Ballast Effect Research Articles

Characteristics of particle fluxes in the Prydz Bay polynya, Eastern Antarctica

The settling of particulate carbon in seawater is a key component of the ocean carbon cycle. We deployed a set of sediment trap in the polynya of Prydz Bay from December 2010 to December 2011 to investigate the seasonal variations in particle fluxes. There was a clear seasonal variation in the particle fluxes, with maximum and minimum fluxes recorded during the summer and winter, respectively. The average total flux over the sampling period was 193.58 mg m−2 d−1, and the average fluxes of organic carbon (Corg), inorganic carbon (Cinorg), and biogenic silica (Sibio) were 721.78, 28.67, and 2382.80 μmol m−2 d−1, respectively. Sibio was the main contributor to the total mass flux, and strongly correlated with Corg. The high Sibio/Corg molar ratios (>1) suggest that Corg was transported to deep sea in association with Sibio. By comparing remote sensing data of sea ice and chlorophyll in the upper water column, we found that the dynamics of carbon fluxes were closely related to changes in sea ice. Algae in sea ice may have a key role in biological pump processes in early summer. Apart from the ice algae bloom period, variations in carbon fluxes generally corresponded with phytoplankton blooms in the upper water. The ballast effect controlled the particle settling velocity and the efficiency of the biological pump. Sea ice rafts initiated the first particle export event and enhanced the particle settling efficiency during melting period. As diatoms might become less dominant in the ice-free area, sea ice loss may cause the efficiency of the biological pump efficiency to decrease over the long term.

The ballast effect of lithogenic matter and its influences on the carbon fluxes in the Indian Ocean

Abstract. Data obtained from long-term sediment trap experiments in the Indian Ocean in conjunction with satellite observations illustrate the influence of primary production and the ballast effect on organic carbon flux into the deep sea. They suggest that primary production is the main control on the spatial variability of organic carbon fluxes at most of our study sites in the Indian Ocean, except at sites influenced by river discharges. At these sites the spatial variability of organic carbon flux is influenced by lithogenic matter content. To quantify the impact of lithogenic matter on the organic carbon flux, the densities of the main ballast minerals, their flux rates and seawater properties were used to calculate sinking speeds of material intercepted by sediment traps. Sinking speeds in combination with satellite-derived export production rates allowed us to compute organic carbon fluxes. Flux calculations imply that lithogenic matter ballast increases organic carbon fluxes at all sampling sites in the Indian Ocean by enhancing sinking speeds and reducing the time of organic matter respiration in the water column. We calculated that lithogenic matter content in aggregates and pellets enhances organic carbon flux rates on average by 45 % and by up to 62 % at trap locations in the river-influenced regions of the Indian Ocean. Such a strong lithogenic matter ballast effect explains the fact that organic carbon fluxes are higher in the low-productive southern Java Sea compared to the high-productive western Arabian Sea. It also implies that land use changes and the associated enhanced transport of lithogenic matter from land into the ocean may significantly affect the CO2 uptake of the organic carbon pump in the receiving ocean areas.

Enhancement of Mesopelagic Sinking Particle Fluxes Due to Upwelling, Aerosol Deposition, and Monsoonal Influences in the Northwestern South China Sea

AbstractTime series data from a sediment trap at approximately 1,000‐m depth in the northwestern South China Sea, July 2012 to April 2013, were used in combination with remote sensing and shipboard physical and biogeochemical data to quantify the effects of multiscale physical processes on sinking particle fluxes and the function of the local biological carbon pump. Total mass flux and the fluxes of its primary components—particulate organic carbon, calcium carbonate, opal, and lithogenic matter—exhibited similar temporal trends, with three conspicuous high‐flux events. These events occurred in the summer, autumn, and winter, attributable to upwelling, aerosol deposition, and the northeast monsoon, respectively. Together, these events accounted for only 40% of the total time but approximately 80% of the 10‐month total mass flux (21% during the upwelling event, 23% during the aerosol event, and 36% during the northeast monsoon event). Each event contributed its own unique biogeochemical overprint. For example, Calcareous phytoplankton benefited from both the upwelling and aerosol deposition events, but siliceous phytoplankton benefited more than calcifiers during the upwelling conditions. The biogenic sinking particles were primarily marine authigenic, while the lithogenic matter was mainly resuspended sediment from the neighboring slope. The high flux of lithogenic matter was due to scavenging by sinking organic matter and the ballasting effect, especially during the high‐flux periods. This study illustrates that episodic intraseasonal physical processes are as important as the most common major seasonal event—the northeast monsoon—in modulating the strength of the South China Sea biological carbon pump.

The Role of Particle Size, Ballast, Temperature, and Oxygen in the Sinking Flux to the Deep Sea

AbstractThe “transfer efficiency” of organic particles from the surface to depth is a critical determinant of ocean carbon sequestration. Recently, direct observations and geochemical analyses have revealed a systematic geographical pattern of transfer efficiency, which is highest in high latitude regions and lowest in the subtropical gyres. We evaluate the possible causes of this pattern using a mechanistic model of sinking particle dynamics. The model represents the size distribution of particles, the effects of mineral ballast, seawater temperature (which influences both particle settling velocity and microbial metabolic rates), and O2. Parameters are optimized within reasonable ranges to best match the observational constraints. Our model shows that no single factor can explain the observed pattern of transfer efficiency, but the biological effect of temperature on remineralization rate and particle size effects together can reproduce most of the regional variability with both factors contributing to low transfer efficiency in the subtropical gyres and high transfer efficiency in high latitudes. Particle density from mineral ballast has a similar directional effect to temperature and size but plays a substantially smaller role in our optimum solution, due to the opposing patterns of silicate and calcium carbonate ballasting. Oxygen effects modestly improved model fit by depressing remineralization rates and thus increasing transfer efficiency in the Eastern Tropical Pacific. Our model implies that climate‐driven changes to upper ocean temperature and associated changes in surface plankton size distribution would reduce the carbon sequestration efficiency in a warmer ocean.

Calcium looping performance under extreme oxy-fuel combustion conditions in the calciner

Calcium looping (CaL) for post-combustion CO2 capture is an emerging technology that has developed rapidly due to its similarities with existing circulating fluidized bed combustion boilers. This work presents an alternative calciner configuration as it is applied in La Pereda CaL pilot plant, the aim of which is to minimize or altogether eliminate the need to recycle CO2 during the oxy-fuel combustion of coal in the calciner. The strategy underlying this configuration is to reduce the heat demand in the calciner, and hence the energy penalty of the whole CaL system. After undergoing several modifications, the pilot was able to operate under O2-rich conditions in a series of experiments with a coal thermal input of up to 2.0 MWth in the calciner and 75 O2%v in the oxidant. No hot spots were detected in the calciner reactor in these conditions due to the thermal ballast effect produced by the circulating solids from the carbonator. This new operation mode in the calciner in no way undermined the performance of the carbonator and CO2 capture efficiencies close to the maximum limit permitted by the equilibrium were achieved during the experimental campaigns. In short, the results of this work indicate that it may well be possible to operate the calciner of a CaL system using pure oxygen.

Simulated effects of interactions between ocean acidification, marine organism calcification, and organic carbon export on ocean carbon and oxygen cycles

Ocean acidification caused by oceanic uptake of anthropogenic carbon dioxide (CO2) tends to suppress the calcification of some marine organisms. This reduced calcification then enhances surface ocean alkalinity and increases oceanic CO2 uptake, a process that is termed calcification feedback. On the other hand, decreased calcification also reduces the export flux of calcium carbonate (CaCO3), potentially reducing CaCO3-bound organic carbon export flux and CO2 uptake, a process that is termed ballast feedback. In this study, we incorporate a range of different parameterizations of the links between organic carbon export, calcification, and ocean acidification into an Earth system model, in order to quantify the long-term effects on oceanic CO2 uptake that result from calcification and ballast feedbacks. We utilize an intensive CO2 emission scenario to drive the model in which an estimated fossil fuel resource of 5000 Pg C is burnt out over the course of just a few centuries. Simulated results show that, in the absence of both calcification and ballast feedbacks, by year 3500, accumulated oceanic CO2 uptake is 2041 Pg C . Inclusion of calcification feedback alone increases the simulated uptake by 629 Pg C (31%), while the inclusion of both calcification and ballast feedbacks increase simulated uptake by 449–498 Pg C (22–24%), depending on the parameter values used in the ballast feedback scheme. These results indicate that ballast effect counteracts calcification effect in oceanic CO2 uptake. Ballast effect causes more organic carbon to accumulate and decompose in the upper ocean, which in turn leads to decreased oxygen concentration in the upper ocean and increased oxygen at depths. By year 2600, the inclusion of ballast effect would decrease oxygen concentration by 11% at depth of ca. 200 m in tropics. Our study highlights the potentially critical effects of interactions between ocean acidification, marine organism calcification, and CaCO3-bound organic carbon export on the ocean carbon and oxygen cycles.

Transport and deposition of the fire biomarker levoglucosan across the tropical North Atlantic Ocean

Biomass burning impacts biogeochemical cycling, vegetation dynamics and climate. However, interactions between fire, climate and vegetation are not well understood and therefore studies have attempted to reconstruct fire and vegetation history under different climatic conditions using sedimentary archives. Here we focus on levoglucosan, a thermal by-product of cellulose generated during biomass burning, and, therefore, a potential fire biomarker in the marine sedimentary archive. However, before levoglucosan can be applied as a biomass burning proxy in marine sediments, there is a need for studies on how levoglucosan is transported to the marine environment, how it is reflecting biomass burning on continents, as well as the fate of levoglucosan in the marine water column and during deposition in marine sediments. Here we present analyses of levoglucosan, using an improved Ultra High Pressure Liquid Chromatography-Electro Spray Ionization/High Resolution Mass Spectrometry (UHPLC-ESI/HRMS) method, in atmospheric particles, in particulate matter settling through the water column and in marine surface sediments on a longitudinal transect crossing the tropical North Atlantic Ocean at 12°N. Levoglucosan was detected in the atmosphere, although in low concentration, possibly due to the sampled particle size, the source area of the aerosols, or the short time interval of sampling by which large burning events may have been missed. In sinking particles in the tropical North Atlantic Ocean we find that levoglucosan deposition is influenced by a mineral ballast effect associated with marine biogenic particles, and that levoglucosan is not transported in association with mineral dust particles. Highest levoglucosan concentrations and seasonal differences in sinking particles were found close to continents and low concentrations and seasonal differences were found in the open ocean. Close to Africa, levoglucosan concentration is higher during winter, reflecting seasonal burning in northwestern Africa. However, close to South America levoglucosan concentrations appear to be affected by riverine transport from the Amazon River. In surface sediments close to South America, levoglucosan concentration is higher than in the middle of the Atlantic Ocean, implying that here the influence from the South American continent is important and perennial. Our study provides evidence that degradation of levoglucosan during settling in the marine water column is not substantial, but is substantial at the sediment–water interface. Nevertheless, levoglucosan was detected in all surface sediments throughout the tropical North Atlantic, indicating its presence in the marine sedimentary record, which reveals the potential for levoglucosan as a biomass burning proxy in marine sediments.

The ballasting effect of Saharan dust deposition on aggregate dynamics and carbon export: Aggregation, settling, and scavenging potential of marine snow

AbstractLithogenic material such as Saharan dust can be incorporated into organic aggregates and act as ballast, potentially enhancing the marine carbon export via increased sinking velocities of aggregates. We studied the ballasting effects of Saharan dust on the aggregate dynamics in the upwelling region off Cape Blanc (Mauritania). Aggregate formation from a natural plankton community exposed to Saharan dust deposition resulted in higher abundance of aggregates with higher sinking velocities compared to aggregate formation with low dust. This higher aggregate abundance and sinking velocities potentially increased the carbon export 10‐fold when the aggregates were ballasted by Saharan dust. After aggregate formation in the surface waters, subsequent sinking through suspended Saharan dust minerals had no influence on aggregate sizes, abundance, and sinking velocities. We found that aggregates formed in the surface ocean off Mauritania were already heavily ballasted with lithogenic material and could therefore not scavenge any additional minerals during their descent. This suggests that carbon export to the deep ocean in regions with high dust deposition is strongly controlled by dust input to the surface ocean while suspended dust particles in deeper water layers do not significantly interact with sinking aggregates.

Phosphorus limitation and heat stress decrease calcification in <i>Emiliania huxleyi</i>

Abstract. Calcifying haptophytes (coccolithophores) sequester carbon in the form of organic and inorganic cellular components (coccoliths). We examined the effect of phosphorus (P) limitation and heat stress on particulate organic and inorganic carbon (calcite) production in the coccolithophore Emiliania huxleyi. Both environmental stressors are related to rising CO2 levels and affect carbon production in marine microalgae, which in turn impacts biogeochemical cycling. Using semi-continuous cultures, we show that P limitation and heat stress decrease the calcification rate in E. huxleyi. However, using batch cultures, we show that different culturing approaches (batch versus semi-continuous) induce different physiologies. This affects the ratio of particulate inorganic (PIC) to organic carbon (POC) and complicates general predictions on the effect of P limitation on the PIC ∕ POC ratio. We found heat stress to increase P requirements in E. huxleyi, possibly leading to lower standing stocks in a warmer ocean, especially if this is linked to lower nutrient input. In summary, the predicted rise in global temperature and resulting decrease in nutrient availability may decrease CO2 sequestration by E. huxleyi through lower overall carbon production. Additionally, the export of carbon may be diminished by a decrease in calcification and a weaker coccolith ballasting effect.

Setting Some Milestones when Modelling Cell Gene Expression Regulatory Circuits Under Variable-Volume Whole-cell Modelling Framework. I. Generalities

The whole-cell simulation of cell metabolic processes under considering a variable-volume modelling framework has been reviewed to prove their advantages when building-up modular model structures that can reproduce complex protein syntheses inside cells. The more realistic whole-cell-variable-volume (WCVV) approach is exemplified when developing modular kinetic representations of the homeostatic gene expression regulatory modules (GERM) that control the protein synthesis and homeostasis of metabolic processes. In the first part, the general concepts of the WCVV modelling is presented, while in the second part of the paper, past and current experience with GERM linking rules is presented in order to point-out how optimized globally efficient kinetic models for the genetic regulatory circuits (GRC) can be obtained to reproduce experimental observations. Based on quantitative regulatory indices evaluated vs. simulated dynamic and stationary environmental perturbations, the paper exemplifies with GERM-s from E. coli, at a generic level, how this methodology can be extended: i) to characterize the module efficiency, species connectivity and system stability; ii) to build-up modular regulatory chains of various complexity; iii) to prove feasibility of the cooperative vs. concurrent construction that ensures an efficient gene expression, system homeostasis, proteic functions and a balanced cell growth during the cell cycle; iv) to prove the effect of the whole-cell content ballast in smoothing the effect of internal/external perturbations on the system homeostasis.

Assessing ballast cleaning as a rehabilitation method for railway masonry arch bridges by dynamic load tests

Dynamic load testing has become a common practice for condition assessment of masonry arch bridges and lays the foundation for their rehabilitation procedures; however, additional dynamic testing after rehabilitation is rare. Carrying out dynamic load tests before and after rehabilitation programs produces valuable results with regard to the structural changes of the bridge. This paper tries to assess the effects of ballast cleaning on the performance of railway masonry arch bridges by conducting dynamic load tests before and after the rehabilitation procedure. To do so, a 70-year-old masonry arch bridge is instrumented with deflection meters and accelerometers. Dynamic load tests are carried out before and after ballast cleaning and results are compared. According to the test results, vertical deflections of different spots on the bridge remain the same, with a deviation of less than 5%. On the other hand, vibrations on the structure are reduced significantly. On average, vibration levels are reduced by 35% in different spots of the structure.

Reply to Giannakos, K. Comment on: Toughness of Railroad Concrete Crossties with Holes and Web Openings. Infrastructures 2017, 2, 3

This paper responds to the discussion [1] by Dr. K. Giannakos over our technical note [2].[...]

The effects of ballast on the sound radiation from railway track

In a conventional railway track, the rails are laid on sleepers, usually made of concrete, which are supported by a layer of coarse stones known as ballast. This paper focuses on quantifying the influence that the ballast has on the noise produced by the vibration of the track, particularly on the rail and sleeper radiation ratios. A one-fifth scale model of a railway track has been used to conduct acoustic and vibration measurements. This includes reduced-scale ballast that has been produced with stone sizes in the correct proportions. Two different scaling factors (1:√5 and 1:5) have been adopted for the stone sizes in an attempt to reproduce approximately the acoustic properties of full-scale ballast. It is shown that, although a scale factor of 1:√5 gives a better scaling of the acoustic properties, the stones scaled at 1:5 also give acceptable results. The flow resistivity and porosity of this ballast sample have been measured. These have been used in a local reaction model based on the Johnson-Allard formulation to predict the ballast absorption, showing good agreement with measurements of the absorption coefficient. The effects of the presence of the ballast on the noise radiation from a reduced-scale steel rail and concrete sleeper have been investigated experimentally with the ballast located on a rigid foundation. Comparisons are made with the corresponding numerical predictions obtained by using the boundary element method, in which the ballast is represented by a surface impedance. Additionally the finite element method has been used in which the porous medium is considered as an equivalent fluid. From these results it is shown that the extended reaction model gives better agreement with the measurements. Finally, the effects of the ballast vibration on the sleeper radiation have also been investigated for a case of three sleepers embedded in ballast. The ballast vibration is shown to increase the sound radiation by between 1 and 4.5dB for frequencies between 20 and 300Hz at full scale whereas at higher frequencies the effect is negligible.

Laboratory and field investigation of the effect of geogrid-reinforced ballast on railway track lateral resistance

Continuous welded rail (CWR) tracks have particular advantages over common tracks with jointed rails such as increased ride comfort, reduced noise and vibration and decreased maintenance costs due to the removal of joints in rail connections. Alternatively, some complications associated with CWR tracks, for instance increased lateral forces, are the main reason of track buckling and its subsequent lateral deformation. These problems are usually more severe in curved tracks. In order to overcome the large lateral forces caused by temperature deviations of CWR tracks which results in railway vehicle instability, the ballasted track lateral resistance should be improved. Among the various methods proposed in this area, no specific study has been carried out on the effect of geogrid reinforcement on ballasted track lateral resistance. Thus, the present research was allocated to investigating the effect of geogrid on the lateral resistances of both single tie and track panel via laboratory and field tests. In this regard, at the first stage, the ballast layer was reinforced with various number of geogrid layers, the effect of which was investigated by conducting the single tie push test (STPT) in the lab environment to assess the optimum number of geogrid layers and their installation levels along the ballast layer thickness. Afterwards, a test track was executed in the field including various sections which were reinforced in the same way as the lab tests. Consequently, many STPTs and track panel displacement tests (TPDTs) were accomplished. As a result, the STPTs in the lab and field confirmed more than 31% and 42% increase in single tie lateral resistance for ballast layers reinforced respectively with one and two geogrid layers, while these values were reached to 29% and 40% in the case of TPDT.

Biodegradation of Emiliania huxleyi aggregates by a natural Mediterranean prokaryotic community under increasing hydrostatic pressure

In the deep ocean, fluxes of particulate organic carbon (POC) and calcium carbonate are positively correlated, suggesting that CaCO3 could increase sinking particle densities and/or protect the organic matter from degradation by prokaryotes, the so called “ballast effect”. Here, we used the PArticle Sinking Simulator (PASS) system to investigate the effect of increasing pressure on the biodegradation of calcifying Emiliania huxleyi aggregates. Incubations were carried out over a period of 10days, simulating the changes in temperature and pressure in the water column of the NW Mediterranean Sea. Aggregates sinking from a depth of 200m to 1700m (assuming an average sinking velocity of 150md−1) were exposed to a natural mesopelagic prokaryotic community collected from 200m. In contrast to previous studies, where silicifying diatom aggregates were used, the calcifying E. huxleyi aggregates were found to be more sensitive to degradation with increasing hydrostatic pressure (relative to constant atmospheric pressure). This was confirmed by changes in lipid composition which suggested increased cell lysis. Changes in particulate inorganic carbon and total alkalinity indicated that CaCO3 dissolution might have been faster under pressure. Increased hydrostatic pressure also had a positive effect on particle aggregation, which may compensate for the effect of increased cell lysis. Our results imply that in coccolithophorid-dominated sinking aggregates, the ballasting and protection effects of coccoliths may collapse throughout the water column. The increased aggregation potential with pressure observed in these controlled conditions, may balance the loss of mineral ballast to a certain extent, although this needs to be confirmed in situ.

Thermal impacts of engineering activities and vegetation layer on permafrost in different alpine ecosystems of the Qinghai–Tibet Plateau, China

Abstract. Climate warming and engineering activities have various impacts on the thermal regime of permafrost in alpine ecosystems of the Qinghai–Tibet Plateau. Using recent observations of permafrost thermal regimes along the Qinghai–Tibet highway and railway, the changes of such regimes beneath embankments constructed in alpine meadows and steppes are studied. The results show that alpine meadows on the Qinghai–Tibet Plateau can have a controlling role among engineering construction effects on permafrost beneath embankments. As before railway construction, the artificial permafrost table (APT) beneath embankments is not only affected by climate change and engineering activities but is also controlled by alpine ecosystems. However, the change rate of APT is not dependent on ecosystem type, which is predominantly affected by climate change and engineering activities. Instead, the rate is mainly related to cooling effects of railway ballast and heat absorption effects of asphalt pavement. No large difference between alpine and steppe can be identified regarding the variation of soil temperature beneath embankments, but this difference is readily identified in the variation of mean annual soil temperature with depth. The vegetation layer in alpine meadows has an insulation role among engineering activity effects on permafrost beneath embankments, but this insulation gradually disappears because the layer decays and compresses over time. On the whole, this layer is advantageous for alleviating permafrost temperature rise in the short term, but its effect gradually weakens in the long term.

Debris size and buoyancy influence the dispersal distance of stranded litter

Recent at sea surveys of floating macro-debris in the southeast Atlantic Ocean found that debris increases in size with distance from shore, suggesting that many smaller items, which dominate litter close to urban source areas, sink before dispersing far into the ocean. We test whether this pattern is evident in beach litter in the same region. Freshly stranded beach litter was collected at increasing distances (0km, 100km, 200km and 2800km) from Cape Town, a major urban litter source. Mean size and buoyancy of litter items increased significantly with distance from Cape Town. Size-specific sedimentation due to the ballasting effect of biofouling is a plausible explanation for the disappearance of smaller, less buoyant items. Our results provide further evidence that many low buoyancy items sink and support the hypothesis that size and buoyancy are strong predictors of dispersal distance for floating debris.

Deep ocean mass fluxes in the coastal upwelling off Mauritania from 1988 to 2012: variability on seasonal to decadal timescales

Abstract. A more than two-decadal sediment trap record from the Eastern Boundary Upwelling Ecosystem (EBUE) off Cape Blanc, Mauritania, is analysed with respect to deep ocean mass fluxes, flux components and their variability on seasonal to decadal timescales. The total mass flux revealed interannual fluctuations which were superimposed by fluctuations on decadal timescales. High winter fluxes of biogenic silica (BSi), used as a measure of marine production (mostly by diatoms) largely correspond to a positive North Atlantic Oscillation (NAO) index (December–March). However, this relationship is weak. The highest positive BSi anomaly was in winter 2004–2005 when the NAO was in a neutral state. More episodic BSi sedimentation events occurred in several summer seasons between 2001 and 2005, when the previous winter NAO was neutral or even negative. We suggest that distinct dust outbreaks and deposition in the surface ocean in winter and occasionally in summer/autumn enhanced particle sedimentation and carbon export on short timescales via the ballasting effect. Episodic perturbations of the marine carbon cycle by dust outbreaks (e.g. in 2005) might have weakened the relationships between fluxes and large-scale climatic oscillations. As phytoplankton biomass is high throughout the year, any dry (in winter) or wet (in summer) deposition of fine-grained dust particles is assumed to enhance the efficiency of the biological pump by incorporating dust into dense and fast settling organic-rich aggregates. A good correspondence between BSi and dust fluxes was observed for the dusty year 2005, following a period of rather dry conditions in the Sahara/Sahel region. Large changes of all bulk fluxes occurred during the strongest El Niño-Southern Oscillation (ENSO) in 1997–1999 where low fluxes were obtained for almost 1 year during the warm El Niño and high fluxes in the following cold La Niña phase. For decadal timescales, Bakun (1990) suggested an intensification of coastal upwelling due to increased winds (''Bakun upwelling intensification hypothesis''; Cropper et al., 2014) and global climate change. We did not observe an increase of any flux component off Cape Blanc during the past 2 and a half decades which might support this. Furthermore, fluxes of mineral dust did not show any positive or negative trends over time which might suggest enhanced desertification or ''Saharan greening'' during the last few decades.

Influence of Mussel Culture on the Vertical Export of Phytoplankton Carbon in a Coastal Upwelling Embayment (Ría de Vigo, NW Iberia)

The goal of this paper is to find out whether suspended mussel culture affects the vertical fluxes of biogenic particles in the Ria de Vigo on a seasonal scale. With this aim, vertical fluxes of particulate organic carbon (POC) and the magnitude and composition of vertical export of phytoplankton carbon (Cphyto) collected in sediment traps were examined by comparing data obtained inside a mussel farming area (RaS) with those found at a reference station (ReS) not affected by mussels. Our results indicate that mussel farming has a strong impact on sedimentation fluxes under the rafts, not only increasing POC flux but also altering the magnitude and composition of Cphyto fluxes. Average POC flux at RaS (2564 ± 1936 mg m−2 day−1) was four times higher than at ReS (731 ± 276 mg m−2 day−1), and much of this increase was due to biodeposit fluxes (Cbiodep) which accounted for large proportion of POC flux (35–60 %). Indeed, because of this high Cbiodep flux, only a small proportion of the POC flux was due to Cphyto flux (3–12 %). At the same time, we observed an increased sedimentation of phytoplankton cells at RaS that could be explained by a combination of mechanisms: less energetic hydrodynamic conditions under mussel rafts, ballast effect by sinking mussel feces, and diatom aggregates. Moreover, mussel farming also altered the quality of the Cphyto flux by removing part of the predatory pressure of zooplankton and thus matching diatom composition in water column and sediment traps.

Effects of frequency dimming electronic ballast on a high‐pressure mercury thallium iodide discharge

AbstractThis study focuses on the behavior of a cylindrical metal halide discharge lamp powered by frequency‐controlled electronic ballast. Half‐bridge electronic ballast was designed and achieved.