Development of absorption spectrophotometry of iron(III) in environmental water and sediments using NEDA and its application to the field.

In this study, we developed a simple method that enables iron(III) in environmental water to be directly determined via spectrophotometry. In water samples, iron(III) formed a yellowish complex with N-1-Naphthylethylenediamine dihydrochloride (NEDA) at pH 2.0-2.8, the maximum absorption wavelength of which was 462 nm. Detection sensitivity increased in the presence of chloride ions and remained constant for 2-24 h with 0.05-0.57 mol L-1 chloride. Therefore, NEDA solution containing chloride ions was used as a chromogenic reagent for the determination of iron(III). The determination range for this method was 0.1-20 mgFe(III) L-1 in a 5 cm glass cell. The developed method is highly selective for iron(III) and has been successfully applied to freshwater, brackish water, seawater, turbid water in rivers, as well as to riverbed and freshwater lake sediments. In addition, a combination of the proposed NEDA method and the 1,10-phenanthroline method enabled simultaneous determination of iron(III) and iron(II).

Sensitive Gas Chromatography Detection of Nanomolar Hydroxylamine in Environmental Water by Fe(III) Oxidation.

Nanomolar concentrations of NH2OH in natural water sources were determined using an Fe3+ oxidation method. A pH of 2.35 - 2.50 was used, which was adjusted by adding a chloroacetate buffer. Equal amounts (1.0 mL) of the chloroacetate solution and ferric chloride solution were added to the water sample (70 mL) to oxidize NH2OH to N2O. The resulting N2O in the sample water was then quantified by headspace analysis using a gas chromatograph with an electron-capture detector (ECD), where a limit of detection of 0.2 µgN L-1 (14 nmol L-1) was achieved. This method was successfully applied to samples of freshwater, brackish water, and seawater, and despite the various salinities no interfering substances were observed. Furthermore, NH2OH was successfully detected in samples collected from the Hii River and Lakes Shinji and Nakaumi (Shimane Prefecture, Japan). In addition, the proposed method was also applicable to samples rich in organic substance derived from phytoplankton.

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4 +/15NH4 + Analyses via Sequential Conversion to N2O.

The importance of understanding the fate of nitrate (NO3-), which is the dominant N species transferred from terrestrial to aquatic ecosystems, has been increasing because global nitrogen loads have dramatically increased following industrialization. Dissimilatory nitrate reduction to ammonium (DNRA) and denitrification are both microbial processes that use NO3- for respiration. Compared to denitrification, quantitative determinations of the DNRA activity have been carried out only to a limited extent. This has led to an insufficient understanding of the importance of DNRA in NO3- transformations and the regulating factors of this process. The objective of this paper is to provide a detailed procedure for the measurement of the potential DNRA rate in environmental samples. In brief, the potential DNRA rate can be calculated from the 15N-labeled ammonium (15NH4+) accumulation rate in 15NO3- added incubation. The determination of the 14NH4+ and 15NH4+ concentrations described in this paper is comprised of the following steps. First, the NH4+ in the sample is extracted and trapped on an acidified glass filter as ammonium salt. Second, the trapped ammonium is eluted and oxidized to NO3- via persulfate oxidation. Third, the NO3- is converted to N2O via an N2O reductase deficient denitrifier. Finally, the converted N2O is analyzed using a previously developed quadrupole gas chromatography-mass spectrometry system. We applied this method to salt marsh sediments and calculated their potential DNRA rates, demonstrating that the proposed procedures allow a simple and more rapid determination compared to previously described methods.

Influence of parasitic chytrids on the quantity and quality of algal dissolved organic matter (AOM).

Algae-derived dissolved organic matter (AOM) is an important nutrient source for heterotrophic bacteria, while AOM such as humic substances pose significant challenges during water treatment processing. We hypothesized that the parasitic infection of algae could change the composition and concentration of AOM. This study investigated the quality and quantity of DOM and bacterial abundance in diatom (Synedra) cultures, with and without parasitic fungi (chytrids). The quality of DOM was analyzed using three-dimensional excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) and was compared to changes in algal and bacterial cell numbers. Bacterial abundance was higher and dissolved organic carbon concentrations were lower in the diatom cultures infected with parasitic fungi. Among the DOM compounds, the concentrations of tryptophan-like material derived from algae were significantly lower and the concentrations of humic substance-like material were higher in the infected treatment. The parasitic fungi may have consumed tryptophan-like material and stimulated the release of humic substances. These results provide the first evidence that fungal infection may modulate algal-bacterial interactions, which are associated with changes in the nature of AOM.

Sensitive Method for the Oxidation-determination of Trace Hydroxylamine in Environmental Water Using Hypochlorite Followed by Gas Chromatography.

We developed a method for quantifying trace NH2OH in brackish- and sea-water samples. Previously reported methods applicable to fresh water cannot be applied to such samples. We determined that interference in seawater owing to the bromide ion can be removed by the addition of phenol. In our procedure, phenol and hypochlorite solutions were added to a sample solution to oxidize NH2OH to N2O. N2O in the sample was then quantified by headspace analysis. The method is not affected by the salt content or ammonia, nitrate, or nitrite at concentrations of 300 µgN L-1 or less. It has a limit of detection of 0.2 µgN L-1, and can quantify NH2OH in natural water samples with a wide range of salinity. It was applied to samples from Lake Nakaumi, a brackish lake located in the eastern part of Shimane Prefecture, Japan.

Determination of Trace Hydrazine in Environmental Water Samples by in situ Solid Phase Extraction.

A simple and rapid in situ method for the determination of hydrazine based on the concentration of aldazine compound formed by the reaction of hydrazine with p-dimethylaminobenzaldehyde was developed. This method was based on solid-phase extraction using a Sep-Pak C18 cartridge, followed by the quantification of hydrazine using a spectrophotometric method. To a sample solution of environmental water, p-dimethylaminobenzaldehyde solution was added to form aldazine by the reaction with hydrazine. The solution was passed through a Sep-Pak C18 cartridge for the adsorption of aldazine. In the laboratory, the aldazine adsorbed on the Sep-Pak C18 cartridge was eluted by passing a hydrochloric acid-ethanol (1:10) solution through the cartridge, and the color intensity of the solution was measured at 457 nm. The limit of detection for the new method was 0.2 mgN L-1 of hydrazine. The determination of hydrazine in solution was not influenced even by hydrogen sulfide and organic matter. This method was then applied to the brackish water of Lake Nakaumi in the eastern area of Shimane Prefecture, Japan. This method was used to determine hydrazine in freshwater, seawater and wastwater.

Colorimetric Determination of Sulfide in Microsamples.

A method for determination of hydrogen sulfide in microsamples (200 µL) was developed by modifying the methylene blue method. Samples were collected using a micropipette and were combined with sulfide coloring reagent and 5 mL of 0.1 M HCl in test tubes. Absorbance of the solution was measured spectrophotometrically at 667 nm. This modified method did not require any special labware or technique, and can be used in a variety of research fields.

Fluxes of carbon dioxide, methane and nitrous oxide in two contrastive fringing zones of coastal lagoon, Lake Nakaumi, Japan.

We measured fluxes of carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O) simultaneously in two typical fringing zones, sandy shore and salt marsh, of coastal lagoon, Lake Nakaumi, Japan, in mid-summer 2003. Our aim was to quantify net the greenhouse gases (GHGs) fluxes and examine key factors, which control variation of the GHGs fluxes in the two sites. Net CO(2) and CH(4) fluxes were markedly different between the two sites; magnitudes and variations of the both fluxes in sandy shore were lower than those of salt marsh. Meanwhile, magnitude and variation of net N(2)O flux in the two sites were similar. In sandy shore, temporal and spatial variation of the three GHGs fluxes were highly controlled by water level fluctuation derived from astronomic tide. In salt marsh, spatial variation of the three GHGs fluxes were correlated with aboveground biomass, and temporal variation of CO(2) and CH(4) fluxes were correlated with soil temperature. The sum of global warming potential, which was roughly estimated using the observed GHGs fluxes, was ca. 174-fold higher in salt marsh than in sandy shore.

A simple and sensitive method for the determination of hydroxylamine in fresh-water samples using hypochlorite followed by gas chromatography.

A new and simple method for the determination of hydroxylamine in environmental water, such as fresh rivers and lakes using hypochlorite, followed by its gas choromatographic detection, has been developed. A glass vial filled with sample water was sealed by a butyl-rubber stopper and aluminum cap without head-space, and then sodium hypochlorite solution was injected into the vial through a syringe to convert hydroxylamine to nitrous oxide. The head-space in the glass vial was prepared with 99.9% grade N2 using a gas-tight syringe. After the glass vial was shaken for a few minutes, nitrous oxide in the gas-phase was measured by a gas chromatograph with an electron-capture detector. The dissolved nitrous oxide in the liquid-phase was calculated according to the solubility formula. The proposed method was applied to the analysis of fresh-water samples taken from Iu river and Hii river, flowing into brackish Lakes Nakaumi and Shinji, respectively.