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Haga H.,Lake Biwa Museum | Ishikawa K.,Lake Biwa Environmental Research Institute
Japanese Journal of Limnology | Year: 2016

The spatial distribution of submerged macrophytes, in terms of biomass and species composition, was surveyed in the southern Lake Biwa basin in September 2014, using SCUBA. Submerged macrophytes were observed in 50 out of 52 sampling stations. The average biomass (dry weight ± 95% confidence limits) of total submerged macrophytes per site was 352 ± 85 g m-2. The area with vegetation cover and the total biomass during the study period in the basin were estimated to be 49.6 km2 and 18173 ± 4387 t, respectively. Fourteen species of submerged macrophytes were found in this study, and the number of species per site and S.D. was 5.7±1.7. Potamogeton maackianus was dominant among them, with a biomass estimated to be 7275±2709 t. Elodea nuttallii (4937 ± 2032 t), Hydrilla verticillata (2927±757 t), and Egeria densa (1481±949 t), Myriophyllum spicatum(825±562 t) followed. These species accounted for 96% of the total biomass of submerged macrophytes in this study. © 2016, Japanese Society of Limnology. All rights reserved.

Kojima H.,Hokkaido University | Tsutsumi M.,Hokkaido University | Ishikawa K.,Lake Biwa Environmental Research Institute | Iwata T.,Yamanashi University | And 2 more authors.
Systematic and Applied Microbiology | Year: 2012

Methane oxidation coupled to denitrification is mediated by '. Candidatus Methylomirabilis oxyfera', which belongs to the candidate phylum NC10. The distribution of putative denitrifying methane-oxidizing bacteria related to " M. oxyfera" was investigated in a freshwater lake, Lake Biwa, Japan. In the surface layer of the sediment from a profundal site, a phylotype closely related to " M. oxyfera" was most frequently detected among NC10 bacteria in PCR analysis of the 16S rRNA gene. In the sediment, sequences related to " M. oxyfera" were also detected in a pmoA gene library. The presence of NC10 bacteria was also confirmed by catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH). Denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR indicated that the abundance of the " M. oxyfera" -related phylotype was higher in the upper layers of the profundal sediment. The horizontal distribution of the putative methanotrophs in lake sediment was also analyzed by DGGE, which revealed that their occurrence was restricted to deep water areas. These results agreed with those in a previous study of another freshwater lake, and suggested that the upper layer of the profundal sediments is the main habitat for denitrifying methanotrophs. © 2012 Elsevier GmbH.

Hsieh C.H.,National Taiwan University | Sakai Y.,Kyoto University | Ban S.,University of Shiga Prefecture | Ishikawa K.,Lake Biwa Environmental Research Institute | And 4 more authors.
Biogeosciences | Year: 2011

We compiled and analyzed long-term (1961-2005) zooplankton community data in response to environmental variations in Lake Biwa. Environmental data indicate that Lake Biwa had experienced eutrophication (according to the total phosphorus concentration) in the late 1960s and recovered to a normal trophic status around 1985, and then has exhibited warming since 1990. Total zooplankton abundance showed a significant correlation with total phytoplankton biomass. Following a classic pattern, the cladoceran/calanoid and cyclopoid/calanoid abundance ratio was related positively to eutrophication. The zooplankton community exhibited a significant response to the boom and bust of phytoplankton biomass as a consequence of eutrophication-reoligotriphication and warming. Moreover, our analyses suggest that the Lake Biwa ecosystem exhibited a hierarchical response across trophic levels; that is, higher trophic levels may show a more delayed response or no response to eutrophication than lower ones. We tested the hypothesis that the phytoplankton community can better explain the variation of the zooplankton community than bulk environmental variables, considering that the phytoplankton community may directly affect the zooplankton succession through predator-prey interactions. Using a variance partition approach, however, we did not find strong evidence to support this hypothesis. We further aggregated zooplankton according to their feeding types (herbivorous, carnivorous, omnivorous, and parasitic) and taxonomic groups, and analyzed the aggregated data. While the pattern remains similar, the results are less clear comparing the results based on finely resolved data. Our research suggests that zooplankton can be bio-indicators of environmental changes; however, the efficacy depends on data resolution. © 2011 Author(s).

Yu H.,Chinese Research Academy of Environmental Sciences | Tsuno H.,Kyoto University | Hidaka T.,Kyoto University | Jiao C.,Lake Biwa Environmental Research Institute
Limnology | Year: 2010

An index that shows chemical stratification strength [IC-i; i = water quality item such as chlorophyll-a (Chl. a) and soluble phosphorus (SP)] was proposed and compared with one of thermal stratification strength indices, Schmidt's stability index (SSI), in Shiozu Bay and Lake Biwa, Japan. The proposed indices of IC-i can be easily calculated with at least one set of each water quality data in both the epilimnion and the hypolimnion. The SSI was shown to be consistent with the traditional thermocline index of thermocline strength index (TSI), but SSI is used as the stability index of the whole lake, whereas TSI is used as the stability index near the thermocline. Analyses showed that chemical stratification strength is determined largely by thermal stratification strength. Totally different characteristics of IC-Chl. a and IC-phosphate (PO4) at high SSI in the main North Basin of Lake Biwa and in Shiozu Bay were possibly due to the difference in their volumes and hydrodynamic conditions. The proposed index and relationships are especially useful to roughly determine thermal and chemical stratification when only few water quality data are available. © 2010 The Japanese Society of Limnology.

Koyama M.,Soka University | Yamamoto S.,Soka University | Ishikawa K.,Lake Biwa Environmental Research Institute | Ban S.,University of Shiga Prefecture | Toda T.,Soka University
Ecological Engineering | Year: 2014

Aquatic weeds including submerged macrophyte have been excessively propagated and causing environmental issues in freshwater environment of many countries, and the sustainable treatments have been investigated. In the present study, five submerged macrophyte species dominant in Lake Biwa, Japan, Ceratophyllum demersum, Egeria densa, Elodea nuttallii, Potamogeton maackianus and Potamogeton malaianus were used as a substrate for anaerobic digestion to investigate the chemical composition and the anaerobic digestibility. The lignin content of the submerged macrophyte widely ranged from 3.2 to 20.7%-TS depending on species. The lignin of all macrophytes contained 27.2-59.4% of hydroxycinnamic acids, suggesting they are relatively alkali-labile as compared with woody plants. The total CH4 yield of submerged macrophytes greatly varied from 161.2 to 360.8mLg-VS-1 depending on species. The CH4 conversion efficiency of C. demersum, El. nuttallii, Eg. densa, P. maackianus and P. malaianus was 57.1, 61.4, 60.6, 33.9 and 72.2%, respectively. The results showed that C. demersum, El. nuttallii, Eg. densa and P. malaianus are feasible for anaerobic digestion due to the high methane recovery, whereas P. maackianus was not preferable for anaerobic digestion. The present study revealed that the methane recovery of submerged macrophytes is regulated by the lignin content, as well as other lignocellulosic biomass. © 2014 Elsevier B.V.

Yamaji N.,Tokyo University of Agriculture and Technology | Hayakawa K.,Lake Biwa Environmental Research Institute | Takada H.,Tokyo University of Agriculture and Technology
Environmental Science and Technology | Year: 2010

To understand the behavior of fluorescent whitening agents (FWAs) in a lake environment, we measured the quantities of two FWAs, DSBP, and DAS1, in water samples collected monthly from six depths of the water column, in sediment trap sample, and a sediment core sample from Lake Biwa, the largest lake in Japan, and in sewage, effluent, and river water in the lake's catchment. We conducted a sunlight exposure experiment and developed a method to estimate the degree of photodegradation by using DSBP/DAS1 ratio in environmental samples. The observed seasonal pattern of the vertical distributions of the FWAs in the water column can be explained by stratification of the water, photodegradation in the euphotic zone, the subsurface loading of river water, and their seasonal changes. The DSBP/DAS1 ratio was much lower in the lake water (0.12-0.52) than in sewage (6.4 ± 1.1), indicating intensive photodegradation in rivers and the lake. A mass balance calculation and DSBP/DAS1 ratio demonstrated that ∼95% of DSBP and ∼55% of DAS1 supplied in sewage were photodegraded in inflowing rivers and the lake, and that sedimentation to the lake bottom is insignificant for DSBP and ∼35% for DAS1. More intensive photodegradation of FWAs, especially more photodegradable DSBP, in Lake Biwa than in Greifensee, a lake in Switzerland, was suggested, attributable to the longer residence time of water in and the larger size of Lake Biwa. These results demonstrate that photodegradation is important to the fate of FWAs in lacustrine environments, and that FWAs and the DSBP/DAS1 ratio are useful markers for understanding the role of direct photodegradation in the behavior of water-soluble chemicals in aquatic environments. © 2010 American Chemical Society.

Thottathil S.D.,Kyoto University | Hayakawa K.,Lake Biwa Environmental Research Institute | Hodoki Y.,Kyoto University | Yoshimizu C.,Kyoto University | And 2 more authors.
Limnology and Oceanography | Year: 2013

The dynamics of fluorescent dissolved organic matter (FDOM) in the large monomictic freshwater Lake Biwa (surface area 675 km2, maximum depth 104 m) was studied from December 2010 to December 2011. The protein-like FDOM (FDOMT) and dissolved organic carbon (DOC) showed epilimnetic accumulation (FDOMT from 4.42 ± 0.22 quinine sulfate units [QSU] to 6.30 ± 0.04 QSU; DOC from 80.8 ± 2.7 μmol L-1 to 102.7 ± 3.5 μmol L-1) between nutrient-replete winter mixing to nutrient-depleted stratified periods. This accumulation is attributed to the reduced heterotrophic activity following severe P-limitation. The positive correlation between accumulated DOC and FDOMT in the epilimnion and their uniform reduction in the hypolimnion (~ 9%) suggest FDOMT as a proxy for semi-labile DOM. The humic-like FDOM (FDOMM) generally increased with depth, a pattern similar to nutrients and total carbon dioxide (TCO2), but adverse to dissolved oxygen. The significant positive correlations of FDOMM with apparent oxygen utilization (r = 0.86, p < 0.001), TCO2 (r = 0.91, p < 0.001), nitrate (r = 0.83, p < 0.001), and phosphate (r = 0.76, p < 0.001) in the deeper layers suggest that FDOMM is formed during hypolimnetic mineralization. We estimated that ~ 8% of the organic carbon degraded in the hypolimnion is transferred into humic substances. The minor contribution of DOC (6.4%) to hypolimnetic mineralization suggests that production of humic substances is mainly fueled by the mineralization of sinking biogenic particles. The production and consumption of FDOM in freshwater lakes may influence the quality and bioavailability of carbon exported from these systems. © 2013, by the Association for the Sciences of Limnology and Oceanography, Inc.

Itoh N.,Japan National Institute of Advanced Industrial Science and Technology | Tamamura S.,Kanazawa University | Kumagai M.,Lake Biwa Environmental Research Institute
Organic Geochemistry | Year: 2010

We analyzed the vertical distributions of 19 polycyclic aromatic hydrocarbons (PAHs), total organic carbon (TOC), total nitrogen (TN) and stable carbon isotope ratio (δ 13C) in a 27cm sediment core from the north basin of Lake Biwa in order to elucidate changes in PAH sources and events possibly affecting the lake over the last few decades. Both TOC and TN increased gradually from the deepest layer (TOC, 1.2wt.%; TN, 0.14wt.%) to the uppermost layer (TOC, 4.0wt.%; TN, 0.45wt.%). The TOC/TN ratio, a useful indicator for distinguishing between aquatic and terrestrial plant sources, increased remarkably at 11-13cm (10.3-11.1 vs. 8.5-9.7 at other depths), indicating that large amounts of terrestrial material entered the lake when that layer was deposited. All PAHs except perylene gradually increased from the deepest layer, but not as clearly as TOC and TN. At 11-13cm, all PAHs except perylene transiently decreased and perylene transiently increased. Since the PAH ratios used for the elucidation of sources did not change greatly throughout the core, we consider that the major source of PAHs in the lake has not changed during the last few decades. The brief decrease in PAHs at 11-13cm could be the result of dilution by a large input of terrestrial material, which brought in perylene. © 2010 Elsevier Ltd.

Population growth rates (λ) of the riparian tree Aesculus turbinata varied from 0.9988 to 1.0524 spatiotemporally. We conducted a series of pair-wise demographic and matrix analyses, including randomization tests, three types of life table response experiments (LTREs), analysis of variance and χ2 tests, to test which life stages had the greatest effect on this variation in λ. Randomization tests detected significant variations in λ between plots affected or not by typhoons in three habitats and between periods with high and low recruitment in one habitat. Mixed-level LTREs identified that the demographic processes and life stages that had the strongest effect on the actual variation in λ were: (1) progressions of small and intermediate juveniles and (2) founding process from seeds to 1-year-old seedlings. These juvenile stages had medium sensitivities and variances that explained high upper-level LTRE contributions. Lower-level LTREs showed that the vital rates contributing the most were the growth rates of these juvenile stages. These findings demonstrate that progression from one stage to the next, growth rates of 1-year-old seedlings, and stunted aging juveniles are the most important stages in the population dynamics of this long-lived primary tree species. Transition matrix elements with high elasticities had little effect on the variation in λ, indicating that high-elasticity vital rates do not necessarily drive variation in population growth. As compared with the results of randomization tests, significant differences in vital rates examined using ANOVA or χ2 tests showed that typhoon disturbance had the greatest effect on the demographic parameters of individual trees. © 2013 The Society of Population Ecology and Springer Japan.

Niiyama Y.,National Museum of Nature and Science | Tuji A.,National Museum of Nature and Science | Tsujimura S.,Lake Biwa Environmental Research Institute
Fottea | Year: 2011

Umezakia natans M.Watan. was described by Dr. M. Watanabe in 1987 as a new species in the family of Stigonemataceae, following the rules of the Botanical Code. According to the original description, this planktonic filamentous species grows well in a growth media with pH being 7 to 9, and with a smaller proportion of sea water. Both heterocytes and akinetes were observed, as well as true branches developing perpendicular to the original trichomes in cultures older than one month. Watanabe concluded that Umezakia was a monotypic and only planktonic genus belonging to the family of Stigonemataceae. Unfortunately, the type culture has been lost. In 2008, we successfully isolated a new strain of Umezakia natans from a sample collected from Lake Suga. This lake is situated very close to the type locality, Lake Mikata in Fukui Prefecture, Japan. We examined the morphology of this U. natans strain, and conducted a DNA analysis using 16S rDNA regions. Morphological characters of the newly isolated strain were in a good agreement with the original description of U. natans. Furthermore, results of the DNA analysis showed that U. natans appeared in a cluster containing Aphanizomenon ovalisporum and Anabaena bergii. Therefore we conclude that Umezakia natans belongs to the family of Nostocaceae, not to Stigonemataceae. © Czech Phycological Society (2011).

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