Emergence of Chironomidae from the shallow eutrophic Lake Kasumigaura,Japan

Seasonal chironomid emergence was monitored in the shallow eutrophic Lake Kasumigaura and 18 species were collected with a battery-operated light trap fixed on a floating stage and with surface emergence traps. During October–December, samples in the light trap comprised exclusively Tokunagayusurika akamusi (Tokunaga) and small numbers of one or two other species. T. akamusi, Procladuis (Holotanypus) culiciformis (L.), and Chironomus plumosus (L.) constituted 91.6% of the annual catch of chironomid adults. The predominance of T. akamusi (75.3 % of chironomid catch) and the high ratio (13) of T. akamusi to C. plumosus was more marked in this lake than other Japanese eutrophic lakes. Glyptotendipes tokunagai Sasa and Dicrotendipes pelochloris (Kieffer) were also caught abundantly with the light trap, but not with surface traps, indicating these were littoral species. The dry weight of emerging adults during May–December 1982 was 2.87 g m^–2, of which 1.92 gm^–2 (67%) was T. akamusi and 0.67 gm^–2 (23%) C. plumosus and 0.23 g m^–2 (8%) Clinotanypus sugiyamai Tokunaga and 0.03 gm^–2 (1%) P. (H.) culiciformis. The weight of emerging Tanypodinae was much higher than the annual mean larval biomass or estimated larval production, which have been due to underestimating the population density using an Ekman-Birge dredge. High numbers of individuals and species of chironomids were caught during April–July, presumably as a result of the high food supply for chironomid communities.     

DNA barcoding of freshwater zooplankton in Lake Kasumigaura,Japan

Although DNA barcoding is a promising tool for the identification of organisms, it requires the development of a specific reference sequence library for sample application. In the present study we developed a Lake Kasumigaura, Japan, zooplankton DNA barcode library to increase the sensitivity of future zooplankton monitoring for detecting lake ecosystem condition changes. Specifically, the mitochondrial cytochrome c oxidase subunit I (mtCOI) haplotype, i.e., the primary DNA barcode, was examined for each zooplankton taxon. In crustaceans, 37 mtCOI haplotypes were obtained from 99 individuals, representing four and 15 morpho-species of Copepoda and Cladocera, respectively. Comparing these sequences with those in GenBank shows that the lake harbors putative non-indigenous species, such as Daphnia ambigua. In rotifers, 132 mtCOI haplotypes were obtained from 302 individuals, representing 11 genera and one unclassified taxon. The automatic barcode gap discovery (ABGD) algorithm separated these haplotypes into 43 species. Brachionus cf. calyciflorus was divided into five ABGD species, and different ABGD species tended to occur in different seasons. Seasonal ABGD-species succession was also observed within Polyarthra spp. and Synchaeta spp. These seasonal successions were not detected by inspections of external morphology alone. Accepting up to 7% sequence divergence within the same species, mtCOI reference sequences were available in GenBank for three, 13, and 17 species in Copepoda, Cladocera, and Rotifera, respectively. The present results, therefore, reveal the serious shortage of mtCOI reference sequences for rotifers, and underscore the urgency of developing rotifer mtCOI barcode libraries on a global scale.     

Long-term light environment variability in Lake Biwa and Lake Kasumigaura, Japan: modeling approach

Light environment variability was investigated in the two Japanese lakes Biwa and Kasumigaura, which offer a broad range of optical conditions in the water bodies due to their diverse morphometries and limnological characteristics. To elucidate their light environments, Secchi depths (SDs) were related to long-term monitored datasets of concentrations of optically active substances (OASs) using two approaches based on statistical and mechanistic models. A good estimate for the nonphytoplanktonic suspended solids (NPSS) concentration gained using a monthly factor ?? (which represents the phytoplanktonic portion in total suspended solids) from a long-term analysis was utilized to develop robust models. Using the mechanistic model, the contribution of each OAS to the SD can be understood and investigated in more detail than possible with a statistical approach, but the statistical model yields better results in terms of SD prediction. Based on the results of an analysis of the contribution of each OAS to the SD, it was clear that NPSS was the component that exerted the most influence on the light environments in the two lakes; in this respect, this study agrees with other studies that show the importance of suspended inorganic particles as the main contributor to the SD in inland waters. Using ANOVA, we analyzed how specific inherent optical properties may have changed spatially and temporally, and the results indicated that the temporal (monthly) effect was primarily responsible for the loss of accuracy in the models. In addition, the ANOVA analysis suggested that grouping the data improved the predictive performances of the statistical models. Finally, we concluded that combining the two models yields the most reliable results in terms of SD prediction and determining the contribution of each OAS to the SD at present.     

Bacterial Contribution to Dissolved Organic Matter in Eutrophic Lake Kasumigaura,Japan

Incubation experiments using filtered waters from Lake Kasumigaura were conducted to examine bacterial contribution to a dissolved organic carbon (DOC) pool. Bacterial abundance, bacterial production, concentrations of DOC, total dissolved amino acids (TDAA), and total dissolved neutral sugars (TDNS) were monitored during the experiments. Bacterial production during the first few days was very high (20 to 35 μg C liter⁻¹ day⁻¹), accounting for 40 to 70% of primary production. The total bacterial production accounted for 34 to 55% of the DOC loss during the experiment, indicating high bacterial activities in Lake Kasumigaura. The DOC degradation was only 12 to 15%, whereas the degradation of TDAA and TDNS ranged from 30 to 50%, suggesting the preferential usage of TDAA and TDNS. The contribution of bacterially derived carbon to a DOC pool in Lake Kasumigaura was estimated using d-amino acids as bacterial biomarkers and accounted for 30 to 50% of the lake DOC. These values were much higher than those estimated for the open ocean (20 to 30%). The ratio of bacterially derived carbon to bulk carbon increased slightly with time, suggesting that the bacterially derived carbon is more resistant to microbial degradation than bulk carbon. This is the first study to estimate the bacterial contribution to a DOC pool in freshwater environments. These results indicate that bacteria play even more important roles in carbon cycles in freshwater environments than in open oceans and also suggests that recent increases in recalcitrant DOC in various lakes could be attributed to bacterially derived carbon. The potential differences in bacterial contributions to dissolved organic matter (DOM) between freshwater and marine environments are discussed.     

Interrelations between Microcystis and Cladocera in the highly Eutrophic Lake Kasumigaura,Japan

The zooplankton community in the highly eutrophic Lake Kasumigaura was investigated and its relation to a bloom of Microcystis was analyzed. The zooplankton community was dominated by small cladocerans, whose biomass and production became highest in summer, when Microcystis bloomed. The high cladoceran production is considered to depend on the production of colonial Microcystis, because the production of nannoplankton was apparently too low to ensure the cladoceran production. Microcystis cells were unsuitable as food for the cladocerans inhabiting Lake Kasumigaura, but became utilizable when decomposed. Decomposed Microcystis may be the main food for Cladocera in the lake in summer. High water temperatures occurring in summer probably promoted decomposition of the Microcystis, leading to increased production of the small cladocerans.     

Diurnal changes in the vertical distribution of phytoplankton in hypertrophic Lake Kasumigaura,Japan

The daily vertical migration of five species;Microcystis aeruginosa (Kütz.) Trevis,Anabaena spiroides Klebahn f.crassa (L.) Elenkin,Aphanizomenon flos-aquae (L.) Ralfs,Melosira granulata (E). Ralfs, andCoscinodiscus lacustris Grun. was studied using a close-interval water sampler on a calm summer day in Lake Kasumigaura. Many colonies ofMicrocystis were observed at the middle of the water column (approx. 1.5 m depth) in the afternoon, and at the surface in the early morning.Anabaena occurred mostly in the upper layer whileAphanizomenon tended to be uniformly distributed. The difference in migration patterns suggests thatMicrocystis is superior toAnabaena andAphanizomenon in obtaining both light and nutrients from this lake. Among diatoms,Melosira remained at the bottom of the water column throughout day and night, but Coscinodiscus was uniformly distributed.     

Isolation of enteroviruses from water, suspended solids, and sediments from Galveston Bay: survival of poliovirus and rotavirus adsorbed to sediments

The distribution and quantitation of enteroviruses among water, suspended solids, and compact sediments in a polluted estuary are described. Samples were collected sequentially from water, suspended solids, fluffy sediments (uppermost layer of bottom sediments), and compact sediment. A total of 103 samples were examined of which 27 (26%) were positive for virus. Polioviruses were recovered most often, followed by coxsackie B viruses and echoviruses 7 and 29. Virus was found most often attached to suspended solids: 72% of these samples were positive, whereas only 14% of water samples without solids yielded virus. Fluffy sediments yielded virus in 47% of the samples, whereas only 5% of compact bottom-sediment samples were positive. When associated with solids, poliovirus and rotavirus retained their infectious quality for 19 days. The same viruses remained infectious for only 9 days when freely suspended in seawater. Collection of suspended solids at ambient water pH appears to be very useful for the detection of virus; it has advantages over collecting and processing large volumes of water, with accompanying pH adjustment and salt addition for processing.     

Performance and design of artificial lagoons for controlling diffuse pollution in Lake Kasumigaura,Japan

Artificial lagoons (ALs) are unique wetland treatment areas for lakes. They use enclosed river mouth areas to retain pollutants, and they mimic the small natural lagoons rimming large lakes, functioning as habitats and limiting the entry of diffuse (non-point-source) pollutants from the river basins. Four ALs have been installed in Lake Kasumigaura (～60 km northeast of Tokyo) since 1998. We evaluated the performance of these ALs as treatment facilities. Rates of removal ranged from 8.2% to 44% for chemical oxygen demand (COD_Mn), from 0.9% to 8.7% for TN, and from 9% to 55% for TP. The long-term rate of pollutant removal was proportional to the average hydraulic retention time and declined exponentially with increasing hydraulic loading rate (annual discharge/area) and loading rate (annual load/area). The ratio of AL surface area to watershed area was also correlated with AL performance, as occurs in stormwater treatment wetlands, although the ratios were much smaller than those in stormwater treatment wetlands. Our results can be used as preliminary design tools for ALs, on the understanding that the data were obtained only from Lake Kasumigaura and should therefore be applied carefully.     

Isolation of enteroviruses from water, suspended solids, and sediments from Galveston Bay: survival of poliovirus and rotavirus adsorbed to sediments.

The distribution and quantitation of enteroviruses among water, suspended solids, and compact sediments in a polluted estuary are described. Samples were collected sequentially from water, suspended solids, fluffy sediments (uppermost layer of bottom sediments), and compact sediment. A total of 103 samples were examined of which 27 (26%) were positive for virus. Polioviruses were recovered most often, followed by coxsackie B viruses and echoviruses 7 and 29. Virus was found most often attached to suspended solids: 72% of these samples were positive, whereas only 14% of water samples without solids yielded virus. Fluffy sediments yielded virus in 47% of the samples, whereas only 5% of compact bottom-sediment samples were positive. When associated with solids, poliovirus and rotavirus retained their infectious quality for 19 days. The same viruses remained infectious for only 9 days when freely suspended in seawater. Collection of suspended solids at ambient water pH appears to be very useful for the detection of virus; it has advantages over collecting and processing large volumes of water, with accompanying pH adjustment and salt addition for processing.     

Restoration of wetland vegetation using soil seed banks: lessons from a project in Lake Kasumigaura, Japan

The restoration of degraded wetland ecosystems and the recovery of wetland biodiversity are important global issues. Generally, wetland restoration projects include activities to recover vegetation. A promising revegetation technique is one in which soil seed banks are utilized as the source of plant recolonization. Using such a technique, a pilot project to restore lakeshore vegetation was launched at Lake Kasumigaura, Japan, in 2002. In the project, lake sediments containing the seed banks were spread thinly (∼10 cm) on the surfaces of artificial lakeshores, which were constructed in front of concrete levees and had microtopographic variations. In total, 180 species, including six endangered or vulnerable species and 12 native submerged plants that had disappeared from the above-ground vegetation of the lake, were recorded in five recreated lakeshores (total area, 65,200 m²) during the first year of the restoration. The distribution of each restored species at the sites suggested the importance of microtopographic relief for recolonizing species-rich lakeshore vegetation. Furthermore, the origin of the source seed banks affected the species composition of the restored vegetation. On the other hand, the restoration sites were subject to exotic plant invasions. Here, we report lessons learned from the Lake Kasumigaura restoration project as a contribution to the establishment of ecologically sound revegetation techniques.     

Photosynthesis and primary production in Lake Kasumigaura (Japan) monitored monthly since 1981

This study reports the primary production of phytoplankton determined with a ¹³C tracer, and their related variables, in Lake Kasumigaura, a shallow, hyper-eutrophic lake, and the second largest lake in Japan. Measurements were conducted monthly from August 1981 to December 2013 at four stations within the lake. Monitoring was a component of the Lake Kasumigaura Long-term Environmental Monitoring program, conducted by the National Institute for Environmental Studies (NIES) since 1977. The program collects data on water quality, and plankton and benthic communities. Lake Kasumigaura is registered as a core site of the Japan Long-term Ecological Research Network (JaLTER), which is a member of the International Long-term Ecological Research Network (ILTER). This dataset includes daily primary production (Pzd gC m^?2 d^?1) and the six parameters required to calculate Pzd: maximum photosynthesis rate (P _max gC gC^?1 h^?1); light irradiance at the junction of the initial slope (α (gC gC^?1 h^?1) (μmol photon m^?2 s^?1)^?1) and P _max of the photosynthesis vs. irradiance (P vs. E) curve (E _k μmol photon m^?2 s^?1); attenuation coefficient of photosynthetically available radiation (PAR) (K _PAR m^?1); water depth at each sampling station (Z _b , m); dissolved inorganic carbon (DIC mgC L^?1) and particulate organic carbon concentrations (POC gC m^?3); and chlorophyll a amounts (Chl.a μg L^?1). Daily primary production was calculated by obtaining a P vs. E curve over a short-term incubation (approximately 1 h) in a water tank using in situ water temperature in the laboratory, based on the field conditions of the sampling date. The dataset has been used for ecological studies as well as for management studies on water quality and ecosystems. This dataset is unique among the available published papers concerning lakes or primary production in various ecosystems, collected over a long period of time and freely available.     

Stratification and mixing processes associated with hypoxia in a shallow lake (Lake Kasumigaura,Japan)

Limnology - Physical processes associated with hypoxia events in a shallow lake, Lake Kasumigaura, Japan, are investigated with long-term mooring observations at the middle of the lake basin....     

Hypoxia tolerance of three native and three alien species of bitterling inhabiting Lake Kasumigaura,Japan

Differences in hypoxia tolerance among three native and three alien bitterling species were examined by means of field surveys and aquarium experiments. I caught fish in minnow traps and measured environmental factors such as dissolved oxygen and current velocity once a month between June and November 2006 at 30 points around Lake Kasumigaura, Japan. In addition, aquarium experiments were carried out to compare aquatic surface respiration thresholds among the bitterling species. Much more individuals of an alien species, Rhodeus ocellatus ocellatus, was caught at the least oxygen range than expected in the field, and showed the highest hypoxia tolerance in the laboratory experiments. Another alien bitterling, Acheilognathus rhombeus, also showed higher hypoxia tolerance than the three native bitterling species. Lake Kasumigaura is well known for eutrophication and water masses with low dissolved oxygen have often been observed there. Differences in hypoxia tolerance among bitterling species might have affected bitterling assemblage structure in Lake Kasumigaura, which is currently characterized by the dominance of R. o. ocellatus.     

Nutrient release rates from the sediments of Saginaw Bay,Lake Huron

Direct measurements of net production rates and pore water profiles of solutes in the fine-grained sediments of Saginaw Bay, imply corresponding steady-state fluxes to the overlying water of 1.1–1.3 (I), 450–1010 (NH₄ ⁺), 1250–2650 (Si(OH)₄), 3000–3400 (Ca²⁺), 440–1330 (Mg²⁺), 1.5–728 (Fe²⁺), and 179–281 (Mn²⁺) moles/m²/day and 11.0–11.8 (alkalinity) meq/m²/day at 17.5 °C. Silica production rates in sediments apparently follow first order kinetics with a rate coefficient of 0.09/day and a steady-state silica concentration of 1.2 mM at 23.5°C. The remaining solutes follow kinetics approximately independent of solute concentration over the range of concentrations observed. Measured solute production rates are consistent with observed solute profiles only if lateral diffusion gradients are maintained in the sediments by the burrowing and irrigation activity of benthic organisms such asChironomous, the dominant burrower in Saginaw Bay. Assuming that solute fluxes from Saginaw Bay are representative of all of the post-glacial sediments of Lake Huron, the iodine flux from sediments is comparable to the total fluvial input of iodine. The extrapolated silica fluxes from Lake Huron sediments balance the estimated biogenic silica flux to the sediments.     

Synchronous decline of native bitterling population detected from 9 years of survey in rivers and agricultural ditches around Lake Kasumigaura,Japan

Ichthyological Research - To assess the population dynamics, abundance of bitterling species and two non-bitterling cyprinid species were investigated in Lake Kasumigaura, Japan. Fish capture was...     

Nocturnal activity and feeding of juvenile channel catfish,Ictalurus punctatus,around offshore breakwaters in Lake Kasumigaura,Japan

Ichthyological Research - Diel changes in occurrence and feeding habits of juvenile channel catfish (Ictalurus punctatus) were examined in offshore breakwater areas in Lake Kasumigaura, Japan, to...     

Effects of water level fluctuation on the growth ofNelumbo nucifera Gaertn. in Lake Kasumigaura,Japan

Investigations were made of the growth ofNelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass ofN. nucifera from the maximum of 291 g d.w. m⁻² in July to a minimum of 75 g d.w. m⁻². The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m² m⁻² in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m² m⁻². The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day⁻¹, respectively. The sudden rise in water level (25 cm day⁻¹) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival ofN. nucifera in Lake Kasumigaura.     

Aerobic methanotrophic communities in the bottom sediments of Lake Baikal

The results of the first methodical investigation into the aerobic methanotrophic communities inhabiting the bottom sediments of Lake Baikal are reported. Use of the radioisotopic method revealed methane consumption in 12 10- to 50-cm-long sediment cores. The maximum methane consumption rates (495-737 microl/(dm3 day) were recorded in sediments in the regions of hydrothermal vents and oil and gas occurrence. Methane consumption was most active in the surface layers of the sediments (0-4 cm); it decreased with the sediment depth and became negligible or absent at depths below 20 cm. The number of methanotrophic bacteria usually ranged from 100 to 1000 cells/cm3 of sediment and reached 1 million cells/cm3 in the regions of oil and gas occurrence. The 17 enrichment cultures obtained were represented mainly by morphotype II methanotrophs. Phylogenetic analysis of the enrichment cultures in terms of the amino acid sequence of the alpha subunit of the membrane-bound methane monooxygenase revealed the predominance of methanotrophs of the genus Methylocystis. The results obtained suggest the presence of an active aerobic methanotrophic community in Lake Baikal.     

Land use/cover change and its drivers: a case in the watershed of Lake Kasumigaura, Japan

Land use/land cover (LULC) changes in the watershed (2,157 km²) of Lake Kasumigaura during 1979–1996 (Period-1: 1979–1990, Period-2: 1990–1996) were analyzed, and their socio-economic and biophysical drivers were compared using time-series, high-quality GIS datasets in order to examine the characteristics of a model forecasting the future LULC. The changes occurred over an area of more than 90 km² during the overall period at changing rates of 0.22% year⁻¹ in Period-1 and 0.25% year⁻¹ in Period-2. Forestland decreased most in both periods at changing rates of 0.45% year⁻¹ in Period-1 and 0.61% year⁻¹ in Period-2. However, predominant changing patterns differed, i.e., from forest to golf course in Period-1 and from forest to artificial field in Period-2. Particularly in Period-2, a significant LULC change was observed in an area of high population increase on the edge of an already high-population area. Relationships examined among LULC change, population, and rate of population change suggested that the urbanized area was highly resistant to LULC change, and that such change was less frequent in areas of population decline. Statistical analyses indicated that the most influential drivers for total LULC changes were population in Period-1 and distance from the Tokyo Station in Period-2. Since the change potentials differed between the periods, we could not assume a stationary process for the corresponding drivers. Somewhat low S values (indices for demonstrability) show that LULC changes in the watershed of Lake Kasumigaura occurred rather randomly, probably resulting in fragmentation of the landscape.     

Phytoplankton species abundance in Lake Kasumigaura (Japan) monitored monthly or biweekly since 1978

This data paper reports the abundance of phytoplankton species in monthly or biweekly samples collected from May 1978 through March 2010 at two stations on Lake Kasumigaura, a shallow lake that is the second-largest lake in Japan. The data set of quantitatively over several decades is unique among the available published data papers concerning lakes or plankton and continues to be freely available. The monitoring has been performed as a component of the Lake Kasumigaura Long-term Environmental Monitoring program, conducted by the National Institute for Environmental Studies since 1977. The data set details 173 phytoplankton species (or taxa), which can be identified by using an optical microscope and records their abundance. The abundance of each species is expressed in units of volume (??m³) per milliliter of lake water. This approach allows quantitative comparisons among taxa because the cell size of phytoplankton varies by several orders of magnitude among taxa. The phytoplankton data include 39 species (taxa) of Cyanophyta, 67 Chlorophyceae (Chlorophyta), 3 Prasinophyceae (Chlorophyta), 1 Raphidophyceae (Heterokontophyta), 6 Euglenophyceae (Euglenozoa), 4 Dinophyceae (Dinophyta), 38 Bacillariophyceae (Heterokontophyta), 6 Chrysophyceae (Heterokontophyta), 7 Xanthophyceae (Heterokontophyta), 1 Cryptophyceae (Cryptophyta) and 1 Prymnesiophyceae (Haptophyta). The data have been used for ecological and environmental studies and for studies on lake management.