High-Resolution, Two-Dimensional Measurement of Dissolved Reactive Phosphorus in Sediments Using the Diffusive Gradients in Thin Films Technique in Combination with a Routine Procedure

Abstract

Dissolved reactive phosphorus (DRP) is the most available P form in sediments and often directly controls phytoplankton blooms in aquatic systems. In this study, a novel procedure was developed for two-dimensional (2D) measurement of DRP in sediments at a spatial resolution of 0.45 mm using the diffusive gradients in thin films (DGT) technique with a revised high-capacity binding phase (Zr oxide gel). This procedure involves DGT uptake of P in sediments, 2D slicing of the binding gel on a 0.45 × 0.45-mm grid system, elution of P from each gel square with 1 M NaOH, and microcolorimetric determination of DRP in each eluted solution using 384-microwell plates. Measurements of DRP via this procedure were tested in homogeneous solutions and sediments and produced an acceptable error (<20% relative standard deviation) for the analysis once the accumulated mass of P in each gel square reached 1.2 μg cm(-2). This method was successfully applied to produce 2D images of the DRP distribution in sediments with and without the influence of tubificid worm bioturbation, revealing a much more pronounced and localized impact from tubificid worms than that found using a one-dimensional measurement of pore water DRP concentrations at 1-cm resolution.

Dynamic characteristics of sulfur, iron and phosphorus in coastal polluted sediments, north China

“…The fluxes of DRP and dissolved sulfide in the sediment profiles were determined in situ using an innovative DGT technique (Ding et al, 2011). An improved ZrO-AgI binding gel was used in this DGT technique, which incorporated AgI particles into the zirconium oxide binding gel previously used in the DGT measurement of DRP, achieving simultaneous measurements of DRP and dissolved sulfide (Ding et al, 2012).…”

“…An improved ZrO-AgI binding gel was used in this DGT technique, which incorporated AgI particles into the zirconium oxide binding gel previously used in the DGT measurement of DRP, achieving simultaneous measurements of DRP and dissolved sulfide (Ding et al, 2012). The fluxes of DRP and sulfide trapped in the binding gel were determined by a conventional slice elution procedure and a computer-imaging densitometry technique, respectively (Di et al, 2012;Ding et al, 2011). The conventional slice extraction procedure involves DGT uptake of P in sediments, 2D slicing of the binding gel on a grid system, elution of P from each gel square with 1 M NaOH, and microcolorimetric determination of DRP in each eluted solution using 384-microwell plates (Ding et al, 2012).…”

“…The ZrO-AgI binding gel was then scanned (resolution set 600 dpi, 0.042 Â 0.042 mm) and its image converted to grayscale intensity to measure sulfide using a S 2À calibration (Ding et al, 2012). Further measurements of DRP were undertaken using procedures developed by Ding et al (2011Ding et al ( , 2012. The ZrO-AgI gels were sliced at 1 mm intervals, and each piece eluted with 40 mL of 1 mol L À1 NaOH.…”

“…Traditional chemical extractions (e.g., sediment core sequential extraction and analysis) are based on an operationally defined response to chemical reagents rather than on a true and in situ reflection of the lability of chemical species of interest (Stockdale et al, 2009). In contrast, the diffusive gradients in thin films technique (DGT) is an in situ, dynamic method capable of rapid measurements of labile P, Fe, and other analytes at high spatial resolution (Zhang et al, 2001;Ding et al, 2011;Lucas et al, 2015). It usually consists of a binding phase overlain by a well defined diffusion phase.…”

“…The flux of an ion through the gel is quantified by Fick's first law of diffusion (Zhang et al, 1995). The DGT technique has become potentially powerful tool for measuring the supply of key ions from the solid phase to the pore water, which can help to understand reactivity and bioavailability of key elements (Ding et al, 2011(Ding et al, , 2012. The flux of solute from pore water to DGT resin can be used to evaluate concentration of labile fractions in pore water or to quantify the sediment-porewater remobilization flux (Wu et al, 2015).…”