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Purpose: The occurrence of harmful algae blooms has been increasing in large lakes worldwide. The mechanism of heavy metals mobilization in sediments during algae blooms is not well understood. As a major pollutant in the sediments of Taihu Lake, cobalt (Co) has been selected to study heavy metal mobilization during algae blooms. Materials and methods: Rhizon and HR-Peeper sampling techniques have been used for in situ investigation and indoor simulation experiments to collect information on dissolved Co, manganese (Mn), and UV absorbance at 254 nm (UV254) in sediments. Excitation–emission matrix (EEM) was combined with parallel factor (PARAFAC) to determine the change of dissolved organic matter (DOM) components during algae blooms. The chemical morphology of Co in pore water was analyzed by visual MINTEQ model. The Stern–Volmer model was used to characterize the stability of different DOM components and Co(II). Results and discussion: Algae blooms significantly increased the dissolved Co concentration in sediments. The release of Co was closely related to DOM in the algae bloom sediments, which was reflected by the similar distribution and significant positive correlation between the dissolved Co and DOM in pore water, during both in situ and laboratory simulation algae blooms experiments. On the other hand, the saturation of oxygen in the sediment–water interface (SWI) rapidly decreased from 100 to 0% during algae blooms, resulting in high mobilization of Co and reduction of Mn oxides in sediments. This was supported by the simultaneous increase of dissolved Co and Mn and significant positive correlation between dissolved Co and Mn in the simulation aerobic–anaerobic sediments. The transformation of most Co(II) into DOM-Co(II) complexes, as calculated by the Visual MINTEQ model, further demonstrated that the mobilization of Co was mainly controlled by the DOM content in the sediments during algae blooms. Further studies revealed that tyrosine-like substance released by algae played a major role in their complexation with Co, possibly due to their relatively high content and high stability after binding Co. Conclusion: The mobilization of Co in sediments during algae blooms was mainly controlled by DOM through complexation, reflected by the observation that dissolved Co concentration and UV254 increased simultaneously and had significant positive correlation during in situ monitoring and indoor simulations experiments. More than 80% of dissolved Co in the pore water during algae blooms was DOM-Co complexes, supporting this conclusion. It was further observed that tyrosine-like substances played an important role in Co complexation. [ABSTRACT FROM AUTHOR]

Purpose: To study the effects of snail (Bellamya aeruginosa) bioturbation on phosphorus (P) mobility in sediment and the relevant mechanisms behind them. Materials and method: A microcosm simulation experiment was carried out at millimeter resolution with an 89 days culture of homogeneous sediments. High-resolution dialysis (HR-Peeper) and diffusive gradient in thin films (DGT) techniques were utilized to simultaneously acquire the vertical distribution of soluble and labile P/iron (Fe) in bioturbation sediments. Results and discussion: Snail bioturbation significantly enhanced soluble reactive P (SRP) and labile P concentrations, with the maximum increment to 306% and 1133% of the control sediments within the influence depths from 0 to − 30 mm and to − 20 mm, respectively. The P fluxes released from the sediment–water interfaces in snail treatments were correspondingly enhanced with the maximum increments to 218% of the control. Also, snail bioturbation significantly enhanced the soluble Fe(II) and labile Fe concentrations by maximum increment of 218% and 199% of the control within 0 to −24 mm and − 19 mm, respectively. Conclusions: The high correlation between soluble/labile P and Fe suggested that P release from the sediment under snail bioturbation was due to the reduction and dissolution of Fe(III) oxyhydroxide. [ABSTRACT FROM AUTHOR]

The effects of chironomid larval (Propsilocerus akamusi) bioturbation on sediment phosphorus (P) mobility were studied over the course of 34 days using the indoor larval cultivation method on in situ sediment cores. High-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) techniques were used to record fine-scale changes of soluble and DGT-labile P and iron (Fe) concentrations in the sediment. The larval-driven irrigation of the overlying water into their burrows significantly increased the oxygen penetration depth (OPD) and redox state (Eh) in sediments. In addition, the soluble and DGT-labile P and Fe decreased with the increase of OPD and Eh in larval-bioturbated sediments. The greatest decrease in the mean concentration of SRP, soluble Fe, and DGT-labile P in the Propsilocerus group was observed on Day 15 of the experiment, with a decrease by over half of the mean concentration of the control group. Furthermore, two-dimensional measurements of DGT-labile P concentration showed notable reductions of DGT-labile P around larval burrows. The DGT-induced fluxes in sediments (DIFS) model also exhibited a much longer response time (420 s) and a much higher rate of P adsorption (0.002 s−1) in the bioturbation sediments than those in the control sediments (116 s and 0.009 s−1, respectively). A significant correlation was shown for DGT-labile P and DGT-labile Fe. We conclude that Fe(II) oxidation and its enhanced adsorption were the major mechanisms responsible for the decrease of soluble and DGT-labile P in sediments. [ABSTRACT FROM AUTHOR]

A large number of ex situ sampling techniques have been used traditionally to investigate the impact and fate of pollutants in soil, sediment and waters. However, the distribution and form of chemical species present are often altered prior analysis, due to the alterations during sampling and transfer to the laboratory. Alternatively, a robust in situ passive sampling technique, diffusive gradients in thin films (DGT), has been developed for the measurement of labile concentrations, species and distribution of various solutes in soil, sediment and waters. Here we review the recent developments in DGT device configurations and components, e.g., binding agents, diffusive phases and filter membranes. We highlight new configurations for effectively reducing the measurement errors and the disturbance of environmental media. We discuss DGT applications for the analysis of soil, sediment and water, such as evaluation of bioavailability and toxicity, measurement of nutrients and organic substances, and assessment of relationships between multiple solutes. We also present the coupling of DGT with other in situ measurement techniques such as dialysis samplers (Peeper), diffusive equilibrium in thin films (DET) and planar optodes (PO). [ABSTRACT FROM AUTHOR]

Purpose: Phosphorus influence on arsenic bioavailability in soils and its toxicity to plants is widely recognized. This work compares competitive influence of P on As bioavailability in dry and flooded soils. Materials and methods: Pot experiments were carried out in dry and flooded soils, respectively. Bioavailable As in soils was measured using diffusive gradients in thin films (DGT), soil solution concentration, and three single chemical extraction methods. Results and discussion: P concentration at 50 mg/kg promoted wheat growth in dry soil. At concentrations above 50 mg/kg, P competition inhibited wheat growth and enhanced As toxicity. In flooded soil, the rice height and biomass decreased with the increase of P addition. P concentrations above 800 mg/kg were lethal to the rice. The content of As absorbed by wheat and rice roots as well as shoots increased with the increase of P concentration. The bioavailability of As in wheat- and rice-grown soils, determined by all methods, also increased with the increase of P concentration. The correlation analysis between the bioavailable As measured by the all three methods and the content of As in plants showed a significant positive correlation. The Pearson correlation coefficient for the DGT method was higher comparing to all other methods. DGT-induced fluxes in soils (DIFS) modeling further showed sharp decreases of Tc (the characteristic time to reach equilibrium between available solid As pool and soil solution As from DGT perturbation) and increases of desorption and adsorption rate constants (k1 and k−1) of As in P-amended soils, reflecting that the kinetic release of As from available solid As pools became much easy from P competition. Conclusions: P competition in both dry and flooded soils could significantly increase bioavailability of As and further increase its toxicity. Competition effect was more pronounced in flooded soil. DGT is a more accurate method for As bioavailability evaluation in both dry and flooded soils. [ABSTRACT FROM AUTHOR]

The release of arsenic (As) from sediments poses a risk to human health especially at high pH levels. Despite this, the distribution and kinetic response of mobile As remains unclear under varying pH conditions. In this study, a microcosm incubation experiment was performed, using sediment cores in combination with dialysis (Peeper) and thin film diffusive gradients (DGT), to investigate the distributions of mobile As (soluble As in pore water and DGT-labile As) at high vertical resolutions (2-4 mm). Results show that the concentrations of soluble As present in the water column increased 1.5-fold with an increase in pH from 5.4 to 11.2. Both soluble As in pore water and DGT-labile As exhibited stable low-level distributions in the uppermost layer beneath the sediment-water interface, followed by increasing concentration distribution with decreasing layers to middle depths. The mean concentrations of mobile As species increased with increased water pH in both sediment profiles and with upward diffusion gradients, showing a 0.2-fold increase of soluble As in the top 20-mm layer and a 0.6-fold increase in deeper 20-52-mm layers, while DGT-labile As showed a 1.0- and 1.1-fold increase in these two layers, respectively. Modeling of DGT-induced flux in sediments (DIFS) showed that the desorption rate constant increased more rapidly than the absorption rate constant, resulting in the increased availability of solid As pools, therefore resupplying the soluble As in pore water from sediments. [ABSTRACT FROM AUTHOR]

To overcome the shortcomings of the conventional variable fuzzy set assessment (VFSA) method in the dynamic water quality assessment, the functional data analysis (FDA) theory is introduced into VFSA method to develop a dynamic variable fuzzy set assessment (DVFSA) model. The procedure of DVFSA is: (1) generating continuous concentration curves through smoothing method, (2) calculating relative membership curves of indicators, (3) generating comprehensive relative membership curves, (4) making dynamic water quality assessment through calculating the ranking feature curve. DVFSA is the generalization of the conventional VFSA from discrete finite time points into continuous time domain through FDA method. DVFSA keeps the property of VFSA in fuzzy domain constructing and comprehensive classification recognizing; and absorbs the advantages of FDA in dealing with different sampling time and missing values, and representing the varying process of aquatic environment comprehensively and intuitively. Furthermore, DVFSA avoids the potential logical error by banning the least square optimization method in comprehensive relative membership generation. The dynamic water quality condition of Jiangdu hydro-junction in 2013 is assessed using DVFSA and the result shows that it belongs to classification 'I' from January to April and 'II' in other months. To further improve the water quality condition of Jiangdu hydro-junction, it is suggested to strengthen the environment protection in Lixiahe region and New Tongyang Canal. [ABSTRACT FROM AUTHOR]