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The dieback of C.japonica is extended over a wide range (more than 5000 km 2 ) covering the western and north western regions of Japan's Kanto District. The affected area was compared with normal areas concerning density of S0 2 , N0, N0 2 and photochemical oxidant mixtures(Ox) in the atmosphere and the amount of acid deposition. As a result it is inferred that acid deposition and oxidant are the principal causes of large scale dieback of C.japonica in the Kanto District.

Composition and abundance of zoobenthos in the profundal zone of Lake Oze-numa (36°56'N, 139°18'E) were studied at two sites, Lake Center and Off Nushiri, from May to September 1986. Among the eight taxa recorded, three species (Tubifex sp., Limnodrilus hoffineisteri, and Chironomus sp.) accounted for more than 95.5% of the macrobenthos in number. Species diversity, density, and biomass of macrobenthos were lower at Lake Center (8.8 m deep in average) than those of Off Nushiri (6.8 m). Oxygen content was probably an important factor in these differences between the sites. At Off Nushiri, Tubifex sp. and L. hoffineisteri reproduced throughout the study period but with low proportions ; pupae of Chironomus sp. were found only in late June.

Preliminary analyses of 137 precipitation samples, tested for ion balance and specific conductance(SC), showed that the major ions existing were-six cations : H + , NH 4 + , Ca 2+ , Na + , K + and Mg 2+

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