 5-year period in the self-purifying part of the Western Scheldt estuary have been studied. In the polluted part of the stream, ammonium concentrations over the period 1967–1977 have been considered as well.This paper demonstrates the high variability of these 3 parameters (oxygen, start of the nitrification process, ammonium) owing to the hydrological conditions: temperature and river discharge.Neither the levels of ammonium in the polluted upper part of the stream, nor the concentrations of nitrate and dissolved oxygen in the recuperation part of the Scheldt estuary have changed significantly during the periods studied (respectively 5, 10 and 14 years). A relation between these parameters and time could be hidden by hydrological factors.Water quality of a stream can be assessed by interpreting oxygen, nitrate, and ammonium concentrations, only if all environmental and hydrodynamical parameters are known simultaneously.     

A model of reaeration rates driven by shear flows

The reaeration rate determines the speed that the dissolved oxygen is restored to the saturation level. The reaeration rate is determined by the surface renewal rates from the friction interfaces in the water bodies, including the water/bed interface, the shear‐flow interface and the air/water interface. The formulae of reaeration rate for the air/water interface and the water/bed interface were developed in prior studies. However, no formula of the reaeration rate driven by the shear flows was developed. In this study, a mechanic model of the reaeration rate driven by the shear flows is developed to fill in the gap. The flow velocity profile in the shear flows and the Surface Renewal Theory are employed to derive the corresponding model. The predictions of the formulae for these three types of friction interfaces are compared for the same phase velocity to investigate the reasonability of the reaeration rate model for the shear‐flow interface. The predictions of the model for the shear‐flow interface are between those for the air/water interface and for the water/bed interface. The model in this study is also verified to have reasonable agreements with the experimental data. The model developed in this study can be applied for the prediction of the low soluble gases’ transfer rate between air and water in shear flows.     

Chemical catalyst interference in the winkler titration determination of dissolved oxygen—a method for correction

A new procedure involving the measurement of a chemical blank is introduced to correct the cobalt interference effect associated with the Winkler titration analysis for dissolved oxygen. Unsteadystate reaeration studies employed for mechanical aerator evaluation tests show that when sodium sulfite is used in the presence of a cobalt ion catalyst to deoxygenate the test basin water, a chemical interference is detected in the Winkler determination of dissolved oxygen content. The source to which this influence is attributed is a chemical precipitate that forms in the reaeration process. Evidence suggests that the cobalt (II) ion is oxidized to the (III) oxidation state forming a cobalt (III) hydroxide in the alkaline test environment. Upon acidification of the test samples during the Winkler procedure, the cobalt (III), a powerful oxidizing agent, is released and in turn effects an increase in the amount of free iodine released and measured by titration. The additional iodine liberated in this manner yields erroneous oxygen concentration values which are then used to calculate the oxygen mass transfer coefficient. Considerable deviation from the true value of the coefficient can result.     

Methyl chloride as a gas-tracer for measuring stream reaeration coefficients—II: Stream studies

A method is described for measuring stream reaeration rate coefficients using methyl chloride as a gas-tracer. Methyl chloride is a stable tracer that is capable of being determined to a lower detection limit of 1 × 10⁻¹² g by a gas chromatographic technique. Laboratory studies are reported, in which k₂ and the analogous transfer coefficient for methyl chloride, k_CH3Cl, are measured simultaneously at different temperatures in the range 5–35°C. The laboratory results indicate a temperature dependence for the transfer coefficient ratio, , fitted empirically to an expression based upon the absolute rate model for diffusion giving where T is the absolute temperature.     

Mechanical cutting of submersed macrophytes: Immediate effects on littoral water chemistry and metabolism

Immediate consequences of mechanical cutting of submersed macrophytes may include suspension of sediments and Aufwuchs and exudation from damaged tissues which can potentially alter water chemistry and metabolism. In the densely vegetated littoral of a shallow hardwater eutrophic lake, effects of cutting on concentrations of seston, dissolved organic carbon, biological oxygen demand of dissolved organic carbon, and particulate, dissolved unreactive, and dissolved reactive phosphorus were short lived or insignificant. In shallow areas, community photosynthesis and respiration were decreased by macrophyte removal. Use of this management approach on the limited basis tested does not appear to cause substantial detriment to the littoral environment.