Surface Photosynthetically Active Radiation Research Articles

The role of heterotrophic plasticity in coral response to natural low-light environments.

Coastal darkening is emerging as a global threat to fringing reefs. While some reef-building corals exhibit resistance to low-light environments, the mechanisms behind this resistance, particularly the role of coral hosts, remain inadequately understood. Here, we investigated variations in underwater photosynthetically active radiation (PAR) and employed the Bayesian stable isotope mixing model (MixSIAR) to estimate the contributions of autotrophic (i.e., dissolved inorganic matter, DIM) and heterotrophic sources (i.e., particulate organic matter, POM, and dissolved organic matter, DOM) to the nutrition of the reef coral Galaxea fascicularis on the Luhuitou turbid reef in the northern South China Sea. Our findings revealed that the heterotrophic contribution to coral nutrition increased to 58.5% with decreasing PAR and that the heterotrophic contribution was significantly negatively correlated with δ13C difference between host and symbiont (δ13Ch-s). Moreover, we observed significant seasonal variations in the respective contributions of POM and DOM to coral nutrition, linked to the sources of these nutrients, demonstrating that G. fascicularis can selectively ingest POM and DOM based on their bioavailability to enhance its heterotrophic contribution. This heterotrophic plasticity improved the low-light resistance of G. fascicularis and contributed to its prominence within coral communities. However, with a low-light threshold of approximately 3.73% of the surface PAR for G. fascicularis, our results underscore the need for effective strategies to mitigate low-light conditions on nearshore turbid reefs. In summary, our study highlights the critical role of heterotrophic plasticity in coral responses to natural low-light environments, suggesting that some reef-building corals with such plasticity could become dominant or resilient species in the context of coastal darkening.

Testing the influence of light on nitrite cycling in the eastern tropical North Pacific

Abstract. Light is considered a strong controlling factor of nitrification rates in the surface ocean. Previous work has shown that ammonia oxidation and nitrite oxidation may be inhibited by high light levels, yet active nitrification has been measured in the sunlit surface ocean. While it is known that photosynthetically active radiation (PAR) influences microbial nitrite production and consumption, the level of inhibition of nitrification is variable across datasets. Additionally, phytoplankton have light-dependent mechanisms for nitrite production and consumption that co-occur with nitrification around the depths of the primary nitrite maximum (PNM). In this work, we experimentally determined the direct influence of light level on net nitrite production, including all major nitrite cycling processes (ammonia oxidation, nitrite oxidation, nitrate reduction and nitrite uptake) in microbial communities collected from the base of the euphotic zone. We found that although ammonia oxidation was inhibited at the depth of the PNM and was further inhibited by increasing light at all stations, it remained the dominant nitrite production process at most stations and treatments, even up to 25 % surface PAR. Nitrate addition did not enhance ammonia oxidation in our experiments but may have increased nitrate and nitrite uptake at a coastal station. In contrast to ammonia oxidation, nitrite oxidation was not clearly inhibited by light and sometimes even increased at higher light levels. Thus, accumulation of nitrite at the PNM may be modulated by changes in light, but light perturbations did not exclude nitrification from the surface ocean. Nitrite uptake and nitrate reduction were both enhanced in high-light treatments relative to low light and in some cases showed high rates in the dark. Overall, net nitrite production rates of PNM communities were highest in the dark treatments.

All-sky surface and top-of-atmosphere shortwave radiation components estimation: Surface shortwave radiation, PAR, UV radiation, and TOA albedo

Surface and top-of-atmosphere (TOA) shortwave radiation components are key parameters in the energy budget of the Earth-atmosphere system, which influence the global climate, ecology, hydrology, etc. However, except for total surface shortwave downward radiation (SWDR), only a few satellite missions consistently release other radiation components such as solar direct/diffuse radiation, photosynthetically active radiation (PAR), ultraviolet radiation-A/B (UVA/UVB), as well as TOA albedo, although they are indispensable for many land and ocean applications. In this study, a unified framework by combining multi-band LUT inversion and classification of the atmospheric condition is proposed, which enables the simultaneous derivation of nine surface and TOA radiation variables and emphasizes the separation of direct and diffuse components. The estimated radiation variables include total and direct components of SWDR, PAR, UVA, UVB, as well as TOA albedo. The proposed method is easy-to-use with only a few inputs and works well with reasonable accuracy. Using Moderate Resolution Imaging Spectroradiometer (MODIS) raw resolution images as test data, the surface radiation variables are validated by 80 global sites from BSRN, SURFRAD, and FLUXNET, and the instantaneous RMSEs (biases) of SWDR, SWDRdir, PAR, PARdiff, and UVB are 103.6 (0.1), 114 (−1.7), 47.8 (6.8), 32.9 (5.7), and 0.14 (0.003) W/m2, respectively, demonstrating comparable or even better accuracy compared with existing products. In particular, the estimated SWDR behaves more accurate than CERES in polar regions. Due to the lack of in-situ measurements, TOA albedo is compared with CERES TOA products and shows good agreement with R2 of 0.9 and RMSE (bias) of 0.055 (−0.003). The unified framework reveals obvious advantages over existing studies in generating almost all physically consistent shortwave components in the same manner with simple inputs, implying the great potentials in globally mapping spatio-temporally continuous multiple components of shortwave radiation with a unified scheme.

Smart Approaches for Evaluating Photosynthetically Active Radiation at Various Stations Based on MSG Prime Satellite Imagery

Photosynthetically active radiation (PAR) is the 400–700 nm portion of the solar radiation spectrum that photoautotrophic organisms including plants, algae, and cyanobacteria use for photosynthesis. PAR is a key variable in global ecosystem and Earth system modeling, playing a prominent role in carbon and water cycling. Alongside air temperature, water availability, and atmospheric CO2 concentration, PAR controls photosynthesis and consequently biomass productivity in general. The management of agricultural and horticultural crops, forests, grasslands, and even grasses at sports venues is a non-exhaustive list of applications for which an accurate knowledge of the PAR resource is desirable. Modern agrivoltaic systems also require a good knowledge of PAR in conjunction with the variables needed to monitor the co-located photovoltaic system. In situ quality-controlled PAR sensors provide high-quality information for specific locations. However, due to associated installation and maintenance costs, such high-quality data are relatively scarce and generally extend over a restricted and sometimes non-continuous period. Numerous studies have already demonstrated the potential offered by surface radiation estimates based on satellite information as reliable alternatives to in situ measurements. The accuracy of these estimations is site-dependent and is related, for example, to the local climate, landscape, and viewing angle of the satellite. To assess the accuracy of PAR satellite models, we inter-compared 11 methods for estimating 30 min surface PAR based on satellite-derived estimations at 33 ground-based station locations over several climate regions in Europe, Africa, and South America. Averaged across stations, the results showed average relative biases (relative to the measurement mean) across methods of 1 to 20%, an average relative standard deviation of 25 to 30%, an average relative root mean square error of 25% to 35% and a correlation coefficient always above 0.95 for all methods. Improved performance was seen for all methods at relatively cloud-free sites, and quality degraded towards the edge of the Meteosat Second Generation viewing area. A good compromise between computational time, memory allocation, and performance was achieved for most locations using the Jacovides coefficient applied to the global horizontal irradiance from HelioClim-3 or the CAMS Radiation Service. In conclusion, satellite estimations can provide a reliable alternative estimation of ground-based PAR for most applications.

Clumped isotopes in globally distributed Holocene coccoliths reveal their habitat depth

Reliable temperature reconstructions are necessary to improve climate reconstructions and comparisons with paleoclimate model simulations. Most existing paleotemperature proxies are based on organic and inorganic remains of marine organisms. Despite the evidence that the habitat depth of coccolithophores and other phytoplankton depend on their ability to balance light, nutrients, and grazing pressure, calibrations of proxies based on photosynthesizers often assume they live in the surface ocean. Here we present the first globally distributed dataset of core top multi-species coccolith clumped isotopes (Δ47), which show a clear latitudinal thermal gradient and demonstrate coccolith Δ47 sensitivity to temperature. The application of the most recent Δ47-temperature calibration for marine biogenic carbonates yields calcification temperatures implying deep habitats of ∼50 to ∼150 m for tropical coccolithophores, which could photosynthesize with 1-10% of surface photosynthetic active radiation (PAR) levels. Because of the uncertainties of Δ47 thermometry and of the low upper ocean temperature gradient, at well-mixed high-latitude locations, coccolith Δ47 cannot be used to reliably constrain a specific habitat depth. Nevertheless, Δ47 is a good indicator of paleotemperatures of the mixed layer. We also use coccolith Δ47 to derive the first regression relating core top coccolith Δ47 and sea surface temperatures (SST). Although this formulation cannot be considered a proper coccolith-specific Δ47 calibration, since it ignores coccolithophore's potential for calcification at depth, it facilitates comparison with temperature proxies like U37k′, which are regressed to SST, rather than production temperature.

Geographical Distribution Variations of Humboldt Squid Habitat in the Eastern Pacific Ocean

The Humboldt squid Dosidicus gigas is a pelagic cephalopod species extensively distributed in the Eastern Pacific Ocean. Geographically separated habitat patterns of D. gigas show large spatiotemporal variations due to the distinct different regional environmental conditions. This study explored geographical variation in seasonal habitat of D. gigas off Peru and the Eastern Pacific Equator using maximum entropy (Maxent) model, with fishing occurrence data and environmental variables including sea surface temperature (SST), sea surface salinity, net primary production (NPP), photosynthetically active radiation (PAR), chlorophyll a concentration, eddy kinetic energy, and sea level anomaly. Results indicated that all the environmental variables exhibited conspicuous seasonal and geographical differences off Peru and the Eastern Pacific Equator. On the basis of the percent contribution from the Maxent model, seasonal and spatial extents of habitat were largely explained by SST, NPP, PAR, and eddy kinetic energy in the Eastern Pacific Equator and SST, sea surface salinity, NPP, and PAR off Peru. Suitable ranges of each environmental variable differed between regions and were controlled by the seasonal variability. Furthermore, movement patterns of longitudinal and latitudinal gravity centers of fishing effort of D. gigas were consistent with spatial and temporal distribution of suitable habitats but showed dramatically geographical variations off Peru and the Eastern Pacific Equator. Our findings highlighted Maxent mode’s ability in exploring Humboldt squid habitat hotspots in the Eastern Pacific Ocean and suggested that constructing the habitat model for D. gigas should consider the geographical differences under environmental conditions.

Estimation of the vertical phytoplankton distribution in the Philippine Sea: Influence of turbulence following passage of typhoons

The subsurface chlorophyll-a maximum (SCM) is a phenomenon that contributes significantly to the total primary production of the open ocean but it is not observable from remote sensing, thus primary production based on satellite information is highly underestimated. In a highly dynamic region such as the Philippine Sea, turbulence caused by tropical storms may exert significant impact on the SCM feature. In this study, we attempt to estimate the vertical phytoplankton profile in the Philippine Sea from remote sensing images by applying a generic quantitative approach. Generalized Additive Models (GAM) followed by Generalized Linear Models (GLMs) were used create predictive equations between response variables (Chl-a profile parameters) and predictor variables (RS parameters). GAM was able to predict integrated Chl-a biomass using photosynthetic active radiation (PAR), wind speed and wind stress, the depth of the Chl-a peak using surface Chl-a, wind speed and wind stress, and the baseline Chl-a concentration using sea surface temperature, sea surface salinity and PAR. GLM found wind stress and wind speed as significant predictors for integrated Chl-a biomass, while surface Chl-a, wind speed and wind stress were significant predictors for depth of the Chl-a peak. When the predictive equations were applied to 2020 monthly satellite images, they were seen to adequately estimate the offshore spatial distribution of the two Chl-a parameters. Increased turbulence due to high wind speed and wind stress during passage of tropical storms was seen to result in shallowing of the SCM and subsequent increase in Chl-a within the water column. These equations could be refined if long-term observational data was available. The capacity to estimate vertical distribution of primary productivity in the Philippines provides a means to better understand fisheries productivity and biogeochemical cycling in the region.

Picophytoplankton Niche Partitioning in the Warmest Oligotrophic Sea

Pico-sizedSynechococcus,Prochlorococcus, and eukaryotes are the dominant photosynthetic organisms in the vast warm and oligotrophic regions of the ocean. In this paper, we aim to characterize the realized niches of the picophytoplanktonic community inhabiting the Red Sea, the warmest oligotrophic sea, which is considered to be a model for the future ocean. We quantify population abundances and environmental variables over several oceanographic surveys, and use stepwise regression, principal-component analysis (PCA), and compositional-data analysis to identify the realized niches of the three picophytoplanktonic groups. Water temperature varied from 21.4 to 32.4°C within the upper 200-m water column, with the warmest waters being found in the South, where nutrients increased.Synechococcusdominated the biomass, contributing 47.6% to the total picophytoplankton biomass, followed by picoeukaryotes (26.4%) andProchlorococcus(25.9%), whose proportions contrast significantly with those reported in the subtropical ocean, whereProchlorococcusprevails. There were positive and significant relationships between temperature and the three populations, although these were weak forProchlorococcus(R2= 0.08) and stronger and steeper forSynechococcus(R2= 0.57). The three populations centered their maximum abundances (Lorentzian fits) at similar low nutrient values.Synechococcuswere centered close to the surface at ≈77% of surface photosynthetically active radiation (PAR) and ≈30.6°C. The picoeukaryotes were centered at lower light (≈6.4% surface PAR) and warm waters (≈30°C).Prochlorococcuswas segregated from the surface waters and centered deep at low light (≈3.2% surface PAR). Light and temperature were the most influential factors determining the community composition, withSynechococcusdominating ∼74% of the picophytoplankton biovolume in the warmest (>30°C) waters. In the warm and mesotrophic southern Red Sea, the moderate abundances of picoeukaryotes andSynechococcussuggest increasing competition with nano and microphytoplankton. Our observations agree with predictions of increasing vertical segregation of picophytoplankton communities with future warming and revealSynechococcus’s significant capacity to adapt to warming.

An Optimization Approach for Estimating Multiple Land Surface and Atmospheric Variables From the Geostationary Advanced Himawari Imager Top-of-Atmosphere Observations

Since a new generation of geostationary satellite data has incredibly high temporal, spatial, and spectral resolutions, new methodologies are now needed to take advantage of both the temporal and spectral signatures of them for accurate estimation of Earth's environmental variables. This article describes a novel optimization method to estimate a suite of 11 physically consistent land surface and atmospheric variables under all-sky conditions from the geostationary advanced Himawari imager (AHI) top-of-atmosphere (TOA) observations. This method is based on a coupled soil, snow, vegetation, and atmospheric radiative transfer (RT) model from 0.28 to 14 μm. The inversion algorithm consists of three major steps. First, the “clearest” observations at each moment during a temporal window were determined and then the essential variables that characterize surface RT models, such as leaf area index (LAI), leaf chlorophyll concentration, and soil parameters were estimated. Second, the atmospheric variables, including aerosol optical depth (AOD) under clear-sky conditions, and cloud optical thickness (COT) and cloud effective particle radius (CER) under cloudy-sky conditions, were inverted given surface reflectance calculated by the surface RT models. Finally, the inverted atmospheric and land surface variables were fed into the coupled RT model to calculate the remaining set of variables, including spectral directional reflectance, surface broadband albedo, thermal emissivity, incident shortwave radiation (ISR), photosynthetically active radiation (PAR), fraction of absorbed PAR by green vegetation (FAPAR), and TOA shortwave albedo. The retrieved variables were validated using in-situ measurements from Ozflux network sites and compared with the other existing satellite products. Intercomparisons demonstrate that the AHI-retrieved atmospheric variables (AOD, CER, and COT) and surface variables (surface reflectance, LAI, FAPAR, PAR, and surface emissivity) are well correlated with the corresponding JAXA released AHI, NASA Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES), and the Global LAnd Surface Satellite (GLASS) products. Direct validation using in-situ measurements indicates that the retrieved ISR achieves higher accuracy than the CERES ISR product (with R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> values of 0.95 and 0.89, and root-mean-square error (RMSE) of 20.3 and 29.6 W/ m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the AHI-retrieved and CERES daily ISR, respectively). Validation also shows that the estimated daily surface albedo has an accuracy comparable to the MODIS daily albedo product (RMSE = 0.03). Both the direct validation and product comparisons have demonstrated that this proposed inversion framework works very well for the AHI data. Unlike other algorithms that are usually used for estimating an individual parameter and rely heavily on a separate atmospheric correction, this inversion framework can effectively estimate a group of atmospheric and land surface variables and be easily applied to other similar multispectral geostationary satellite data. A comprehensive sensitivity and validation study is still needed to quantify the uncertainties of the retrieval variables.

Light environment drives the shallow‐to‐mesophotic coral community transition

AbstractLight quality is a crucial physical factor driving coral distribution along depth gradients. Currently, a 30 m depth limit, based on SCUBA regulations, separates shallow and deep mesophotic coral ecosystems (MCEs). This definition, however, fails to explicitly accommodate environmental variation. Here, we posit a novel definition for a regional or reef‐to‐reef outlook of MCEs based on the light vs. coral community–structure relationship. A combination of physical and ecological methods enabled us to clarify the ambiguity in relation to the mesophotic definition. To characterize coral community structure with respect to the light environment, we conducted wide‐scale spatial studies at five sites along shallow and MCEs of the Gulf of Eilat/Aqaba (0–100 m depth). Surveys were conducted by technical‐diving and drop‐cameras, in addition to one year of light spectral measurements. We quantify two distinct coral assemblages: shallow (&lt;40 m) and MCEs (40–100 m), exhibiting markedly different relationships with light. The depth ranges and morphology of 47 coral genera were better explained by light than depth, mainly, due to photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) (1% at 76 and 36 m, respectively). Branching coral species were found mainly at shallower depths, that is, down to 36 m. Among the abundant upper‐mesophotic specialist corals, Leptoseris glabra, Euphyllia paradivisa, and Alveopora spp. were found strictly between 40 and 80 m depth. The only lower‐mesophotic specialist, Leptoseris fragilis, was found deeper than 80 m. We suggest that shallow coral genera are light‐limited below a level of 1.25% surface PAR and that the optimal PAR for mesophotic communities is at 7.5%. This study contributes to moving MCE ecology from a descriptive phase into identifying key ecological and physiological processes structuring MCE coral communities. Moreover, it may serve as a model enabling the description of a coral zonation worldwide on the basis of light quality data.

Scotch broom (Cytisus scoparius) modifies microenvironment to promote nonnative plant communities

Scotch broom [Cytisus scoparius (L.) Link] is a globally important nitrogen (N)-fixing invasive plant species that has potential to alter soil water dynamics, soil chemistry, and plant communities. We evaluated the effects of Scotch broom on soil moisture, soil chemistry, soil temperature, photosynthetically active radiation (PAR), and vegetation communities over 4 years at a site recently harvested for timber. Treatments of Scotch broom (either present via planting or absent) and background vegetation (either present or absent via herbicide treatments) were applied to 4 m2 plots. Background vegetation was associated with the greatest decrease of soil water content (SWC) among treatments. During the driest year, Scotch broom showed some evidence of increased early-and late-season soil water usage, and, briefly, a high usage relative to background vegetation plots. On a percent cover basis, Scotch broom had a substantially greater negative influence on SWC than did background vegetation. Surprisingly, Scotch broom was not consistently associated with increases in total soil N, but there was evidence of increasing soil water N when Scotch broom was present. Scotch broom-only plots had greater concentrations of soil water magnesium (Mg2+) and calcium (Ca2+) than other treatments. On a percent cover basis, Scotch broom had a uniquely high demand for potassium (K+) relative to the background vegetation. Average soil temperature was slightly greater, and soil surface PAR lower, with Scotch broom present. Scotch broom-absent plots increased in species diversity and richness over time, while Scotch broom-present plots remained unchanged. Scotch broom presence was associated with an increase in cover of nonnative sweet vernalgrass (Anthoxanthum odoratum L.). Scotch broom generated positive feedbacks with resource conditions that favored its dominance and the establishment of nonnative grass.

Long-term variation in light intensity on a coral reef

An important goal of coral reef science is to understand the roles played by environmental conditions in determining benthic community structure. Pursuit of this goal typically involves testing for associations between community structure and environmental conditions, and in recent years, attention has focused on temperature and seawater pH. Such analyses are helpful in projecting coral reef community structure into the future, but their efficacy depends on the extent to which changes in community structure are correctly associated with causative processes, and whether future conditions are a subset of those experienced in the past. Here, we describe variation from 2014 to 2017 in one environmental factor, photosynthetically active radiation (PAR), at 19-m depth on the reefs of St. John, US Virgin Islands, and evaluate the extent to which this factor could cause changes in benthic community structure. The transmission of downwelling surface PAR to 19-m depth (TPAR-19) varied from 2.0 to 40.0% among days, and from 4.8 to 15.8% among months within a year, and was lower and more variable in the autumn versus other seasons. Monthly TPAR-19 was inversely associated with monthly rainfall, suggesting that runoff affected seawater clarity. The monthly diffuse attenuation coefficient (Kd-PAR) varied 1.7-fold from 0.097 to 0.164 m−1 and was within the range expected for coral reefs. Given the high temporal variation in underwater light intensity, and its importance to foundational reef taxa, understanding of the response of coral reefs to temperature and pH (and other factors) will remain incomplete without closer attention to this physical environmental condition.

An efficient algorithm for calculating photosynthetically active radiation with MODIS products

Photosynthetically active radiation (PAR) is the critical forcing data in ecological and agricultural fields. Remote sensing can be utilized to derive spatiotemporally continuous PAR. Empirical algorithms can be used to quickly retrieve surface PAR data sets, but their accuracy cannot be guaranteed in regions without local calibration. Physical algorithms generally incorporate all relevant physical processes and can be used globally, but their computational efficiency is often low. In this paper, an efficient algorithm is developed to calculate surface PAR by combining a clear-sky PAR model and the parameterizations for cloud transmittances. In the algorithm, the transmittances for water vapor, ozone, Rayleigh, aerosol, and cloud are each handled across the whole PAR band (400–700nm). In addition, the contribution of the multiple reflections between surface ground and the atmosphere are also expressly considered. The new algorithm is applied to estimate instantaneous PAR with inputs from Moderate Resolution Imaging Spectroradiometer (MODIS) products onboard both Terra and Aqua platforms. The daily PAR is estimated from these two instantaneous values by an upscaling method. The instantaneous and daily PAR estimates were validated with in situ data collected in the USA and China. The results indicate that the new algorithm, based on MODIS products, can effectively retrieve PAR with root mean square errors (RMSE) of about 40Wm−2 and 15Wm−2 at instantaneous and daily-mean time scales, respectively. These performances are generally better than those of previous studies.

Influence of iron precipitated condition and light intensity on microalgae activated sludge based wastewater remediation

The indigenous microalgae-activated sludge (MAAS) process during remediation of municipal wastewater was investigated by studying the influence of iron flocculation step and light intensity. In addition, availability of total phosphorous (P) and photosynthetic activity was examined in fed-batch and batch mode under northern climatic conditions and limited lighting. This was followed by a semi-continuous operation with 4 d of hydraulic retention time and mean cell residence time of 6.75 d in a photo-bioreactor (PBR) with varying P availability. The fed-batch condition showed that P concentrations of 3–4 mg L−1 were effective for photosynthetic chl. a development in iron flocculated conditions. In the PBR, the oxygen evolution rate increased with increase in the concentration of MAAS (from 258 to 573 mg TSS L−1) at higher surface photosynthetic active radiation (250 and 500 μmol m−2 s−1). Additionally, the rate approached a saturation phase at low MAAS (110 mg L−1) with higher light intensities. Semi-continuous operation with luxury P uptake and effective P condition showed stable average total nitrogen removal of 88 and 92% respectively, with residual concentrations of 3.77 and 2.21 mg L−1. The corresponding average P removal was 68 and 59% with residual concentrations of 2.32 and 1.75 mg L−1. The semi-continuous operation produced a rapidly settleable MAAS under iron flocculated condition with a settling velocity of 92–106 m h−1 and sludge volume index of 31–43 ml g−1 in the studied cases.

Seasonal occurrence and species specificity of fishy and musty odor in Huajiang Reservoir in winter, China

This paper describes the results of measurements from one year period on the existence of fishy and musty odor in drinking water at low temperatures (1–2°C) in Baotou, China, using an open-loop stripping analysis (OLSA) systems and Gas chromatography spectrometry (GC). The main results show that it is micro-contaminated water body of the raw water in Huajiang Reservoir. The average phytoplankton abundance was 2.06×107L−1, Cyanobacteria counts were at 2.0×106L−1 and the dominate family of the algae are Chlorophyta, Cryptophyta, and Bacillariophyta. Experimental results indicated that under the ice whose thickness was 0.55m, the photosynthetically active radiation (PAR) of the surface varied from 70 to 636Wm−2 from November to March of next year. The average surface PAR was 114.8Wm−2, and the lowest value was 70.57Wm−2 (in December) and the average bottom PAR was 19.04Wm−2, and the lowest value was 3.84Wm−2 (in December). The surface PAR, bottom PAR, eutrophic conditions in ice-covered Huajiang reservoir satisfied the growth and MIB/geosmin production of Cyanobacteria algae in winter. The 2-methyl-isoborneol (MIB) concentration ranged from 29ngL−1 to 102ngL−1. The concentration of trans-1,10-dimethyl-trans-9-decalol (geosmin) ranges from 20ngL−1 to 65ngL−1 and it is 2 to 5 times of the odor threshold concentrations (OTC). The correlations between MIB/geosmin and nitrogen are 0.63–0.37. Eutrophication is the most important factor influencing synthesis of taste and odors, but not temperature. Using bypassing pipe pumping Yellow River water directly to the Water treatment plant (WTP) is an efficient way about T&O compounds׳ control in drinking water of Baotou city in winter.

Generating Global LAnd Surface Satellite incident shortwave radiation and photosynthetically active radiation products from multiple satellite data

Incident shortwave radiation (ISR) at the surface is an essential parameter in the land surface radiation budget and in many land surface process models. Incident photosynthetically active radiation (PAR) is required by nearly all terrestrial ecosystem models. Although several global radiation products from numeric models and satellite observations have been released, their coarse spatial resolutions and low accuracy, especially at high altitude regions, limit their applications in land community. In this study, the Global LAnd Surface Satellite (GLASS) ISR and PAR products are developed based on an improved look-up table method from 2008 to 2010 at a 5km spatial resolution and a 3hour temporal resolution, the first global radiation products at such high resolutions, from multiple polar-orbiting and geostationary satellite data, including the Moderate Resolution Imaging Spectroradiometer (MODIS), the Meteosat Second Generation (MSG2) SEVIRI, the Multi-functional Transport Satellite (MTSAT)-1R, and the Geostationary Operational Environmental Satellite (GOES) Imager. The look-up table algorithm primarily considers the influences of surface elevation, atmospheric water vapor because sensitivity experiments indicate that ISR and PAR are more sensitive to surface elevation, and less sensitive to atmospheric profiles and ozone amount. The water vapor absorption has strong impact on ISR but weak on PAR. Moreover, the surface bi-directional reflectance distribution function (BRDF) is taken into account to retrieve spatially and temporally continuous surface reflectances from the geostationary satellite observations, which is an input parameter in the revised look-up table method. Ground-based measurement data from 34 sites are used to validate the improved algorithm and the GLASS products. The validation results of the instantaneous ISR and PAR products at all validation sites are notably good with coefficient of determination values of 0.83 and 0.84, respectively, and root mean square error values of 115.0Wm−2 and 49.0Wm−2, respectively. We also aggregate the GLASS ISR product for comparing with the corresponding ISCCP and CERES data at 7 SURFRAD sites and demonstrate that the GLASS ISR product is more accurate. The GLASS ISR and PAR products have been made publicly available.

The Mechanisms of Plant Stress Mitigation by Kaolin-based Particle Films and Applications in Horticultural and Agricultural Crops

Kaolin-based particle films have use in reducing insect, heat, photosynthetically active radiation (PAR), and ultraviolet radiation stress in plants resulting from the reflective nature of the particles. Particle films with a residue density of 1 to 4 g·m−2 have been evaluated in a range of crops and agricultural environments. The particle film is a general insect repellant resulting from the change in the plant’s leaf/fruit texture but also because it changes the reflected light signature of the plant causing insect avoidance for many pests. The alteration of reflected light is the result of the ability of the particle film to reflect infrared (IR), PAR, and ultraviolet radiation. Reflection of IR can reduce canopy temperature as much as 5 °C, which will reduce potential transpiration. The reduction of PAR by the film at the leaf level is compensated in varying degrees by diffusion of PAR into the interior of the canopy. Whole canopy photosynthesis can be increased by the combined particle film effects of reduced canopy temperature and increased diffusion of PAR into the interior of the canopy. In apple, reducing fruit surface temperature, PAR, and ultraviolet is an effective means of reducing sunburn damage. The use of a reflective particle film is effective in mitigating environmental stress and has significant economic benefits in agricultural crops.

Calibration of MODIS-based gross primary production over an alpine meadow on the Tibetan Plateau

Moderate-resolution imaging spectroradiometer (MODIS) gross primary production (GPP) was compared with estimated GPP (GPP_EC) from eddy covariance measurements over an alpine meadow on the Tibetan Plateau in 2005–2007. The MODIS GPP (GPP_MOD17A2) with a bias of −0.38 g C m−2 d−1 (i.e., about −40.58% of the mean of the GPP_EC) strongly underestimated the GPP_EC for the alpine meadow. The MODIS GPP was recalibrated using measured surface meteorological data, including photosynthetically active radiation (PAR), daily minimum air temperature (Tamin) and daytime mean vapor pressure deficit (VPD), revised fractional photosynthetically active radiation (FPAR), and the revised maximum light use efficiency (LUEmax) of 0.81 g C MJ−1 (compared with the default value of 0.68 g C MJ−1 for grassland in the MODIS GPP algorithm) for the alpine meadow. The MODIS-based FPAR was about 14.70% larger than the surface-estimated FPAR using surface-measured leaf area index (LAI) data. Additionally, the temporal resolution of surface-measured LAI data was relatively low. Therefore, the linear relationship between surface-measured LAI and MODIS-based LAI was established (R2 > 0.80, P < 0.001). Then the revised MODIS LAI datasets were used to calculate the revised FPAR. The revised LUEmax was optimized from the MOD17A2 algorithm using daily surface measurements, including LAI, PAR, VPD, Tamin and GPP_EC. The calibrated MOD17A2 algorithm could explain 88% of GPP_EC variance for the alpine meadow. The bias between GPP_MOD17A2 and calculated GPP from the MOD17A2 algorithm using surface-measured PAR, Tamin, and VPD, MODIS-based FPAR, and the default LUEmax of 0.68 g C MJ−1 was −0.17 g C m−2 d−1 (i.e., about −17.60% of the mean of the GPP_EC). The underestimation of LUEmax caused a 13.78% underestimation of GPP. In contrast, the overestimation of FPAR resulted in a 7.17% overestimation of GPP. The net effect of meteorology data and FPAR resulted in a 13.84% underestimation of GPP. These results showed that MODIS-based meteorology data, FPAR, and LUEmax for the alpine meadow needed to be adjusted.

Expected and observed conditions during the SAGE iron addition experiment in Subantarctic waters

The SAGE iron addition experiment was conducted from R.V. Tangaroa east of South Island, New Zealand, in late March–early April 2004. A desktop survey of climatological data was completed before the experiment, providing information to inform site selection and experiment design. The desktop survey is presented here in updated and enhanced form in order to explain the site selection and describe the conditions expected at the site during the experiment in comparison with those actually encountered. The experiment site was in Subantarctic waters between the Subtropical and Subantarctic Fronts. These waters are characterised by high surface macronutrient concentration, low iron concentration and low chlorophyll. The preferred site based on the desktop survey was in the vicinity of 173.5°E, 47.5°S, in Southern Bounty Trough. The actual release location was chosen immediately before the release and was 112 km to the northwest of this at 172°32′E, 46°44′S. The surface water here has typically come from the southwest (over the northern Campbell Plateau) or the southeast (through Pukaki Gap) and the mean current is directed towards ENE at ∼0.1 m s −1. The release location is well removed from regions of high eddy kinetic energy to the east (where the Subantarctic Front reaches its northern limit) and the west (where fine-scale instabilities develop on the Southland Front, which flows along the continental shelf). Typical conditions at the release site at the end of March are: surface temperature 12 °C; mixed layer depth 40 m; surface chlorophyll concentration ∼0.3 mg m −3; surface photosynthetically active radiation (PAR) 23 E m −2 d −1; surface nutrient concentrations 8–10 mmol m −3 (nitrate), 0.5–0.8 mmol m −3 (phosphate), 1–2 mmol m −3 (silicate) and 0.1–0.5 nM (iron); 99th percentile wind speed 19–21 m s −1. At this time of year, surface PAR is well below its summer maximum, the mixed layer is beginning its seasonal deepening and the silicate concentration is at its seasonal minimum. These factors may have limited the phytoplankton response to iron addition and were compounded in March–April 2004 by strong winds early in the experiment (substantially exceeding the 99th percentile in speed), lower than the average SST, larger than the average mixed layer depth, silicate concentration at the bottom end of the expected range and initially low PAR.

Stable isotopes reveal limitations in C and N assimilation in the Caribbean reef corals Madracis auretenra, M. carmabi and M. formosa

We used tissue δ 15 N and δ 13 C to elucidate nitrogen and carbon utilization in 3 branching coral species of the genus Madracis. Coral branches were sampled between 5 and 47 m water depth, and tissue was sub-sampled from the tips and sides of branches. Photosynthetically active radiation (PAR) ranged between 1 and 71% of surface PAR. There was a good correlation between δ 15 N and δ 13 C, and these had similar ranges of 5.6 and 5.2‰, respectively, suggesting that light-driven photo- synthesis is a strong factor in isotope fractionation. However, at shallow depths, δ 13 C decreased more strongly while δ 15 N remained constant, while at deeper depths δ 15 N decreased while δ 13 C remained constant. Comparisons of δ 13 C in polyps and zooxanthellae revealed that prey capture at the tips of branches was more pronounced than at the corresponding sideward-facing positions and that corals at deeper depths did not increase their food uptake to compensate for a decrease in photosynthetic carbon assimilation. This indicates that foraging in branching Madracis depends on current regimes and prey encounter rather than selective food capture. The systematic analysis of tissue δ 15 N along a steep depth gradient revealed that the shallow-water coral M. auretenra was nitrogen limited throughout its entire depth range.