Lakes Sagami and Tsukui are reservoirs of nearly equal size, with a short residence time and constructed by connection to the Sagami River. Because of eutrophication of the lakes, cyanobacteria appear every year. However, the occurrence of cyanobacteria in each lake was different. Therefore, in order to investigate these factors, we conducted both biotic and abiotic investigations and compared defined parameters over the past 40 years. Cyanobacteria are found in the surface layer of the lakes. In Lake Sagami, the surface layer was not largely retained and some of the cyanobacteria were found in the outflow water. When the surface layer became disturbed, Dolichospermum dominated, and Microcystis dominated when the layer stabilized due to weather effects. The outflow from Lake Tsukui was taken from a deep layer ( depth 24-32 m ) and the cyanobacteria were not affected by the outflow. Prior to the installation of the aeration systems, Microcystis dominated, and after the installation, the cyanobacteria were dispersed and Nostocales dominated, but Microcystis still dominated when the surface layer stabilized owing to the influence of the weather. As a result, the influence of nutrients and water temperature was limited and the changes in the abundance and dominant species of cyanobacteria may be influenced by the weather, the difference in the outlet structure, and ancillary facilities such as aeration systems. data, Microcystis Nostocales,
{"title":"Trends in the appearance of cyanobacteria and factors influencing the bloom formation of cyanobacteria in two eutrophic reservoirs (Lakes Sagami and Tsukui): 40 years of monitoring","authors":"Suzue Arii, K. Tsuji, K. Harada","doi":"10.3739/RIKUSUI.81.1","DOIUrl":"https://doi.org/10.3739/RIKUSUI.81.1","url":null,"abstract":"Lakes Sagami and Tsukui are reservoirs of nearly equal size, with a short residence time and constructed by connection to the Sagami River. Because of eutrophication of the lakes, cyanobacteria appear every year. However, the occurrence of cyanobacteria in each lake was different. Therefore, in order to investigate these factors, we conducted both biotic and abiotic investigations and compared defined parameters over the past 40 years. Cyanobacteria are found in the surface layer of the lakes. In Lake Sagami, the surface layer was not largely retained and some of the cyanobacteria were found in the outflow water. When the surface layer became disturbed, Dolichospermum dominated, and Microcystis dominated when the layer stabilized due to weather effects. The outflow from Lake Tsukui was taken from a deep layer ( depth 24-32 m ) and the cyanobacteria were not affected by the outflow. Prior to the installation of the aeration systems, Microcystis dominated, and after the installation, the cyanobacteria were dispersed and Nostocales dominated, but Microcystis still dominated when the surface layer stabilized owing to the influence of the weather. As a result, the influence of nutrients and water temperature was limited and the changes in the abundance and dominant species of cyanobacteria may be influenced by the weather, the difference in the outlet structure, and ancillary facilities such as aeration systems. data, Microcystis Nostocales,","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44546262","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}
Tetuo Murakami, Ryoji Kuno, Mai Okada, Shouki Hotta, M. Minami
The term “ spring-fed marshes ” characterizes wetlands without peat accumulation on the bottom gravel layer, contrasting with “ peat mire ” . Because this type of wetland is usually small and has a very short lifespan as an isolated habitat, it received little attention until the 1990s; even now information is quite limited. We herein describe the limnological features of spring-fed marshes distributed in Oomori-okuyama ( Kani City, Gifu Prefecture, Tokai Region, Japan ) . These marshes develop on hill slopes, in gradients of 5-20 ° . They receive oozing waters at their upper margins, and typically lack inflowing waterways. The water flows over hill surfaces or as ground water in a shallow layer over an impermeable ground layer composed of Oniita ( plate-like limonite ) . The volume of water decreases as it flows downstream. As a result, the wetland develops a fan-like shape. The water is characterized by low pH and low conductivity, and the small algal communities are dominated by filamentous Tribonema affine ( Xanthophyceae ) and desmids. These features are common in dystrophic environments distributed in high and cool regions in Japan. In contrast, the aquatic insect communities are composed of taxa that also inhabit ponds and swamps from lower altitudes.
{"title":"Spring-fed marshes in Oomori-okuyama, Kani City, Gifu Prefecture, Central Japan: Landform, water characteristics, and aquatic flora and fauna","authors":"Tetuo Murakami, Ryoji Kuno, Mai Okada, Shouki Hotta, M. Minami","doi":"10.3739/RIKUSUI.81.45","DOIUrl":"https://doi.org/10.3739/RIKUSUI.81.45","url":null,"abstract":"The term “ spring-fed marshes ” characterizes wetlands without peat accumulation on the bottom gravel layer, contrasting with “ peat mire ” . Because this type of wetland is usually small and has a very short lifespan as an isolated habitat, it received little attention until the 1990s; even now information is quite limited. We herein describe the limnological features of spring-fed marshes distributed in Oomori-okuyama ( Kani City, Gifu Prefecture, Tokai Region, Japan ) . These marshes develop on hill slopes, in gradients of 5-20 ° . They receive oozing waters at their upper margins, and typically lack inflowing waterways. The water flows over hill surfaces or as ground water in a shallow layer over an impermeable ground layer composed of Oniita ( plate-like limonite ) . The volume of water decreases as it flows downstream. As a result, the wetland develops a fan-like shape. The water is characterized by low pH and low conductivity, and the small algal communities are dominated by filamentous Tribonema affine ( Xanthophyceae ) and desmids. These features are common in dystrophic environments distributed in high and cool regions in Japan. In contrast, the aquatic insect communities are composed of taxa that also inhabit ponds and swamps from lower altitudes.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47179866","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}
Recent studies have provided evidence that consumers such as benthic larval chironomids assimilate methane-derived carbon ( MDC ) by foraging on methane-oxidizing bacteria in lake ecosystems. Trophic transfer of MDC can be detected by measuring carbon stable isotope ratios in consumers as biogenic methane is extremely 13 C-depleted. In this paper, I review trophic transfer of MDC mediated by larval chironomids. Trophic transfer of MDC is closely related to methane cycles ( i.e. methane production and oxidation ) in sediment, and is often enhanced by depletion of dissolved oxygen above the lake bottom. The robust tube built in sediment by larval chironomids could function as a microhabitat for methane-oxidizing bacteria, and promote trophic transfer of MDC. In stratified dimictic lakes, autumnal supply of oxygenated water to the lake bottom can stimulate the activity of methane-oxidizing bacteria, resulting in enhanced trophic transfer of MDC. In shallow polymictic lakes, transfer of MDC can be enhanced in late summer or early autumn when methane production increases. As dissolved oxygen could be depleted within aquatic plant vegetation even in shallow waters, seasonality of trophic transfer of MDC within vegetation could be similar to that in dimictic lakes. Although some studies reported that fish assimilated MDC, the extent to which MDC is transported to lake food webs is unclear. Trophic transfer of MDC has been mainly studied in deep stratified lakes. MDC may be transferred to aquatic consumers in shallow waters which are a hot spot of methane production, though further studies are necessary.
{"title":"Trophic transfer of methane-derived carbon in lakes: with special reference to benthic food chain pathways mediated by larval chironomids","authors":"Natsuru Yasuno","doi":"10.3739/RIKUSUI.81.33","DOIUrl":"https://doi.org/10.3739/RIKUSUI.81.33","url":null,"abstract":"Recent studies have provided evidence that consumers such as benthic larval chironomids assimilate methane-derived carbon ( MDC ) by foraging on methane-oxidizing bacteria in lake ecosystems. Trophic transfer of MDC can be detected by measuring carbon stable isotope ratios in consumers as biogenic methane is extremely 13 C-depleted. In this paper, I review trophic transfer of MDC mediated by larval chironomids. Trophic transfer of MDC is closely related to methane cycles ( i.e. methane production and oxidation ) in sediment, and is often enhanced by depletion of dissolved oxygen above the lake bottom. The robust tube built in sediment by larval chironomids could function as a microhabitat for methane-oxidizing bacteria, and promote trophic transfer of MDC. In stratified dimictic lakes, autumnal supply of oxygenated water to the lake bottom can stimulate the activity of methane-oxidizing bacteria, resulting in enhanced trophic transfer of MDC. In shallow polymictic lakes, transfer of MDC can be enhanced in late summer or early autumn when methane production increases. As dissolved oxygen could be depleted within aquatic plant vegetation even in shallow waters, seasonality of trophic transfer of MDC within vegetation could be similar to that in dimictic lakes. Although some studies reported that fish assimilated MDC, the extent to which MDC is transported to lake food webs is unclear. Trophic transfer of MDC has been mainly studied in deep stratified lakes. MDC may be transferred to aquatic consumers in shallow waters which are a hot spot of methane production, though further studies are necessary.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48705236","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}
Eutrophication and cyanobacterial blooming are still a worldwide problem. Our knowledge of lake restoration has improved extensively in the past couple of decades owing to geo-engineering studies. Furthermore, newly developed analytical techniques have clarified the processes behind elemental cycling. In this review, I have discussed several environmental restoration methods developed for restoration of dams and shallow eutrophic lakes in Japan; the importance of each process in phosphorus (P) cycling has been ascertained. Furthermore, I have also reviewed the cycling of inorganic and organic P based on the restoration measure applied. Finally, I have discussed future perspectives by incorporating information on lake restoration techniques and P cycling studies from recent literature.
{"title":"Studies of eutrophication in shallow lakes and the future","authors":"R. Shinohara","doi":"10.3739/RIKUSUI.81.19","DOIUrl":"https://doi.org/10.3739/RIKUSUI.81.19","url":null,"abstract":"Eutrophication and cyanobacterial blooming are still a worldwide problem. Our knowledge of lake restoration has improved extensively in the past couple of decades owing to geo-engineering studies. Furthermore, newly developed analytical techniques have clarified the processes behind elemental cycling. In this review, I have discussed several environmental restoration methods developed for restoration of dams and shallow eutrophic lakes in Japan; the importance of each process in phosphorus (P) cycling has been ascertained. Furthermore, I have also reviewed the cycling of inorganic and organic P based on the restoration measure applied. Finally, I have discussed future perspectives by incorporating information on lake restoration techniques and P cycling studies from recent literature.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46675416","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}
Invasive alien species of the genus Corbicula (Bivalvia), originally from Asia, were introduced and spread over North and South America, Europe, and Japan during the 20th century. Dense populations established in the introduced areas have resulted in negative impacts on aquatic ecosystems and local economies. To raise public awareness about this issue, I have written two review papers on the alien Corbicula species: the first summarizes previously published data on taxonomy, native ranges, introduction routes, and dispersion pathways; the present (second) paper summarizes data on biological characteristics, including mode of reproduction, feeding behaviour, physiological tolerance to abiotic changes, impacts of established Corbicula populations on ecosystems and economies, and the response of native ecosystems to the introduced Corbicula species. Future measures and research tasks to resolve the problems associated with Corbicula are also noted. The successful invasive behaviour of Corbicula species can be explained by their reproduction/life-history traits (hermaphroditism, unreduced biflagellate sperm, androgenesis, ovoviviparity, r-strategy with rapid individual growth, early maturity, high fecundity, and high dispersal ability), plasticity in feeding behaviours (suspensionand deposit-feeding), and high filtration rates rather than by their physiological tolerance to abiotic changes (salinity, temperature, oxygen, etc.).
{"title":"Taxonomy and ecology of alien Corbicula species - II Biological characteristics of clams and their impacts on ecosystems","authors":"H. Yokoyama","doi":"10.3739/rikusui.80.145","DOIUrl":"https://doi.org/10.3739/rikusui.80.145","url":null,"abstract":"Invasive alien species of the genus Corbicula (Bivalvia), originally from Asia, were introduced and spread over North and South America, Europe, and Japan during the 20th century. Dense populations established in the introduced areas have resulted in negative impacts on aquatic ecosystems and local economies. To raise public awareness about this issue, I have written two review papers on the alien Corbicula species: the first summarizes previously published data on taxonomy, native ranges, introduction routes, and dispersion pathways; the present (second) paper summarizes data on biological characteristics, including mode of reproduction, feeding behaviour, physiological tolerance to abiotic changes, impacts of established Corbicula populations on ecosystems and economies, and the response of native ecosystems to the introduced Corbicula species. Future measures and research tasks to resolve the problems associated with Corbicula are also noted. The successful invasive behaviour of Corbicula species can be explained by their reproduction/life-history traits (hermaphroditism, unreduced biflagellate sperm, androgenesis, ovoviviparity, r-strategy with rapid individual growth, early maturity, high fecundity, and high dispersal ability), plasticity in feeding behaviours (suspensionand deposit-feeding), and high filtration rates rather than by their physiological tolerance to abiotic changes (salinity, temperature, oxygen, etc.).","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45477564","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}
Wataru Higashikawa, M. Yoshimura, Tsuyoshi Yagi, K. Maeto
Recent decreases in population size of some Sympetrum species (Odonata: Libellulidae) that used to flourish in paddy fields in Satoyama, Japan, are thought to be caused by the development of rice cropping systems. As habitat use is species-specific, some conservation studies have shown that the causes of the decline in darter populations may also be species-specific. While eggs and larvae of lentic species like Sympetrum frequens decrease owing to the effect of pesticides, those of S. pedemontanum elatum, which lives along weakly flowing water, are not influenced by these chemicals, although they have decreased with the modernization of water management in paddy fields. It is also known that drying of the soil surface in no-till farming areas does not reduce the population size of S. infuscatum, whose eggs have a higher resistance to drought than those of other darter species. For the conservation of darters, we should investigate habitat use during the developmental stages of each species, identify the causes of population decline, and maintain a suitable balance within the microhabitats required by each darter species. Such designed habitats will contribute to the conservation of not only darters, but also many other aquatic organisms endangered in the paddy fields of Satoyama.
{"title":"Conservation study focusing on habitat use in darter (meadowhawk) populations that used to flourish in the rice paddy fields of Japan","authors":"Wataru Higashikawa, M. Yoshimura, Tsuyoshi Yagi, K. Maeto","doi":"10.3739/rikusui.80.107","DOIUrl":"https://doi.org/10.3739/rikusui.80.107","url":null,"abstract":"Recent decreases in population size of some Sympetrum species (Odonata: Libellulidae) that used to flourish in paddy fields in Satoyama, Japan, are thought to be caused by the development of rice cropping systems. As habitat use is species-specific, some conservation studies have shown that the causes of the decline in darter populations may also be species-specific. While eggs and larvae of lentic species like Sympetrum frequens decrease owing to the effect of pesticides, those of S. pedemontanum elatum, which lives along weakly flowing water, are not influenced by these chemicals, although they have decreased with the modernization of water management in paddy fields. It is also known that drying of the soil surface in no-till farming areas does not reduce the population size of S. infuscatum, whose eggs have a higher resistance to drought than those of other darter species. For the conservation of darters, we should investigate habitat use during the developmental stages of each species, identify the causes of population decline, and maintain a suitable balance within the microhabitats required by each darter species. Such designed habitats will contribute to the conservation of not only darters, but also many other aquatic organisms endangered in the paddy fields of Satoyama.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45967769","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}
Invasive alien bivalve species of the genus Corbicula , originally from Asia, were first introduced into North America in the 1920s and have spread around the world, including South America and Europe. In the 1980s, these species also entered Japan. The worldwide expansion of Corbicula species has resulted in negative ecological and economic impacts. To raise public awareness about this issue, I have written two review papers addressing questions such as "What are the scientific names and origins of Corbicula species?", "How and why have they been successfully introduced into new habitats?", "Why have they expanded their distribution areas?", "How have they influenced native ecosystems and local economies?", and "What types of measures should we take against the Corbicula issues?" The present paper is the first review, and it describes the taxonomic problems of Corbicula species and summarizes the information currently available on phylogenetic systematics using morphological and molecular data, which indicate sources, dispersion pathways, and introduction and dispersion mechanisms. Recent results of the phylogenetic systematics can be summarized as follows: 1 ) species and lineages cannot be identified based solely on morphology; 2 ) alien Corbicula species are composed of a few freshwater lineages, characterized by hermaphroditic and androgenetic reproduction; 3 ) considering the very subtle differences in shell morphology and the low genetic distance between the Japanese native species C. leana and the invasive C. fluminea , C. leana is estimated to be closely related to C. fluminea or a lineage within C. fluminea . The origin, introduction routes, and dispersion pathways of alien Corbicula species are being partly revealed by analyzing habitat preference, morphology, karyotype, sperm morphology, mode of reproduction, and genetic mitochondrial and nuclear DNA markers.
{"title":"Taxonomy and ecology of alien Corbicula species - I Invasion and dispersal in Japan and the world","authors":"H. Yokoyama","doi":"10.3739/rikusui.80.125","DOIUrl":"https://doi.org/10.3739/rikusui.80.125","url":null,"abstract":"Invasive alien bivalve species of the genus Corbicula , originally from Asia, were first introduced into North America in the 1920s and have spread around the world, including South America and Europe. In the 1980s, these species also entered Japan. The worldwide expansion of Corbicula species has resulted in negative ecological and economic impacts. To raise public awareness about this issue, I have written two review papers addressing questions such as \"What are the scientific names and origins of Corbicula species?\", \"How and why have they been successfully introduced into new habitats?\", \"Why have they expanded their distribution areas?\", \"How have they influenced native ecosystems and local economies?\", and \"What types of measures should we take against the Corbicula issues?\" The present paper is the first review, and it describes the taxonomic problems of Corbicula species and summarizes the information currently available on phylogenetic systematics using morphological and molecular data, which indicate sources, dispersion pathways, and introduction and dispersion mechanisms. Recent results of the phylogenetic systematics can be summarized as follows: 1 ) species and lineages cannot be identified based solely on morphology; 2 ) alien Corbicula species are composed of a few freshwater lineages, characterized by hermaphroditic and androgenetic reproduction; 3 ) considering the very subtle differences in shell morphology and the low genetic distance between the Japanese native species C. leana and the invasive C. fluminea , C. leana is estimated to be closely related to C. fluminea or a lineage within C. fluminea . The origin, introduction routes, and dispersion pathways of alien Corbicula species are being partly revealed by analyzing habitat preference, morphology, karyotype, sperm morphology, mode of reproduction, and genetic mitochondrial and nuclear DNA markers.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48401206","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 spatial distribution of submerged macrophytes, in terms of dry weight and species composition, was surveyed in the southern Lake Biwa basin in September 2017, using SCUBA. Submerged macrophytes were observed at 40 out of 52 sampling stations. The average total biomass of submerged macrophytes per site was 54 g dry wt. m. During study period, the area covered by vegetation in the basin was estimated to be 39.7 km and the total biomass was estmated to be 2761 t. Thirteen species of submerged macrophytes were observed in this study, and the average number of species per site and its standard deviation was 4.5±3.0. Hydrilla verticillata and Elodea nuttallii dominated the observed submerged macrophytes, with biomass of 777 t and 776 t, respectively. Potamogeton maackianus (556 t), Egeria densa (283 t), and Myriophyllum spicatum (257 t) followed. Biomasses of other species were each less than 100 t. We also observed that a substantial amount of filamentous algae existed in the south basin, and its biomass (1161 t) is equivalent to about 40% of the total biomass of submerged macrophytes in the basin.
{"title":"Spatial distribution of the biomass of submerged macrophytes in the southern Lake Biwa basin in September 2017","authors":"H. Haga, Yoichiro Sakai, K. Ishikawa","doi":"10.3739/rikusui.80.13","DOIUrl":"https://doi.org/10.3739/rikusui.80.13","url":null,"abstract":"The spatial distribution of submerged macrophytes, in terms of dry weight and species composition, was surveyed in the southern Lake Biwa basin in September 2017, using SCUBA. Submerged macrophytes were observed at 40 out of 52 sampling stations. The average total biomass of submerged macrophytes per site was 54 g dry wt. m. During study period, the area covered by vegetation in the basin was estimated to be 39.7 km and the total biomass was estmated to be 2761 t. Thirteen species of submerged macrophytes were observed in this study, and the average number of species per site and its standard deviation was 4.5±3.0. Hydrilla verticillata and Elodea nuttallii dominated the observed submerged macrophytes, with biomass of 777 t and 776 t, respectively. Potamogeton maackianus (556 t), Egeria densa (283 t), and Myriophyllum spicatum (257 t) followed. Biomasses of other species were each less than 100 t. We also observed that a substantial amount of filamentous algae existed in the south basin, and its biomass (1161 t) is equivalent to about 40% of the total biomass of submerged macrophytes in the basin.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46206689","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. Kawagoshi, H. Koga, Y. Suenaga, T. Hama, Hiroaki Ito
We investigated the influence of the 2016 Kumamoto earthquake on groundwater quality at 12 sampling points in the area near its seismic centre. We statistically evaluated the difference in the measured values of each waterquality index before and after the earthquake based on bi-weekly or monthly monitoring data for three years across the earthquake area. We also visualised water-quality characteristics using a hexa-diagram (Stiff diagram) and statistically evaluated differences before and after the earthquake using non-hierarchical cluster analysis. The results showed that there was not a large variation in water-quality characteristics as represented by the hexa-diagram shape. However, statistical analysis showed a significant difference at nine sampling points, suggesting earthquake influence on groundwater quality. In addition, it is possible that the influence of the earthquake appeared later in a groundwater-discharge area. On the other hand, no topographic relationship between the location of the sampling points and seismic centre or the fault was shown; thus, it is likely that groundwater quality varied at arbitrary points within the study area where slip on the fault was observed.
{"title":"Influence of the 2016 Kumamoto earthquake on groundwater quality","authors":"Y. Kawagoshi, H. Koga, Y. Suenaga, T. Hama, Hiroaki Ito","doi":"10.3739/rikusui.79.147","DOIUrl":"https://doi.org/10.3739/rikusui.79.147","url":null,"abstract":"We investigated the influence of the 2016 Kumamoto earthquake on groundwater quality at 12 sampling points in the area near its seismic centre. We statistically evaluated the difference in the measured values of each waterquality index before and after the earthquake based on bi-weekly or monthly monitoring data for three years across the earthquake area. We also visualised water-quality characteristics using a hexa-diagram (Stiff diagram) and statistically evaluated differences before and after the earthquake using non-hierarchical cluster analysis. The results showed that there was not a large variation in water-quality characteristics as represented by the hexa-diagram shape. However, statistical analysis showed a significant difference at nine sampling points, suggesting earthquake influence on groundwater quality. In addition, it is possible that the influence of the earthquake appeared later in a groundwater-discharge area. On the other hand, no topographic relationship between the location of the sampling points and seismic centre or the fault was shown; thus, it is likely that groundwater quality varied at arbitrary points within the study area where slip on the fault was observed.","PeriodicalId":35602,"journal":{"name":"Japanese Journal of Limnology","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2018-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.3739/rikusui.79.147","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43895242","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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