High Radiation Levels Research Articles

Sun Protection Behavior in Danish Outdoor Workers Following a Multicomponent Intervention.

BackgroundOutdoor workers can be exposed to relatively high levels of ultraviolet radiation and are at risk of developing occupational skin cancer. Implementing the use of sun protection in outdoor workers at work is therefore important. The objective of this follow-up study was to evaluate the effect of a multicomponent intervention to improve the use of sun protection in Danish outdoor workers.MethodA total of 237 Danish outdoor workers were asked to complete surveys in 2016/17 and in 2020. Multicomponent interventions, between surveys, included information on skin cancer risk and use of sun protection, personal dosimetry and skin examination for signs of photodamage and skin cancer. Survey items on awareness of occupational skin cancer risk and perceived importance of sun protection as well as availability and use of sun protection at work were compared and analyzed in relation to the multicomponent intervention.ResultsOverall, the use of sun protection at work increased significantly (composite score [95% CI] 4.0 [3.7, 4.3] in 2016/17 and 4.6 [4.3, 4.9] in 2020, p < 0.001). Sunscreen was by far the biggest contributor, and the only type of sun protection used at work, which changed significantly (often/always use 37% in 2016/17 and 52% in 2020, p < 0.001). The biggest influence on the increased use of sun protection at work seemed to be a significant increase in the awareness of occupational skin cancer risk (moderate/high 43% in 2016/17 and 63% in 2020, p < 0.001) and perceived importance of sun protection at work (moderate/high 69% in 2016/17 and 83% in 2020, p < 0.001).ConclusionThe results of this study indicate that awareness of occupational skin cancer risk as well as the perceived importance and use of sun protection at work in Danish outdoor workers may be improved by means of multicomponent intervention.

Probing Different Approaches in Ultraviolet Radiation Personal Dosimetry - Ball Sports and Visiting Parks.

Solar ultraviolet radiation (UVR) continues to be a decisive influencing factor for skin health. Besides acute damage (e.g. erythema), chronic light damage is of particular relevance. Skin cancer can develop on the basis of this light damage. Knowledge about irradiation is crucial for the choice of preventive measures, but has so far been incomplete in many occupational and leisure activities. Often a methodological problem in study design is the cause. Here we report on the clarification of two issues. First, further values are to be determined on the way to a comprehensive exposure register of leisure-related activities. Furthermore, it is to be determined to what extent the measurement setting can have an influence on the measurement campaigns. For long-term measurements, football referees were equipped with dosimeters over several months, selective measurements during visits to parks were carried out by on-site recruitment of test persons. It turned out that the choice of method also depends on the expected compliance of the test persons. Long-term measurements of specific activities such as playing football are particularly suitable for observing the course of UV exposure over the year and generating resilient mean values. Point measurements such as visits to parks can also do this if there are enough such events spread over the year. However, they are particularly suitable for such on-site campaigns, as they may be combined with awareness campaigns of the issue of skin cancer. They also allow many measurements to be taken at the same time in one place. Both playing football and visiting parks are associated with high levels of radiation, so specific prevention concepts need to be developed. We were able to determine that the sunburn dose for light skin types was reached or exceeded for both of the investigated activities.

Sexually-manifested variations in pigmentation of Boeckella poppei (Copepoda, Calanoida) from Livingston Island (Maritime Antarctica)

Antarctic environments are exposed to high levels of ultraviolet radiation (UVR) that are often detrimental to their biota. Recent studies suggest that the genus Boeckella (Copepoda, Calanoida) has a high level of plasticity in terms of its reaction to UVR, which enables its wide distribution in various water bodies in Antarctica. Boeckella poppei is common in freshwater habitats of all three main biogeographic regions in Antarctica: sub-Antarctic islands, maritime and continental. We present for the first time a specific photoprotective response in populations of B. poppei from Livingston Island, Maritime Antarctica. In non-ovigerous females and in males, we observed uniform distribution of carotenoids in the body, while these pigments were almost entirely concentrated in the ovisacs of mature females. We consider this as a means of progeny protection from the teratogenic influence of the high level of UVR in Antarctic environments. Unequivocally, such adaptation would facilitate the expansion of B. poppei on the continent through colonisation and survival in shallow freshwater habitats. Given that the Antarctic environment is dynamically changing over the past decades and the accelerated retreat of permanent ice cover is a premise for the formation of shallow ponds, B. poppei could be a suitable indicator for reflecting the ongoing global environmental changes in Antarctica.

Computational simulation of surface tension and gravitation-induced convective flow of a nanoliquid with cross-diffusion: An optimization procedure

The control of heat transfer in the hydromagnetic semiconductor crystal involves Marangoni convection with buoyancy forces. In this study, the conventional thermo-solutal Marangoni mixed flow model is modified by incorporating the solutal buoyancy effects that are significant in the flow phenomenon. The heat and mass transfer (HMT) characteristics of the Marangoni convective flow of a Cu − H2O nanofluid subjected to the assisting/resisting buoyancy forces and cross-diffusion are numerically studied. The homogeneous single-phase nanoliquid model is used in conjunction with experimental data of dynamic viscosity and thermal conductivity. The Dufour and Soret effects are considered. Governing equations are solved using the finite difference-based algorithm. The problem is analyzed in a unified way considering the cases of buoyancy-assisted flow and buoyancy-opposed flow. The response surface methodology (RSM) based on the face-centered composite design (CCD) is used to optimize the heat and mass transfer rates. A multivariate regression model is proposed and authenticated prior to optimization. Additionally, sensitivity analysis is performed using the full quadratic regression model. The increase in the temperature profile is more significant due to the radiative heat flux than the inclined magnetic field. Heat transfer has a high sensitivity to the appearance of thermal radiation, while mass transfer has a high sensitivity to the Soret effect. Simultaneous optimization of HMT rates is achieved with the high level of thermal radiation and low levels of the cross-diffusion aspects.

Clinical and bronchoscopic aspects of bronchial healing after sleeve resection for lung cancer: a multivariate analysis on 541 cases.

BackgroundAnastomotic insufficiency is a feared complication after sleeve lobectomy. Bronchoscopy can help to identify anastomoses at risk. We evaluated negative predictors of anastomotic healing using a bronchoscopic grading system in a large collective of lung cancer patients.MethodsFrom 2006 to 2019, 541 sleeve lobectomies for lung cancer were performed. Anastomotic healing was documented by bronchoscopy on the seventh postoperative day using a standardized classification system for anastomotic grading (grade 1, perfect healing to 5, insufficiency). Grade 1 and 2 were considered satisfactory and the patients were discharged. Grade 3 or higher was considered critical. These patients received systemic antibiotic treatment and re-bronchoscopy was performed 4 days later.ResultsIn 18.5% of the patients, the anastomosis was assessed as critical. 19% of patients with critical anastomosis on the 7th postoperative day developed anastomotic insufficiency during the postoperative course, compared to 0.2% in patients with satisfactory anastomotic healing. Bilobectomies, low preoperative forced expiratory volume in 1 second (FEV1) values, high preoperative levels of C-reactive protein and neoadjuvant radiation were identified as independent risk factors for critical anastomotic healing.ConclusionsBronchoscopic assessment of anastomotic healing is an effective tool to identify critical anastomoses. Neoadjuvant radiation, bilobectomies and acute or chronic inflammation were independent risk factors for bronchial healing disorders and should be considered at the planning stage of surgery.

Theory, Design, and Characterization of Nanoelectromechanical Relays for Stiction-Based Non-Volatile Memory

Diverse areas such as the Internet of Things (IoT), aerospace and industrial electronics increasingly require non-volatile memory to work under high-temperature, radiation-hard conditions, with zero standby power. Nanoelectromechanical (NEM) relays uniquely have the potential to work at 300 °C and absorb high levels of radiation, with zero leakage current across the entire operational range. While NEM relays that utilise stiction for non-volatile operation have been demonstrated, it is not clear how to design a relay to reliably achieve given programming and reprogramming voltages, an essential requirement in producing a memory. Here, we develop an analytical, first-principle physics-based model of rotational NEM relays to provide detailed understanding of how the programming and reprogramming voltages vary based on the device dimensions and surface adhesion force. We then carry out an experimental parametric study of relays with a critical dimension of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx ~\mathrm {80~~\, \text {n} \text {m} }$ </tex-math></inline-formula> to characterise the surface adhesion force, and derive guidelines for how a NEM relay should be dimensioned for a given contact surface force, feature size constraints and operating requirements. We carry out a scaling study to show that voltages of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx ~\mathrm {1~~\, \text {V}}$ </tex-math></inline-formula> and a footprint under <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx ~\mathrm {2~~\, \mu \text {m} ^{2}}$ </tex-math></inline-formula> can be achieved with a critical dimension of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx ~\mathrm {10~~\, \text {n} \text {m} }$ </tex-math></inline-formula> , with this device architecture. [2021-0138]

Epoxy-POSS/silicone rubber nanocomposites with excellent thermal stability and radiation resistance

Due to the rigid Si-O-Si backbone, silicone rubber (SR) have a widespread application in extreme environment such as high temperature and high-level radiation. However, the radiation stability of SR still does not meet the practical needs in special radiation environments. Herein we prepared epoxy POSS(ePOSS)/SR nanocomposites with excellent thermal stability and radiation resistance. As a physical crosslinking point in the SR, addition of small amount of ePOSS not only enhanced the mechanical properties of the matrix, but also improved its thermal stability greatly due to their good compatibility. ePOSS/SR had higher radiation stability in air than SR owing to the inhibition of radiation oxidation by ePOSS, and the yield of main gaseous radiolysis products (CH4, H2, CO and CO2) of SR and ePOSS/SR nanocomposites was determined. By analyzing the changes of chemical structure, thermal properties and mechanical properties of the ePOSS/SR nanocomposite, combined with the characteristics of gas products after γ-irradiation, the radiation induced crosslinking and degradation mechanism of the nanocomposites was proposed comprehensively.

Role of meteorological factors on SARS-CoV-2 infection incidence in Italy and Spain before the vaccination campaign. A multi-city time series study

Numerous studies have been conducted worldwide to investigate if an association exists between meteorological factors and the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection incidence. Although research studies provide conflicting results, which can be partially explained by different methods used, some clear trends emerge on the role of weather conditions and SARS-CoV-2 infection, especially for temperature and humidity. This study sheds more light on the relationship between meteorological factors and SARS-CoV-2 infection incidence in 23 Italian and 52 Spanish cities. For the purposes of this study, daily air temperature, absolute and relative humidity, wind speed, ultraviolet radiation, and rainfall are considered exposure variables. We conducted a two-stage meta-regression. In the first stage, we estimated the exposure-response association through time series regression analysis at the municipal level. In the second stage, we pooled the association parameters using a meta-analytic model. The study demonstrates an association between meteorological factors and SARS-CoV-2 infection incidence. Specifically, low levels of ambient temperatures and absolute humidity were associated with an increased relative risk. On the other hand, low and high levels of relative humidity and ultraviolet radiation were associated with a decreased relative risk. Concerning wind speed and rainfall, higher values contributed to the reduction of the risk of infection. Overall, our results contribute to a better understanding of how the meteorological factors influence the spread of the SARS-CoV-2 and should be considered in a wider context of existing robust literature that highlight the importance of measures such as social distancing, improved hygiene, face masks and vaccination campaign.

An In-Depth Experimental Investigation of the Outdoor Performance of Wafer and Thin Film Photovoltaics Technologies in a Tropical Climate

Abstract The photovoltaics (PV) industry is booming at an impressive rate. Knowledge of the outdoor performance of different PV technologies under different climatic conditions is becoming increasingly important for all stakeholders. The aim of this research was to perform the outdoor characterization of three PV technologies in a tropical climate and evaluate their performances with the aid of a set of key performance indicators. An innovative energy autonomous outdoor test facility has been used to measure the weather conditions and the IV curves of mono-Si, poly-Si, and Copper Indium Gallium diSelenide (CIGS) PV modules. Each IV curve was sampled within less than a second, for every 10 min, between sunrise and sunset for a whole year, representing a data set of around 28,000 IV curves of 240 points each. The variations of current, voltage, and power were thoroughly studied for changes in temperature and irradiance. This paper reports the variations of temperature coefficients of current, voltage, and power with the intensity of light. While PV module documentation only presents the temperature coefficients of the short circuit current and open circuit voltage at standard test conditions, this paper additionally provides highly valuable information to PV system designers on the variation of these coefficients in the field. The research is also the first to report the variations of the fill factor with temperature and irradiance. In general, the wafer technologies were found to have a better performance than the thin film technology. Moreover, the open-circuit temperature coefficient was found to improve for higher irradiances only for the wafer technologies, while that for the thin-film technology experienced a degradation. The temperature coefficient of current for the mono-Si module was found to be positive at low irradiance levels, but negative at higher irradiance levels.

Technical effectiveness of cement-based mortar for high-reflective building envelope through building energy simulations: preliminary results

In areas with high levels of solar radiation, decreasing the amount of solar energy absorbed by the building envelope is useful to reduce the need of air conditioning and "heat island" effects. Most high-reflective products, however, suffer from low durability. The COOL-IT project is developing an innovative high-reflective cement based mortar for precast products to be used as outer layer in buildings for both vertical and horizontal surfaces, or for road pavement. The mix design is aimed at increasing the durability of this cement-based component while retaining high reflectance to solar radiation. This paper presents the preliminary results of the project, based on the simulation of the energy demand of a residential building, intended as a support to optimize the proposed mixes. The model is analysed in three different locations in Italy, for one year of operation. This allows evaluating the trade-off of the energy demand between the winter increase and the summer reduction.

The radiation tolerance of a low voltage LDO developed for the CMS HGCAL on-detector electronics system

The CMS detector will undergo the replacement of its current endcap calorimeter by a new high granularity calorimeter (HGCAL). The new HGCAL will need to withstand much higher radiation levels than the present endcaps. This poses tight requirements on the front-end electronics, including the powering chain. As part of this chain, a low-dropout linear regulator (LDO) has been designed and prototyped for post-regulation for HGCAL, providing extremely low noise and stable power to the analog front-end. We present results from tests of the LDO, including from a detailed irradiation campaign.

Influence of X-Ray Radiation on Historical Paper

Historical books are often so fragile that they cannot easily be opened in order to read the contents without damaging them. Current research shows, that industrial X-ray computed tomography (CT) can be used to examine closed historical manuscripts. However, the effect of X-rays on ancient paper has rarely been studied, making it difficult to assess the impact of CT measurements on fragile historical manuscripts in terms of additional destruction. To address this problem, various types of paper were exposed to high levels of X-ray radiation in order to examine them for change in optical properties. The investigations showed increasing yellowing due to the increased radiation energy. However, the severity of the yellowing is strongly dependent on the composition of the paper.

TDZ induces a dual morphogenetic pathway on leaf explants of the beach huckleberry – Gaylussacia brasiliensis

Gaylussacia brasiliensis is a bush from the Ericaceae family native to South America. It is considered an underutilized fruit species, despite its importance as a food source, medicinal plant, and forage for the native fauna. In the Florianópolis island, south of Brazil, it occurs in sand deposits between the Atlantic Ocean and the mountain chains of the Atlantic Rain Forest, in a vegetation type called “Restinga”, a harsh environment where plants are exposed to stressful conditions. Constand winds, high solar radiation, saltwater sprays, and low nutrient levels are common in the Restinga environment, making G. brasiliensis an important genetic resource to face the expected effects of climate change. Despite its importance, there are no sexual or asexual protocols available for its propagation. This is the first record of a micropropagation protocol for a plant of the Gaylussacia genus. We report a reliable protocol for in vitro establishment of G. brasiliensis cultures from seeds, and an efficient micropropagation protocol using leaf explants. A dual regeneration pathway, i.e., somatic embryos and adventitious shoots, can be obtained directly from leaf explants without an intermediating callus tissue. A low concentration of TDZ can be used to achieve this goal, and a high number of plants can be obtained rapidly, allowing advances in the research of this underutilized plant species and enabling its propagation for commercial or conservation purposes.

Radiation Doses in Patients Undergoing Computed Tomographic Coronary Artery Calcium Evaluation With a 64-Slice Scanner Versus a 256-Slice Scanner.

Computed tomographic coronary artery calcium scanning enables cardiovascular risk stratification; however, exposing patients to high radiation levels is an ongoing concern. New-generation computed tomographic systems use lower radiation doses than older systems do. To quantify comparative doses of radiation exposure, we prospectively acquired images from 220 patients with use of a 64-slice GE LightSpeed VCT scanner (control group, n=110) and a 256-slice GE Revolution scanner (study group, n=110). The groups were matched for age, sex, and body mass index; statistical analysis included t tests and linear regression. The mean dose-length product was 21% lower in the study group than in the control group (60.2 ± 27 vs 75.9 ± 22.6 mGy·cm; P <0.001) and also in each body mass index subgroup. Similarly, the mean effective radiation dose was 21% lower in the study group (0.84 ± 0.38 vs 1.06 ± 0.32 mSv) and lower in each weight subgroup. After adjustment for sex, women in the study group had a lower dose-length product (50.4 ± 23.4 vs 64.7 ± 27.6 mGy·cm) than men did and received a lower effective dose (0.7 ± 0.32 vs 0.9 ± 0.38 mSv) (P=0.009). As body mass index and waist circumference increased, so did doses for both scanners. Our study group was exposed to radiation doses lower than the previously determined standard of 1 mSv, even after adjustment for body mass index and waist circumference. In 256-slice scanning for coronary artery calcium, radiation doses are now similar to those in lung cancer screening and mammography.

Development of a CsI(Tl) scintillator based gamma probe for the identification of nuclear materials in unknown areas

In case of nuclear accident or an act of terrorism, such as planting a dirty bomb, the nuclear and radioactive materials could be spread over a large area. The environmental radioactivity information has to be obtained rather fast in order to secure the safety of any activity in these potentially high-level radiation contaminated areas. In addition, a lack of both social infrastructure and environmental radiation information may be expected in this area. Therefore, the sampling process must be carried out in a timely and efficient manner. In this study, a probe operated via a distribution method was developed to improve the efficiency of the sampling process by identifying the location and nuclides of leaked materials. For distribution type operation, CsI(Tl) and SiPM were applied to the sensor part of the probe to operate at low voltage operation and for durability. In addition, the power consumption of the data acquisition module and the weight of the probe were optimized for distribution through drones, battery operation, and wireless communication. The energy resolution of this probe was 10.84% at 662 keV and it showed adequate characteristics in the spectrum of nuclear materials. In addition, the practical operability of this probe was verified through determination of the minimum detectable dose rate condition and the difference in the measured values based on the landing orientation.

Radiological, geochemical, and environmental assessment in Xuancheng, China: The airborne gamma-ray spectrometric view

Radionuclides in the environment have been considered a health risk for many years owing to their contribution to the radiation dose to the human body. A great deal of field survey research has been conducted in this area. However, few researchers have studied the key sources of geological and geochemical substances that pose radioactive environmental problems from the perspective of airborne gamma-ray spectrometry. This study aims to determine the radiation variations in geological units caused by rocks containing radionuclides, evaluate the level of radiation, and analyze as well as identify the key radio-elements. The content of 40K, 238U, 232Th, and the total count (TC) in 15 different geological units were studied based on the concentration data. The gamma absorbed dose rate (D) of the whole region was calculated to identify and evaluate the main areas of high radiation. The quantitative statistical methods, the Pearson correlation analysis, principal component analysis (PCA), hierarchical cluster analysis (HCA), and geochemical mapping were used to analyze the selected high radiation areas and reveal potential key lithological factors. The results indicate that the Cretaceous intrusive rock, in the northeast of the study area, is a major source of natural radionuclides and continuous radiation. The high radiation in this area is strongly associated with the Yaocun rock mass containing K-feldspar granite, and the correlation coefficient of the 232Th with effective dose was the highest (0.91), whereas that of 238U was the lowest (0.49). The study has determined that 232Th is the key radio-element, causing high radiation by comparing the results of HCA of field gamma-ray measurement data. The findings from this study are valuable for determining the key factors causing high radiation levels in similar exposure conditions.

Differential expression profiling of heat stressed tardigrades reveals major shift in the transcriptome

Tardigrades are renowned for their extreme stress tolerance, which includes the ability to endure complete desiccation, high levels of radiation and very low sub-zero temperatures. Nevertheless, tardigrades appear to be vulnerable to high temperatures and thus the potential effects of global warming. Here, we provide the first analysis of transcriptome data obtained from heat stressed specimens of the eutardigrade Ramazzottius varieornatus, with the aim of providing new insights into the molecular processes affected by high temperatures. Specifically, we compare RNA-seq datasets obtained from active, heat-exposed (35 °C) tardigrades to that of active controls kept at 5 °C. Our data reveal a surprising shift in transcription, involving 9634 differentially expressed transcripts, corresponding to >35% of the transcriptome. The latter data are in striking contrast to the hitherto observed constitutive expression underlying tardigrade extreme stress tolerance and entrance into the latent state of life, known as cryptobiosis. Thus, when examining the molecular response, heat-stress appears to be more stressful for R. varieornatus than extreme conditions, such as desiccation or freezing. A gene ontology analysis reveals that the heat stress response involves a change in transcription and presumably translation, including an adjustment of metabolism, and, putatively, preparation for encystment and subsequent diapause. Among the differentially expressed transcripts we find heat-shock proteins as well as the eutardigrade specific proteins (CAHS, SAHS, MAHS, RvLEAM, and Dsup). The latter proteins thus seem to contribute to a general stress response, and may not be directly related to cryptobiosis.

Confinement improvement during detached phase with RMP application in deuterium plasmas of LHD

In order to explore the compatibility of good core plasma performance with divertor heat load mitigation, the interaction between cold edge plasma and core plasma transport, including the edge transport barrier (ETB), has been analysed in the divertor detachment discharges of deuterium plasmas in LHD with resonant magnetic perturbation (RMP) field application. The RMP application introduces a widened edge stochastic layer and sharp boundary in the magnetic field structure between the confinement region and the edge stochastic layer. The widened edge stochastic layer enhances impurity radiation and provides stable detachment operation as compared with the case without RMP. It is found that ETB is formed at the confinement boundary at the onset of detachment transition. However, as the detachment deepens, the resistive pressure gradient-driven MHD mode is excited, which degrades the ETB. At the same time, however, the core transport decreases to keep global plasma stored energy (W p) unchanged, showing clear core-edge coupling. After a gradual increase of density fluctuation during the MHD activity, a spontaneous increase of W p and the recovery of ETB are observed while the detachment is maintained. Then, the coherent MHD mode ceases and ELM-like bursts appear. In the improved mode, impurity decontamination occurs, and the divertor heat load increases slightly. Key controlling physical processes in the interplay between core and cold edge plasma are discussed. A comparison between deuterium and hydrogen plasmas shows that hydrogen plasmas exhibit similar features to the deuterium ones in terms of density and magnetic fluctuations, impurity decontamination towards higher confinement, etc. But most of the features are modest in the hydrogen plasmas and thus no clear confinement mode transition with clear ETB formation is defined. Better global confinement is obtained in the deuterium plasmas than the hydrogen ones at a higher radiation level.

Modelling of indoor external and internal exposure due to different building materials containing NORMs in the vicinity of a HNBRA in Mahallat, Iran

In this study, by considering the Naturally Occurring Radioactive Materials (NORMs) contained in the building materials used in Mahallat, Iran - an area exposed to a high level of natural background radiation - residential scenarios were simulated by applying the computer code RESRAD-BUILD to estimate the long-term Effective Dose rate of three different cases of basic building materials utilized in walls, floors and ceilings. Maximum effective dose rates of between 504 and 1433 μSv yr−1 were calculated in the second case study, tiled cement floor. The highest external and radon doses were also calculated to be 369 and 1064 μSv, respectively. The simulation results revealed that 232Th and 40K contribute the most and least to the indoor dose, respectively. As a result of a sensitivity analysis, it was found that the air exchange rate is a key variable to easily reduce the radiological impacts of building materials. It was also shown that due to the presence of 226Ra, the sensitivity of effective dose to changes in wall thickness was higher than other radionuclides found in the building materials.

The effects of temperature and light on ecosystem metabolism in a Japanese stream

Ecosystem metabolism is a fundamental process that governs biogeochemical C cycling through the fixation and mineralization of C by all the organisms in a system; however, the functional responses of ecosystem metabolism to light and temperature variability remain unknown in streams and rivers. In this study, we assessed the effects of temperature and light on ecosystem metabolism, namely gross primary production (GPP) and ecosystem respiration (ER), in a Japanese stream by monitoring the seasonal diel changes in dissolved oxygen. We found that the temperature dependence of metabolism, which is expressed as activation energy, was higher for ER (0.48 eV) than for GPP (0.39 eV), supporting the metabolic theory of ecology. Both daily GPP and ER increased with the daily integrated photosynthetically active radiation (PAR), peaking at moderate PAR values and decreasing at higher irradiance levels. This unimodal relationship between daily GPP and PAR was due to the rapid increase of instantaneous PAR during the early morning, suppressing the maximum rate of area-specific productivity, which was a main determinant of daily GPP. Moreover, daily GPP and ER were closely associated in this study stream, resulting in a unimodal pattern of daily ER with daily integrated PAR. Our results suggest that both temperature and light regulate stream ecosystem metabolism but that the sunlight regime (i.e., the rapid increase of solar irradiance in the early morning) rather than light intensity per se may be a critical factor for both GPP and ER in the study stream.