The Enigmatic Snow Microorganism, Chionaster nivalis, Is Closely Related to Bartheletia paradoxa (Agaricomycotina, Basidiomycota).

Chionaster nivalis is frequently detected in thawing snowpacks and glaciers. However, the taxonomic position of this species above the genus level remains unclear. We herein conducted molecular analyses of C. nivalis using the ribosomal RNA operon sequences obtained from more than 200 cells of this species isolated from a field-collected material. Our molecular phylogenetic analyses revealed that C. nivalis is a sister to Bartheletia paradoxa, which is an orphan basal lineage of Agaricomycotina. We also showed that C. nivalis sequences were contained in several previously examined meta-amplicon sequence datasets from snowpacks and glaciers in the Northern Hemisphere and Antarctica.

Seasonal dynamics of the activities of dissolved 137Cs and the 137Cs of fish in a shallow, hypereutrophic lake: Links to bottom-water oxygen concentrations.

Remobilization of radiocesium from anoxic sediments can be an important mechanism responsible for long-term contaminations of lakes. However, it is unclear whether such remobilization occurs in shallow lakes, where concentrations of dissolved oxygen in the hypolimnion (bottom DO) change temporally in response to meteorological conditions, and whether remobilized radiocesium influences the activity in fish. We examined the seasonal dynamics of the activities of dissolved 137Cs and 137Cs in fish (pond smelt and crucian carp) from Lake Kasumigaura, a shallow, hypereutrophic lake, five years after the Fukushima Daiichi Nuclear Power Plant accident. The activities of both dissolved 137Cs and 137Cs in fish declined during that time, but the declines showed a clear seasonal pattern that included a summer peak of 137Cs activity. The activity of dissolved 137Cs increased when the bottom DO concentration decreased, and a nonlinear causality test revealed significant causal forcing of dissolved 137Cs activity by bottom DO. The fact that NH4-N concentrations in bottom waters were higher in the summer suggested that remobilization of 137Cs from sediments could result from highly selective ion-exchange with NH4-N. Despite the shallow depth of Lake Kasumigaura, winds had little influence bottom DO concentrations or dissolved 137Cs activities. The fact that seasonal means of 137Cs activities in pond smelt and crucian carp were positively correlated with the seasonal means of dissolved 137Cs activities suggested that remobilized 137Cs may have influenced the seasonal dynamics of radiocesium in fish through food-chain transfer, but higher feeding rates in warm water could may have also contributed to the seasonal dynamics of 137Cs activity in fish. Our findings suggest that in shallow lakes, intermittent but repeated hypoxic events may enhance remobilization of radiocesium from sediments, and remobilized radiocesium may contributed to long-term retention of radiocesium in aquatic organisms.

Sexual reproduction of the snow alga Chloromonas fukushimae (Volvocales, Chlorophyceae) induced using cultured materials.

Snow algae are microalgae, growing in melting snowpacks, and are thought to act as primary producers in the snow ecosystem. Chloromonas (Volvocales, Chlorophyceae) contains more than 15 snow-inhabiting species. Although vegetative cells and zygotes, or asexual cysts, of snow species of the genus are frequently collected in the field, sexual reproduction and zygote formation in culture have only been induced in C. tughillensis. Here we describe the sexual reproduction of another snow-inhabiting species, C. fukushimae, which was induced using both previously examined and newly established Japanese strains. Mating of isogamous gametes began after mixing two different strains, implying that C. fukushimae is an outcrossing species. Motile and nonmotile zygotes of the species were also described in this report. The nonmotile zygote of C. fukushimae was distinguishable from those of the other snow-inhabiting species of Chloromonas, based on the zygote shape and the presence of several large lipid bodies within the cell. In addition, C. fukushimae carried out sexual reproduction and produced zygotes even under the nitrogen-sufficient condition.

Radiocesium dynamics in the aquatic ecosystem of Lake Onuma on Mt. Akagi following the Fukushima Dai-ichi Nuclear Power Plant accident.

Understanding ecosystem dynamics of radionuclides is necessary to ensure effective management for food safety. The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on March 11, 2011 released large amounts of radiocesium (134Cs and 137Cs) and contaminated the environment across eastern Japan. In this study, we aimed to elucidate the temporal dynamics of 137Cs in the aquatic ecosystem of Lake Onuma on Mt. Akagi. The effective ecological half-life (Teff) of 137Cs in fishes, western waterweed (Elodea nuttallii), seston (phytoplankton and zooplankton), and lake water was estimated using survey data of 137Cs concentration collected from 2011 to 2016, and single- and two-component decay function models (SDM and TDM, respectively). The decay processes of 137Cs concentrations in wakasagi (Hypomesus nipponensis), pale chub (Zacco platypus), phytoplankton, and total 137Cs concentrations of the water column (WC) in the lake were well suited by the TDMs. The Teff in the fast component of the TDMs in these samples ranged from 0.49 to 0.74years. The Teff in the slow component of the TDMs could converge towards the physical half-life of 137Cs. Nearly five and a half years after the FDNPP accident, we concluded that 137Cs concentrations approached a state of dynamic equilibrium between some aquatic organisms (wakasagi, pale chub, and phytoplankton) and the environment (lake water). However, the decay processes of 137Cs concentrations in Japanese dace (Tribolodon hakonensis), western waterweed, zooplankton, and particulate- and dissolved-forms in the WC were better predicted for the SDM. The total 137Cs concentrations in inflowing river and spring waters were one to two orders of magnitude lower than lake water under normal flow conditions. However, particulate 137Cs contamination level in the river water was high after heavy rains. Overall, 137Cs contamination levels have significantly decreased in Lake Onuma, but monitoring surveys should be continued for further understanding of the reduction processes.

Fractionation of radiocesium in soil, sediments, and aquatic organisms in Lake Onuma of Mt. Akagi, Gunma Prefecture using sequential extraction.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has resulted in the contamination of the environment in Gunma Prefecture with radioisotope cesium (radio-Cs, 134Cs and 137Cs). Concentrations of radio-Cs >500Bqkg-1 were found in wakasagi (Hypomesus nipponensis) in Lake Onuma at the top of Mount (Mt.) Akagi in August 2011. To explain the mechanism of this contamination, monitoring studies have been conducted around Lake Onuma by measuring radio-Cs concentrations in samples of fish, aquatic plants, plankton, lake water, lake sediments, and surrounding soil. The leachability of radio-Cs was evaluated using sequential extraction by Tessier et al. The total concentration of radio-Cs in Lake Onuma ecosystems decreased gradually with time. In the brown forest soil, radio-Cs concentrations of 2000 to 6000Bqkg-1 were detected. The abundance ratio of the easy-elution form (exchangeable and carbonate forms) in the samples was <10%. The concentrations in phytoplankton samples were 3-6 times higher than those in wakasagi samples. The ratios of easy-elution forms increased by the rank in the food chain; 37% in phytoplankton, 78% in zooplankton, and 97% in wakasagi. It is likely that the lower ratio of the easy-elution form in phytoplankton is related to the adsorption of radio-Cs on suspended substances in the lake, as suggested by the analyses of aluminum and titanium in the phytoplankton, zooplankton, and wakasagi samples. The high concentrations of radio-Cs in wakasagi would be related also to the characteristics of closed mountain lakes.

Potential effects of hydroelectric dam development in the Mekong River basin on the migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus) elucidated by otolith microchemistry.

The migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus), two of the most economically important fish species in the Mekong River, was studied using an otolith microchemistry technique. Fish and river water samples were collected in seven regions throughout the whole basin in Thailand, Laos and Cambodia over a 4 year study period. There was coherence between the elements in the ambient water and on the surface of the otoliths, with strontium (Sr) and barium (Ba) showing the strongest correlation. The partition coefficients were 0.409-0.496 for Sr and 0.055 for Ba. Otolith Sr-Ba profiles indicated extensive synchronized migrations with similar natal origins among individuals within the same region. H. siamensis movement has been severely suppressed in a tributary system where a series of irrigation dams has blocked their migration. H. lobatus collected both below and above the Khone Falls in the mainstream Mekong exhibited statistically different otolith surface elemental signatures but similar core elemental signatures. This result suggests a population originating from a single natal origin but bypassing the waterfalls through a passable side channel where a major hydroelectric dam is planned. The potential effects of damming in the Mekong River are discussed.

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.