曽根沼産の水草は8科10種2変種で, その中ヒシと人工的に栽殖されたと思われるハスが優占種である.他の種は湖中に殆どなく, 琶琶湖に通ずる水路に繁茂しているに過ぎない.
曽根沼産の淡水藻類には琵琶湖産のものとは異つた種が多い.琵琶湖産のものは浮游性でかつ湖性のものが多く, 曽根沼産のものは富栄養池沼性のものが多い.曽根沼内では中央部と北部のヒシ群落中では淡水産藻類に大きい差異が見られた.中央部では36種検出されているのに, ヒシ群落中では81種を算え, 種も異つたものが現われていた.後者には特に鼓藻類が多かつたが, 琵琶湖と比較すると種の点で異つていた.曽根沼産のものは富栄養の池沼に現われるもの, 特に水草の繁茂した所に生活するものが多い.
以上の諸点から曽根沼は既に老衰期にある沼沢状の湖で, 人工による湖の切半は東北部と西南部とでは異つた性質の水域を形成する結果となり, 水草, 藻類相に或程度のちがいが見られるに到つたのだと思われる.

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1. As the water of a shallow pond, Sarusawa-ike, in the city of Nara has suddenly become brown in color in February, 1955, the author has studied this phenomenon in regard to the water color and phytoplankton, what changes took place in the water color and phytoplankton during the course of recovering of the color from brownish to normal.
2. The water colors were measured by the method used by YAMAZAKI and WATANABE (1955) and the results obtained were indicated by the C. I. E. color language (Table 1). The brightness (Y) and excitation purity (Pe) became greater in February than in the other months. It is presumed from this fact that the reflected light from the upper layer of water is greater in February than in the other months.
3. The curves of spectral transmittance to the pond water in February (Fig.1) have shown no similarity to the curves of that to individual cells of both Anabaena subcylindrica and brown-colored Tracherornonas Dybowskii (Fig. 2). However, from the fact that A. subcylindrica was the dominant species more than 90 percent in composition of the plankton, its occurrence seemed to be restricted to the period of February. In that time the water color was markedly brown.
4. The change of phytoplankton in this pond from February to July is shown in Fig. 2. From this and a normal condition observed in 1949 suggest that the recovery of water color to normal condition will be in July. It will be clear in Table 2 that there are two types of change in the representative species. i. e. the one is that which is due to the seasonal succession of both Anabaena subcylindrica and Lyngbya contorta, and the other seems to be caused by the change of Microcystis aeruginosa, Melosira italica and Synedra berolinensis in the course of recovering from uncommon to the common condition.

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新しく造つたコンクリート池での魚の飼育は順調に行かないことが多い.これは “アク” が出るからだといわれている。即ち, セメント中の石灰その他のアルカリが原因 [1] と考えられるが, 筆者はモルタルブロツクの海水, 淡水等での浸漬試験をして, これについて吟味, 考察を行つた.
コンクリートの “アク” についてモルタルブロックの浸漬試験により次の結果を得た.
(1) コンクリートの “アク” はその固化に際し著量の炭酸を吸収すること。遊離アルカりの溶出することが原因と考えられる.
(2) この結果pHの上昇, アルカリ度の低下, カルシウムの沈澱等がみられる.
(3) コンクリート作製後1ヵ月で “アク” は少くなるが, その後カルシウムの溶出等があり, 水に殆ど影響を及ぼさなくなるのは数ヵ月後であろう.
(4) “アク” の防禦法としてはアルミニウム塩や水ガラスでの洗滌塗布よりビニールペイントの塗布が有効であろう。

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We had hitherto no suitable method to measure or notate the color grades of inland waters, especially of the extremely eutrophic ones like the piscicultureponds. The FOREL-ULE'S color standards do not agree with the actual water-colors, and the method by the platinum-cobalt standard, which can express exactly the brownish waters, is ineffective to other colors.
In the recent time, YAMAZAKI and WATANABE reported a new colorimetric method which can indicate the three values of the C. I. E. color language, in combination with the principle of “MAXWELL's disc”. While this method has a merit in its exactness, it seems to involve a complicated treatment. In general, it seems to be more convenient in measuring and denoting the color grades by direct comparison with the standard papers.
Now, the MUNSELL Book of Color provides an orderly arrangement of standard papers which serve as guide for the measurement and notation of all colors, and, in addition, it has the characteristics in that these standards represent equally spaced divisions of the three attributes of color, known in the MUNSELL System of Color Notation as Hue, Value and Chroma.
By using the MUNSELL Book of Color, we can easily and quickly specify and notate the color of a substance by simple numerals, instead of obscure, nonrelated, customary name of color, and can also let it know internationally. Strictly speaking, the MUNSELL Color System is a method for the notation of the surface color of substances, but is impossible to use for either the color of a liquid or the source of light. This method can, however, be employed in the case under consideration, because the water-color of pisciculture-ponds is the characteristic “Vegetätionsfarbung”, which is caused chiefly by the thriving of phytoplankton, etc., and can be considered as a sort of surface color.
In 1955, the author has measured and recorded the water-color of eel-cultureponds in the Tokai region by using the MUNSELL Book of Color. By these records, he has investigated the seasonal variation of water-color, the comparison of water-colors of fish-ponds in different districts, the relationship between the water-color and the salinity of the pond-water, and also the relationship between the composition of phytoplankton and the water-color respectively. The results obtained are as follows :
(1) Seasonal variation of the water-colors of the ponds in the Izumi district is shown in Table 1, in which the maximum value of Hue, 35.0 (5.0 BG), in August, is recorded.
(2) The Hue value was usually very high in the ponds in both the Kawajiri and Hamana districts (both in Shizuoka Pref.), considerably high in those in various districts of Aichi Pref., and the lowest (30.0 in average) in the ponds in Mié Pref.
(3) As shown in Fig. 2, there was a clear tendency that the higher the salinity of pond-water, the lower the Hue value of the water-color.
(4) While the blue-green algae, such as Microcystis, Oscillatoria, etc., are the source of the higher Hue value, as 37.5-40.0 (distinct bluish green coloration), the green algae (Scenedesmus and others) show the tendency to manifest a little lower Hue value, as 30.0-35.0 (green or yellowish green coloration). There is also a tendency that the predominance of green algae and in particular the planktonic diatoms reduces not only the Hue but also the Value and Chroma.

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Lake Yogo-ko is a small lake of 1.63 sq. km. in superficies, which lies only 1.5 km. distant from the northern shore of Lake Biwa-ko, and has a maximum depth of 13.5 m. It occupies the northernmost part of the same depression as Lake Biwa-ko, from which it is isolated by a low range called Mt. Shizugadake (422 m. above sea level). Its water-surface, which is 134 m. high above the sea, is 48 m. higher than that of Lake Biwa-ko. The outlet, the River Yogo-gawa, starts at the north-eastern corner of the lake and flows into Lake Biwa-ko, after circa 15 km. running down along the eastern side of Mt. Shizuga-dake.
The analysis of diatom shells in the bottom deposits has been made on a core of 13 cm. in length below the mud surface, which was taken up in the deepest part of the lake. The core-sample was cut into the 7 zones below the mud-surface as follows : 0, 2, 4, 6, 8, 10, and 13 cm. Each zone contains shells of about 30 species respectively, whose associations are always constant. The frequency of the occurrence of the dominant and subdominant species in average percentages are as follows :
Stephanodiscus carconensis…84.4%
Melosira italiaca and M. granulata…5.6
Cyclotella comta…3.4
Surirella Capronii…1.3
The constancy of the diatom-association in every zone of the deposit of Lake Yogo-ko is similar to that of Lake Biwa-ko, whose deposits were already reported in regard to the diatom shells by the present author in 1954. In Lake Biwa-ko, the diatom-communities of the bottom deposits consist chiefly of two species, Stephanodiscus carconensis (80.5%) and Melosira solida (16.2%). The dominant species is common to two lakes, whereas the subdominant one is different from each other. It seems to the author that such a result will throw light on the limnological types of two lakes. Lake Biwa-ko is of a typical oligotrophic water, while Lake Yogo-ko may be in a state of progressive eutrophication.

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The Mogami River, which rises from Mt. Azuma in the southern part of Yamagata Prefecture, flows through the centre of the prefecture and empties itself into the Japan Sea at Sakata Port. At its mouth, it is about 400m. wide and 6m. in depth. On August 24 th and 25th, 1954, the author made analyses of water which were taken at the twelve stations as shown on the accompanying map. The age of the moon on those days was at 9.45 and 11.30 respectively. According to the results of observations, the author has become the following conclusions : 1) The sea water goes up to Shinwatari, 5.3 km. as far distant from the mouth, 2) There is a linear relation between the Cl^- content and the hardness of water, showing a positive correlation which is given by a coefficientγ=0.9962, 3) Even at the estuary, the sea water is mixed by only its 1/31 with river water.

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