Yukiko Senga

Seasonal variation in nutrients and chlorophyll a in the stratified brackish Lake Nakaumi, Japan

The major inorganic nitrogenous compounds in aquatic environments are nitrate, ammonium and sometimes nitrite. Previously we studied the uptake of ammonium and nitrate by natural phytoplankton (SEIKE et al. 1986a), denitrification (SEIKE et al. 1986b, l986c ), nitrification (SEIKE et al. 1986c, 1997), the behavior of nitrate (SEIKE et al. 1990) and nitrous oxide (SENGA et al. 2001, 2002) in the brackish Lake Nakaumi, Japan. The present study was undertaken to explain seasonal variation in inorganic nitrogen compounds in the water column of Lake Nakaumi, on the basis of existing knowledge of nitrogen cycling in the lake. Data on nitrogenous nutrients such as nitrate, nitrite and ammonium in the lake were collected monthly during 1990-1999. Chlorophyll a was analyzed from data collected at monthly intervals from 1990 to 2002. A further aim of this paper was to evaluate the importance o f coupled nitrifi-

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.