Concentrations of acid volatile sulfides (AVS) as metal sulfides in three different size fractions (<30 nm, 30–200 nm, >200 nm) at Lake Teganuma were measured using a nano-filtration followed by a purge-trap gas chromatography with a flame photoionization detector (GC-FPD). Fresh water samples were collected at four sites in the lake and sequentially filtered with 30 nm and 200 nm pore size filters on site immediately after the sampling. The concentrations of unfiltered AVS (AVStotal) ranged from 0.6 to 1.4 nmol/kg, among which the highest concentration was found in a lotus colony site. Except for the lotus colony site, the relative AVS abundances in the three size-fractions were quite similar. It was found that >80% of AVStotal existed in the <30 nm size fraction, while only 10~20% in 30–200 nm and >200 nm size fractions. In the lotus colony site, on the other hand, <30 nm fraction contributed only ~5% but the 30–200 nm size fraction exhibited most dominant contribution (~80%), although the AVStotal concentration in the lotus colony site was similar to those in other sites. Present observation shows that metal sulfides exist in fresh water environment and mainly reside in <30 nm size fraction, but even larger metal sulfide nanoparticles with the size of 30–200 nm can be formed, which seem to be formed from <30 nm size fraction through a relatively rapid process.
Abstract. We developed a mass spectrometric soil-gas flux measurement system using a portable high-resolution multi-turn time-of-flight mass spectrometer, called MULTUM, and we combined it with an automated soil-gas flux chamber for the continuous field measurement of multiple gas concentrations with a high temporal resolution. The developed system continuously measures the concentrations of four different atmospheric gases (NO2, CH4, CO2, and field soil–atmosphere flux measurements of greenhouse gases (NO2, O2) ranging over 6 orders of magnitude at one time using a single gas sample. The measurements are performed every 2.5 min with an analytical precision (2 standard deviations) of ±34 ppbv for NO2; ±170 ppbv, CH4; ±16 ppmv, CO2; and ±0.60 vol %, O2 at their atmospheric concentrations. The developed system was used for the continuous field soil–atmosphere flux measurements of greenhouse gases (NO2, CH4, and CO2) and O2 with a 1 h resolution. The minimum quantitative fluxes (2 standard deviations) were estimated via a simulation as 70.2 µgNm-2h-1 for NO2; 139 µgCm-2h-1, CH4; 11.7 mg C m−2 h−1, CO2; and 9.8 g O2 m−2 h−1, O2. The estimated minimum detectable fluxes (2 standard deviations) were 17.2 µgNm-2h-1 for NO2; 35.4 µgCm-2h-1, CH4; 2.6 mg C m−2 h−1, CO2; and 2.9 g O2 m−2 h−1, O2. The developed system was deployed at the university farm of the Ehime University (Matsuyama, Ehime, Japan) for a field observation over 5 d. An abrupt increase in NO2 flux from 70 to 682 µgNm-2h-1 was observed a few hours after the first rainfall, whereas no obvious increase was observed in CO2 flux. No abrupt NO2 flux change was observed in succeeding rainfall events, and the observed temporal responses at the first rainfall were different from those observed in a laboratory experiment. The observed differences in temporal flux variation for each gas component show that gas production processes and their responses for each gas component in the soil are different. The results of this study indicate that continuous multiple gas concentration and flux measurements can be employed as a powerful tool for tracking and understanding underlying biological and physicochemical processes in the soil by measuring more tracer gases such as volatile organic carbon, reactive nitrogen, and noble gases, and by exploiting the broad versatility of mass spectrometry in detecting a broad range of gas species.
Concentrations and stable isotopic compositions ( δ 18 O) of dissolved O 2 in samples collected in May 2005 from the eastern Japan Sea were measured. The O 2 consumption rate and the isotopic fractionation factor ( α r ) during dissolved O 2 consumption were obtained from the field observations by applying a simple model to the deep water. The in‐situ O 2 consumption rates were calculated from the apparent O 2 utilization and the turnover time of deep water obtained in the previous tracer studies. The rates were 1.2–1.4 μ mol kg −1 yr −1 in the deep water below 2000 m. The α r estimated was 0.9875 ± 0.0003 applying a Rayleigh distillation equation to the quasi‐deep water mass of 298–3584 m. The estimated α r and the turnover time mean that δ 18 O of dissolved O 2 will increase with a rate of 0.05–0.06‰ yr −1 for the closed Japan Sea deep water mass.
