Decrease In Light Intensity Research Articles

Live event reconstruction in an optically read out GEM-based TPC

Combining strong signal amplification made possible by Gaseous Electron Multipliers (GEMs) with the high spatial resolution provided by optical readout, highly performing radiation detectors can be realized. An optically read out GEM-based Time Projection Chamber (TPC) is presented. The device permits 3D track reconstruction by combining the 2D projections obtained with a CCD camera with timing information from a photomultiplier tube. Owing to the intuitive 2D representation of the tracks in the images and to automated control, data acquisition and event reconstruction algorithms, the optically read out TPC permits live display of reconstructed tracks in three dimensions. An Ar/CF4 (80/20%) gas mixture was used to maximize scintillation yield in the visible wavelength region matching the quantum efficiency of the camera. The device is integrated in a UHV-grade vessel allowing for precise control of the gas composition and purity. Long term studies in sealed mode operation revealed a minor decrease in the scintillation light intensity.

Do large-seeded herbs have a small range size? The seed mass-distribution range trade-off hypothesis.

We aimed to introduce and test the “seed mass–distribution range trade‐off” hypothesis, that is, that range size is negatively related to seed mass due to the generally better dispersal ability of smaller seeds. Studying the effects of environmental factors on the seed mass and range size of species, we also aimed to identify habitats where species may be at risk and need extra conservation effort to avoid local extinctions. We collected data for seed mass, global range size, and indicators for environmental factors of the habitat for 1,600 species of the Pannonian Ecoregion (Central Europe) from the literature. We tested the relationship between species’ seed mass, range size, and indicator values for soil moisture, light intensity, and nutrient supply. We found that seed mass is negatively correlated with range size; thus, a seed mass–distribution range trade‐off was validated based on the studied large species pool. We found increasing seed mass with decreasing light intensity and increasing nutrient availability, but decreasing seed mass with increasing soil moisture. Range size increased with increasing soil moisture and nutrient supply, but decreased with increasing light intensity. Our results supported the hypothesis that there is a trade‐off between seed mass and distribution range. We found that species of habitats characterized by low soil moisture and nutrient values but high light intensity values have small range size. This emphasizes that species of dry, infertile habitats, such as dry grasslands, could be more vulnerable to habitat fragmentation or degradation than species of wet and fertile habitats. The remarkably high number of species and the use of global distribution range in our study support our understanding of global biogeographic processes and patterns that are essential in defining conservation priorities.

White spot lesions: Does etching really matter?

The clinical significance of acid etching prior to orthodontic bonding is controversial. In the present study, we evaluated the effect of 15seconds of acid etching on enamel demineralization. Twenty-seven human molars were sectioned and assigned to two groups. Under standardized conditions, the enamel surfaces were imaged using FluoreCam to obtain baseline data. Group 1 was etched using 37% phosphoric acid for 15seconds, rinsed with water, and then imaged again; group 2 was only rinsed with water. Water rinse was collected for calcium chemical analysis using inductively-coupled plasma auger electron spectrometry. Both groups were subjected to 9days of pH cycling, after which final FluoreCam images were obtained. Group 1 showed a significant increase in lesion area (P=.012), decrease in light intensity (P=.009), and decrease in impact (P=.007) after acid etching. The amount of calcium that leached out over the 15seconds was 14ppm ±2.4 (0.35 mmol/L±0.06). Following pH cycling, there was no statistically-significant between-group difference in overall enamel demineralization. Initial demineralization caused by 15seconds of acid etching does not increase enamel susceptibility to further demineralization. This suggests that acid etching does not increase the risk of developing white spot lesions during orthodontics.

Characteristics of exploding metal wires in water with three discharge types

This paper presents the characteristics of underwater electrical wire explosion (UEWE) with three discharge types, namely, Type-A, Type-B, and Type-C. Experiments were carried out with copper and tungsten wires (4 cm long and 50–300 μm in diameter) driven by a microsecond time-scale pulsed current source with 500 J stored energy. A time-integrated spectrometer and a photodiode were used to measure the optical emission of UEWE. A Polyvinylidene Fluoride probe was adopted to record the pressure waveforms. Experimental results indicate that from Type-A to Type-C, more energy deposits prior to the voltage peak and the first peak power increases drastically. This variation of energy deposition influences the optical emission and shock wave generation process. Specifically, the light intensity decreases by more than 90% and the peak of continuous spectra moves from ∼400 nm to ∼700 nm. In addition, the peak pressure of the first shock wave increases from ∼2 MPa to more than 7.5 MPa.

Leaf Starch Turnover Occurs in Long Days and in Falling Light at the End of the Day.

We investigated whether starch degradation occurs at the same time as starch synthesis in Arabidopsis (Arabidopsis thaliana) leaves in the light. Starch accumulated in a linear fashion for about 12 h after dawn, then accumulation slowed and content plateaued. Following decreases in light intensity, the rate of accumulation of starch declined in proportion to the decline in photosynthesis if the decrease occurred <10 h after dawn, but accumulation ceased or loss of starch occurred if the same decrease in light intensity was imposed more than 10 h after dawn. These changes in starch accumulation patterns after prolonged periods in the light occurred at both high and low starch contents and were not related to time-dependent changes in either the rate of photosynthesis or the partitioning of assimilate between starch and Suc, as assessed from metabolite measurements and 14CO2 pulse experiments. Instead, measurements of incorporation of 13C from 13CO2 into starch and of levels of the starch degradation product maltose showed that substantial starch degradation occurred simultaneously with synthesis at time points >14 h after dawn and in response to decreases in light intensity that occurred >10 h after dawn. Starch measurements in circadian clock mutants suggested that the clock influences the timing of onset of degradation. We conclude that the propensity for leaf starch to be degraded increases with time after dawn. The importance of this phenomenon for efficient use of carbon for growth in long days and for prevention of starvation during twilight is discussed.

Analytical solution of the nitracline with the evolution of subsurface chlorophyll maximum in stratified water columns

Abstract. In a stratified water column, the nitracline is a layer where the nitrate concentration increases below the nutrient-depleted upper layer, exhibiting a strong vertical gradient in the euphotic zone. The subsurface chlorophyll maximum layer (SCML) forms near the bottom of the euphotic zone, acting as a trap to diminish the upward nutrient supply. Depth and steepness of the nitracline are important measurable parameters related to the vertical transport of nitrate into the euphotic zone. The correlation between the SCML and the nitracline has been widely reported in the literature, but the analytic solution for the relationship between them is not well established. By incorporating a piecewise function for the approximate Gaussian vertical profile of chlorophyll, we derive analytical solutions of a specified nutrient–phytoplankton model. The model is well suited to explain basic dependencies between a nitracline and an SCML. The analytical solution shows that the nitracline depth is deeper than the depth of the SCML, shoaling with an increase in the light attenuation coefficient and with a decrease in surface light intensity. The inverse proportional relationship between the light level at the nitracline depth and the maximum rate of new primary production is derived. Analytic solutions also show that a thinner SCML corresponds to a steeper nitracline. The nitracline steepness is positively related to the light attenuation coefficient but independent of surface light intensity. The derived equations of the nitracline in relation to the SCML provide further insight into the important role of the nitracline in marine pelagic ecosystems.

Increased soil nutrition and decreased light intensity drive species loss after eight years grassland enclosures

Enclosures (fenced, grazing or clipping) within a certain period of years are the most common tools for restoration of degraded grasslands in temperate regions. Short-term enclosures can improve biodiversity and productivity by effectively relieving grazing pressure, while long-term enclosures can reduce species diversity. We therefore carried out a field experiment to investigate the specific causes of the reduced species diversity in Hulunbeier grassland of northern China. After eight years of enclosure, the significantly increased soil available nitrogen (AN) and available phosphorus (AvP) in enclosure community reduced nitrogen (N) limitation but most vegetation was still N limited. Many environmental factors led to decreased species richness, but increased soil AN and decreased light intensity at the community bottom were the most significant ones. Community density decreased independently of soil nutrition but significantly related to decreased species richness. Density of dominant canopy species increased, while dominant understory species decreased during assemblage-level thinning; therefore, the random-loss hypothesis was not supported. The dominant understory species responded to lower light availability by increasing their height, leaf area, and chlorophyll content. Moreover, our results were expected to provide some specific guidance for the restoration mode selection of degraded grasslands in northern China.

Photoacclimation by Arctic cryoconite phototrophs.

Cryoconite is a matrix of sediment, biogenic polymer and a microbial community that resides on glacier surfaces. The phototrophic component of this community is well adapted to this extreme environment, including high light stress. Photoacclimation of the cryoconite phototrophic community on Longyearbreen, Svalbard, was investigated using in situ variable chlorophyll fluorescence. Rapid light curves (RLCs) and induction-recovery curves were used to analyse photosystem II quantum efficiency, relative electron transport rate and forms of downregulation including non-photochemical quenching (NPQ) and state transitions in cyanobacteria. Phototrophs used a combination of behavioural and physiological photochemical downregulation. Behavioural downregulation is hypothesised to incorporate chloroplast movement and cell or filament positioning within the sediment matrix in order to shade from high light, which resulted in a lack of saturation of RLCs and hence overestimation of productivity. Physiological downregulation likely consisted of biphasic NPQ, comprising a steadily induced light-dependent form and a light-independent NPQ that was not reversed with decreasing light intensity. State transitions by cyanobacteria were the most likely physiological downregulation employed by cyanobacteria within the mixed phototroph community. These findings demonstrate that cryoconite phototrophs combine multiple forms of physiological and behavioural downregulation to optimise light exposure and maximise photosynthetic productivity. This plasticity of photoacclimation enables them to survive productively in the high-light stress environment on the ice surface.

Thermal Variations of Operative Microscopes in Otology.

Objectives (1) Measure temperature variations achieved by common otomicroscopes. (2) Raise awareness about possible thermal injury during otologic procedures with the advent of newer, high-powered otomicroscopes. (3) Describe optical technology that aims to reduce the potential for thermal injury. Methods A variety of otomicroscopes, with different light sources (ranging from 100W halogen to 300W xenon), were studied. Temperatures were recorded from human auricular skin with a noncontact infrared thermometer at various microscope light intensities and with use of irrigation. Multiple recordings were done at 5-minute intervals, and a working distance of 225 mm was maintained. Results Maximum skin temperatures were found to plateau relatively quickly, with higher-wattage xenon light sources reaching greater temperatures. One-way analysis of variance revealed significant differences in temperatures with decreased light intensities. High-wattage xenon light sources reached significantly higher temperatures when compared with halogen models. Discussion There is substantial variation in maximal skin temperatures reached by otomicroscopes. Temperatures can be decreased to safe levels by reducing light intensity and with use of irrigation. The maximum temperature obtained in our study was 41.4°C. Second-degree skin burns have been described with prolonged exposures to temperatures >44°C. Implications for Practice Given the described potential for burns, surgeons performing procedures on the ear and temporal bone should take precautions to diminish temperature in the operative field.

Laser-light backscattering response to water content and proteolysis in dry-cured ham

Laser backscattering imaging (LBI) is a low-cost technology proposed to determine non-invasively composition and microstructural characteristics of agro food and dairy products. The aim of this work was to define the effect of different acquisition conditions (wavelength, object distance and angle of laser incidence) and to analyse the laser-light backscattering changes caused by additional hot air drying and proteolysis of dry-cured ham slices. The feasibility of the technology to determine water content and proteolysis (which is related to textural characteristics) of commercial sliced dry-cured ham was also evaluated. Results showed that a red laser (635 nm) is more convenient than a green laser (532 nm) to analyse dry-cured ham but no preferable angle or object distance to evaluate dryness or proteolysis was found. Nevertheless, light scattering parameters were modified depending on the acquisition conditions used. Laser backscattering was influenced by both dryness and proteolysis intensity showing an average light intensity decrease of 0.2 when decreasing water content (1% weight loss) and increasing proteolysis (equivalent to one-hour enzyme action). However, a decrease of scattering area was only detected when the water content was decreased (618 mm2 per 1% weight loss). Changes on scattering of light profiles were only observed when the water content changed. Although there is a good correlation between water content and LBI parameters when analysing commercial samples, proteolysis index has an important effect on the response. This fact hinder estimation of dry-cured ham composition and textural characteristics of dry-cured ham.

Response of photosynthetic characteristics and accumulation and distribution of assimilation products in tobacco to different light environments

In order to reveal the photosynthetic characteristics and the mechanism about accumulation and distribution of photosynthetic assimilation products under different light environments, potted tobacco was cultivated in a climate control chamber, there were three light intensity treatments (shading: (400±15)-(500±15) μmol·m-2·s-1; natural light: (800±15)-(1000±15) μmol·m-2·s-1; high light: (1500±15)-(1800±15) μmol·m-2·s-1). The results showed that with the decrease of light intensity, the biomass and root allocation, the net photosynthetic rate (Pn), stomata conductance (gs) and transpiration rate (Tr) were decreased, but the intercellular CO2 concentration (Ci) increased. The maximum net photosynthetic rate (Amax), light saturation point (LSP), light saturation point (LCP) and dark respiration rate (Rd) reached the maximum level under high light condition while the apparent quantum efficiency was higher in low light environment. The effects of light intensity on the absorption, accumulation and distribution of 13C in tobacco were significant, with a reduced proportion of enriched 13C distributed to the root under shading. The changes in the external light environment not only significantly affected the photosynthetic cha-racteristics and biomass accumulation of tobacco leaves, but also the distribution pattern of photosynthetic carbon in tobacco plant-soil system.

Effect of Acclimatization Temperature and Light Intensity on the Graft-Take of Cucumber Seedlings

The main aim of this work is to optimize the environmental condition for best grafting by control the temperature and light of grafting conditions. To achieve that was study the effect of ambient temperatures (20, 23, 26 and 29A‚°C), light intensity (0, 2500 and 5400 Lux) and type of tunnel (truss and flat) on stem diameter, shoot length, leaf area, shoot dry mass, grafted-take and energy consumption. The obtained results indicated that the average temperature was 20.45, 23.61, 27.01 and 29.71A‚°C at 20, 23, 26 and 29A‚°C ambient temperatures in truss tunnel, while, it was 20.61, 24.21, 27.53 and 30.09A‚°C at 20, 23, 26 and 29A‚°C ambient temperatures in flat tunnel. The stem diameter values were 4.626 and 4.476 mm in truss and flat tunnel under study with ambient temperature 20 to 29A‚°C and light intensity 0 to 5400 Lux. The shoot length values were 8.254 and 8.131 cm in truss and flat tunnel under study with ambient temperature 20 to 29A‚°C and light intensity 0 to 5400 Lux. The leaf area values were 56.074 and 53.214 cm2 in truss and flat tunnel under study with ambient temperature 20 to 29A‚°C and light intensity 0 to 5400 Lux. The shoot dry mass values were 396.448 and 386.585 mg in truss and flat tunnel under study with ambient temperature 20 to 29A‚°C and light intensity 0 to 5400 Lux. The grafted-take values were 84.525 and 78.460% in truss and flat tunnel under study with ambient temperature 20 to 29A‚°C and light intensity 0 to 5400 Lux. The energy consumed decreased with increasing ambient temperature and decreasing light intensity.

Theoretical investigation of polarization control in ultraviolet wavelength region using eigenmode within subwavelength grating

The optical characteristics of a subwavelength grating (SWG) were examined as a means of achieving ultraviolet (UV) polarization control based on the interaction between a light wave and Bloch eigenmode wave in the SWG, which results in a spatial periodic refractive index distribution. The relation of dispersion of the eigenmode wavevector was calculated to reveal the light propagation mechanism in this structure. The expected optical characteristics proved the feasibility of obtaining highly polarized UV light with no significant decrease in light intensity. The effects of the higher-order eigenmode on the SWG optical characteristics were also examined and discussed via the finite-difference time-domain method. This approach provides new insight into the SWG design for UV polarization control using the above interaction.

Migratory behavior, metabolism, oxidative stress and mercury concentrations in marine and estuarine European glass eels (Anguilla anguilla)

The relationships between the migratory behavior, methylmercury (MeHg) concentrations, oxidative stress response and detoxification processes were investigated in glass eels collected in marine (Molliets) and estuarine (Urt) waters (Adour estuary, South West France) at the end of the fishing season (April). Glass eel migratory behavior was investigated in an experimental flume according to their response to dusk. Fish responding to the decrease in light intensity by ascending in the water column and moving with or against the flow were considered as having a high propensity to migrate (migrant). Glass eels still sheltering at the end of the 24h catching period were considered as having a low propensity to migrate and were called non-migrant. Our results provide some evidence that estuarine glass eels were bigger, presented a higher propensity to migrate and a lower oxidative stress response than marine glass eels. This might reflect a selection process, some marine glass eels progressively settling or dying before reaching Urt and/or a change in feeding behavior. In April, glass eels restart feeding in the Adour estuary which might decrease the oxidative stress possibly related to starvation, and enhance migration. MeHg concentrations was significantly higher in non-migrant than in migrant glass eels and it is suggested that non-migrant glass eels might present a higher vulnerability to stress (at least contamination and/or starvation), although the underlying mechanisms remain to be elucidated.

Structural changes of Arthrospira sp. after low energy sonication treatment for microalgae harvesting: Elucidating key parameters to detect the rupture of gas vesicles

The buoyancy suppression by low energy sonication (LES) treatment (0.8W·mL−1, 20kHz, 10s) has recently been proposed as an initial harvesting step for Arthrospira sp. This paper aims to describe the structural changes in Arthrospira sp. after LES treatment and to present how these structural changes affect the results obtained by different analytical techniques. Transmission electron microscopy (TEM) micrographs of trichomes evidenced the gas vesicles rupture but also revealed a rearrangement of thylakoids and more visible phycobilisomes were observed. Differences between treated and untreated samples were detected by confocal microscopy, flow cytometry and optical microscopy but not by electrical impedance spectroscopy (EIS). After LES treatment, 2-fold increase in autofluorescence at 610/660nm was measured (phycocyanin/allophycocyanin emission wavelengths) and a ten-fold decrease in side scatter light intensity (due to a reduction of trichome’s inner complexity). This was further confirmed by optical microscopy showing changes on trichomes appearance (from wrinkled to smooth).

How Sound Modulates Responses to Light with Different Time Intervals Between Stimuli of Different Modalities

Extracellular recording of 34 neurons in the primary visual cortex of three conscious rabbits was performed in chronic experimental studies addressing the effects of sound (2000 Hz, 70 dB, 40 msec) on the discrimination of weak light intensities (0.3–1 cd/m2). Sound was delivered with different time intervals before and after substitution of one light intensity by another (using a total of 15 intervals in the range –750 to +150 msec). Factor analysis of variance (ANOVA) showed that the time interval between the sound and the light had statistically significant influences on neuron responses. Sound itself provoked no response. Neuron reactions consisted of responses to increases (on responses) and decreases (off responses) in light intensity. The most marked effect of sound was seen in the initial phase of the response (40–100 msec from the moment at which intensities were substituted). For every interval, neurons demonstrated both increases and decreases in reactions to complexes as compared with their responses to light. Wilcoxon’s T test was used to assess differences in sets of responses to light and to complexes. For the on responses of the whole group of neurons, the absolute values of responses to sound + light complexes were significantly (p < 0.05) different from responses to light (increased reactions) at intervals of –150, –40, and 0 msec. Two groups of neurons were identified, for which the effects of sound on responses to light were markedly different. Neurons of group 1 (n = 16) showed significant positive influences of light on on responses over a wide range of intervals (–150, –40, –20, 0, +20, +100 msec), along with a larger increase in the number of spikes due to sound (by 18–28%) as compared with responses to light. Neurons of group 2 (n = 18) had no significant intervals, i.e., at which reactions to complexes were not significantly different from responses to light. None of the study groups of neurons showed intervals with significant decreases in responses to complexes, though there was a tendency for reactions to complexes to shift towards weakening of responses at intervals of –750 and –80 msec for group 1 (p < 0.07) and at intervals of –500 and +20 sec for group 2 (p < 0.1). On responses were found to be more strongly affected by sound than off responses. The effects of sound on the second phases of responses to light (120–160 msec and later, n = 23) were also studied. Sound had markedly weaker effects on the second phase than the first. For the whole group of neurons with late phases, sound had significant influences on on responses with an interval of 0 msec and on off responses with intervals of +100 and +150 msec. Our study demonstrated similarity in the time intervals for modulation of reactions to light by sound in experiments on animals and psychophysical studies in humans. These data provide for more detailed studies of the integration of light and sound when used simultaneously.

The acclimation of Tilia cordata stomatal opening in response to light, and stomatal anatomy to vegetational shade and its components.

Stomatal anatomical traits and rapid responses to several components of visible light were measured in Tilia cordata Mill. seedlings grown in an open, fully sunlit field (C-set), or under different kinds of shade. The main questions were: (i) stomatal responses to which visible light spectrum regions are modified by growth-environment shade and (ii) which separate component of vegetational shade is most effective in eliciting the acclimation effects of the full vegetational shade. We found that stomatal opening in response to red or green light did not differ between the plants grown in the different environments. Stomatal response to blue light was increased (in comparison with that of C-set) in the leaves grown in full vegetational shade (IABW-set), in attenuated UVAB irradiance (AB-set) or in decreased light intensity (neutral shade) plus attenuated UVAB irradiance (IAB-set). In all sets, the addition of green light-two or four times stronger-into induction light barely changed the rate of the blue-light-stimulated stomatal opening. In the AB-set, stomatal response to blue light equalled the strong IABW-set response. In attenuated UVB-grown leaves, stomatal response fell midway between IABW- and C-set results. Blue light response by neutral shade-grown leaves did not differ from that of the C-set, and the response by the IAB-set did not differ from that of the AB-set. Stomatal size was not modified by growth environments. Stomatal density and index were remarkably decreased only in the IABW- and IAB-sets. It was concluded that differences in white light responses between T. cordata leaves grown in different light environments are caused only by their different blue light response. Differences in stomatal sensitivity are not dependent on altered stomatal anatomy. Attenuated UVAB irradiance is the most efficient component of vegetational shade in stimulating acclimation of stomata, whereas decreased light intensity plays a minor role.

Bumblebees Perform Well-Controlled Landings in Dim Light

To make a smooth touchdown when landing, an insect must be able to reliably control its approach speed as well as its body and leg position—behaviors that are thought to be regulated primarily by visual information. Bumblebees forage and land under a broad range of light intensities and while their behavior during the final moments of landing has been described in detail in bright light, little is known about how this is affected by decreasing light intensity. Here, we investigate this by characterizing the performance of bumblebees, B. terrestris, landing on a flat platform at two different orientations (horizontal and vertical) and at four different light intensities (ranging from 600 lx down to 19 lx). As light intensity decreased, the bees modified their body position and the distance at which they extended their legs, suggesting that the control of landing in these insects is visually mediated. Nevertheless, the effect of light intensity was small and the landings were still well controlled, even in the dimmest light. We suggest that the changes in landing behavior that occurred in dim light might represent adaptations that allow the bees to perform smooth landings across the broad range of light intensities at which they are active.

Iron plays a critical role in stomatal closure in cauliflower

Studies have been made of the effects of iron deficiency on water status and transpiration parameters in iron-deficient plants. Cauliflower (Brassica oleracea L. var Botrytis cv Pusa) plants were grown in sand culture with 0.1mM (control) and 0.001mM (deficient) iron supply. Young leaves of Fe-deficient plants showing mild interveinal chlorosis were thin and soft with lesser epicuticular wax than the green leaves of Fe-sufficient plants. Fe deficiency induced increases in specific water content, water potential, stomatal aperture and transpiration and a decrease in diffusive resistance in the young leaves. Although Fe deficiency enhanced stomatal and cuticular transpiration, the greater stomatal opening was mainly responsible for increased transpiration. Fe deficiency stifled diurnal changes in diffusive resistance, ABA accumulation and guard cell K+ content in the leaves. Though Fe deficiency did not affect maximum stomatal opening under favourable conditions, it retarded stomatal closure under conditions of developing water deficit or decreasing light intensity. Higher rates of transpirational water loss in Fe-deficient leaves are appearing to be related to the slow and incomplete stomatal closure, which are attributable to the putative involvement of Fe in the biosyntheses of wax and ABA in Fe-deficient leaves.

Influence of light, nutrients, and temperature on the toxicity of atrazine to the algal species Raphidocelis subcapitata: Implications for the risk assessment of herbicides

The acute toxicity of herbicides to algae is commonly assessed under conditions (e.g., light intensity, water temperature, concentration of nutrients, pH) prescribed by standard test protocols. However, the observed toxicity may vary with changes in one or more of these parameters. This study examined variation in toxicity of the herbicide atrazine to a representative green algal species Raphidocelis subcapitata (formerly Pseudokirchneriella subcapitata) with changes in light intensity, water temperature, concentrations of nutrients or combinations of these three parameters. Conditions were chosen that could be representative of the intensive corn growing Midwestern region of the United States of America where atrazine is used extensively. Varying light intensity (4–58µmol/m2s) resulted in no observable trend in 96-h EC50 values for growth rate. EC50 values for PSII yield generally increased with decreasing light intensity but not significantly in all cases. The 96-h EC50 values for growth rate decreased with decreases in temperature (20–5°C) from standard conditions (25°C), but EC50 values for PSII yield at lower temperatures were not significantly different from standard conditions. Finally, there was no clear trend in 96-h EC50 values for both endpoints with increases in nitrogen (4.1–20mg/L) and phosphorus (0.24–1.2mg/L). The 96-h EC50 values for both endpoints under combinations of conditions mimicking aquatic systems in the Midwestern U.S. were not significantly different from EC50 values generated under standard test conditions. This combination of decreased light intensity and temperature and increased nutrients relative to standard conditions does not appear to significantly affect the observed toxicity of atrazine to R. subcapitata. For atrazine specifically, and for perhaps other herbicides, this means current laboratory protocols are useful for extrapolating to effects on algae under realistic environmental conditions.