335 research outputs found
Evolution of multi-annual and large-scale phytoplankton patterns in the Scheldt estuary: The disappearance of phytoplankton accumulation in the brackish region
No full textEstuaries often show regions in which Chlorophyll-a (Chl-a) accumulates. The location and magnitude corresponding to such accumulation result from a complex interplay between processes such as river flushing, salinity, nutrients, grazing on phytoplankton, and the light climate in the water column. An example is the multi-annual evolution of the estuary-scale Chl-a distribution in the Scheldt estuary (Belgium/Netherlands) in spring. From 2004–2007, we observed a limited spring bloom in the brackish region (km 60–90 from the mouth, salinity ∼ 1–10 ppt). This bloom intensified in 2008–2014 and disappeared after 2015. This multi-annual evolution of Chl-a has been hypothesized to be linked to simultaneous multi-annual trends in the suspended particulate matter (SPM) distribution in summer and winter between 1995–2015 and the improvement of the water quality (e.g., reduction of ammonium), which affects grazing on phytoplankton by zooplankton. However, this hypothesis has not been systematically investigated. In this contribution, we apply a modeling approach in which observations are the core. We first analyze multi-annual in situ observations covering the full estuary. These observations include the SPM concentration, zooplankton abundance, and other variables affecting the Chl-a concentration. They show a multi-annual estuary-scale evolution not only in the SPM distribution but also in zooplankton abundance, freshwater discharge, and phytoplankon photosynthetic characteristics. Next, we apply a model approach that consists of an extensive sensitivity study and four model scenarios that are supported by these observations to constrain the processes and corresponding parameter variability that may have caused the observed change in Chl-a. Our results suggest that a change in SPM alone cannot explain the Chl-a observations. Instead, a multi-annual change in mortality rate, which we can attribute to both grazing by zooplankton and phytoplankton community (i.e., mortality dependence on salinity), may explain the multi-annual estuary-scale evolution of Chl-a in spring. Different model parameter choices may thus lead to similar model results (equifinality). Our results highlight that insight into the zooplankton dynamics and phytoplankton community characteristics is essential to understand the phytoplankton (cf. Chl-a) dynamics in the Scheldt estuary and that additional data regarding mortality and grazing rates is required to further constrain the model parameters.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Mathematical Physic
Combined Wave and Surge Overtopping of Levees: Flow Hydrodynamics and Articulated Concrete Mat Stability
No full textA 1-to-25 scale physical model of a typical cross section of the levee along the Mississippi River Gulf Outlet (MRGO) was con-structed at the U.S. Army Engineer Research and Development Center\u92s Coastal and Hydraulics Laboratory in Vicksburg, MS. The purpose of the physical model was to obtain hydrodynamic measurements of unsteady flow conditions caused by combined wave and surge overtopping of the levee, and to examine the feasibility of using articulated concrete mats (ACMs) for levee protection during this type of overtopping event. Specifically, the U.S. Army Engineer District, New Orleans, was interested in determining whether the same ACMs used by the Corps\u92 Mat Sinking Unit to protect river banks could be used to protect the MRGO levee against surge and wave overtopping. When the storm surge elevation was 0.75 ft above the levee crest, the stability tests indicated the ACMs were prone to uplift on the lower portion of the levee protected-side slope for even relatively mild wave overtopping. An increase in wave height created mat roll-up instability at the toe of the flood-side levee slope, indicating the need to bury or anchor the leading and tailing edges of the mats. Mat stability could be increased with additional anchoring or increasing mat thickness. Tests were also conducted to document the hydrodynamics associated with combined wave and surge over-topping. The primary parameters were three overtopping surge levels (+1, +3, and +5 ft); three significant wave heights (3, 6, and 9 ft); and three peak wave periods (6, 10, and 14 sec) for a total of 27 unique conditions. Measurements included the incident irregular waves and time series of water elevations at seven locations on the crest and protected-side slope of the levee. Horizontal flow velocity was recorded near the leeward levee crest shoulder, and the velocity was then combined with water elevation to estimate the unsteady instantaneous discharge over the levee. Discharge cumulative probability distributions were determined using the Weibull probability distribution, and a predictive equation was developed for the distribution of overtopping discharge as a function of wave and surge parameters
Flood-Side Wave Erosion of Earthen Levees: Present State of Knowledge and Assessment of Armoring Necessity
No full textThis report is a compilation of facts and information that summarizes the present state of knowledge related to wave attack on the flood side of earthen levees. Particular emphasis was placed on the need for providing flood-side armoring (beyond the protection afforded by grass) for the New Orleans Hurricane & Storm Damage Risk Reduction System (HSDRRS). The report includes: (1) a summary of observations from Hurricane Katrina; (2) an extensive overview of large-scale experiments conducted in Europe, (3) a critical examination of proposed methodologies for predicting wave-induced damage on flood-side grass and bare-clay slopes, (4) an analysis of wave-induced erosion expected to occur on the flood side during hypothetical storms approximating the 100-yr and the 500-year events, (5) and a comprehensive list of conclusions and associated caveats. The erosion estimation methodologies for wave-induced erosion discussed in this report were applied to three sets of hypothetical extreme storm parameters to assess the need for providing wave erosion protection (i.e., armoring) on grass-covered and bare-clay flood-side slopes
Diethyl sulfate induced Cdk2-dependent centrosome amplification in CHL cells
No full textThe function of centrosome that serves as the main microtubule organizing center is essential to ensure the genomic integrity during the cell division cycle. Centrosome abnormalities are frequently observed in many tumors and cells exposed to genotoxic agents. Here, we investigated the centrosome abnormalities induced by diethyl sulfate (DES) in Chinese hamster lung (CHL) fibroblasts and the underlying molecular mechanisms. Our results showed that DES exposure at 0.3, 1 and 3 mM for 48 h caused centrosome amplification in a dose dependent manner. This effect was associated with transient S and G2/M phase delay and up-regulating of Cdk2, Cyclin A expressions. Furthermore, inhibition of Cdk2 activities reversed the centrosome amplification induced by DES. These results reveal that centrosome is one of the key subcellular targets of DES. Centrosome abnormalities might be important mechanisms behind the aneuploidy induction and carcinogenicity of DES.(C) 2010 Elsevier Ireland Ltd. All rights reserved.Pharmacology & PharmacyToxicologySCI(E)PubMed2ARTICLE1-358-6427
Evolution of a New Chlorophyll Metabolic Pathway Driven by the Dynamic Changes in Enzyme Promiscuous Activity
No full textOrganisms generate an enormous number of metabolites; however, the mechanisms by which a new metabolic pathway is acquired are unknown. To elucidate the importance of promiscuous enzyme activity for pathway evolution, the catalytic and substrate specificities of Chl biosynthetic enzymes were examined. In green plants, Chl a and Chl b are interconverted by the Chl cycle: Chl a is hydroxylated to 7-hydroxymethyl chlorophyll a followed by the conversion to Chl b, and both reactions are catalyzed by chlorophyllide a oxygenase. Chl b is reduced to 7-hydroxymethyl chlorophyll a by Chl b reductase and then converted to Chl a by 7-hydroxymethyl chlorophyll a reductase (HCAR). A phylogenetic analysis indicated that HCAR evolved from cyanobacterial 3,8-divinyl chlorophyllide reductase (DVR), which is responsible for the reduction of an 8-vinyl group in the Chl biosynthetic pathway. In addition to vinyl reductase activity, cyanobacterial DVR also has Chl b reductase and HCAR activities; consequently, three of the four reactions of the Chl cycle already existed in cyanobacteria, the progenitor of the chloroplast. During the evolution of cyanobacterial DVR to HCAR, the HCAR activity, a promiscuous reaction of cyanobacterial DVR, became the primary reaction. Moreover, the primary reaction (vinyl reductase activity) and some disadvantageous reactions were lost, but the neutral promiscuous reaction (NADH dehydrogenase) was retained in both DVR and HCAR. We also show that a portion of the Chl c biosynthetic pathway already existed in cyanobacteria. We discuss the importance of dynamic changes in promiscuous activity and of the latent pathways for metabolic evolution
In Vitro Enzymatic Activity Assays Implicate the Existence of the Chlorophyll Cycle in Chlorophyll b-Containing Cyanobacteria
No full textIn plants, chlorophyll (Chl) a and b are interconvertible by the action of three enzymes-chlorophyllide a oxygenase, Chl b reductase (CBR) and 7-hydroxymethyl chlorophyll a reductase (HCAR). These reactions are collectively referred to as the Chl cycle. In plants, this cyclic pathway ubiquitously exists and plays essential roles in acclimation to different light conditions at various developmental stages. By contrast, only a limited number of cyanobacteria species produce Chl b, and these include Prochlorococcus, Prochloron, Prochlorothrix and Acaryochloris. In this study, we investigated a possible existence of the Chl cycle in Chl b synthesizing cyanobacteria by testing in vitro enzymatic activities of CBR and HCAR homologs from Prochlorothrix hollandica and Acaryochloris RCC1774. All of these proteins show respective CBR and HCAR activity in vitro, indicating that both cyanobacteria possess the potential to complete the Chl cycle. It is also found that CBR and HCAR orthologs are distributed only in the Chl b-containing cyanobacteria that habitat shallow seas or freshwater, where light conditions change dynamically, whereas they are not found in Prochlorococcus species that usually habitat environments with fixed lighting. Taken together, our results implicate a possibility that the Chl cycle functions for light acclimation in Chl b-containing cyanobacteria
TIME RESOLVED AND FREQUENCY SELECTIVE FLUORESCENCE OF THE CHL a DIMER
No full textassignment^{1}CCl_{4}$, hexane and benzene is reported
Evolution of Green Plants Accompanied Changes in Light-Harvesting Systems
No full textPhotosynthetic organisms have various pigments enabling them to adapt to various light environments. Green plants are divided into two groups: streptophytes and chlorophytes. Streptophytes include some freshwater green algae and land plants, while chlorophytes comprise the other freshwater green algae and seawater green algae. The environmental conditions driving the divergence of green plants into these two groups and the changes in photosynthetic properties accompanying their evolution remain unknown. Here, we separated the core antennae of PSI and the peripheral antennae [light-harvesting complexes (LHCs)] in green plants by green-native gel electrophoresis and determined their pigment compositions. Freshwater green algae and land plants have high Chl a/b ratios, with most Chl b existing in LHCs. In contrast, seawater green algae have low Chl a/b ratios. In addition, Chl b exists not only in LHCs but also in PSI core antennae in these organisms, a situation beneficial for survival in deep seawater, where blue-green light is the dominant light source. Finally, low-energy Chl (red Chl) of PSI was detected in freshwater green algae and land plants, but not in seawater green algae. We thus conclude that the different level of Chl b accumulation in core antennae and differences in PSI red Chl between freshwater and seawater green algae are evolutionary adaptations of these algae to their habitats, especially to high-or low-light environments
Remote sensing of North Sea water quality: A comparison between Sentinel-3 OLCI and in-situ measurements
No full textChlorophyll (Chl) and Total Suspended Matter (TSM) are both important water quality parameters since they influence the amount of oxygen & amount of light penetrating the water. Oxygen and light are vital in marine ecosystems. The Dutch governmental organisation, Rijkswaterstaat (RWS), has been monitoring the water quality of the Dutch part of the North Sea for the last 35 years. A research vessel takes off to sample parameters such as chlorophyll and TSM every few weeks at fixed locations. Recently, Sentinel-3 satellites started to provide satellite-based information on air or water quality. It is expected that products from the Ocean Land Colour Instrument (OLCI) sensor, on board of Sentinel-3, can greatly improve both the geographical and temporal coverage of these parameters. For the Dutch coastal waters this is challenging, because they predominantly consist of complex coastal waters. This study focusses on the validation of water quality parameters (Chl and TSM) available from Sentinel-3A OLCI observations. To verify the processing line of the OLCI data products it was desired to evaluate the following variables as well: 1) the aerosol optical thickness used in the atmospheric aerosol correction process, which is an important step for deriving the water-leaving reflectance, and 2) the water-leaving reflectance itself used as the main signal for deriving Chl and TSM. OLCI water quality data products were compared to Rijkswaterstaat in-situ measurements for the months May until September of 2017. Furthermore, OLCI’s Chl and TSM were compared with climatologies of MERIS data. The OLCI water-leaving reflectance and aerosol optical thickness data products were compared with observations from the Belgian AERONET-OC station Thornton. To evaluate the spatial distribution of OLCI's aerosol optical thickness comparisons with nearly coincident MODIS-AQUA observations were made. To evaluate the spatial variability of OLCI's data products boxplots were created of Chl, TSM and the aerosol optical thickness. The water quality products of OLCI consist of a Chl product determined by the OC4Me algorithm and a Chl & TSM product derived from a neural network. OLCI Chl obtained from the OC4Me algorithm showed an overestimation of a factor 2 compared to the in-situ measurements. The Chl results of the neural network compared well with the in-situ measurements showing a correlation coefficient of 0.77. OLCI TSM showed an unrealistic underestimation of a factor 4 compared to in-situ measurements. Boxplots showed that the largest spatial variability is found at stations <50 km from the coast for the three water quality products. This unrealistic underestimation of scattering TSM would imply an underestimation of the water-leaving reflectance in all the bands. Comparing OLCI's water-leaving reflectance with AERONET's showed underestimations in the blue and green bands only. OLCI’s water-leaving reflectance of the red and near-infra-red (NIR) bands correlated well with the AERONET-OC measurements. The aerosol optical thickness data product showed unrealistic overestimations of OLCI compared to AERONET-OC, but had a correlation coefficient of 0.58 when comparing it to MODIS aerosol optical thickness product. The spatial variability of OLCI's aerosol optical thickness is very high with differences of more than 40% per kilometre. In general, all products seem to have unrealistic values around clouds and in coastal areas, especially the aerosol optical thickness product. The pixels in those regions are different from other pixels. These results imply that further research into the software implementation of the radiative transfer models, lookup tables, vicarious calibrations and Neural Networks is needed to understand how retrievals of Chl and TSM concentrations are influenced. Such a fundamental understanding is ultimately also of interest for end users and all parties providing products and services for marine applications
Congenital deficiency of 11beta-hydroxysteroid dehydrogenase (apparent mineralocorticoid excess syndrome): diagnostic value of urinary free cortisol and cortisone
No full textThe syndrome of apparent mineralocorticoid excess (AME) is an inherited form of hypertension. This disorder results from an inability of the enzyme 11beta-hydroxysteroid dehydrogenase (11beta-OHSD) to inactivate cortisol to cortisone. The diagnosis of AME is usually based on an elevated ratio of cortisol to cortisone reduced metabolites in the urine [tetrahydrocortisol plus allotetrahydrocortisol to tetrahydrocortisone (THF+alloTHF/THE)]. The principal site of "A" ring reduction is the liver, but AME arises from mutation in the gene encoding 11beta-OHSD2 in the kidney. We used a gas chromatographic/mass spectrometric method to measure the urinary free cortisol (UFF) and free cortisone (UFE) in 24 patients affected by the two variants of AME [19 with the classical form (type I) and 5 with the mild form called AME type II] in order to provide a more reproducible in vivo measure of the renal enzymatic activity. Type I patients were divided into two groups: children under 12 and adults. UFF levels (microg/24 h) did not differ between under-12 controls and AME type I children (mean+/-SD, 9+/-4 and 15+/-12, respectively), but was significantly higher in affected adults compared to controls: (62+/-32 vs 29+/-8,
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