松本城の濠の富栄養化の現状とその対策

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1) The progressive grade of eutrophication of moats around the Castle of Matsumoto has been distingushed during these twenty years. Recently the conservation of the water in these moats has been taken up as a momentous social problem from the points of urban environment and sightseeing of Matsumoto City. Ecological studies on the actual state of water quality and biotic community in the moats had been made monthly from 1973 to 1975, and counter plans to pollution of the moat water were investigated. 2) The five moats, where the surveys were carried out, are situated in the centre of the City of Matsumoto, in the central portion of Honshu in Japan, and were designated as Moat A, B, C, D and E. They have the areas of 1950 (Moat B) to 13699 (Moat E) m2, and the deepest depths of 0.7 (Moat B) to 0.92 (Moat E) m. The capacities of them indicate the range between 954 and 10274 m3, their increasing order being Moat B, A, C, D and E. The water of Moat E was supplied by municipal drainage of about 2500 tons per day, and Moat A and B by natural spring waters less than 20 tons per day. Further, some amount of ground water always ooze out from the bottom of each moat. 3) The diurnal changes of chemical water quality were monthly measured in Moat E and in the inflowing drainage which was markedly influenced from human activity. The amounts of COD, PO4-P and NH4-N in the drainage increased twice a day, in the morning and the evening, and decreased from the midnight to the dawn. The diurnal fluctuations of temperature and of pH were small in both the moat and the drainage, that of COD amount large in the drainage and small in the moat, those of PO4-P and NH4-N large in both the waters. The diurnal fluctuation in dissolved oxygen content was wide during the summer in the moat, but in winter being narrow in both the waters. 4) The ranges of annual changes in pH and dissolved oxygen content among the moats were from 6.9 (Moat E) to 10.7 (Moat E) and from 5.1 (Moat E) to 35.1 (Moat D) ppm respectively, and were bigger in Moat E than in any other moat. In Moat A pH kept more than 8.3 and dissolved oxygen did more than 13.4 ppm through the year. The seasonal fluctuations in PO4-P and NH4-N amounts showed the wide ranges from 0.005 to 0.72 ppm and from 0.005 to 0.435 ppm in Moat E respectively. In general the concentration of these nutrients increased in winter and decreased in summer in each moat. 5) Judging from the results of this chemical water quality, it was recognized that the progressive grade of eutrophication was the highest in Moat E, next in order are Moat C, D and B, the lowest being in Moat A. 6) Total number of phytoplankton species which appeared for the year ranged from 52 (Moat E) to 60 (Moat D) among the moats, 18-19 of which were Chlorophyta, 24-28 being Bacillariophyta. Cyclotella kiitzingiana were the most abundant in each moat during winter, in Moat A likewise in other seasons. In the seasons when the "water bloom" occurred remarkably, the dominant species were Micractinium pusillum (spring) and Pediastrum boryanum (summer) in Moat B, Anabaena flos-aque (spring) and Monas group (summer) in Moat C, Anabaena f. (spring) and Microcystis aeruginosa (mid-summer) in Moat D, and Microcystis a. (during summer) in Moat E. In the seasonal changes in number of cells, biomass and chlorophyll-a content, they had their maximal abundance twice in a year in spring and summer in each moat. The maximum of total cells among the moats showed the range from 7700 (Moat A) to 88700 (Moat E) cells/ml, the maximum amounts of chlorophyll-a being 128-424 mg/m3 and the annual means of biomass (dry weight) were within the range between 10.9 and 18.0 g/m3, and became bigger in the order, Moat A, B, D, C and E. 7) Total number of zooplankton species taken for the year ranged from 26 (Moat C) to 29 (Moat A), 20-22 of which belonged to Rotatoria. Rotifers were the most prevalent through the year, Protozoa and Copepoda were next to them, and Cladocera were very scanty in all the moats. Brachionus calyciflorus were overwhelmingly dominant in each moat through all the seasons. In the annual yields of zooplankton, three increasing periods took place in early spring, early summer and autumn. The maximum numbers of total individuals among the moats were within the range between 97.2 (Moat A) and 1140 (Moat D) inds./l, and the annual means of biomass (dry weight) showed the range from 5.2 to 45.5 g/m3, being Moat B, A, C, D and E in increasing order. 8) The zoobenthic community was dominated by Chironomus plumosus in each moat for the year, and next by Tubificidae (Limnodrilus sp. and Tubifex sp.) in the other moats without Moat A, where Sinotaia quadrata histrica was abundant. In the annual yields of zoobenthos, two maxima were seen in winter and summer in each moat, and the biggest of total individuals among the moats were between a minumum value of 563 (Moat E) and a maximum value of 6110 (Moat C) inds./m2. The annual means of biomass (dry weight) indicated the range from 0.23 to 23.24 g/m2, and the decreasing order of them among the moats were as follows; Moat A>C>B>D>E. 9) The number of fish species was counted six in each moat, the dominant species were Carassius carassius and Pseudorasbora parva, the former was numerous in Moat A, B and C, while Moat A and E abounded in the latter. The annual means of population density of fish ranged from 1.13 to 3.11 inds./m3 among the moats, and decreased in the order, Moat A, C, B, D and E. These values were 1.5-10 times larger than that of the fish obtained in Lake Suwa, which is ranked as the most eutrophic lake in Japan. 10) Coliform group of bacteria was comparatively plentiful (103-4/ml) in Moat E and the drainage, but few in the other moats and the spring waters. The number of total bacteria ranged among the level of less than 103/ml in Moat A and B, and of 103-4/ml in Moat C, D, E and the drainage. 11) The distribution of cover degree of aquatic weeds (Myriophyllum spicatum) which began to grow in whole area of Moat E since 1975 was surveyed in the season of maximum abundance, September. The standing crop calculated from the cover degree showed about 29 tons in wet weight per whole moat (102 d. w. g/m2). 12) On the basis of the species component, the population density and the biomass of four communities, phytoplankton, zooplankton, zoobenthos and fish, it was estimated that Moat A was the type of mesotrophic lake, Moat B, C and D were eutrophic, Moat E being excessive eutrophic. The rank of saprobic systems in water quality of each moat was judged by means of the index organisms of various kinds of communities, that is, Moat A and B were β-mesosaprobic, Moat C and D α-β-msosaprobic, and Moat E and the inflowing drainage α-mesosaprobic. 13) The inflowing drainage to Moat E indicated the most pollutional load, namely the amounts of COD matter, phosphorus and inorganic nitrogen were 650g, 42.3g and 507g/m2/year respectively, these values of phosphorus and nitrogen were corresponding to 850 and 380 times severally the permissiible loading levels (OECD). The amounts of COD matter, phosphorus and inorganic nitrogen supplied by the fallen leaves from trees growing around the moats and with the excreta of breedeng aquatic birds were calculated in each moat. Each pollutional load by the fallen leaves and with the excreta exceeded the allowance loads. 14) The main pollution sources in each moat were found to be the fallen leaves in Moat A, the fallen leaves and the excreta of birds in Mort B, the bird excreta in Moat C, the fallen leaves and the drainage in Moat D, and the drainage in Moat E. 15) As a portion of counter plans to pollution of moat water, two measures, namely-stoppage of discharge of the drainage to Moat E and pourring much ground water into Moat E and C, have been carried out since autumn in 1974, and effects of the attempts were discussed. 16) From the results of the present study, as the positive measures, revolving micro-strainer, transplantation of aquatic weeds, planting of phytoplankton feeders, shortening of replacement time of moat water and removal of bottom mud etc., and as the negative measures, stoppage of drainage discharge, and removal of breeding birds and weed eaters etc. are taken into consideration.
信州大学理学部の論文

松本城の濠の富栄養化の現状とその対策

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