Japanese Journal of Limnology (Rikusuigaku Zasshi)

Lake Hakuryû-ko is situated about thirty kilometers south-west of Yamagata City and occupies 7.13 ha in the northeastern part of Yonezawa Basin. From the geological point of view, this lake is considered to be the relic of the Paleo-Yonezawa Lake.
Even at the present time, in the surroundings the muddy marsh called “Ôyachi” spreads to an area of 900 ha.
The present study has been carried on with the aim at elucidating the limnological features with special reference to the ecology.
The annual deposition of suspended matter is estimated to be 70 mm in thickness. In other words, the lake has become shallower year by year. Under the circumstances, its maximum depth is now only 1.5 m. The bottom mud is composed of black organic matter under the reduced condition. The input of polluted water accelerates the rate of the eutrophication of this bog lake.
In the summer and the season of thaws, the development of thermal stratification is observed. The transparency of this lake is only 0.40.7 m. This value is rather small as compared with that of other lakes in the same latitude.
So far as the quality-of-water is concerned, this is characterized by the high concentration of chloride ion. At the littoral region, are found about 130 species of plants which contains 15 species of the alpine plants.

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The Nishiyoge River in Osaka Prefecture is 14 km long with the average width of 7 m. In recent years, water pollution of this river has aggravated while doing a great deal of damage to city water supply and become a serious social problem. A series of investigations have been under way along the whole length of this river since July 1969 and the following is known thus far.
The overall degree of pollution remains essentially the same as it was in 1965 or thereabouts, but migration of pollution sites has apparently occurred when looked at the whole length. The largest source of pollution in 1965 was at station L., 12 km downstream from the riverhead, whereas it is now at station G, 6 km upstream from L.
The largest factor contributing to water pollution is organic waste water discharged from pig farms, followed by waste waters from poultry farms and slaughter houses, domestic sewage, and industrial waste water.
The degree of pollution varies considerably with time of inflow of waste water and also with season.
The electrical conductivity (x) and the residue on evaporation (y) rise and fall as the river flows down and increase 2-to 3-fold at the end of the river. The following relationship is observed between these two.
y=0.767x+18.992 (γ=0.964)
Dissolved matters which increase rapidly with inflow of waste water from pig farms are ammonium nitrogen and phosphorus compounds, and they increase more than 103 times. The values of BOD and COD also rise rapidly and the relationship between the two is expressed by the following equation.
BOD=0.445COD^1.465
Purification of water is possible only by treatment of waste water from domestic animal farms before inflow or by prohibition of inflow itself, and perfection of the sewage system is very much desired. An increase in the flux will assist the purification process.

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