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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.

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).

Haga H.,Lake Biwa Museum | Ishikawa K.,Lake Biwa Environmental Research Institute
Japanese Journal of Limnology | Year: 2014

The spatial distribution of submerged macrophytes, in terms of biomass and species composition, was surveyed in the south basin of Lake Biwa in September, 2012 using scuba. Submerged macrophytes were observed in 48 out of 52 sampling stations, and 12 species were found in this study. The number of species of submerged macrophytes per site was 4.6+2.0. The area with vegetation cover and the total biomass (dry weight' during the study period were estimated to be 47.6 km2 and 3264+1445 t, respectively. Although the area with vegetation cover was only 1 km2 less than in 2007, total biomass of submerged macrophytes declined by 6360 t during the same period. Biomass of Potamogeton maackianus, Egeria densa, and Ceratophyllum demersum decreased significantly between 2007 and 2012 (paired Student’s t-test, P < 0.05, n = 52), 4107 t, 879 t, and 804 t, respectively. Biomass reduction in these three species accounted for 91% of the entire reduction. The biomasses of the other species also declined, with excepthion of two, Potamogeton malaianus and P. anguillanus. © 2015, Japanese Society of Limnology. All rights reserved.

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