Automatic potentiometric determination of dissolved oxygen

Commercially available automatic titration systems were tested in 1988 for potentiometric titration of liberated iodine by the Winkler method of oxygen determination. The potentiometric equivalence point was also compared to the manual starch end point. Finally the automatic method was used in order to estimate belowhalocline respiration in the Kattegat, Sweden. Standard deviations of 0.007 ml O₂ l^–1 or 0.1 to 0.3% coefficients of variation (% standard deviation of the mean) were achieved when titrating 25 ml from replicate 60-ml oxygen bottles using the automatic method, or 50 ml manually. The precision for replicate titrations of 50-ml aliquots of 0.001N KIO₃ was <0.05% (0.002 ml 0.01N Na₂S₂O₃) for the automatic method. Titration time for 25-ml aliquots was 2 to 4 min, somewhat longer than for manual titrations (1 to 1.5 min). However, during titration the operator is free to perform other tasks. It is not possible to use automatic sample changers, due to rapid iodine volatilization. The equipment can be handled by relatively unskilled analysts and is suitable for use on board research vessels or in field stations [weight for a Mettler^TM titrator (Mettler Instrumente AG, Greifensee, Switzerland) <10 kg, volume <0.1 m³]. Below-halocline oxygen consumption in the SE Kattegat ranged from 0 to 6 ml O₂ m^–3 h^–1 (mean values for September and October 1988=1.69 and 0.66 ml O₂ m^–3 h^–1, respectively, with 95% confidence limits of ca. ±0.6 ml O₂ m^–3 h^–1).     

Mathematical models of dissolved oxygen concentration in fresh water

An adequate reserve of dissolved oxygen in a receiving stream is extremely important for protecting aquatic plants and animals, and for conserving our water resources. This paper briefly describes the environmental engineering significance of the stream self-purification, the current stream quality standards on dissolved oxygen concentration, and the solubility of dissolved oxygen in water. Special emphasis is placed on the modelling of the biological reactions and the dissolved oxygen saturation concentration in fresh water. The model can be used for calculating the dissolved oxygen saturation concentration, in turn, for determining the dissolved oxygen deficits, the critical dissolved oxygen concentration, and the allowable dissolved oxygen drop in a stream into which the waste water is discharged.     

低温下曝气生物滤池预处理污染河水的试验研究

采用两段曝气生物滤床串联工艺预处理入滇新运粮河河水,研究了其在冬天低温条件下对有机物和氨氮的去除效果,并考察了pH值的变化。结果表明,在进水流量为2.4 m3.d-1、水温为13-16℃、原水ρ（CODCr）为66.46-107.82 mg·L-1、ρ（氨氮）为22.15-30.68 mg·L-1的水质特征条件下,系统对CODCr和氨氮的去除率分别为36.08%-50.37%和76.98%-93.56%。其中,碳氧化段以去除有机物为主,硝化段以去除氨氮为主;系统中硝酸氮质量浓度明显升高,无亚硝氮的积累;装置对总氮的平均去除率为19.56%,可以认为总氮的去除是同步硝化反硝化的结果。系统中pH值有所变化但维持在7-8之间,其中碳氧化段pH值升高,硝化段pH值下降。系统对有机物和氨氮良好的去除效果为后续进一步的生物处理提供了条件。     

Spatio-temporal dissolved oxygen dynamics in the Orbetello lagoon by fuzzy pattern recognition

This paper models the dissolved oxygen (DO) dynamics in the Orbetello lagoon as a function of the physico-chemical and ecological system variables, including the submerged vegetation, nutrients, and hydrodynamics. It should be viewed as the concluding sequel to a previous paper describing the dynamics of the lagoon ecosystem [Giusti, E., Marsili-Libelli, S., 2006. An integrated model for the Orbetello lagoon ecosystem, Ecol. Model. 196, 379–394] by introducing the missing DO dynamics. The model considers the oxygen demand originating from the decay of carbonaceous and nitrogenous compounds, as well as photosynthesis and natural reaeration by winds and currents as the oxygen producing processes. With a fixed-parameter set the model could accurately reproduce each single circadian DO cycle, but in the long run it failed to extend this fit and could not accommodate the large DO fluctuations induced by the seasonal variability. In order to enhance the model flexibility, a fuzzy pattern recognition algorithm was designed to classify the circadian DO patterns into four typical behaviours, related to the season, and estimate the corresponding parameters, with the overall model output being a fuzzy combination of these sets. The paper discusses several methods to patch the parameter sets and compares their performance in tracking long-term DO variations. A final assessment of the model validity is obtained by incorporating the whole DO dynamics (model, fuzzy pattern recognition and parameter combination) into the general lagoon model and producing a consistently correct series of DO daily distributions over a yearly cycle. Thus the paper contains both a practical and a methodological aspect. The practical one is the linking of all the lagoon dynamics to the dissolved oxygen kinetics in order to clarify to what extent macroalgae and macrophytes influence the oxygen balance. The methodological aspect consists of extending the validity of short-term models to long time-horizons through a patching technique supported by fuzzy pattern recognition.     

The influence of dissolved oxygen and carbon dioxide on fish schooling behavior

Slow reduction of dissolved oxygen concentrations or slowly increased carbon dioxide (reduced pH) did not cause measurable changes in the density, nearest neighbor orientation, or the swimming speed of experimental schools of the northern anchovy Engraulis mordax, until near-lethal levels were reached. Rapid reductions of oxygen or pH, however, caused significant increases in average swimming velocity. Positive reactions were correlated to rapid reductions of no more than 0.55 mg O₂/l or 0.25 pH units. These responses are related to the hypothesis that metabolic reductions of environmental dissolved oxygen and/or pH may influence the internal structure and behavior of fish schools.     

地面氧化亚氮排放静态箱测定技术

氧化亚氮是最重要的温室效应气体之一,国际科学界对其进行了大量的研究。开展氧化亚氮研究最重要的方面是测定技术,目前主要有静态箱法和微气象法,而以静态箱技术的使用最为广泛。静态箱技术也有其优点和缺点。文章从基本原理、取样箱设计、取样时间策略、自动采样箱设计、气相色谱测定技术参数、计算方法及自动测定系统等方面,系统介绍静态箱技术。我国在氧化亚氮研究上还较少,已被测定的土地类型非常有限,文章将有助于促进我国在这方面的研究。     

The effects of varying dissolved oxygen concentrations on the hemoglobin levels of the polychaetous annelid Neanthes arenaceodentata

Hemoglobin compensation in the polychaete Neanthes arenaceodentata was induced experimentally by lowered dissolved oxygen concentrations under laboratory and field conditions. Hemoglobin concentrations were measured colorimetrically and compared to the C57BL/6 strain of the house mouse. Compensation was initiated at about 4.2 mg/l dissolved oxygen, significantly increased at 3.0 mg/l, and continued to increase down to lethal levels.     

施肥对稻田甲烷与氧化亚氮排放的影响

大气温室气体浓度的升高引起太阳辐射加强,导致全球变暖已成为不争的事实。农田是温室气体排放的重要来源之一,采用静态箱-气相色谱法探讨不同氮肥类型与施氮水平对华南稻田甲烷（CH4）与氧化亚氮（N2O）排放的影响。试验共设置5个处理,每处理3次重复,分别（以N计）为U6（90 kg·hm-2）,U10（150 kg·hm-2）,U12（180 kg·hm-2）,SR10（150 kg·hm-2,缓释肥）,CR10（150 kg·hm-2,控释肥）。各处理磷钾肥用量一致,分别为45 kg·hm-2（以P2O5计）和127.5 kg·hm-2（以K2O计）。研究结果表明：稻田CH4与N2O排放量随氮肥用量的增加呈增加趋势。晚稻CH4排放呈单峰型,其峰值出现在水稻移栽后16~23 d,N2O排放并未出现明显的排放峰。CH4累积排放主要发生在返青-分蘖初期和分蘖盛期-幼穗分化期两个时段,而N2O的累积排放主要集中在灌浆-成熟期（U6处理除外）。不同氮肥类型处理CH4季节排放总量与平均排放量表现为：处理SR10〉处理U10〉处理CR10,其中,控释肥处理甲烷排放总量较常规尿素处理减少了11.3%;而N2O季节排放总量与平均排放量表现为：处理CR10〉处理U10〉处理SR10。综上,初步认为氮肥的施用能够促进CH4与N2O的释放,缓释肥处理能有效减少稻田N2O的排放,而控释尿素处理能明显降低稻田CH4气体的排放,且稻田CH4与N2O的排放存在一定的互为消长关系,因此如何平衡稻田甲烷与氧化亚氮释放,使稻田增温潜势最小化是下一步研究的重点和方向。     

曝气生物滤池不同填料处理河道污水的效果

曝气生物滤池处理河道污水,具有容积负荷大、处理效率高,占地面积小的特点,但除磷效果差.为了提高曝气生物滤池除磷效果和去除COD、NH3-N和Ss的能力,本文利用贝壳、珊瑚和经过盐酸处理的铝硅酸盐作为曝气生物滤池的填料来处理河道污水.试验结果表明:在pH为中性的条件下,贝壳和珊瑚填料不能去除河道污水的磷酸盐,但经过盐酸处理后的铝硅酸盐填料对河道污水磷酸盐的去除率可达到52.19%,与传统处理方法相比,去除率提高了30%以上;贝壳填料对COD、NH3-N和SS的去除率分别为52.73%、36.75%、53.04%,珊瑚填料去除率分别为57.29%、33.44%、51.03%,经过盐酸处理的铝硅酸盐填料去除率分别为49.29%、33.20%、64.94%;珊瑚填料处理COD效果最好,去除率达到57.29%,这与该填料具有较大的比表面有关;贝壳填料去除NH3-N效果最好,达到36.75%,但与珊瑚填料和铝硅酸盐填料相比,差异不大,最大极差仅3.55%;铝硅酸盐填料去除Ss的效果最好,达到64.94%,这可能与其颗粒小,比较致密有关.综合比较各种填料处理PO4-3-、COD、NH3-N和SS的能力,采用经过盐酸处理铝硅酸盐填料作为曝气生物滤池处理河道污水的填料是适宜的,其最佳水力停留时间为4 h.     

Spatial and seasonal variability of dissolved oxygen and nutrients in the Southern Adriatic coastal waters

The main objective of this paper is to present vertical and horizontal patterns of dissolved oxygen and nutrients found during four seasonal surveys (March, June, September and December 2000) in the Southern Adriatic Sea coastal waters. The multivariate technique Principal Component Analysis has been applied to our dataset considering the following parameters: seawater temperature, salinity, dissolved oxygen and nutrients (nitrate, nitrite, phosphate, silicate). The resulting plot shows in a self-explanatory way that a seasonal trend was not observable in the investigated period and that no significant differences occur between the stations sampled in the Taranto Gulf and those along the Adriatic coast. Water column stratification persists in all seasons, except in spring, in the shallowest stations. The surface layer is characterized by a low nutrient content. The influence of the Northern Adriatic Surface Water in the Southern Adriatic sub-basin seems to be very low and can be traced by nitrate and silicate only in spring and winter. Regarding deep waters, nitrate distribution shows an increasing gradient moving from the coast to the open sea, having the lowest concentration in the shelf area and the highest in the most offshore stations of the Otranto Strait. In the Otranto Strait area the vertical distributions of physical and chemical parameters show, at middle depths, the inflow of Levantine Intermediate Water, traced by both the maximum of salinity, nitrate and phosphate and the minimum of oxygen. The LIW signal is lost moving northward. The outflow of Adriatic Dense Water is less evident, being traced only in spring by an oxygen increase at the bottom layer in the shelf area. The N:P ratio is highly variable but in the range already observed in the Southern Adriatic, suggesting a P-limitation, which can both contribute to the low primary productivity of the area and support the N:P ratio anomaly of the Eastern Mediterranean.     

Non-photosynthetic oxygen production and non-respiratory oxygen uptake in the dark: a theory of oxygen dynamics in plankton communities

Plankton respiration is commonly measured in terms of oxygen uptake, usually employing the Winkler method, much less commonly the polarographic method. Both methods produce results that can be misinterpreted when H₂O₂ production and decomposition are ignored. This paper: (1) presents experimental evidence of significant H₂O₂ involvement during plankton incubation in dark bottles, (2) explains how results differ between the Winkler and polarographic methods in the presence of H₂O₂, (3) discusses how this difference is clouded by side issues of variability inherent in the Winkler technique and the use of different bottle sizes, and (4) shows that unexpected and variable results of light-/dark-bottle incubations can all be explained by a theory of H₂O₂ production and decomposition. During an initial period in the dark, when plankton respiration has been poisoned by mercuric chloride or chloroform, O₂ increase can be measured with a polarographic oxy‐gen sensor (POS). The trend in O₂ changes is linear for several days when only respiration is occurring, but curvilinear when there is concurrent O₂ production. O₂ production in the dark and H₂O₂ decomposition are one and the same process. Measurement of oxygen by Winkler analysis and POS produce different results when H₂O₂ is present because the former method measures oxidizing equivalent while a POS measures O₂ pressure. A real difference in results between the two methods is prima facie evidence that H₂O₂ is involved. The synthesis of this new empirical evidence with diverse knowledge from various fields shows that the common practice of estimating gross community primary production from oxygen changes in light and dark bottles is based on untenable assumptions. Received: 15 April 1997 / Accepted: 17 June 1997     

种植蔬菜地与裸地氧化亚氮排放差异比较研究

采用大型原状土柱试验研究了种植蔬菜地与未种植蔬菜裸地土壤氧化亚氮（N2O）排放的差异。试验结果表明,施肥但未种植蔬菜的裸地土壤N2O排放量远大于种植蔬菜地的土壤N2O排放量,裸地土壤N2O平均排放通量为193μg.m-2.h-1,而种植蔬菜后土壤N2O平均排放通量减少至60μg.m-2.h-1;相应地,裸地的N2O排放总量也要远高于种植蔬菜地的N2O排放总量。同时,低施氮量（N1,500 kg.hm-2）下裸地的N2O排放量要比高施氮量（N2,750 kg.hm-2）且种植蔬菜时裸地的N2O排放量大,如2007年10月至2008年9月试验期间,N1处理下裸地总N2O-N排放量为9.54 kg.hm-2,而N2处理（种植蔬菜）下总N2O-N排放量仅为4.21 kg.hm-2。此外,未种植蔬菜时裸地土壤N2O排放系数远大于种植蔬菜时,如N1种植蔬菜时为0.39%,但未种植蔬菜的裸地土壤排放系数为1.76%。研究说明种植作物与否对土壤N2O排放有重要影响,因此在估算农田土壤N2O排放温室气体量时,需考虑裸地的贡献能力。     

水稻生长后期水分管理对CH4和N2O排放的影响

通过温室盆栽试验研究相同施肥条件下,水稻生长后期水分管理(穗肥后落干时间及干湿交替频度)对CH4和N2O排放的影响.结果表明,与水稻生长前期较高CH4和N2O排放相比,后期排放均较低,但穗肥后提前落干时出现明显N2O排放峰值,且干湿交替过程中土壤落干时出现CH4排放.就穗肥后开始落干至水稻收获特殊阶段而言,穗肥后提前落干(相对于正常落干)可降低44%CH4排放量,却提高88%N2O排放量;穗肥后5 d落干-5 d淹水和3 d落干.3 d淹水干湿交替频度对N2O排放影响不大,却一定程度上影响CH4排放量.就综合温室效应而言,穗肥后正常落干且5 d落干-5 d淹水干湿交替处理最小.     

Variation in dissolved organic matter controls bacterial production and community composition

An ongoing debate in ecology revolves around how species composition and ecosystem function are related. To address the mechanistic controls of this relationship, we manipulated the composition of dissolved organic matter (DOM) fed to aquatic bacteria to determine effects on both bacterial activity and community composition. Sites along terrestrial to aquatic flow paths were chosen to simulate movement of DOM through catchments, and DOM was fed to downslope and control bacterial communities. Bacterial production was measured, and DOM chemistry and bacterial community composition (using denaturing gradient gel electrophoresis of 16S rRNA genes) were characterized following incubations. Bacterial production, dissolved organic carbon (DOC)-specific bacterial production, and DOC consumption were greatest in mesocosms fed soil water DOM; soil water DOM enhanced lake and stream bacterial production by 320-670% relative to lake and stream controls. Stream DOM added to lake bacteria depressed bacterial production relative to lake controls in the early season (-78%) but not the mid-season experiment. Addition of upslope DOM to stream and lake bacterial communities resulted in significant changes in bacterial community composition relative to controls. In four of five DOM treatments, the bacterial community composition converged to the DOM source community regardless of the initial inoculum. These results demonstrate that shifts in the supply of natural DOM were followed by changes in both bacterial production and community composition, suggesting that changes in function are likely predicated on at least an initial change in the community composition. The results indicate that variation in DOM composition of soil and surface waters influences bacterial community dynamics and controls rates of carbon processing in set patterns across the landscape.     

Effects of tetrahydrofuran on dissolved oxygen,pH, culturable aerobic microbes and enzyme activity in wastewater

Tetrahydrofuran (THF) is easy to volatilize and hard to biodegrade. Little is known about the influence and fate of tetrahydrofuran in the environment. The effects of THF were examined on dissolved oxygen, pH, culturable aerobic microbes (bacteria, actinomycetes, and fungi) and four selected enzymes (protease, phosphatase, amylase, and lipase) in wastewater. The wastewater containing some activated sludge was taken from the aeration basin in Sibao sewage plant in Hangzhou, China. THF at lower concentrations of enhanced aerobic respiration and higher concentrations decreased utilization of oxygen in wastewater. The short-term influence of THF on pH was not obvious, but the long-term effect was apparent. Inhibition of THF on culturable aerobic microbes rose with increasing THF concentrations but decreased with prolongation of incubation time. No effect of THF on the activity of protease, phosphatase, amylase, and lipase was found. Data indicate that lower concentrations of THF exert no marked influence on wastewater in an urban sewage plant.     

Variability of dissolved reactive phosphate and apparent oxygen utilization along the west coast of India

This work focuses on the spatial variability of dissolved reactive phosphate along the west coast of India. In this study, samples of surface and bottom water was collected from each of the 27 sites during a single pre-monsoon transect along the west coast of India to study the variation of dissolved reactive phosphate. Phosphate showed an enrichment pattern with increase in depth of the water column. In addition to this, an offshore increase in phosphate concentrations was noticed for both surface and bottom stations. Almost all the surface stations of this study area were found to be characterized by negative apparent oxygen utilization (AOU) values, and bottom stations of the deeper offshore zone (200 m depth) displayed large positive AOU values. The bottom stations of shallow near coastal waters and the deeper offshore zone are characterized by an inverse relationship between phosphate and dissolved oxygen, whereas at these depths, a direct relation was observed between phosphate and AOU. AOU is calculated as the difference between oxygen saturation value at the in situ temperature and salinity and the actual measured concentration. This oxidative re-mineralization mechanism decreases the observed dissolved oxygen well below the expected theoretical values, which is concordant with the higher concentration of phosphate and high positive AOU values.     

Behavioral response of fish larvae to low dissolved oxygen concentrations in a stratified water column

Density stratification and respiration lead to vertical gradients in dissolved oxygen in many aquatic habitats. The behavioral responses of fish larvae to low dissolved oxygen in a stratified water column were examined during 1990–1991 with the goal of understanding how vertical gradients in dissolved oxygen may directly affect the distribution and survival of fish larvae in Chesapeake Bay, USA. In addition, the effects of low oxygen on 24-h survival rates were tested so that results of behavior experiments could be interpreted in the context of risk to the larve. Naked goby [Gobiosoma bosc (Lacépède)] and bay anchovy [Anchoa mitchilli (Valenciennes)] larvae strongly avoided dissolved oxygen concentrations <1 mg 1^-1, which were lethal within 24 h at 25 to 27°C. In addition, naked goby larvae, whose behavior was tested at a wider range of dissolved oxygen concentrations, also showed a reduced preference for an oxygen concentration of 2 mg 1^-1, which leads to reduced survival during long-term exposures and to reduced feeding rates. There were no major differences in behavior or survival between the two species, or between the two age classes of naked gobies tested. Results suggest that behavioral responses to oxygen gradients will play a large role in producing marked vertical changes in abundance of feeding-stage larvae in Chesapeake Bay; mortality from direct exposure to low oxygen will likely be much less important in producing vertical patterns of larval abundance.     

Respiratory and behavioral responses of the grass shrimp Palaemonetes pugio to cadmium and reduced dissolved oxygen

Adult grass shrimp (Palaemonetes pugio) were collected during July and August, 1973, and exposed for 48-h periods to a series of sublethal cadmium (Cd) concentrations: 0.1 and 0.56 mg l^-1 for metabolic studies; and 0.01, 0.05, 0.1, 0.3, 0.56 mg l^-1 for locomotor studies. Treatment effects were tested singly and in combination at selected dissolved oxygen (DO) concentrations ranging from near saturation to 0.8 mgl^-1. Shrimp not exposed to Cd exhibited metabolic regulation between 6.5 and, 4.6 mg DOl^-1, with progressively lower O₂ consumption rates at lower DO concentrations. Oxygen consumption of Cd-exposed shrimp was suppressed overall relative to the non-Cd treated shrimp, and with one exception, the magnitude of metabolic suppression directly corresponded to Cd concentration. Locomotor activity of non-Cd exposed shrimp was relatively independent of DO concentration down to 2.8 mg DO l^-1 and became significantly suppressed at 1.8 mg DO l^-1 and below. Significant suppression of locomotion was evident in shrimp exposed to 0.56 mg Cd l^-1, but was not seen in treatment groups of 0.3 mg Cd l^-1 or lower. No interaction on locomotor activity of shrimp was detected between Cd exposure and oxygen concentration. The reduction of locomotor activity and metabolism at 0.56 mg Cd l^-1 exposure is similar to that occurring under reduced oxygen condition. It is hypothesized that Cd acts in some manner to suppress O₂ availability to P. pugio, a suggestion consistent with literature reports on adverse effects of Cd on fish respiratory enzymes and gill tissue.Contribution No. 351 of the U.S. Environmental Protection Agency, Environmental Research Laboratory, Narragansett, Rhode Island. Although the research described in this article was funded by the U.S. Environmental Protection Agency, it has not been subjected to Agency review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred     

Distinguishing modes of dissolved organic carbon production in marine macrophytes by tracer kinetic analysis

Tracer kinetic analysis of radioisotope incorporation into dissolved organic compounds reveals two distinct patterns of photosynthate release by macroalgae. In experiments employing Sargassum lacerifolium, dissolved organic carbon was produced at a constant rate during light incubations. Steady state rates of production were never achieved in experiments employing either Ecklonia radiata (Turn.) J. Agardh. or Ulva lactuca L. Analysis of the time-varying radioactivity curves obtained in experiments using these algae always resulted in models consistent with dissolved organic carbon production being an autocatalytic process. Preincubation of U. lactuca in the dark resulted in a diminished (ca. 40%) rate of dissolved organic carbon production during the subsequent light incubations. In no case did the radioisotope content of the dissolved organic carbon approach a limiting value, indicating that in contrast to phytoplankton, uptake rates of photosynthate by macroalgae are always less than the rates of production.     

潮汐作用下短叶茳芏湿地N2O排放规律及踩踏干扰研究

采用静态箱-气相色谱及浮箱-气相色谱法,对闽江河口鳝鱼滩湿地潮间带短叶茳芏（Cyperus malaccensis var.brevifolius）湿地和踩踏造成的裸露湿地N2O通量进行测定。结果表明,短叶茳芏湿地在涨潮前、涨落潮中和落潮后N2O通量差异性极显著（P=0.001〈0.01）,不同潮日（7 d内）的N2O通量差异性不显著（P=0.103〉0.05）。涨潮前、涨落潮过程中和落潮后,短叶茳芏湿地平均通量分别为19.48μg.m-2.h-1、12.80μg.m-2.h-1和51.41μg.m-2.h-1,总平均通量为33.1μg.m-2.h-1,表明白天短叶茳芏湿地为N2O的排放源。涨潮前,末次观测短叶茳芏湿地N2O通量最低,多数都为负值,落潮后过2~3 h,短叶茳芏湿地N2O通量出现日最大值。踩踏改变了短叶茳芏湿地N2O通量规律并降低了短叶茳芏湿地N2O通量。涨潮前,裸露湿地N2O平均排放量（27.25μg.m-2.h-1）低于短叶茳芏湿地（42.51μg.m-2.h-1）,但差异性不显著（P=0.527〉0.05）;落潮后,裸露湿地N2O平均排放量（0.86μg.m-2.h-1）极显著低于短叶茳芏湿地（63.59μg.m-2.h-1）（P=0.006〈0.01）。