Simultaneous Nitrite/Nitrate Imagery at Millimeter Scale through the Water–Sediment Interface

Abstract

The present study describes new procedures to obtain at millimeter resolution the spatial distribution of nitrite and nitrate in porewaters, combining diffusive equilibrium in thin films (DET), colorimetry and hyperspectral imagery. Nitrite distribution can be easily achieved by adapting the well-known colorimetric method from Griess (1879) and using a common flatbed scanner with a limit of detection about 1.7 μmol L(-1). Nitrate distribution can be obtained after reduction into nitrite by a vanadium chloride reagent. However, the concentration of vanadium chloride used in this protocol brings coloration with a wide spectral signature that creates interference only deconvolvable by imaging treatment from an entire visible spectrum for each pixel (spectral analysis). This can be achieved by hyperspectral imaging. The protocol retained in the present study allows obtaining a nitrite/nitrate image with micromolar limit of detection. The methods were applied in sediments from the Loire Estuary after different treatments and allowed to precisely describe two-dimensional millimeter features. The present technique adds to the combination of gel-colorimetry and hyperspectral imagery a very promising new application of wide interest for environmental issues in the context of early diagenesis and benthic fluxes.

Total nitrate uptake by an invasive benthic foraminifer in marine sediments

“…A summary of the NO2 -/ NO3 -2D gel method is presented in Figure 4 (details see, Metzger et al, 2016). For each core, a DET (Diffusive Equilibrium in Thin films) gel probe (16 cm x 6.5 cm and 0.1 cm thickness, Fig.…”

“…For each core, a DET (Diffusive Equilibrium in Thin films) gel probe (16 cm x 6.5 cm and 0.1 cm thickness, Fig. 4 a) was hand-made prepared (Metzger et al, 2016). The gel probe was inserted into the sediment and left for 5 hours to allow for a diffusive equilibration time between the gel and porewaters (Fig.…”

“…To characterize these microenvironments at submillimeter/ millimeter scales, new approaches have to be used. Recently, a 2D-DET (Diffusive Equilibrium in Thin-film) technique combining colorimetry and hyperspectral imagery was developed to obtain the distribution of nitrite and nitrate in sediment porewater at millimeter resolution in two dimensions (Metzger et al, 2016). This method avoids mixing of intracellular nitrate and nitrate contained in the sediment porewater.…”

Innovative TEM-coupled approaches to study foraminiferal cells

“…Also, recent advances on fine-scale analyses of porewater chemistry in sediments indicate both vertical and horizontal gradients and heterogeneity of constituents such as oxygen (Glud et al 2005), nitrate (Glud et al 2009;Metzger et al, 2016), dissolved reactive phosphorus, dissolved iron (Thibault de Chanvalon et al 2015), and probably other compounds as well, at sub-millimeter length scales. Many benthic foraminifera are infaunal, particularly in mesotrophic to eutrophic sediments where they can utilize organic matter even in deep sediments (e.g., >3 cm below the sediment-water interface; Jorissen et al 1995).…”

Microliter Operation for Determination of Nitrate-Nitrogen via Simple Zinc Reduction and Color Formation in a Well Plate with a Smartphone

“…Nitrate is reduced to nitrite with suitable reducing agents, for example, cadmium, 3 copperised cadmium, 4,5,10,11 zinc, 12,13 hydrazine sulfate, 14 or vanadium (III). 15,16 Copperised cadmium is a highly effective reductant with reduction efficiency of over 90%. 17 However, cadmium is a toxic heavy metal that is harmful to humans and the environment.…”