{"title":"Preface “Recent advances in limnological studies of Oze mire ecosystem”","authors":"M. Sakamoto","doi":"10.3739/rikusui.82.149","DOIUrl":"https://doi.org/10.3739/rikusui.82.149","url":null,"abstract":"","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43865723","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Interannual changes in benthic macroinvertebrate communities at the profundal bottoms of the North Basin of Lake Biwa, Japan, during 1992–2019","authors":"A. Ohtaka, M. Nishino, E. Inoue","doi":"10.3739/rikusui.82.17","DOIUrl":"https://doi.org/10.3739/rikusui.82.17","url":null,"abstract":"","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49349082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Takechi, H. Tsuji, M. Koshikawa, Shoko Ito, H. Funaki, S. Hayashi
{"title":"Evaluation of Bioavailable Radiocesium in the Sediment in Forest River and Dam Reservoir","authors":"S. Takechi, H. Tsuji, M. Koshikawa, Shoko Ito, H. Funaki, S. Hayashi","doi":"10.3739/rikusui.82.1","DOIUrl":"https://doi.org/10.3739/rikusui.82.1","url":null,"abstract":"","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41573209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Masaki Kuwabara, Hiromichi Kuwabara, T. Kuwabara, Toshiaki Esumi, Y. Tabayashi, H. Kamiya, Shogo Sugahara, Yu Ishitobi
In May 2009, Moriyama Dike was opened in Honjo area, which lies near Lake Nakaumi along the coast of San-in District, Japan, and is isolated by two dikes for land reclamation. This study was conducted to examine the impact of the opening of the dike on water quality as well as fi sh and crustacean life. We carried out a statistical analysis using monthly water-quality observations and a small catch net survey through 2004 to 2014. The analysis results showed that seawater likely flowed into Honjo, and salinity stratification developed. Furthermore, the oxygen deficient layer became thicker and progressed with prolonged duration. From the catch net survey, we found that the number of species of marine fi sh greatly increased; however, no signi fi cant increase in the catch per net was observed. In terms of fi sh and crustacean types, the number of horse mackerel ( Trachurus japonicus ) and Taiwan blue crab ( Portunus pelagicus ) significantly increased. This was considered to be due to the easy access provided by the opening to the Sea of Japan. However, the catch of rock fi sh ( Sebastes schlegeli ) and spiny goby ( Acanthogobius flavimanus ) , decreased after the opening. Because these species prefer benthic life, it was considered to have been a ff ected by oxygen depletion in the lower layer of the Honjo area.
{"title":"Impact of the opening of Moriyama Dike on water quality and aquatic fauna in Honjo Area of Lake Nakaumi, Japan","authors":"Masaki Kuwabara, Hiromichi Kuwabara, T. Kuwabara, Toshiaki Esumi, Y. Tabayashi, H. Kamiya, Shogo Sugahara, Yu Ishitobi","doi":"10.3739/rikusui.81.205","DOIUrl":"https://doi.org/10.3739/rikusui.81.205","url":null,"abstract":"In May 2009, Moriyama Dike was opened in Honjo area, which lies near Lake Nakaumi along the coast of San-in District, Japan, and is isolated by two dikes for land reclamation. This study was conducted to examine the impact of the opening of the dike on water quality as well as fi sh and crustacean life. We carried out a statistical analysis using monthly water-quality observations and a small catch net survey through 2004 to 2014. The analysis results showed that seawater likely flowed into Honjo, and salinity stratification developed. Furthermore, the oxygen deficient layer became thicker and progressed with prolonged duration. From the catch net survey, we found that the number of species of marine fi sh greatly increased; however, no signi fi cant increase in the catch per net was observed. In terms of fi sh and crustacean types, the number of horse mackerel ( Trachurus japonicus ) and Taiwan blue crab ( Portunus pelagicus ) significantly increased. This was considered to be due to the easy access provided by the opening to the Sea of Japan. However, the catch of rock fi sh ( Sebastes schlegeli ) and spiny goby ( Acanthogobius flavimanus ) , decreased after the opening. Because these species prefer benthic life, it was considered to have been a ff ected by oxygen depletion in the lower layer of the Honjo area.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43412606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Toshiaki Esumi, H. Kamiya, Toshikuni Kato, Y. Nakashima, H. Ohshiro, Shogo Sugahara, Y. Tabayashi, M. Yamamuro
{"title":"Impacts of Moriyama Dike opening on the water quality in summer at Honjo area, Lake Nakaumi","authors":"Toshiaki Esumi, H. Kamiya, Toshikuni Kato, Y. Nakashima, H. Ohshiro, Shogo Sugahara, Y. Tabayashi, M. Yamamuro","doi":"10.3739/rikusui.81.223","DOIUrl":"https://doi.org/10.3739/rikusui.81.223","url":null,"abstract":"","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45917657","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Toshiaki Esumi, Toshikuni Kato, Y. Matsuo, H. Kamiya, Yu Ishitobi
Many birds migrate during late autumn and stay until early spring at Lakes Nakaumi and Shinji in San-in district, western Honshu, Japan. The numbers of diving duck species Aythya ferina, Aythya fuligula, and Aythya marila, which constitute the majority of wintering bird populations, were determined monthly during the winter season from 1999 to 2015 in the main area of L. Nakaumi, Honjo Area, which is separated from L. Nakaumi by reclamation dikes, and L. Shinji. The mean value in December and January, obtained from changes in the monthly numbers of each diving duck in the three areas, was used as the wintering number. The long-term data showed a declining trend in the numbers of A. ferina and A. fuligula wintering in L. Nakaumi and Honjo Area. In L. Shinji, long-term data for A. fuligula also showed a decline trend, however, the data for A. marila indicated an upward trend. In L. Nakaumi and Honjo Area, the main diet for these diving duck species is the mussel Musclista senhousia, while in L. Shinji they feed on Corbicula japonica. The long-term changes in wintering bird numbers were investigated in relation to changes in food availability and habitat in the two lakes.
{"title":"Long-term changes in the number of diving ducks wintering in Lakes Nakaumi and Shinji, Japan","authors":"Toshiaki Esumi, Toshikuni Kato, Y. Matsuo, H. Kamiya, Yu Ishitobi","doi":"10.3739/rikusui.81.233","DOIUrl":"https://doi.org/10.3739/rikusui.81.233","url":null,"abstract":"Many birds migrate during late autumn and stay until early spring at Lakes Nakaumi and Shinji in San-in district, western Honshu, Japan. The numbers of diving duck species Aythya ferina, Aythya fuligula, and Aythya marila, which constitute the majority of wintering bird populations, were determined monthly during the winter season from 1999 to 2015 in the main area of L. Nakaumi, Honjo Area, which is separated from L. Nakaumi by reclamation dikes, and L. Shinji. The mean value in December and January, obtained from changes in the monthly numbers of each diving duck in the three areas, was used as the wintering number. The long-term data showed a declining trend in the numbers of A. ferina and A. fuligula wintering in L. Nakaumi and Honjo Area. In L. Shinji, long-term data for A. fuligula also showed a decline trend, however, the data for A. marila indicated an upward trend. In L. Nakaumi and Honjo Area, the main diet for these diving duck species is the mussel Musclista senhousia, while in L. Shinji they feed on Corbicula japonica. The long-term changes in wintering bird numbers were investigated in relation to changes in food availability and habitat in the two lakes.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49366352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The transparency of pure water is the maximum of all transparencies; it is a value required for transparency analysis. However, it is difficult to determine the pure water transparency value directly through experiments, and no universal value has been obtained theoretically thus far. Therefore, the transparency of a colour image is estimated by observing it on a luminance-calibrated LCD screen that displays the tristimulus values calculated for light arriving from the direction of a Secchi disk and background. The light scattered by water molecules was approximated to the first order. For incident angles of 0°, 10°, 20°, ..., 80°, and 89°, the colour-image transparencies (CITs) were in the range of 101 ± 2.6 m to 124 ± 1.1 m. The monochromatic image transparencies (MITs) observed were similar to the research and the transparency-judgment mechanism was in the range of 95 ± 1.3 m to 117 ± 3.4 m. The total error was determined as the sum of the 95% confidence interval and trueness with respect to the transparency of light, calculated using the first-order scattering approximation. The root mean square of the relative error to CITs of the automatically determined transparency based on colour difference and threshold was 6.3 % while that to MITs based on contrast and threshold was 3.6 %. To improve the accuracy of colour-imagetransparency measurements, it is necessary to increase the order of calculating molecular scattering, improve image observation accuracy, and establish an evaluation standard. One methodology considered is to obtain an approximate pure water transparency value using a scaled-down transparency measurement experiment based on adding an absorbent to pure water.
纯水的透明度是所有透明度中最高的;这是透明度分析所需的值。然而，纯水的透明度值很难通过实验直接确定，理论上也没有得到普遍的值。因此，彩色图像的透明度是通过在亮度校准的LCD屏幕上观察它来估计的，该屏幕显示了从塞奇盘和背景方向到达的光计算的三刺激值。水分子散射的光近似于一阶。入射角为0°，10°，20°，…， 80°和89°，彩色图像透明度(CITs)范围为101±2.6 m ~ 124±1.1 m。观察到的单色图像透明度(MITs)与本研究相似，透明度判断机制在95±1.3 m ~ 117±3.4 m范围内。总误差确定为95%置信区间和真实度与光的透明度的总和，使用一阶散射近似计算。基于色差和阈值的自动确定透明度的相对误差均方根为6.3%，基于对比度和阈值的自动确定透明度的相对误差均方根为3.6%。为了提高彩色图像透明度测量的精度，需要提高分子散射的计算顺序，提高图像观测精度，建立评价标准。考虑的一种方法是使用基于在纯水中添加吸收剂的按比例缩小的透明度测量实验来获得近似的纯水透明度值。
{"title":"Estimation of pure water transparency using a calculated image","authors":"Shinya Sato","doi":"10.3739/RIKUSUI.81.119","DOIUrl":"https://doi.org/10.3739/RIKUSUI.81.119","url":null,"abstract":"The transparency of pure water is the maximum of all transparencies; it is a value required for transparency analysis. However, it is difficult to determine the pure water transparency value directly through experiments, and no universal value has been obtained theoretically thus far. Therefore, the transparency of a colour image is estimated by observing it on a luminance-calibrated LCD screen that displays the tristimulus values calculated for light arriving from the direction of a Secchi disk and background. The light scattered by water molecules was approximated to the first order. For incident angles of 0°, 10°, 20°, ..., 80°, and 89°, the colour-image transparencies (CITs) were in the range of 101 ± 2.6 m to 124 ± 1.1 m. The monochromatic image transparencies (MITs) observed were similar to the research and the transparency-judgment mechanism was in the range of 95 ± 1.3 m to 117 ± 3.4 m. The total error was determined as the sum of the 95% confidence interval and trueness with respect to the transparency of light, calculated using the first-order scattering approximation. The root mean square of the relative error to CITs of the automatically determined transparency based on colour difference and threshold was 6.3 % while that to MITs based on contrast and threshold was 3.6 %. To improve the accuracy of colour-imagetransparency measurements, it is necessary to increase the order of calculating molecular scattering, improve image observation accuracy, and establish an evaluation standard. One methodology considered is to obtain an approximate pure water transparency value using a scaled-down transparency measurement experiment based on adding an absorbent to pure water.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44787291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Nakagawa, Miki Okamoto, M. Akasaka, N. Takamura
The dense growth of aquatic macrophytes can affect lake water quality. We studied the water chemistry at 40 sites on Lake Shirarutoro when dense beds of water chestnut (Trapa japonica) expanded in 2007–8. The distribution patterns between the early (June) and middle (August) vegetation water plant seasons were compared. In this lake, the dense beds of water chestnut did not necessarily correspond to the lack of dissolved oxygen at the lake bottom. Principal component analyses (PCA) of 20 variables showed that the lake could be divided into two areas: one was a central area from the main inflowing river to the outflow (‘area A’) and the other was an area adjacent to the southern wetland (‘area B’). The factor loadings of the first principal component (PC) showed high positive value for K, Ca, Na, Cl, Mg, and D-Si, and high negative for dissolved organic phosphorus (DOP), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and dissolved iron (D-Fe). ‘Area A’ was influenced by the high concentration loading of K, Ca, Na, and Cl from a northern tributary; ‘area B’ was influenced by the adjacent wetlands. The factor loadings of the second PC showed high negative values for the total phosphorus (TP), total nitrogen (TN), volatile solids (VS), and chlorophyll a, all of which were indicators of eutrophication. The variables whose factor loading in the first PC changed between June and August were only the soluble reactive phosphorus (SRP) and SO4 . Therefore, we concluded that the distribution of the lake water chemistry was more influenced by watershed condition rather than the dense water plant beds.
{"title":"Horizontal distribution of water quality between early and dense water plant seasons in Lake Shirarutoro, Kushiro Wetland","authors":"M. Nakagawa, Miki Okamoto, M. Akasaka, N. Takamura","doi":"10.3739/RIKUSUI.81.137","DOIUrl":"https://doi.org/10.3739/RIKUSUI.81.137","url":null,"abstract":"The dense growth of aquatic macrophytes can affect lake water quality. We studied the water chemistry at 40 sites on Lake Shirarutoro when dense beds of water chestnut (Trapa japonica) expanded in 2007–8. The distribution patterns between the early (June) and middle (August) vegetation water plant seasons were compared. In this lake, the dense beds of water chestnut did not necessarily correspond to the lack of dissolved oxygen at the lake bottom. Principal component analyses (PCA) of 20 variables showed that the lake could be divided into two areas: one was a central area from the main inflowing river to the outflow (‘area A’) and the other was an area adjacent to the southern wetland (‘area B’). The factor loadings of the first principal component (PC) showed high positive value for K, Ca, Na, Cl, Mg, and D-Si, and high negative for dissolved organic phosphorus (DOP), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and dissolved iron (D-Fe). ‘Area A’ was influenced by the high concentration loading of K, Ca, Na, and Cl from a northern tributary; ‘area B’ was influenced by the adjacent wetlands. The factor loadings of the second PC showed high negative values for the total phosphorus (TP), total nitrogen (TN), volatile solids (VS), and chlorophyll a, all of which were indicators of eutrophication. The variables whose factor loading in the first PC changed between June and August were only the soluble reactive phosphorus (SRP) and SO4 . Therefore, we concluded that the distribution of the lake water chemistry was more influenced by watershed condition rather than the dense water plant beds.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46904542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Mochizuki, H. Sasamoto, Daiya Bamba, Kayoko Ikigaki
The characterization of humic substances in groundwater is usually performed using isolated humic substances from a large volume of groundwater. However, the isolation process requires extensive time and effort, and is not feasible for small-volume samples. In this study, characterization methods available for small-volume ( approximately 1 L ) samples were applied to groundwater and surface water in the Horonobe area, Hokkaido. The methods, 3D- fl uorescence analysis, gel permeation chromatography, and ion chromatography, were used to characterize dissolved organic matter ( DOM ) in the samples, including humic substances. The results indicated that the 3D- fl uorescence spectrum obtained from a small volume of groundwater was similar to that obtained from isolated humic substances and showed little variation with depth. However, the peak position in surface water was di ff erent from that in groundwater. Gel permeation chromatography showed that the DOM in groundwater mainly consisted of humic substances with a molecular weight of approximately 1200–2000 Da, and that the molecular weight decreased with depth. These results are consistent with the characteristics of isolated humic substances. Ion chromatography revealed that organic matter with low molecular weight was a minor component of DOM in the groundwater, which is consistent with gel permeation chromatography results. These results indicate that the methods applied in this study are useful for the characterization of DOM in groundwater using small sample volume.
{"title":"Characterization of dissolved organic matter in deep groundwater by simple analytical methods applicable for small sample volumes","authors":"A. Mochizuki, H. Sasamoto, Daiya Bamba, Kayoko Ikigaki","doi":"10.3739/RIKUSUI.81.153","DOIUrl":"https://doi.org/10.3739/RIKUSUI.81.153","url":null,"abstract":"The characterization of humic substances in groundwater is usually performed using isolated humic substances from a large volume of groundwater. However, the isolation process requires extensive time and effort, and is not feasible for small-volume samples. In this study, characterization methods available for small-volume ( approximately 1 L ) samples were applied to groundwater and surface water in the Horonobe area, Hokkaido. The methods, 3D- fl uorescence analysis, gel permeation chromatography, and ion chromatography, were used to characterize dissolved organic matter ( DOM ) in the samples, including humic substances. The results indicated that the 3D- fl uorescence spectrum obtained from a small volume of groundwater was similar to that obtained from isolated humic substances and showed little variation with depth. However, the peak position in surface water was di ff erent from that in groundwater. Gel permeation chromatography showed that the DOM in groundwater mainly consisted of humic substances with a molecular weight of approximately 1200–2000 Da, and that the molecular weight decreased with depth. These results are consistent with the characteristics of isolated humic substances. Ion chromatography revealed that organic matter with low molecular weight was a minor component of DOM in the groundwater, which is consistent with gel permeation chromatography results. These results indicate that the methods applied in this study are useful for the characterization of DOM in groundwater using small sample volume.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41272948","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Y. Nagahama, T. Fukushima, T. Ouchi, Miyuki Yuzawa
The large shallow lake complex of Lake Kasumigaura comprises of three water bodies: Lake Nishiura, Lake Kitaura, and Lake Sotonasakaura, which are connected by three rivers. The community structure and biovolume of phytoplankton are important factors for the ecology and water quality of the lake. However, few studies have been conducted recently on the phytoplankton communities of the entire Lake Kasumigaura. The aim of this study was to clarify the changes in community structure and biovolume of phytoplankton from 2005 to 2019 in Lake Kasumigaura. The results showed that the dominant phytoplankton taxa were Bacillariophyceae from 2005 to 2007, Planktothrix ( Oscillatoriales, Cyanophyceae ) from 2008 to approximately 2010, and Bacillariophyceae since 2011. The change in the phytoplankton community structure differed between lakes Nishiura and Kitaura: the ratios of the dominant genera Cyclotella and Aulacoseira ( Centrales, Bacillariophyceae ) were higher in Nishiura than in Kitaura; the ratio of the dominant genus Synedra ( Pennales, Bacillariophyceae ) was lower in Nishiura than in Kitaura. Moreover, while the abundance of Planktothrix in Nishiura was higher than that in Kitaura, the period of Planktothrix dominance in Nishiura was shorter than that in Kitaura. The phytoplankton biovolume decreased in all three water bodies during the research period because the biovolumes of the main phytoplankton genera, Planktothrix , Cyclotella , and Cryptomonas , decreased. The values of the biodiversity indices decreased drastically in 2007 at all stations. The results suggested that Planktothrix was dominant from 2007 to 2011 across Lake Kasumigaura. Furthermore, the values of biodiversity indices increased rapidly in 2011 in Nishiura and Sotonasakaura, while the increase was slower in Kitaura.
{"title":"Phytoplankton community in Lake Kasumigaura: 2005 to 2019","authors":"Y. Nagahama, T. Fukushima, T. Ouchi, Miyuki Yuzawa","doi":"10.3739/RIKUSUI.81.167","DOIUrl":"https://doi.org/10.3739/RIKUSUI.81.167","url":null,"abstract":"The large shallow lake complex of Lake Kasumigaura comprises of three water bodies: Lake Nishiura, Lake Kitaura, and Lake Sotonasakaura, which are connected by three rivers. The community structure and biovolume of phytoplankton are important factors for the ecology and water quality of the lake. However, few studies have been conducted recently on the phytoplankton communities of the entire Lake Kasumigaura. The aim of this study was to clarify the changes in community structure and biovolume of phytoplankton from 2005 to 2019 in Lake Kasumigaura. The results showed that the dominant phytoplankton taxa were Bacillariophyceae from 2005 to 2007, Planktothrix ( Oscillatoriales, Cyanophyceae ) from 2008 to approximately 2010, and Bacillariophyceae since 2011. The change in the phytoplankton community structure differed between lakes Nishiura and Kitaura: the ratios of the dominant genera Cyclotella and Aulacoseira ( Centrales, Bacillariophyceae ) were higher in Nishiura than in Kitaura; the ratio of the dominant genus Synedra ( Pennales, Bacillariophyceae ) was lower in Nishiura than in Kitaura. Moreover, while the abundance of Planktothrix in Nishiura was higher than that in Kitaura, the period of Planktothrix dominance in Nishiura was shorter than that in Kitaura. The phytoplankton biovolume decreased in all three water bodies during the research period because the biovolumes of the main phytoplankton genera, Planktothrix , Cyclotella , and Cryptomonas , decreased. The values of the biodiversity indices decreased drastically in 2007 at all stations. The results suggested that Planktothrix was dominant from 2007 to 2011 across Lake Kasumigaura. Furthermore, the values of biodiversity indices increased rapidly in 2011 in Nishiura and Sotonasakaura, while the increase was slower in Kitaura.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48445740","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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