Mitigation of CyanoHABs Using Phoslock® to Reduce Water Column Phosphorus and Nutrient Release from Sediment

Cyanobacterial blooms can be stimulated by excessive phosphorus (P) input, especially when diazotrophs are the dominant species. A series of mesocosm experiments were conducted in a lake dominated by a cyanobacteria bloom to study the effects of Phoslock®, a phosphorus adsorbent. The results showed that the addition of Phoslock® lowered the soluble reactive phosphate (SRP) concentrations in water due to efficient adsorption and mitigated the blooms. Once settled on the sediments, Phoslock® serves as a barrier to reduce P diffusion from sediments into the overlying waters. In short-term (1 day) incubation experiments, Phoslock® diminished or reversed SRP effluxes from bottom sediments. At the same time, the upward movement of the oxic–anoxic interface through the sediment column slightly enhanced NH4+ release and depressed N2 release, suggesting the inhibition of nitrification and denitrification. In a long-term (28 days) experiment, Phoslock® hindered the P release, reduced the cyanobacterial abundance, and alleviated the bloom-driven enhancements in the pH and oxygen. These results suggest that, through suppression of internal nutrient effluxes, Phoslock® can be used as an effective control technology to reduce cyanobacteria blooms common to many freshwater systems.

Diffusion Coefficients at Infinite Dilution of Carbon Dioxide and Methane in Water, Ethanol, Cyclohexane, Toluene, Methanol, and Acetone: A PFG-NMR and MD Simulation Study

Diffusion coefficients at infinite dilution are important basic data for all processes involving mass transfer. They can be obtained from studying samplesin equilibrium using nuclear magnetic resonance spectroscopy with pulsed field gradients (PFG-NMR), a technique which is widely used in chemistry but isonly rarely applied in engineering studies. This advantageous technique was employed here to measure the self-diffusion coefficients of diluted solutions ofcarbon dioxide and methane in the pure solvents water, ethanol, cyclohexane, toluene, methanol, and acetone at 298.15 K. For the systems (carbon dioxide +water) and (carbon dioxide + ethanol), measurements were also carried out at 308.15 K, 318.15 K and 333.15 K. Except for (methane + water) and (methane +toluene), no literature data for the methane-containing systems were previously available. At the studied solute concentrations, there is practically no differencebetween the self-diffusion coefficient and the mutual diffusion coefficient. The experimental results are compared to experimental literature data as well as toresults from semi-empirical methods for the prediction of diffusion coefficients at infinite dilution. Furthermore, molecular dynamics simulations were carried outfor all systems to determine the diffusion coefficient at infinite dilution based on force fields that were taken from the literature, and the results are compared tothe experimental data and those from the classical prediction methods.

Nitrogen and Phosphorus Diffusion Fluxes: Insight from High-Resolution Technology and Hydrodynamic Modeling

Nitrogen and phosphorus are key elements in controlling eutrophication in the aquatic system. Water and sediment samples were collected from Hongfeng Lake, a seasonally stratified reservoir in southwest China, in winter and summer. Diffusion fluxes of NH4+, NO3−, and labile P in summer using diffusive gradients in thin films technology were 3.4, −37.2, and 0.9 mg m−2 day−1, respectively, based on Fick’s first law. The diffusion flux of labile P was 2.05 mg m−2 day−1 in winter. The contributions fraction of the labile P diffusion flux from sediment to the overlying water were higher in winter than those in summer, because of the relatively lower external input, concentrations and higher diffusion fluxes in winter. After the external input decreased, all of the three diffusion fluxes were lower than the previous record. To understand the influence effect of hydrodynamics, environmental fluid dynamics code modeling was used to simulate the flow and temperature field in winter and summer. Modeling results showed that velocity in summer was higher than that in winter due to concentrated rainfall within the catchment. Moreover, the velocity and temperature in the euphotic zone were higher than that of the hypolimnion in summer. Less variation of velocity and temperature in vertical profile in winter than that in summer was observed, which may be attributable to the high specific heat capacity and the low heat conductivity of water. There was no significant correlation among velocity, hydrochemistry, nitrogen, and phosphorus concentrations. Hydrodynamics, solar radiation, and water depth affect the position of the thermocline, which was consequently to water temperature, hydrochemistry, dissolved nitrogen, and phosphorus concentration. Correlation analysis suggested that the higher bottom velocity and total bed shear may accelerate labile P, NH4+, and NO3− diffusion fluxes. These results provide evidence and suggestions for preventing and controlling reservoir eutrophication and water safety management.

White matter properties underlying reading abilities differ in 8-year-old children born full term and preterm

Diffusion magnetic resonance imaging (dMRI) studies find differences in associations between reading and white matter fractional anisotropy (FA) in children born full term (FT) versus preterm (PT). Use of complementary neuroimaging modalities may reveal neurobiological factors driving these associations. We used two MRI methods to interpret associations of reading abilities and white matter properties in FT and PT children. Participants (N=79; 36 FT; 43 PT) were administered Gray’s Oral Reading Test at age 8 years. We segmented two dorsal and two ventral white matter tracts associated with reading skills and quantified (1) FA from dMRI and (2) R1 from quantitative relaxometry, as a proxy for myelin content. We examined correlations between reading scores and imaging metrics, assessing trajectories along the tracts. Mean reading scores fell in the typical range in both groups. Reading positively correlated with FA in segments of the left arcuate and the left and right superior longitudinal fasciculi, but only in FT children, not in PT children. Reading positively correlated with R1 in segments of the left superior longitudinal, right uncinate, and left inferior longitudinal fasciculi, but only in PT children, not in FT children. The significantly different patterns of associations between reading abilities and white matter properties across FT and PT groups suggest variations in the neurobiology of typical reading abilities.

The Effect of Incentives: Diffusion of Responsibility

Diffusion of responsibility refers to the problem that when something is everyone’s job, it in effect ends up being nobody’s job. This explains why many collective problems arise. People face perverse incentives to free ride on others’ actions and not to do their part. As a result, agents often think in short-term rather than long-term ways. Problems such as climate change can be modeled as instances of the tragedy of the commons, one form of a collective action problem that arises due to perverse incentives created by the diffusion of responsibility.

The Influence of Cascade Reservoir Construction on Labile Phosphorus in the Sediment of Lancang River

The influence of cascade reservoirs construction on labile phosphorus (P) is an important scientific problem in the Lancang River. The concentration of labile P in cascade deep-water reservoirs were determined, and the influence of cascade reservoirs construction on the DGT-labile P was analyzed. The construction of cascade reservoirs led to significant differences in concentrations of DGT-labile P, which in the upstream of Xiaowan (XW) Reservoir were differences from that in the downstream Nuozhadu (NZD) Reservoir. The P diffusion fluxes in XW Reservoir were − 8.59–250.50 ng·cm− 2·d− 1, and that in NZD Reservoir were 3.82–24.80 ng·cm− 2·d− 1. The P pollution of XW Reservoir was higher, highlighting the importance of controlling P pollution of XW Reservoir. The construction of cascade reservoirs had made the release of DGT-labile P more dependent on the reductive dissolution of Mn oxides. The early diagenesis transformed bio-availability P (BAP) remobilization into DGT-labile P that made the increase of DGT-labile P/BAP with depth. However, the DGT-labile P/BAP of upstream XW Reservoir was 7.8 times larger than that of downstream NZD Reservoir, which indicated that the construction of cascade reservoirs weakened the remobilization of P in sediment.

Spatiotemporal assessment of phosphorus release from a fertiliser granule and its diffusion into bulk soil: a combined experimental and modelling study

<p>Phosphorus (P) is a limiting nutrient for crops and it is therefore highly managed in human activities such as agriculture. Not only the global phosphate rock reserves are going to be exhausted in a century, but P can also be lost from fields with the runoff ending up contaminating water bodies and causing eutrophication.</p> <p>This study is aimed at investigating P release from a fertiliser granule at high spatial and temporal resolution to optimise fertilisation timing, match crop requirements and reduce runoff. Experimental data consist of time-resolved P concentration in the soil solution at three different depths and total P concentration profile determined via total soil digestion. We observed a rapid, single-pulse release of P from the fertiliser granule shortly after soil wetting (<2h). The pulse reaches the furthest probe (3 cm) within the same timeframe, then P concentration in the soil solution gradually decreases over the following 150 hours due to adsorption.</p> <p>As the experimental data did not match the model-predicted P diffusion behaviour, a new modelling approach was used to reproduce the data. The model accounts for P diffusion and adsorption onto soil particles, resulting in the temporal evolution of P concentrations both in the soil solution and adsorbed onto soil particles. As the final total P concentration in soil reflects the initial P concentration profile in the soil solution, the model shows that adsorption onto soil particles happens faster than diffusion. Additionally, the model gives an estimate of diffusion, adsorption and desorption rates, as well as the maximum distance that P can travel from the source.</p> <p>Combining high-resolution experiments with modelling provided a new insight into P release and diffusion from a fertiliser granule. The results can inform optimal fertilisation timings to improve crop yields while reducing P application rates and undesirable side effects such as eutrophication.</p>

Diffusion imaging perspectives on brain development in childhood and adolescence

Diffusion magnetic resonance imaging (dMRI) is a versatile tool which can be applied to investigate brain microstructure. This chapter outlines brain development trajectories from infancy to adulthood as described by dMRI. The chapter focuses on white matter development, as dMRI is particularly well suited to describing white matter tissue properties. The chapter also discusses sources of individual variation which are simultaneously fascinating and confounding to research efforts. Next, the chapter discusses links between white matter development and cognition, with specific examples drawn from reading research. Additional techniques which may complement future diffusion-based research are introduced in the chapter’s final section.

Preparation of high-strength and high-toughness sodium alginate fibers based on the study of multi-ion diffusion kinetics in a low temperature dissolution system

Diffusion kinetics under different coagulation conditions of high-strength and high-toughness sodium alginate fibers obtained through a low temperature dissolution method.

Natural Products Dereplication by Diffusion Ordered NMR Spectroscopy (DOSY)

Diffusion-ordered NMR spectroscopy (DOSY) can be used to analyze mixtures of compounds since resonances deriving from different compounds are distinguished by their diffusion coefficients (D). Previously, DOSY has mostly been...