陸水のNa, Cl及びNa/Clに就て

Abstract

1. In view of the fact that precipitation constitutes the primary source of the salt of inland waters, comparison was made between sea water and rain and snow for major salt components in order to discuss the cause of difference in relative composition between these two different categories of water.2. The next step was to compare rain and snow, and inland waters, whereby possible factors contributing to the deviation of the concentrations of Na and Cl and the ratio Na/Cl in inland waters from those in rain and snow were made clear. As such factors, dissolution of windborne salt, erosion of rock and soil materials, addition of mineral and thermal spring waters, agriculturally used chloride manure, sodium chloride waste from domestic life including excreta, sodium and chloride contained in mine and other industrial wastes were considered. Climatic factors were also to be considered, and among them annual averages of regional temperatures are especially important in relation to evaporation and soil erosion. Furthermore, annual precipitation is one of the fundamental factors.3. The magnitude of contribution by some of these factors to the Japanese inland waters was estimated by using the data available. The data for rain and snow were from the author's own laboratory, those for river waters from J. KOBAYASHI and those for ground water from S. OANA'S laboratory, Institute of Earth Sciences, Nagoya University.4. The conclusion is : a). In comparison with the waters in the regions facing the Pacific Ocean, those in the regions facing the the Japan Sea are enriched by Na and Cl with a low Na/Cl. The strong winter monsoon from Siberian air mass transports sea spray from the Japan Sea into the regions facing that sea, where the spray falls down in the forms of snow and rain.b). Geologically speaking, the Japanese inland waters are categorized into three fundamental types : volcanic material type, granitic material type and sedimentary rock type.The waters of Hokkaido, the northernmost island, and the Tohoku District, the northernmost region of Honshu, the Main Island of Japan, represent the volcanic material type and are characterized by high contents in Na, Mg, Cl, SO4and SiO2 with a low Na/Cl. The waters of the Kyushu District, the southernmost among the four large islands constituting Japan, are also of volcanic material type. The waters, however, are characterized by less enrichment of chloride with a higher Na/Cl.The waters of the Chugoku District, the southwestern part of Honshu, where granite is dominant, represent the granitic material type characterized by a low salinity. It is evident that rocks of granite type are less soluble than other types of rocks such as sedimentary or volcanic.The characteristic of sedimentary rock type water is richness in Ca. There is no calcite area extensive enough to form a special district representing this type of water. The waters of the Kanto District with Tokyo on its verge are of composite nature of two water types, volcanic and sedimentary rock.5. Finally, the ratio Na/Cl of inland waters was reviewed world-wide, and explanations were given to unusually low Na/Cl for some Antarctic waters and the water of the Dead Sea.