On the occurrence of bimodal diel dissolved oxygen curves in aquatic systems

Although diel dissolved oxygen curves in aquatic ecosystems usually have a unimodal shape, occasionally bimodal curves are observed. Examples of bimodal curves are found throughout literature for various types of aquatic systems; nevertheless, the phenomenon has been generally ignored. In the present study diel changes in dissolved oxygen, temperature, and irradiation were continuously monitored over a 2 year period in an artificial pond. Through analysis of variance an attempt was made to isolate the physical circumstances under which bimodal oxygen curves can be expected. It is suggested that a persistent high irradiation level and/or its accessory high rate of temperature increase and/or a usually simultaneous high rate of primary production may induce bimodal oxygen curves. However, a conclusive explanation could not be given.     

Temporal and spatial variations of dissolved oxygen concentrations in some Dutch polder ditches

This study deals with the temporal and spatial variations of dissolved oxygen concentration, temperature and occasionally pH in three polder ditches in the Netherlands. A routine programme including different environmental parameters served to characterize the ditch environment. Conclusions concerning water quality criteria are presented briefly.     

Bimodal diel dissolved oxygen curves and thermal stratification in polder ditches

In a polder ditch with a water depth of 50 cm, oxygen and temperature were measured continuously during 24 hours at 10 cm above the bottom and 10 cm below the surface. Two examples are given in which the diel oxygen curve of the lower electrode was bimodal. The curve of the upper electrode was unimodal in both cases. The occurrence of the bimodal curve could be explained by the turnover of the stratified water column after the surface started to cool in the late afternoon.     

Assessing constructed wetland functional success using diel changes in dissolved oxygen, pH, and temperature in submerged, emergent, and open-water habitats in the Beaver Creek Wetlands Complex, Kentucky (USA)

We assessed the functional success of restored wetlands by determining if the patterns in dissolved oxygen (DO), temperature, and pH were similar to those conditions observed in natural wetlands. The Beaver Creek Wetlands Complex consists of dozens of marshes and ponds built in a former Licking River floodplain, in the hills of east Kentucky, USA. In natural wetland ecosystems, aquatic primary production is highest in emergent and submerged vegetations zones; where daybreak dissolved oxygen (DO) is often near zero, and DO may rise to well over 100% saturation past mid-day. Open-water areas, dominated by phytoplankton, have less dramatic diel DO fluctuations—often without pre-dawn anoxia. Compared to open water, temperatures fluctuate less dramatically in vascular vegetation, due to shading and suppression of wind and waves. Measurements of ecosystem metabolism (diel changes in DO and pH) in three aquatic habitats of the constructed wetlands (emergent vegetation, submerged vegetation, open water) were compared to these natural ideals. In Beaver Creek Wetlands, water temperature patterns were not as dramatic as in natural habitats, nor did they did follow a similar trend. Waters in emergent vegetation (29.5 °C) were warmest; submerged vegetation coolest (26.5 °C); open-water intermediate (27.4 °C). Diel DO and pH patterns were not similar to natural habitats. Highest net primary production (NPP) and gross primary production (GPP) were measured in emergent vegetation waters (mean GPP = 7.58 g m⁻² d⁻¹); lowest in submerged vegetation (mean GPP = 5.48 g m⁻² d⁻¹); and intermediate in open-water (mean GPP = 6.95 g m⁻²d⁻¹). Diel pH changes were greatest in the highly productive emergent waters (median maximum daily difference of 0.36), and not as pronounced in submerged vegetation and open-water (median maximum change = 0.16 and 0.22, respectively). Water-column respiration was generally about double NPP. Like natural ecosystems, near anoxic DO concentrations were consistently measured in emergent and submerged plants before dawn; whereas open-water zones were generally >4 mg l⁻¹. These restored wetland systems may need more time to be functionally equivalent to natural marshes.     

Release of sedimentary nitrogen and phosphorus in polder ditches of a low-moor peat area

The release of N and P from the sediment of two ditches, one (A) dominated by filamentous algae and the other (B) by water-lilies, was estimated by core and enclosure experiments. The release rates for ditch A tended to be higher than those for ditch B. Sediment cores covered by a filamentous algae layer released about 1.5 times more N and P than those from which the layer had been removed. During the incubation of the cores in the dark at 20°C for 2–3 weeks, about 10% of the N in the filamentous algae layer was mineralized. The mineralization could be described as a first-order reaction with a rate constant of about 0.2 d^–1. On average the cores of ditches A and B released about 40 mg mineral N and 3 mg.m^–2.d^–1 soluble reactive phosphorus. Defining the release from the sediment in the enclosures as the net increase of N and P in the water phase and in the vegetation minus the input, a negative net release,i.e. net accumulation of N and P in the sediment, was found over the summer half of the year. The negative values were due to the significant N and P input, resulting from pumping ditch water into the enclosures in order to compensate for downward seepage. From the enclosure experiments a downward seepage rate of 14 mm.d^–1 and an external load of about 6 g.m^–2 total N and 0.6 g.m^–2 total P during the summer half of the year —i.e. 33 mg.m^–2.d^–1 N and 3 mg.m^–2.d^–1 P. respectively — was calculated for the ditches. Tentative gross release rates — based on the sum of the positive net release of N and P into the water phase over 1–2 weeks intervals and the net increase of N and P in the vegetation — converted to 20°C and allowing for underestimation of the primary production by a factor of 5, amounted to 58 mg mineral N and 7 mg.m^–2.d^–1 soluble reactive phosphorus during the summer half of the year. Combining the rates estimated by cores and enclosures and converting them to rates at the mean water temperature during the summer half of the year, the release of mineral N and soluble reactive phosphorus roughly amounted to 40 and 4 mg.m^–2.d^–1, respectively. The release rates as well as the external load indicated a relatively low eutrophication of the ditches.     

Annual and daily activity rhythms of loathes in an irrigation creek and ditches around paddy fields

Synopsis This study deals with the daily activity rhythm and its change in a loath,Misgurnus anguillicaudatus, by season and age. We set traps in an irrigation creek and ditches around the paddy fields near Nara city every month for 2 years. The fish appeared in spring, declined in early summer, and increased in mid-summer again, and disappeared in late autumn. The number of fish captured at night was greater than that during the daytime in summer. There were some differences in the daily rhythms by sex and age. Nocturnal activities of males and immatures were more prominent than those of females. Younger generation were more nocturnally active than elders in summer. Changes in the daily activity rhythms of the loath are possibly adaptive to unstable environments around paddy fields.     

Bolivian Altiplano streams with low richness of macroinvertebrates and large diel fluctuations in temperature and dissolved oxygen

We sampled benthic macroinvertebrates and recorded oxygen and temperature regime during 2-day periods in 12 stream sites at an altitude of 3,800–4,000 m a.s.l. on the Bolivian Altiplano, during low flow conditions at the end of the dry season. Eight of the sites were relatively unpolluted, while the remaining four sites were affected by domestic/industrial sewage. Compared to other Andean streams, the fauna was poor with a total of 28 and a mean of 11 taxa (mostly families) in the unpolluted sites. The entire EPT group was represented by just five families. Of these, only Baetidae and Hydroptilidae were common. At all sites, the dominant taxa were found among just four taxa (Elmidae, Chironomidae, Oligocheata and Hyallelidae). Mean water temperature was 12.9°C, while mean diel amplitude was 13.4°C and the maximum range 17.4°C. Ten richness and biotic indices were used to analyse for effects of temperature and oxygen on the fauna. Most measures of fauna richness were negatively correlated with mean and max temperature (even excluding the four polluted sites), while biotic indices were mostly uncorrelated with temperature. Thus, the large fluctuations in temperature seemed to exclude taxa, thereby reducing overall diversity of Altiplano streams. Oxygen saturation also varied considerably, with a mean diel range of 48% and a maximum range of 93%. Richness measures were uncorrelated with oxygen %, while all biotic indices were positively correlated with either mean or min oxygen %. Most measures of faunal composition showed a marked shift at levels of 10–30% min oxygen saturation. Earlier studies of high Andean streams in Ecuador have shown a major shift in faunal composition at 50–60% oxygen saturation. The fauna in the Altiplano streams may be adapted to the large fluctuations in oxygen saturation, and therefore more robust towards low oxygen saturations. The implications for biotic assessment of Altiplano streams are discussed.     

Benthic oxygen flux in the highly productive subarctic Lake Myvatn, Iceland: In situ benthic flux chamber study

In situ paired light and dark-stirred benthic flux chambers were used to estimate dissolved oxygen flux across the sediment–water interface in Lake Mývatn, Iceland. Three sampling stations were selected, each station reflecting a specific sedimentary environment, benthic communities, and water depth. During this study the phytoplankton density was low. Spatial and seasonal variations of bottom DO concentration and DO flux have been observed during this study. The oxygen consumption rate at all study sites had a mean of –89 (±44) mmol m^–2 d^–1 while the oxygen production rate due to benthic algae had a mean of 131 (±103) mmol m^–2 d^–1. There was a strong correlation (r=0.91) between oxygen consumption rate and temperature. This was presumably because of the temperature influence on rates of microbial and macrobenthic processes. The mean benthic primary production rate at all study sites was 1216 (±957) mg C m^–2 d^–1 between June 2000 and February 2001. Annual gross benthic primary production was estimated from the gross mean daily benthic DO production (P) and Redfield's C:O₂ ratio of 106:138 to be 420 g C m^–2 y^–1 at station HO, 250 g C m^–2 y^–1 at B2 and 340 g C m^–2 y^–1 at station 95. Thus, the mean gross benthic primary production was estimated as 1151 mg C m^–2 d^–1 at station HO, 685 mg C m^–2 d^–1 at station B2, and 932 mg C m^–2 d^–1 at station 95.     

Durations of development and production estimates by two crustacean zooplankton species Thermocyclops oblongatus Sars (Copepoda) and Diaphanosoma excisum Sars (Cladocera), in Lake Naivasha,Kenya

Durations of embryonic and post-embryonic development of the two dominant zooplankton crustaceans Thermocyclops oblongatus (Copepoda) and Diaphanosoma excisum in Lake Naivasha were determined at various lake water temperatures to provide the time element for the calculation of their production. Developmental times were temperature dependent in as much as food resource was not limiting. Production estimates were calculated. The turnover times of their biomass was 11.4 and 13.7 days, with production rates of 11.0 and 6.0 µg dw m^-3 d^-1 for T. oblongatus and D. excisum, respectively. Annual production was estimated as 3302 mg m^-3 yr^-1 for T. oblongatus and 2176 mg m^-3 yr^-1 for D. excisum. Production was continuous but with several irregular peaks particularly during the wet seasons when plankton biomass was high.     

Absence of typical diel vertical migration in Daphnia: varying role of water clarity, food, and dissolved oxygen in Lake Eymir, Turkey

Diel vertical migration (DVM) is a complex and dynamic behaviour against predation because the reaction of migrating organisms to light intensity plays a primary role, but is modified by other factors. In the relatively shallow but thermally stratified Lake Eymir, Daphnia pulex de Geers utilized vertical refugia afforded by the hypolimnion during both day and night. Differences in general vulnerability to fish predation determined the differences in their mean residence depths (MRDs) of different population categories such as most conspicuous and vulnerable individuals of adult with eggs inhabited the deepest depth, whereas juveniles stayed close the thermocline. In late spring, profoundly high amplitude of displacement within the hypolimnion, probably due to the hypolimnion being well-lit and relatively well-oxygenated for the fish and rather unsafe for the large-sized daphnids, was recorded. Therefore, the large-sized daphnids daytime refuge was close to the bottom whereas at night they moved upward to benefit from warmer water temperature along with food availability in the presence of fish predation but still remained below the thermocline. In summer, the insignificant amplitude of the hypolimnetic, which later became epilimnetic, displacements were probably due to the near-anoxic condition found below the thermocline. This might have deterred the fish, thus providing a safer refuge for daphnids in the below thermocline, which afterwards became the above thermocline. Low oxygen availability was regarded as the summer proximate factor. The abundant food and warmer water conditions found in the below/above thermocline also accounted for absence of DVM in summer. Consequently, this study suggests that DVM by Daphnia is an adaptation that is plastic to changing environmental conditions.     

Ultraviolet irradiation induces autofluorescence enhancement via production of reactive oxygen species and photodecomposition in erythrocytes

Ultraviolet (UV) light has a significant influence on human health. In this study, human erythrocytes were exposed to UV light to investigate the effects of UV irradiation (UVI) on autofluorescence. Our results showed that high-dose continuous UVI enhanced erythrocyte autofluorescence, whereas low-dose pulsed UVI alone did not have this effect. Further, we found that H₂O₂, one type of reactive oxygen species (ROS), accelerated autofluorescence enhancement under both continuous and pulsed UVI. In contrast, continuous and pulsed visible light did not result in erythrocyte autofluorescence enhancement in the presence or absence of H₂O₂. Moreover, NAD(P)H had little effect on UVI-induced autofluorescence enhancement. From these studies, we conclude that UVI-induced erythrocyte autofluorescence enhancement via both UVI-dependent ROS production and photodecomposition. Finally, we present a theoretical study of this autofluorescence enhancement using a rate equation model. Notably, the results of this theoretical simulation agree well with the experimental data further supporting our conclusion that UVI plays two roles in the autofluorescence enhancement process.     

Relation between dissolved oxygen concentration and ajmalicine production rate in high-density cultures of Catharanthus roseus

The relation between dissolved oxygen (DO) and the ajmalicine production rate of Catharanthus roseus was investigated in 15-L tank reactors at constant stirrer speed and gas flow rate. Below a DO concentration of 29% of air saturation the ajmalicine production rate was less than 0.06 mumol/g/d. Above a DO of 43% the ajmalicine production rate was constant at 0.21 mumol/g/d. Between a DO of 29% and 43% there was a strong relation between the ajmalicine production rate and the DO concentration. After a period of at least 12 days at DO /=57%. A kinetic equation is proposed for the relation between DO and the specific ajmalicine production rate. (c) 1995 John Wiley & Sons, Inc.     

Daily cycles of dissolved oxygen and nutrient content in a shallow fishpond: The impact of water renewal

This study was conducted in a shallow fishpond located on the eastern side of Arcachon Bay, France.Dissolved oxygen, pH and nutrient content (NH₄, NO₂, NO₃ and PO₄) showed pronounced diel variations.These phenomena seemed to be directly controlled by biological processes. Microbially mediated degradation of organic matter constitutes the main source of nutrients in the water column and primary producers consume the major part of these products. These processes are closely coupled to the light-dark cycle.Man-induced water renewal caused low modifications in nutrient concentration and did not alter its temporal dynamics.     

Physicochemical and morphological characterization of two small polluted streams in southwest Germany

As a supporting component of the VALIMARproject, physicochemical investigations wereconducted monthly from 1995 to 1999 at theKrähenbach/Aich stream system (two samplingsites) and at the Körsch stream (sixsampling sites). Several physicochemicalparameters were analysed continuously bydataloggers during the entire sampling period.Moreover, a selection of the most importantmorphological parameters of the stream wererecorded in 1998.The results of these physicochemicalinvestigations demonstrated that theKrähenbach/Aich system could becharacterized as a natural rhithral submontanecarbonate stream system that is welloxygenated. Low temporal variations in pH,conductivity and chloride occurred at allsampling sites in the Krähenbach whichcoincided with the geological conditions atthis test stream. Because of relatively lowconcentrations of organic and inorganiccompounds during the entire study period thesites AB and AC in the Krähenbach/Aichsystem were classified as slightly polluted.The morphological assessment of the streamindicated a moderately affected status atboth of these streams.Physicochemical and morphologicalinvestigations along the Körsch streamsystem (KA to KE including the tributary streamSulzbach) indicated a highly affected rhithralsubmontane carbonate system characterized byhigh water velocity, flow rate and dissolvedoxygen. The Körsch, however, differssignificantly with respect to watertemperature, conductivity, pH, BOD₅,nutrients, and chloride concentrations from theKrähenbach. As a result of differentanthropogenic inputs (e.g. several sewageplants, agriculture activities and waste waterdumping) the Körsch sites KA to KD wereclassified as critically to heavilypolluted. The morphological assessmentindicated a clearly affected to damagedstatus. The upstream site KE could becharacterized as slightly polluted and itsmorphological structure as moderatelyaffected.     

Sensitivity of infrared water vapor analyzers to oxygen concentration and errors in stomatal conductance

Use of infrared analyzers to measure water vapor concentrations in photosynthesis systems is becoming common. It is known that sensitivity of infrared carbon dioxide and water vapor analyzers is affected by the oxygen concentration in the background gas, particularly for absolute analyzers, but the potential for large errors in estimates of stomatal conductance due to effects of oxygen concentration on the sensitivity of infrared water vapor analyzers is not widely recognized. This work tested three types of infrared water vapor analyzers for changes in sensitivity of infrared water vapor analyzers depending on the oxygen content of the background gas. It was found that changing from either 0 or 2% to 21% oxygen in nitrogen decreased the sensitivity to water vapor for all three types of infrared water vapor analyzers by about 4%. The change in sensitivity was linear with oxygen mole fraction. The resulting error in calculated stomatal conductance would depend strongly on the leaf to air vapor pressure difference and leaf temperature, and also on whether leaf temperature was directly measured or calculated from energy balance. Examples of measurements of gas exchange on soybean leaves under glasshouse conditions indicated that changing from 21% to 2% oxygen produced an artifactual apparent increase in stomatal conductance which averaged about 30%. Similar errors occurred for `conductances' of wet filter paper. Such errors could affect inferences about the carbon dioxide dependence of the sensitivity of photosynthesis to oxygen. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of oxygen and nutrients limitation on ajmalicine production and related enzyme activities in high density cultures of Catharanthus roseus

Oxygen and nutrient limitation was investigated in order to identify the origin of a lower specific ajmalicine production in Catharanthus roseus cultures at high cell densities in an induction medium. The effect of oxygen limitation was explored by comparing two identically aerated and agitated high cell density bioreactor cultures with dissolved oxygen (DO) concentration of 15% and 85% of air saturation, with respect to alkaloid formation and related enzymes activities. Oxygen had an evident effect on ajmalicine production: in the high DO cultures production was more than 5 times higher than in the low DO cultures. The difference in ajmalicine production between high and low DO could not be explained by the enzyme activity profiles. Moreover, the productivity in the high density culture could not restored to the level of a low density culture (at a high DO) by increasing the DO alone. The effect of nutrient limitation was studied with response surface methodology in shake flask cultures. Nutrient limitation could not be demonstrated to be responsible for the productivity loss. Alkaloid and enzyme measurements in the shake flask cultures supported previous findings that the tryptamine pathway may regulate alkaloid production, provided that the terpenoid pathway is sufficiently active. (c) 1994 John Wiley & Sons, Inc.     

Effects of hydrologic changes on aboveground production and surface water chemistry in two boreal peatlands in Alberta: Implications for global warming

Aboveground net primary production (NPP) and surface water chemistryvariables were monitored in a lacustrine sedge fen and a bog for four years.There were no significant differences in precipitation, mean growing seasonannual temperature, and number of growing degree days from 1991 to 1994. Themean annual water levels in the lacustrine sedge fen differed significantly,whereas they were similar in the bog during these four years. We measured 15surface water variables in the lacustrine sedge fen and the bog, and foundthat only two correlated significantly with water level fluctuations. In thelacustrine sedge fen, calcium correlated positively (r²= 0.56) and nitrate correlated negatively (r² =0.20) with water levels. In the bog, potassium correlated positively(r² = 0.88) and total dissolved phosphorus correlatednegatively (r² = 0.62) with water levels. The remainingchemical variables showed no significant correlations with water levelfluctuations. Net primary production of the different vegetation strataappeared to respond to different environmental variables. In the lacustrinesedge fen, graminoid production was explained to a significant degree bywater levels (r² = 0.53), whereas shrub production wasexplained to a significant degree by surface water chemistry variables, suchas nitrate (r² = 0.74) and total phosphorus(r² = 0.22). In the bog, temperature was the onlyvariable that explained moss production to a significant degree(r² = 0.71), whereas ammonium explained graminoidproduction (r² = 0.66) and soluble reactive phosphorusexplained shrub production to significant degrees (r² =0.71). There are few direct data on the impact of climatic warming in borealwetlands, although paleoecological and 2×CO₂ model datahave provided some indications of past and possibly future changes invegetation composition, respectively. Our results suggest that thelacustrine sedge fen may succeed to a bog dominated by Sphagnum spp. andPicea mariana, whereas the bog may succeed to an upland-type forestecosystem. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of water stress on oxygen, hydrogen and carbon isotope ratios in two species of cotton plants

Abstract. Two cotton species ( Gossypium hirsutum L. cv. SJ-2 and Gossypium barbadence cv. S-5) were grown under irrigated (wet) and non-irrigated (dry) conditions in the same field. Leaf water was enriched in ¹⁸O and deuterium in the dry treatment relative to the wet treatment for both species. Only in plants of S-5 was a similar enrichment observed in leaf cellulose. In both species, the isotopic composition of leaf cellulose must reflect the isotopic composition of the actual water pool involved in cellulose synthesis. Therefore, our observations indicate that one species (SJ-2) can maintain a relative isolation of this water pool from direct evapotranspirational effects. Such plant species will more faithfully record, in the isotopic composition of organic matter, the isotopic composition of ground water. In contrast, the isotopic composition of organic matter in plants such as S-5 could be used as an integrated signal reflecting humidity conditions during growth. Water use efficiency, based on seed-cotton yield and total water applied, correlated linearly with differences in carbon isotopic ratios between species in both the wet and dry treatments and between treatments in each species.     

体质量和水温对太湖秀丽白虾人工驯养子代耗氧率和排氨率的影响

以太湖秀丽白虾(Exopalaemon modestus)人工驯养子代为实验样本,实验共设置6个体质量梯度及7个温度梯度,样本体质量范围为(0.12±0.01)～(1.93±0.05)g,实验温度范围为12℃～30℃,研究了体质量及水温对耗氧率和排氨率的影响。结果表明:秀丽白虾耗氧率变幅为0.1497～0.9053mg·g-1·h-1,均值为0.3901mg·g-1·h-1;排氨率变幅为0.0165～0.0866mg·g-1·h-1,均值为0.0379mg·g-1·h-1。体质量、水温及两者的交互效应均对耗氧率和排氨率具有极显著的影响(P0.01)。体质量与耗氧率和排氨率之间的回归关系分别符合幂函数方程Ro=0.3114W-0.2414(r=-0.436)和Rn=0.0307W-0.3007(r=-0.653);水温与耗氧率和排氨率之间的回归关系分别符合指数方程Ro=0.0711e0.0749t(r=0.877)和Rn=0.0113e0.0530t(r=0.747);体质量、水温与耗氧率及排氨率的二元回归方程分别为Ro=0.028T-0.147W-0.053(r=0.948)和Rn=0.002T-0.017W+0.013(r=0.922)。耗氧率和排氨率Q10变幅分别为1.17～4.20和1.15～2.29,均值分别为2.10和1.64。在实验温度范围内,氧氮比均随着水温的上升而增大,变幅为7.42～13.62,均值为10.04。秀丽白虾在低温阶段(12℃～18℃)主要以蛋白质为供能物质,在高温阶段(21℃～30℃)对脂肪的利用有所增加,中等规格个体的脂肪代谢率最高。