Photo-production of excited triplet-state of dissolved organic matters in inland freshwater and coastal seawater.

The excited triplet-state of dissolved organic matter (3DOM*) is a major reactive intermediate in sunlit waters. Its quantum yield is important in understanding the fate of organic micropollutants. The degradation efficiency of its chemical probe, 2,4,6-trimeythlphenol (fTMP), is generally used as a proxy of the quantum yield. However, fTMP has been described and modelled only for freshwater systems. Therefore, this study quantified fTMP in inland freshwater and coastal seawater sampled in Japan by conducting steady-state photochemical experiments. Optical properties of water were then used to model fTMP. Results indicated that the inland freshwater DOM originated mainly from terrestrial sources, while the coastal seawater DOM were microbial-dominated. On average, inland freshwater exhibited lower fTMP (61.2 M-1) than coastal seawater (79.7 M-1) and the coastal seawater exhibited significant variations in the proportion of high-energy 3DOM* (> 250 kJ/mol). In addition, E2:E3 (ratio of absorbance at 254 to 365 nm) was positively correlated with fTMP of inland freshwater, coastal seawater, and the overall dataset. Catchment conditions such as forest coverage also influenced the production of 3DOM* and high-energy 3DOM* in inland freshwater. Furthermore, the developed models estimated fTMP based on the optical properties of both freshwater and seawater, providing valuable insights about 3DOM* photochemistry in the aquatic environment.

Occurrence and potential activity of denitrifiers and methanogens in groundwater at 140 m depth in Pliocene diatomaceous mudstone of northern Japan.

Anaerobic microbial activity has a major influence on the subsurface environment. We investigated the denitrification and methanogenesis in anoxic groundwater at a depth of 140 m in two boreholes drilled in a sedimentary geological setting, where the redox potential fluctuated. The average maximum potential denitrification rates, measured under anaerobic conditions in the two boreholes using an (15) N tracer, were 0.060 and 0.085 nmol (30) N2  mL(-1)  h(-1) . The deduced NirS amino acid sequences obtained from in situ samples were similar to those of isolates belonging to the α-, ß-, and γ-Proteobacteria, and the Firmicutes (72-100% similarity). Based on the nirS gene, the same operational taxonomic unit dominated incubated samples from each borehole. Methanogenesis candidates were detected by 16S rRNA gene analysis, but no sequence was detected using primers for the functional methanogenesis gene mcrA. Although the stable isotope signatures suggested that some of the dissolved methane was of biogenic origin, no potential for methane production was evident during the incubations. The groundwater at 140 m depth did not contain oxygen, had an Eh ranging from -144 to 6.8 mV, and was found to be a potential field for denitrification.

Population dynamics of Crenarchaeota and Euryarchaeota in the mixing front of river and marine waters.

A transect from the Tomoe River Mouth through Shimizu Port to Suruga Bay, Japan, was examined between 2005 and 2009 to reveal the population dynamics of Crenarchaeota and Euryarchaeota in an estuary environment. Crenarchaeota tended to increase in abundance in waters deeper than 100 m compared with Euryarchaeota, and comprised 11% of total direct counts. Archaeal abundance was highest in the Tomoe River Mouth, with a strong negative correlation between surface euryarchaeal abundance and salinity (P<0.001). The diversity index for the phylotypic archaeal community in the mouth was three times higher than that at sites St1-1m and St1-10m in the estuary, and OTUs represented most of the OTU groups at the sites. Three of the seven total OTUs, which comprised 83.6% of the 140 sequenced clones in the estuary, were related to the OTUs in the mouth with similarities higher than 97%. A significant proportion of the archaeal community appears to be derived from the Tomoe River. The two dominant phylotypes of the archaeal community in Shimizu Port, belonging to MGI and MGII, occurred ubiquitously.