Lake Yunoko Research Articles

Estimation of the Number of Freshwater Anglers in Japan Based on the Number of Anglers Fishing Lake Yunoko

Estimation of the Number of Freshwater Anglers in Japan Based on the Number of Anglers Fishing Lake Yunoko

3D-view Generation and Species Classification of Aquatic Plants Using Acoustic Images

In this study, we used a new integrated measurement system that combines the acoustic imaging sonar of DIDSON (Dual-frequency IDentification SONar) with concentrator lenses, motion sensors, and GPS receivers to find and identify different species of aquatic plants. Two types of experiments were performed at two lakes in Japan: Lake Yamanaka and Lake Yunoko. In the first experiment at Lake Yamanaka, the image was captured with a one-degree concentrator lens. Multi-beam image processing was used to generate 3-D images of aquatic plants. The lens used in this experiment concentrated the vertical beam width within 1 degree. The second experiment at Lake Yunoko DIDSON with a 3-degree concentrator lens was applied, and histogram and spatial spectrum analyses were performed for plant species classification. Three species of aquatic plants, Myriophyllum spicatum, Chara globularis, and Elodea nuttallii, were classified by the parameters obtained from the current methods. The ability to visualize the features of each aquatic plant for species classification, e.g., leaf and branch dimensions, was attributed to spatial spectrum and scattering analyses of the acoustic images. The high spatial resolution of the integrated DIDSON measurement system will contribute protection of endangered species in rapidly changing underwater environment.

Development of a water temperature-ecological model to stimulate global warming effects on lake ecosystem

This paper describes a newly developed combined water temperature-ecological (WT-ECO) model which is employed to simulate the effects of global warming on lake and reservoir ecosystems. The WT model includes (i) variations in the eddy diffusion coefficient based on the degree of thermal stratification and the velocity of wind, and (ii) a sub-model for simulating the freezing and thawing processes of surface water, water temperatures, and the mixing rates between two adjacent layers of water. The ECO model then uses these results to calculate the resultant effect on a lake's ecological dynamics, e.g., composition of phytoplankton species, their respective concentrations, and nutrient concentrations. When the model was benchmarked against Lake Yunoko, a dimictic lake, fairly good agreement was obtained over a 4-yr period; thereby indicating it is suitably calibrated. In addition, to assess the effects of global warming on a lake ecosystem, changes in Lake Yunoko's water temperature/quality were simulated in response to an increase in air temperature of 2 - 4°C. Results indicate that such an increase will (i) increase thermal stratification in summer, which increases the nutrient concentrations in bottom water due to nutrient release from bottom sediment, (ii) increase the concentration of phytoplankton at the beginning of the autumn circulation period, and (iii) change the composition of phytoplankton species.

Development of a water temperature-ecological model to stimulate global warming effects on lake ecosystem

This paper describes a newly developed combined water temperature-ecological (WT-ECO) model which is employed to simulate the effects of global warming on lake and reservoir ecosystems. The WT model includes (i) variations in the eddy diffusion coefficient based on the degree of thermal stratification and the velocity of wind, and (ii) a sub-model for simulating the freezing and thawing processes of surface water, water temperatures, and the mixing rates between two adjacent layers of water. The ECO model then uses these results to calculate the resultant effect on a lake's ecological dynamics, e.g., composition of phytoplankton species, their respective concentrations, and nutrient concentrations. When the model was benchmarked against Lake Yunoko, a dimictic lake, fairly good agreement was obtained over a 4-yr period; thereby indicating it is suitably calibrated. In addition, to assess the effects of global warming on a lake ecosystem, changes in Lake Yunoko's water temperature/quality were simulated in response to an increase in air temperature of 2 - 4 °C. Results indicate that such an increase will (i) increase thermal stratification in summer, which increases the nutrient concentrations in bottom water due to nutrient release from bottom sediment, (ii) increase the concentration of phytoplankton at the beginning of the autumn circulation period, and (iii) change the composition of phytoplankton species.

Short- and long-term control of external and internal phosphorus loads in lakes—A scenario analysis

In this paper the structure and validation of the deterministic eutrophication model SALMOSED is discussed. It is applied to two lakes of different depths with a long history of cultural eutrophication. The simulation results are used to assess the short- and long-term efficiency of alternative measures for eutrophication control considering external and internal phosphorus loads. In the case of the shallow Lake Mueggelsee the control of the phosphorus release from the sediment by sediment dredging seems to be the only efficient method. To consolidate a mesotrophic steady state of Lake Mueggelsee in a long-term perspective, 10-year simulation runs show that single sediment dredging should be followed by a reduction of the external phosphorus load by at least 50%. The eutrophication of the medium-deep Lake Yunoko can be controlled by a significant reduction of the effluent phosphorus concentration. Additionally it is recommended to control the considerable internal phosphorus load of Lake Yunoko by artificial aeration/destratification or the more costly sediment dredging.

Redescription of Ophidonais serpentina(MUELLER, 1773) (Naididae, Oligochaeta) from Lake Yunoko, Central Japan, with Record of the Oligochaete Composition in the Lake.

A naidid oligochaete, Ophidonais serpentine (MÜLLER, 1773) is redescribed based on specimens from Lake Yunoko, central Japan. This is the first record of this species from Pacific Asia. Among 1988 specimens, eleven species of oligochaetes were recorded from Lake Yunoko. Ophidonais serpentine was abundant in the littoral zone, but disappeared in the deeper profundal. Tubifex sp. and Limnodrilus spp. (L. hoffineisteri and L. claparedianus) composed 86-100% of the oligochaete assemblage except at the central eastern inlet. The oligochaete densities were higher in the northern basin, accounting for several tens of thousands of individuals m-2 in the upper profundal.

Distribution and Population Dynamics of Chironomidae (Diptera) in Lake Yunoko, Japan.

Fauna and seasonal change of larval populations of Chironomidae were investigated in the eutrophic Lake Yunoko from May 1988 to June 1989. A total of 1, 213 adults belonging to 16 species were obtained by rearing of larvae in sediment collected from 10 stations as well as those in epiphytic matter on submerged plants, mainly Elodea nuttallii (PLANCH)ST. JOHN collected from littoral zones. Diclotendipes lobiger (KIEFFER) and Psectrocladius yunoquartus SASA emerged from sediment samples at≤7 m depth, Tanytarsus nippogregarius SASA et KAMIMURA emerged at≤10 m. Chironomus nipponensis TOKUNAGA, collected from all the stations, was the only species emerging at>10 m depth. C. nipponensis and T. nippogregarius constiuted 93 % of the total adults emerging. From the epiphytic matter on submerged plants, nine species were obtained, of which D. lobiger, P. yunoquartus and Cricotopus trifasciatus (MEICEN), constituted 96 % of the total.Annual mean density and annual mean biomass of chironomid larvae at 7 m depth were, 2, 210 m-2 and 3.8 g d.w.⋅m-2, respectively, in which C. nipponensis larvae comprised 1800 m-2 (81%) and 3.5 g d.w.⋅m-2 (93%), respectively. Annual mean biomass of Oligochaeta was as high as 13.7 g d.w.⋅m-2.Population of C. nipponensis consisted of two cohorts which overlapped each other. One emerged in April with earlier emergence in the preceding October. The other emerged during late May to July. A large amount of inflowing hot ground water elevated the bottom water temperature, enabling C. nipponensis to reach maturity within a year.Five out of 15 species recorded in the 1979-1981 survery were not collected in the present study. Changes in submerged plants in both species composition and biomass might have affected chironomid communities.

Assessment of Eutrophication Control Programs Using an Ecological Model for a Dimictic Lake

An ecological model of Lake Yunoko, a dimictic lake, was developed to assess various programs for eutrophication control. A multi-component dynamic model for nutrients in the bottom sediment-water system was incorporated into the model, a one-dimensional water temperature-water quality-ecological model. Good agreement between the model calculations and observed nutrients, chlorophyll-a, and dissolved oxygen concentrations in the water and nutrient concentrations in the bottom sediment was noted. The agreement between the model calculations and the measured nutrient flux from bottom sediment during the summer stagnation period was good. The effectiveness of sediment dredging, artificial circulation, and reduction of external phosphorus loading as eutrophication control programs on chlorophyll-a, PO4−P, and dissolved oxygen concentration in the water was assessed using a calibrated model.

Significance of a low oxygen layer for a Daphnia population in Lake Yunoko, Japan

Population dynamics and vertical migration of Daphnia longispina in Lake Yunoko were studied. The Daphnia population was small in spring and early summer, probably because of high predation pressure by fish. The population grew in midsummer, when thermal stratification developed and the dissolved oxygen became very low in the deeper layer of the hypolimnion. In this season, adults of D. longispina concentrated in the daytime near the lake bottom, where fish were absent because of the anoxic conditions, but ascended at night to the upper layer of the hypolimnion, where food was most abundant. The low oxygen layer near the bottom kept out the predators and protected Daphnia from predation, and consequently contributed to the built-up of its population. However, the low oxygen layer was unfavorable for reproduction of Daphnia, as reflected in the low egg ratio and high percentage of males in the population. The population decreased in the fall, when thermal stratification disappeared and predation pressure seemed to increase.

中禅寺湖および湯の湖におけるＵｒｏｇｌｅｎａ ａｍｅｒｉｃａｎａの発生状況

Seasonal changes and vertical distribution of Uroglena americana, which is known to cause fishy odor of tap waters, were surveyed in Lakes Chuzenji-ko, Yuno-ko, and the mouth of the Yukawa River, which connects the two lakes, during 1983 to 1985. The results were as follows (1) Remarkable increases in cell number of U. americana were observed from the end of May to the middle of June in Lake Yuno-ko and from the end of June to the middle of July in Lake Chuzenji-ko. The fishy odor of tap water, where Lake Chuzenji-ko was its source, occurred for the same period as that in blooming of U. americana in 1983. (2) The maximum cell numbers of U. americana were observed at surface layer in Lake Yuno-ko and at the depth of about 10 m in Lake Chuzenji-ko, where the river water flowed into the same water temperature layer during May to July, suggesting that most of U. americana might flow into Lake Chuzenji-ko through the Yukawa River and grow there. (3) Since Lake Yuno-ko has sufficient nutrient levels for growth of U. americana and the water temperature from June to October is nearly 15 C, a condition favoring growth of U. americana, Lake Yuno-ko would have supplied U. americana for Lake Chuzenji-ko for long period.

A study on dissolved oxygen budgets in natural and artificial lakes

Field survey was conducted to evaluate the major factors which control dissolved oxygen (DO) concentration in water bodies at Lake Yunoko (0.33 km 2) and Lake Kamafusa (2.66 km 2). Seasonally measured DO profiles resulted from phenomena such as oxygen production by photosynthesis, oxygen consumption by respiration and/or sediment oxygen demand were also presented. A mathematical model for calculating DO concentration in the lakes was developed. Major factors to control hypolimnetic oxygen depletion were calculated. As the results of calculation, it was demonstrated that the largest depletion in DO at the bottom layer was caused mainly by the sediment oxygen demand on the oxygen budget at Lake Yunoko in early summer. However, after DO depletion in the hypolymnion, water column oxygen demand became to a dominant factor to control vertical DO profiles.

日光湯ノ湖堆積物中の炭水化物 深度分布および供給源について

Cellulose, non-cellulose carbohydrates and lignin were investigated in a 30 cm core collected from Lake Yunoko, Nikko, Japan. Organic and mineral analyses indicated that two sediment layers (0-8 cm and 19-25 cm : AL layers) are mainly from soil-derived materials, while the other two layers (9-16 cm and 25-27 cm : AU layers) are composed of a larger amount of autochthonous materials relative to soil derived materials. On the basis of the compositional patterns within non-cellulose carbohydrates which fluctuate in correspondence with the extent of the contribution of soil-derived organic matter relative to lake derived organic matter, it was concluded that rhamnose, fucose and galactose mainly originated from autochthonous organic matter, glucose from soil organic matter, and xylose and arabinose from land higher plant detritus. From these results Gluc/ (Rham+Fuco+ Gala), (Xylo+Arab) / (Rham+Fuco+Gala) and (Gluc+Xylo+Arab) / (Rham+Fuco+Gala) ratios were proposed as useful indices for estimating a relative contribution of allochthonous organic matter to autochthonous organic matter in sediments. Cellulose showed a vertical profile similar to that of lignin, where the abundance is generally higher in AL layers than in AU layers. Both cellulose and lignin were concluded to be useful as indicators of higher plant contribution.

Carbohydrates in Lake Yunoko sediment : characteristics of carbohydrate composition in relation to source organic matter

Carbohydrates in Lake Yunoko sediment : characteristics of carbohydrate composition in relation to source organic matter

Interrelation between plankton and benthos in the littoral algal community of Lake Yunoko, Central Japan

To ascertain the floristic interaction between phytoplankton and benthos in the littoral, the composition of each community was investigated and the effect of the substrata on the benthic communities was also examined.

The Distribution of Urea in Lake Yunoko

Urea in waters collected from a central water column of Lake Yunoko was determined from July of 1971 to April of 1972. The annual minimum of the urea standing stack in the central water column was 3.75 mg-at-N·m-2 in November of 1971. The annual maximum was 61.0mg-at-N·m-2 in ice-covered March of 1972. Three depth profiles of urea out of six appeared to be nutrient types with depression of urea in the traphogenic layer, but increase in the tropholytic layer. In these cases, photosynthetic activities might regulate the urea depth profile. The ratios of urea-N/TIN (total inorganic nitrogen) suggest that urea was a major constituent of nitrogenous nutrients in ice-covered March, but a minor component throughout the rest of the year. Allochthonous urea, which originated from waste water treatment, seems to have been an important source of urea in water of Lake Yunoko.

密度の違いを利用した湖底堆積物中の外来性および自生性物質の分離

A density gradient centrifugation method by using Thoulet's liquid (HgI2/KI : density 1.92.4g/cm3) was applied for separating autochthonous and allochthonous materials in lacustrine sediments.The measurement of density distribution of sediment samples showed that a sediment sample can be divided into three main fractions in terms of density : Fraction 1 (density : <1.9g/cm3), which consists of wood, leaf fragments and sometimes phytoplanktons (nearly living?); Fraction 2 (density : 1.92.2g/cm3), which is predominantly composed of diatoms whose organic constituents seem to have been considerably lost; Fraction 3 (density : >2.2g/cm3), which consists of microscopically shapeless materials with a much lesser amount of diatoms. The former materials are probably flocks of clay minerals and chemical deposits.It was shown that the vertical change of carbon/nitrogen ratio in sediment of Lake Yunoko is closely related with that of relative amounts of the three fractions with different density. The weight percentage of autochthonous materials in the total was estimated to be 80 and 22 for the near surface sediment sample of Lakes Haruna and Aoki-ko, respectively.

Seasonal variation of the planktonic population in lake yunoko, as followed by the assay of chlorophyll, protein, RNA and DNA in the total harvested planktonic samples

AbstractSeasonal variation of the biomass of plankton in Lake Yunoko, a eutrophic lake in Japan at an altitude of 1478 in, was followed by measuring simultaneously the quantities of chlorophyll, protein, RNA and DNA in water samples harvested from different depths at a definite site in different seasons of a year. The contents of the four cellular constituents and the sum of them in a given water column showed characteristic seasonal changes during the year. Various ratios derived from the four contents were grouped into two distinct types; one is the winter‐spring type and the other the summer‐autumn type. It was found that the sum of the four contents and the ratio of the protein‐content to the RNA‐content were quantitatively related to the chlorophyll‐content of the water. Based on the assumption that a certain water sample contained only photosynthetic plankton, analyses were made to estimate the proportions of photosynthetic and non‐photosynthetic plankton to the total planktonic mass, the growth rates of these plankton, and the net productivity of the lake.

中禅寺湖,湯の湖,菅沼および丸沼の底生動物相の研究

1. Lakes Tyuzenji-ko, Yuno-ko, Suge-numa and Maru-numa were investigated in 1972 and 1973 in regard to their bottom fauna. The results obtained were compared with the data by MIYADI during the years from 1928 to 1930. They are shown in Table 10.2. Lake Tyuzenji-ko : Micropsectra sp. (A), which is a characteristic species of oligotrophic lakes, occurred on the bottom between the littoral and profundal zones. Tubifex sp. is abundant in the profundal zone ; an azoic zone does not exist at present.3. Lake Yuno-ko : Though Tubifex sp. and Chironomus plumosus occurred in the profundal zone where oxygen was absent in summer stagnation period, some of them seemed to move to the shallow bottom. This lake belongs to “eutrophic Plumasus lake” at present.4. Lake Suge-numa : In the main basin Kitamata-numa Micropsectra sp. (A), Spaniatoma sp. (B-5) and Tubifex sp., though not abundant, were found in the profundal zone. This lake belongs to “oligotrophic Tanytarsus lake” as it was so at the time of MIYADI's investigation. As for the auxiliary basin Shimizu-numa there was found an azoic zone existing partly in the profundal zone. Some kinds of chironomid larvae occurred in the littoral zone.5. Lake Maru-numa : Chironomus plumosus larvae are abundant on the shallow bottom. Tubifex sp. is distributed widely in the profundal zone.

Dynamic status of primary production in lake yunoko, a small eutrophic subalpine lake in central Japan

Investigation was made of the primary productivity of Lake Yunoko. The concentrations of PO4-P and NH3-N were highest in summer. The total amount of chlorophylla in the entire water column varied from 45 mg/m2 to 405 mg/m2 during the year with the maximum values occurring in late spring and in December. These values are very high compared with those reported for other lakes in the same district. The standing crop of phytoplankton as organic carbon was approximately 50∼70% of the total particulate organic carbon in the lake with values as high as 80∼90% being obtained in the spring and autumn. The rate of phytosynthesis under saturated light conditions was 3.7 mg C/mg chla/hr in the case of phytoplankton of the sun type and 1.2∼1.6 mg C/mg chla/hr in those of the shade type. The daily gross primary production in the lake varied from a low of 134 mg C/m2 to a high of 1,003 mg C/m2 during the year, the mean value being 372 mg C/m2. The total amount of daily microbial respiration varied from 177 mg C/m2 in winter to 1,476 mg C/m2 in summer. Thus, the daily balance of production and consumption of organic matter in the lake itself was concluded to be negative. The main factor contributing to the rectification of this imbalance of material budget seems to be the leaf litter coming from the forest surrounding the lake. In conclusion, Lake Yunoko is a very productive and at the same time, fairly heterotrophic lake.

日光湯ノ湖の湖岸帯でえた水生小動物の消化管内容物

1. Aquatic small animals collected in the littoral region of Lake Yuno-ko on November3, 1968 were investigated concerning the contents of their digestive tracts. 2. One individual of Ephemera sp. (Ephemeroptera) seems to take algae attached to the shore or deposited on the bottom. 3. A large quantity of algae was found in 11 individuals of Nemoura sp. (Plecoptera). It seems likely that they take attached or deposited algae. 4. As regards Trichoptera, only each one individual of Goera japonica and Polycentropus sp. and an undetermined species were examined concerning their foods. Goera japonica mainly takes attached or deposited algae, while Polycentropus sp. takes abundantly either floating Chlamydomonas sp. or that which may be a zoospore of any green alga. In the digestive tract of the species of undetermined genus contains abundant planktonic diatoms. 5. No alga was found in Platambus sp. (Coleoptera) Helichus sp. belonging also to the same order takes a large quantity of attached algae. 6. The main contents of the digestive tracts of 21 individuals of a crustacean, Asellus sp. are Chlamydomonas sp., Melosira italica f, curvata, Ulothrix sp. and Fragilaria sp., all of which are the species mostly attached to fallen leaves on the lake bottom. 7. For comparison of similarity in the composition of algal flora in the digestive tracts of the larval samples collected at the same place, it is attempted to analyse according to the c'λ method. 8. The floral composition is similar among Nemoura sp. and among Asellus sp. It implies that the composition of the flora in the same species of aquatic small animals is similar, but that similarity is not found between the different species. s. In regard to the construction of the flora in the digestive tracts of the same species collected at the different places, a great similarity is found in the individuals collected at the resembling environments, while there is less similarity between the individuals collected at the different environments. Such a phenomenon will attribute to the construction of different algal communities at the different environments.