Two-dimensional ammonium distribution in sediment pore waters using a new colorimetric diffusive equilibration in thin-film technique

Current Trends of Analytical Techniques for Total Alkalinity Measurement in Water Samples: A Review

Increasing acidity of seawater caused by increasing anthropogenic carbon dioxide absorbed into the seawater attracted the interest of researchers due to increased concern on the deterioration of marine systems and food supply to humans. Total alkalinity (TA) is one of the important parameters in determining carbonate chemistry and is described as the capacity of the sample to neutralize acids. Over the last two decades, many analytical techniques have been developed to determine TA. This article presents a review of different analytical techniques including titration, colorimetric, spectrophotometric, and potentiometric analyses in measuring TA. Among these analytical techniques, potentiometry analysis, which utilizes electrode systems such as glass electrode and ion-selective electrode used as indicator electrodes, is the most used technique. Important features such as principle, limitations, and challenges of the involved technique are discussed in detail.

Innovative microcosm experiments for the evaluation of the regeneration rates of nutrients in sediments of a hypersaline lagoon

The aim of this study was to evaluate the regeneration of nutrients from the sediments to the water column in varying salinities, with an innovative experiment that closely simulates real environment. In vitro experiments were carried out simulating six scenarios with two sediment types (low carbonate and high carbonate). Local water and sediments were added to microcosms where circulation was forced. Results showed nitrogen release from low carbonate sediment in the lagoon, mixed and seawater (1.69, 4.68 and 7.36 μmol m^-2 day^-1, respectively). Phosphate diffusive fluxes were positive in lagoon water and low carbonate sediment (2.24 μmol m^-2 day^-1), negative with mixed water (-0.30 μmol m^-2 day^-1) and seawater (-0.51 μmol m^-2 day^-1). A phosphate release surge was observed in the low-carbonate sediment with overlying mixed water and seawater that, in the natural environment, may boost primary production.

Development and evaluation of a new colorimetric DGT technique for the 2D visualisation of labile phosphate in soils

A new colorimetric technique for the measurement of labile phosphate in soils using the diffusive gradients in thin films (DGT) technique was developed in this study. This technique can determine the mass of phosphate accumulated on the precipitated Zr-oxide based binding gel by forming the blue colour following the standard molybdate-ascorbic acid method. The optimal reaction temperature and coloration time were 20 °C (room temperature) and 26 min. After determining a well-fitted calibration equation, the technique was able to measure phosphate concentration up to 2.5 mg/L for 24 h deployment with a detection limit of 10.1 μg/L. Two-dimensional quantitative visualisation of phosphate diffusion in three phosphorus (P) fertilised soils were obtained using the colorimetric technique. The results from the colorimetric DGT technique were compared to the elution DGT technique and Colwell P extraction. The DGT techniques (colorimetric and elution) and Colwell P measurements demonstrated similar patterns of phosphate diffusion in soil. Both DGT techniques showed similar phosphate concentration along the concentric rings around the fertiliser application. A new, convenient, and fast DGT colorimetric technique was developed, and successfully used to measure the distribution of potentially available phosphate in soils. The new technique is less laborious than current techniques as it does not require any pre-treatment of the binding gel layers or heating during scanning, thus providing faster results. Therefore, the technique may be more suitable for in-field applications and can be used to investigate the in situ diffusion of potentially available phosphate from fertilisers, and relate this to the plant uptake of P.

In situ, high-resolution measurement of labile phosphate in sediment porewater using the DET technique coupled with optimized imaging densitometry

Obtaining two-dimensional distributions of reactive phosphorus in sediment porewater is very important for understanding fine-scale phosphorus mobilization and sequestration processes in sediments. In this study, the diffusive equilibrium in thin films (DET) measurement based on computer imaging densitometry (CID) was studied in detail with optimal conditions described. This study focuses on evaluating the two-dimensional colorimetric DET method coupled with CID (DET-CID method) for porewater labile phosphate measurements. The result shows that the red channel filter is the optimum channel for sensitivity to process the image. Additionally, staining time and temperature have great influence on the method, and 20 min staining time and ≥25 °C staining temperature were recommended. The minimum detection limit of labile phosphate of this method was 0.300 mg P/L, and the maximum detection limit could reach 50.00 mg P/L. The DET-CID technique can be used to measure labile phosphate in a wide range of acidic and alkaline water bodies (pH = 2-10 and water hardness from 0 to 2000 mg/L as CaCO₃). The linear regression analysis shows that this technique presents very similar results compared with other two existing methods (R² = 0.999). Our results would give insights into the precisely measurements of labile phosphate in field applications.