Multi-Year Winter Variations in Suspended Sediment Flux through the Bohai Strait

The Bohai Strait is the only channel that allows material exchanges between the Bohai Sea and the Yellow Sea. It is also the only channel for the transportation of materials from the Yellow River to the Yellow Sea and the East China Sea. The supply of suspended sediment from the Bohai Sea plays a decisive role in the evolution of the mud area in the northern Yellow Sea and even the muddy area in the southern Yellow Sea. Previous studies have demonstrated that sediment exchange through the Bohai Strait occurs mainly in winter, but due to the lack of long-term observational data, changes in the sediment flux over multiple years have not been studied. In this paper, based on L1B data from the MODIS (Moderate Resolution Imaging Spectroradiometer) -Aqua satellite, an interannual time series of the suspended sediment concentration (SSC) at each depth layers in the Bohai Strait in winter was established through 16 cruises that benefited from the complete vertical mixing water in the strait in winter. The numerical model FVCOM, (Finite-Volume Community Ocean Model) which is forced by the hourly averaged wind field, reflected the effect of winter gales. With the model simulated winter current from 2002 to the present and the SSC at each layer, multi-year winter suspended sediment flux data were obtained for the Bohai Strait. This study found that in the winter, the suspended sediment output from the Bohai Sea to the Yellow Sea through the southern part of the Bohai Strait, while the suspended sediment input from the Yellow Sea to the Bohai Sea is through the northern part. In terms of long-term changes, the net flux ranged between 1.22 to 2.70 million tons in winter and showed a weak downward trend. The output flux and input flux both showed an upward trend, but the increase rate of the input flux was 51,100 tons/year, which was higher than the increase of the output flux rate (46,100 tons/year). These changes were mainly controlled by the increasing strength of east component of winter wind. And the weak decrease in net flux is controlled by the difference of output and input flux.

Modelling of long term Zn, Cu, Cd, Pb dynamics from soils fertilized with organic amendments

Soil contamination by trace elements (TEs) is a major concern for sustainable land management. One potential source of excessive inputs of TEs into agricultural soils are organic amendments. Here, we use dynamic simulations carried out with the IDMM-ag model to describe observed trends of topsoil Zn, Cu, Pb and Cd concentrations in a long-term crop trial in Switzerland, where soils plots have been treated with differing organic amendments, particularly farmyard manure, sewage sludge and compost. IDMM-ag requires the definition of a parsimonious set of boundary conditions. The model adequately reproduced the metal EDTA-extractable concentrations in ZOFE when site-specific soil lateral mixing, due to mechanically ploughing of small plots, was introduced. Calibration of an additional metal input flux was necessary to fit the measured data, indicating that knowledge gaps in quantifying historical metal inputs can affect field-scale simulations even in a well-characterized field. Projections of soil metal content in the long-term showed that, under stable organic amendment application rates, Zn and Cu labile concentrations might pose toxicological hazard for the soil ecosystem, particularly in the sewage sludge-amended plots. The sewage sludge topsoil was characterized by some variability in the organic matter composition, potentially due to the applied sewage sludge quality, which might affect the metal lability: this effect should be accounted for in models. This study takes a step forward in assessing potential and limitations of the IDMM-ag model to predict TEs long-term dynamics in agricultural fields, paving the way to quantitative applications of TEs modelling at field and larger scales.

Turbulence in a Coronal Loop Excited by Photospheric Motions

Photospheric motions are believed to be the source of coronal heating and of velocity fluctuations detected in the solar corona. A numerical model, based on the shell technique applied on reduced magnetohydrodynamics equations, is used to represent energy injection due to footpoint motions, storage and dissipation of energy in a coronal loop. Motions at the loop bases are simulated by random signals whose frequency-wavenumber spectrum reproduces features of photospheric motions: the p-mode peak and the low-frequency continuum. Results indicate that a turbulent state develops, dominated by magnetic energy, where dissipation takes place in an intermittent fashion. The nonlinear cascade is mainly controlled by velocity fluctuations, where resonant modes are dominant at high frequencies. Low frequency fluctuations present a power-law spectra and a bump at p-mode frequency; similar features are observed in velocity spectra detected in the corona. For typical loop parameters the energy input flux is comparable with that necessary to heat the quiet-Sun corona.

Pollution and Health Risk Assessment of Carcinogenic Elements As, Cd, and Cr in Multiple Media—A Case of a Sustainable Farming Area in China

The high concentrations of trace elements in the environment, especially the carcinogenic elements Cr, Cd, and As, in populated areas can lead to an increased non-carcinogenic risk and carcinogenic risk in humans via the effective exposure pathways (inhalation and dermal contact). In this study, the concentrations of the trace elements Cd, Cr, and As in four media were comprehensively evaluated by collecting samples from atmospheric precipitates (A), wheat (W), soil (S), and groundwater (G) in the agricultural plain. This study not only considers the health risk level, but also focuses on the relationship between soil properties and the soil–wheat system. First, according to the results of the analysis, the concentration of carcinogenic elements in atmospheric precipitates was higher than that in other media. The sequence follows the order A > S > W > G. Moreover, the input flux of A was at a relatively higher level (determined via an input flux calculation) than other farming areas. Second, the pollution of Cr, Cd, and As in A and S were analyzed using the geoaccumulation method, and the level of Cd reached mild to moderate pollution. In addition, it was found that the bioaccumulation factors (BAFs) of Cd were much higher than those of As and Cr in the soil–wheat system. Furthermore, it was found that the negative relationship between BAFs and pH, CEC (cation exchange capacity), Corg (soil organic carbon), and clay was significant. Lastly, the hazard quotient (HQ) of the non-carcinogenic risk and carcinogenic risk (CR) of the three elements in multiple media were calculated using the health risk model. The HQ results showed that the total non-carcinogenic risk index (HI) of Cd, As, and Cr in the multiple-media did not exceed the risk limit (1.00), and there was no significant risk to the locally exposed population. However, the total carcinogenic risk index (TCR) indicated that the risk index of Cr, As and Cd in multiple media exceeded the safety index range (≈10−6–10−4), and the three elements posed a significant carcinogenic risk to local residents via the main pathways. In terms of individual elements, the risk of cancer was highest via the ingestion of the carcinogenic element Cd in G and W.

Heterosis is a systemic property emerging from nonlinear genotype-phenotype relationships: evidence from in vitro genetics and computer simulations

Heterosis, the superiority of hybrids over their parents for quantitative traits, represents a crucial issue in plant and animal breeding. Heterosis has given rise to countless genetic, genomic and molecular studies, but has rarely been investigated from the point of view of systems biology. We hypothesized that heterosis is an emergent property of living systems resulting from frequent concave relationships between genotypic variables and phenotypes, or between different phenotypic levels. We chose the enzyme-flux relationship as a model of the concave genotype-phenotype (GP) relationship, and showed that heterosis can be easily created in the laboratory. First, we reconstituted in vitro the upper part of glycolysis. We simulated genetic variability of enzyme activity by varying enzyme concentrations in test tubes. Mixing the content of “parental” tubes resulted in “hybrids”, whose fluxes were compared to the parental fluxes. Frequent heterotic fluxes were observed, under conditions that were determined analytically and confirmed by computer simulation. Second, to test this model in a more realistic situation, we modeled the glycolysis/fermentation network in yeast by considering one input flux, glucose, and two output fluxes, glycerol and acetaldehyde. We simulated genetic variability by randomly drawing parental enzyme concentrations under various conditions, and computed the parental and hybrid fluxes using a system of differential equations. Again we found that a majority of hybrids exhibited positive heterosis for metabolic fluxes. Cases of negative heterosis were due to local convexity between certain enzyme concentrations and fluxes. In both approaches, heterosis was maximized when the parents were phenotypically close and when the distributions of parental enzyme concentrations were contrasted and constrained. These conclusions are not restricted to metabolic systems: they only depend on the concavity of the GP relationship, which is commonly observed at various levels of the phenotypic hierarchy, and could account for the pervasiveness of heterosis.

Inversion of a glacier hydrology model

ABSTRACTThe subglacial hydrologic system exerts strong controls on the dynamics of the overlying ice, yet the parameters that govern the evolution of this system are not widely known or observable. To gain a better understanding of these parameters, we invert a spatially averaged model of subglacial hydrology from observations of ice surface velocity and outlet stream discharge at Kennicott Glacier, Wrangell Mountains, AK, USA. To identify independent parameters, we formally non-dimensionalize the forward model. After specifying suitable prior distributions, we use a Markov-chain Monte Carlo algorithm to sample from the distribution of parameter values conditioned on the available data. This procedure gives us not only the most probable parameter values, but also a rigorous estimate of their covariance structure. We find that the opening of cavities due to sliding over basal topography and turbulent melting are of a similar magnitude during periods of large input flux, though turbulent melting also exhibits the greatest uncertainty. We also find that both the storage of water in the englacial system and the exchange of water between englacial and subglacial systems are necessary in order to explain both surface velocity observations and the relative attenuation in the amplitude of diurnal signals between input and output flux observations.

Prototype Testing of a Centrifugal Particle Receiver for High-Temperature Concentrating Solar Applications

A novel concept of a particle receiver for high-temperature solar applications was developed and evaluated in the present work. The so-called Centrifugal Particle Receiver (CentRec) uses small bauxite particles as absorber, heat transfer, and storage medium at the same time. Due to advantageous optical and thermal properties, the particles can be heated up to 1000 °C without sintering in the storage. High thermal efficiencies at high outlet temperatures are expected indicating a promising way for cost reduction in solar power tower applications. A 15kWth prototype was designed, built, and tested in order to demonstrate the feasibility and potential of the proposed concept. Extensive high flux experiments were conducted, investigating the thermal receiver performance and efficiency. For an input flux of 670 kW m−2, the target outlet temperature of 900 °C at a receiver efficiency of about 75% was successfully demonstrated.

Fluid invasion of an unsaturated leaky porous layer

We study the flow and leakage of gravity currents injected into an unsaturated (dry), vertically confined porous layer containing a localized outlet or leakage point in its lower boundary. The leakage is driven by the combination of the gravitational hydrostatic pressure head of the current above the outlet and the pressure build-up from driving fluid downstream of the leakage point. Model solutions illustrate transitions towards one of three long-term regimes of flow, depending on the value of a dimensionless parameter $D$, which, when positive, represents the ratio of the hydrostatic head above the outlet for which gravity-driven leakage balances the input flux, to the depth of the medium. If $D\leqslant 0$, the input flux is insufficient to accumulate any fluid above the outlet and fluid migrates directly through the leakage pathway. If $0<D\leqslant 1$, some fluid propagates downstream of the outlet but retains a free surface above it. The leakage rate subsequently approaches the input flux asymptotically but much more gradually than if $D\leqslant 0$. If $D>1$, the current fills the entire depth of the medium above the outlet. Confinement then fixes gravity-driven leakage at a constant rate but introduces a new force driving leakage in the form of the pressure build-up associated with mobilizing fluid downstream of the outlet. This causes the leakage rate to approach the injection rate faster than would occur in the absence of the confining boundary. This conclusion is in complete contrast to fluid-saturated media, where confinement can potentially reduce long-term leakage by orders of magnitude. Data from a new series of laboratory experiments confirm these predictions.