Studies on the Coastal Oceanography in the Vicinity of Fukuyama，Hiroshima Pref. : I. Distribution Patterns of Temperature， Chlorinity， pH and lnorganic Nutrient (Phosphate-P， Ammonia-N， Nitrite-N ， Nitrate-N) Contents of Sea Water in Early February，1968.

In the coldest and driest season of the year (i.e., February 3 and 4, 1968) measurements were taken on water temperature, chlorinity, pH and phosphate-P, ammonia-N, nitrite-N and nitrate-N contents of sea water off the estuary of the Ashida River, occupying 14 stations both at a high and a low water. The water temperature was within a range of 6-8°, its vertical variation being very slight reflecting the vertical circulation of water due to convective cooling. Chlorinity also demonstrated a slight vertical variation due to the same cause in all places except in the close vicinity of the river mouth and in the waste water discharged from a chemical plant. Normal pH values were encountered everywhere except in the vicinity of the chemical plant where values as low as 2.4～8.0pH were measured. Nutrient contents of sea water were low in the offing, and somewhat higher near the estuary of the Ashida River, and abnormally high in the water samples affected by the waste water from the chemical plant. Possible effects of such distribution patterns of sea water properties on the cultured laver were discussed

Studies on the Coastal Oceanography of the Bingo-nada and Hiuchi-nada Regions of the Se to Inland Sea : I. Distribution Patterns of Temperature, Chlorinity, Inorganic Nutrient Contents (Phosphate-P, Ammonia-N, Nitrite-N, Nitrate-N) and Some Other Properties of sea Water in Early February, 1968

About in the middle of the Seto Inland Sea extending east and west, a somewhat pear-shaped sea region is observed; its northern border (i.e., the tip of the pear-shape) being that part of the southern shore of Honshu where Fukuyama and Kasaoka cities are located; its southern border (the bottom of the pear) being the middle portion of the northern shore of Shikoku, where Kan-onji, Iyo-mishima, Niihama and Imabari cities are situated in an east to west line. This sea extension communicates with the shallower Bisan Straits in the northeast; the commonly accepted boundary between them runs from Konoshima on, south to Obi-shima, and then southeast to Misaki. In the west, this sea region is bordered by the eastern edges of the island chain (the Geiyo Islands) extending from Tomo southwest to Imabari, and communicates with the less neritic Aki-nada region by several straits. This sea region measures nearly 1,900 km2 in area and contains about 36 km3 of water. Its diameters are ca. 58 km laterally (Imabari to Kan-onji) and ca. 60 km longitudinally (along the 133°30' E meridian) (Fig. 1). This region can be subdivided into a northern and a southern portion by the arc of small islands including Uo-shima and Ibuki-shima; the former is called Bingo-nada and the latter, Hiuchi-nada. As part of the efforts to clarify the dynamics of organic production in this sea region, the authors performed, in early February, 1968, the measurements of the oceanographical factors named in the title above as well as pH, dissolved oxygen and turbidity of the sea water and also the depth of disappearance of the Secchi disc ('transparency'). Eleven stations were surveyed altogether during a 2-day cruise (Fig. 2). The driest and coldest season of the year was chosen for the observation. This paper presents the results of this examination (Table 1). The survey should be regarded as a preliminary attempt, since the authors did not yet succeed in elucidating the real mechanisms underlying the apparently complicated distributions of some of the measured factors. Following are the noticeable features of the results. Reflecting the convective cooling, the water temperatures proved vertically uniform at all stations except St. 6 (Fig. 3); chlorinity and dissolved oxygen were also nearly uniform vertically at all stations. Geographically, both temperature and chlorinity were highest along the western border of the sea region, and lowered towards the east (Figs. 4 & 5). Both elements reached a minimum near the Bisan Straits; they reached another minimum at the innermost part of Hiuchi-nada (near Iyo-mishima). This distribution pattern may point to the following tendency: the more saline and warmer water distributed to the westward was flowing into Bingo-nada and Hiuchi-nada through the straits of the Geiyo Islands and was then cooled and diluted while flowing eastward. It is also inferable that less saline and colder water was found in the Bisan Straits. The percentage saturation of dissolved oxygen was vertically uniform at all stations. Along the western border it was somewhat lower (ca. 96%); it showed a general trend towards increase towards the east except for the considerably low values (ca. 93%) at St. 15 (Table 1). Concentrations of inorganic nutrients, which were determined by absorptiometry using unfiltered water samples, showed to be within the following ranges: phosphate-P, 0.28-0.53; nitrite-N, 0.0-0.40; nitrate-N, 0.6-1.7 and ammonia-N, 0.0-5.3 µg-atoms/l (Figs. 7 & 8). It was difficult to find any pronounced regularity regarding the vertical and/or geographic variations in their concentrations. This difficulty might have been overcome to a considerable extent if simultaneous measurements had been taken of organic phosphorus and nitrogen of dissolved and particulate forms as well as of the activities of marine organisms in situ (particularly of phytoplankton). The Secchi disc 'transparency' was about 7 m along the western border, about 5 m in the central part, and between 6 and 8 m in the eastern part of the surveyed region. The only exception was the unexpected high value (11.6 m) at St. 15 (Fig. 6). The light scattering capability (‘turbidity’) of the water samples from various depths (except the bottom layer) was comparable with that of kaoline suspensions of 0.7-2.6 ppm. In neither vertical nor geographic distribution of turbidity, any pronounced regularity could be detected.Special Project Research “Studies on the Dynamic Status of Biosphere” supported by the Ministry of Education. This study was carried out as a part of JIBP Project

富栄養沿岸海域における懸濁態リンの変動要因

前報で瀬戸内海備後灘におけるリンの存在様式とその季節変動を，海水中のリンを懸濁態リン(particulate phosphorus，PP)，溶存態無機リン(DIP)，溶存態有機リン(DOP)の3態に分別定量する方法により明らかにし，PPとchlorophyll αの相関について考察を加えた。本研究は前報に報告したPPについて，その内容と変動要因を，同時に測定した懸濁態炭素(particulate carbon，PC)，懸濁態窒素(particulate nitrogen，PN)，全懸濁物乾重量(seston weight，SW)，chlorophyll α(chl.α) および透明度の値を用いて解析したものである。 1. SWは，暖季には値が大きく変動も大きいが，低温期には値が小さい場合が多かった。地点別では，沖合のSt.BG-1に比べ，沿岸の浅所の観測点St.2で値が大きく特に海底に接近した5m層では大きい値が観測された(Fig.1，Table 3)。 2. 透明度(Tr，m)と0m層におけるSW(mg/l)との関係は，極めて特殊な3例を除き，ほぼ双曲線的で分布範囲は(Tr)・(SW)=9～20であった(Fig 2)。 3. PCがPNと非常に高い相関を示したこと，回帰式から得られたPC/PN 比が約7.0であったことから(Fig.3)，今回測定したPC，PNはともに主として有機懸濁物成分であったと考えられた。 4. PC/SW比は，懸濁物の有機性の強弱(懸濁物中に有機物が占める割合の大小)の指標として考えることができる。この比の平均値から判断すると，懸濁物の有機性は暖季の沖合点St.BG-1で最も強く，低温期(鉛直循環期)のSt.2で最も弱かった(Table 3)。この比の変動は植物プランクトンによるPCの生成と，河川水の流入や底質の再懸濁に伴う無機懸濁粒子の増加とによって，ほぼ説明できた。 5. 懸濁物のリン含有率は，無機的性質の強い懸濁物では一般に低く，一方，有機性の強い懸濁物ではリン含有率の高い例が相当数あった(Fig.5)。最も有機性の強い懸濁物は赤潮時やSt.BG-1の0m層で観測され，その際，リン含有率は0.32～0.45%に達した。最小値はSt.BG-1の底層で観測され0.06%であった。 6. PCのchl.αに対する回帰およびPC/chl.α比の値から，St.2の懸濁有機物は主として植物プランクトンであり，一方St.BG-1にはデトリタス状の懸濁有機物が多かったと考えられた。 7. 有機懸濁物量(Org)を2・PCと見積り，従って無機懸濁物量(Inorg) をSW-2・PCと計算して，PPのOrg，Inorgに対する重回帰を調べると，一般にPPの増減はOrgのそれに強く依存していた(Table 5)。PPがInorgと有意の回帰を示したのはSt.BG-1の20m層においてのみであった。 8. 前項の関係をさらに理解するため，懸濁態炭素(PC)を計算によって植物プランクトン態炭素(chl.α量の30または60倍)と非植物プランクトン態炭素に二分し，両者に対するPPの重回帰を季節・深度別に解析したところ，St.2においては暖季の底層を除いて，またSt.BG-1では暖季の0，10m層において，PPの変動は植物プランクトン態炭素に強く依存しており，非植物プランクトン態炭素とは明瞭な関係になかった(Table 6)。 9. PPと他の懸濁物成分との共存状態を把握するため，この研究で取扱った懸濁物をその分析測定値にもとづいて，赤潮型，植物プランクトン型，デトリタス型，無機懸濁物型の4種類に分類し，各類型毎に出現状況およびPPの関係する成分比を整理した(Table 7，8; Fig.6)。On the particulate materials collected at two stations in the central part of the Seto Inland Sea, Japan, at roughly monthly intervals from April 1972 to February 1974, particulate phosphorus (PP), particulate carbon (PC), particulate nitrogen (PN), sestonic chlorophyll α(chl. α) and dry weight of total particulate matter ("seston weight", SW) were determined. PC was regarded as particulate organic carbon from the regression of PC to PN. The ratio PC/SW, i.e., the carbon content of the particulate material, was regarded as an index of organic feature of the particulate matter. The mean of this ratio was greater at the offshore station than at the inshore station, and was generally great during the high temperature season especially at 0 m layer. The phosphorus content of the particulate material increased generally with the carbon content. The highest carbon contents were observed on the occasions of the red tide and also at 0 m layer of the offshore station, with phosphorus contents amounting to 0.32-0.45% of SW. Low phosphorus contents were observed mainly in the bottom layer or in the low temperature season. The regression analysis of PC to chl.α indicates that living phytoplankton accounted for major portions of PC at the inshore station; in contrast, large proportions of PC were represented by detrital carbon at the offshore station. SW was divided into the organic and the inorganic matter by calculation, and their contributions to PP was evaluated by multiple regression analysis. The multiple correlation of PP to these two variables was always significant, and this significant correlation derived chiefly from the positive contribution made by particulate organic matter. Therefore, it is concluded that the abundance of PP depended mostly on that of particulate organic matter in all layers of both stations. PC was subdivided into the phytoplankton carbon and the non-phytoplankton carbon by calculation, and their contributions to PP was evaluated also by multiple regression analysis. The result shows that the abundance of PP depended on the abundance of phytoplankton carbon especially in the upper layers of both stations during the high temperature season. In the shallow inshore waters the dependence of PP upon phytoplankton carbon prevailed also in the low temperature season. Recovered particulate materials were classified into four types on the basis of C, N and chlorophyll α contents. The occurrence of each type was discussed with regard to the season, station and depth. A hexagonal diagram was devised to illustrate the chemical characteristics of individual particulate material.This study was supported partly by the Grant in Aid for Fundamental Scientific Research of the Ministry of Education and partly by the Research Fund on the Ecosystem under contract with the Fishery Agency, Ministry of Agriculture and Forestry

1970年および1971年における福山周辺海域のビタミンB12の分布

赤潮が頻発する福山周辺海域に8定点を設け,1970-1971年の間,冬期を除きほぼ毎月海水中のビタミンB12含量を測定した.採水は2m層から行ない,メンブランフィルターで沪過後,沪液についてLactobacillus leichmaniiを用いてビタミンB12を定量した. 結果を要約すると次の通りである. 1) この海域において,ビタミンB12は海水中からたえず検出され,その量は0.42～6.43mμg/lであった. 2) この両年にも赤潮は頻発したが,発生時に海水中のビタミンB12の含量に顕著な低下は認められなかった.季節変化は著しくはなかったが,高水温期(約18℃以上)にはビタミンB12含量は概して高く,梅雨期の塩分低下期である6-7月に最高を示し,9-10月にもやや増加の傾向を示した. 3) 河口から最も遠い(約6㎞)定点では,他の定点よりも幾分含量が低かった.なお,ビタミンB12の補給は,河水によるほか,海底泥にも由来するものと考えられた. 4) この海域においては,暖期には一般に2mμg/l以上のビタミンB12が海水中に溶存した.これはビタミンB12を要求するプランクトンが105cells/ml程度の集群を形成するに足る濃度である.従って,少なくともこの海域においては,ビタミンB12が暖期における赤潮の消長現象を制約する因子とは考えにくい.In the nearshore region of the Seto Inland Sea off Fukuyama, where red water blooms of phytoplankton frequently occur, the vitamin B12 content of the sea water was determined at nearly monthly intervals except in winter during 1970 and 1971. Water samples were taken from a depth of 2 m. The vitamin B12 content of the sample water filtered through a membrane filter was determined by the microbiological assay depending on Lactobacillus leichmanii. The results can be summarized as follows: 1) Vitamin B12 was detected in all the samples. Its concentration varied between 0.42 and 6.43 mµg/l 2) The vitamin B12 content was not conspicuously low in the sea water samples taken within red water blooms. Though its seasonal variation was not conspicuous, it was generally high in the months of high water temperatures (ea. 18°C or above); the maximum occurred in June or July when the chlorinity of sea water dropped due to the rainy season; a secondary maximum occurred in September or October. 3) At the station most distant from the river mouth (viz., 6 km) the sea water showed somewhat lower contents of vitamin B12 than at other stations. Besides the river drainage, the bottom mud was also considered as source of vitamin B12 supply. 4) In the present waters the fluctuation and succession of phytoplankton blooms took place during warm months. It does not seem probable, however, that these phenomena were controlled by any paucity of vitamin B12, because the latter was present in these months usually in concentrations of 2 mµg/l or above, which is sufficient to grow some of the vitamin B12 requiring plankters to a population density of about 105 cells/mlThis study was partly supported by a grant from the Ministry of Education

Hydrographic conditions of Fukuyama Habor

A series of hydrographic observations were carried out from September, 1958 through July, 1960 in order to clarify the physical and chemical properties of sea water and bottom muds of Fukuyama Harbor, Hiroshima Pref. (Text-figs. 1,2, Table 4). The results are presented in Tables 6, A-F and Text-figs. 4-12 and discussed in comparison with previously published data on the hydrography, ecology and fishery of this water area. Fukuyama Harbor is the former estuary of Ashida River. It occupies the western part of Kasaoka Bay and measures 6.1km2 in area. Being trapezoidal in shape, it is bordered by a reclaimed land in the west, by hilly peninsula in the south and north, and opens wide in the east. The fiat muddy bottom slopes down gently toward the east. Water depth does not exceed 7m below the mean sea level at any part of the harbor. Tidal flats are exposed along the shore at low waters. Water temperature differs very little from air temperature all the year, the monthly mean varying between 7o (January and February) and 28oC (August) at the surface (Text-fig. 3). Water is turbid with the Secchi disc depth seldom exceeding 4 m. These two features can be ascribed partly to such local conditions as the small water depth and the muddy bottom, but are principally due to the fact that the water can not freely pass from the high sea (i. e., the Pacific Ocean off Bungo Strait) to this locality owing to the channels and shallow seas lying on the course. Monthly mean of chlorinity varies within the range of 16.6-17.9‰ at the surface (Text-fig. 3). Seasonal variation of chlorinity is not very great and reaches minima in summer when local precipitation and the drainage of Ashida River reach maxima (Tables 1, 2). Tidal range is comparatively great owing to the interference of the two tidal waves traversing the Seto Inland Sea in opposite directions, one wave from Bungo strait toward the east and the other from Kii Strait toward the west. In an average tide, tidal range measures 2.2m (Table 3) and 50% of the water that is present in the harbor at the high water is drained off during the ebb. Since water is mixed and replaced by the tide, vertical stratification seldom develops and the water is rich in dissolved oxygen from surface to bottom throughout the seasons. Tidal current, however, is not very fast. At low tides C.O.D. increases and dissolved oxygen decreases in the water in the northwestern part of the harbor, where polluted water is discharged from Fukuyama Inlet. In rainy months fresh water is discharged from flood-gates at low tides, temporarily lowering the chlorinity of the surface layer nearby. In the area where the effect of the polluted water or fresh water is not appreciable, various measurements on water are generally within the following range: water color in Forel's scale, 5 or more; pH, 8.2-8.3; C.O.D. by Saeki's alkaline permanganate method, 0.9-1.9ppm; acid-soluble total iron by aa' –dipyridyl method, less than 0.05ppm. The water near the sea bottom often gives greater values of C.O.D. and acid-soluble total iron than those mentioned above. The bottom mud is principally composed of the silt of particle diameters between 2 and 20f-b. The bottom is harder on the inshore side of the 2m depth contour than on the offshore side: the penetration value obtained with the Furukawa's penetrometer averages 30 and 50cm respectively. Other measurements on the bottom mud are within the following range: ignition loss, 3.2-13.9%; organic carbon by Tiurin's rapid titration method, 4.3-18.2mg/g (chlorine error not corrected); total nitrogen by Kjeldahl method, 0.34-1.64mg/g (Table 6). Carbon-nitrogen ratio (chlorine error corrected) is usually close to I 0. Ignition loss, Kjeldahl nitrogen and the oxygen consumption of mud (measured at room temperatures) respectively hold linear relation with organic carbon content (Text-fig. 13). Bottom mud is rich in organic matter and gives small carbon-nitrogen ratio in the area affected by the drainage from Fukuyama Inlet, flood-gates or Ashida River. Major fisheries in Fukuyama Harbor are the "masu-ami" fishery and the culture of the ark shell (Anadara subcrenata) and the laver (Porphyra tenera). The "masuami" is a pound net consisting of a pound 25m wide and 13m long and a leader net about 40m long. It is usually set between the 0 and 2m depth contours, being held in place by bamboo poles driven into the bottom (Text-fig. 14). Fishes, crustaceans and cephalopods are trapped in it as they move with the tide. In 1959 about 70 nets were operated in Fukuyama Harbor with the total catch of 79 metric tons. In the same year, 333 tons of ark shell and 1.8 tons of dried laver were produced by culture and 390 tons of littleneck clam (Venerupis semidecussata) were harvested from the natural beds on tidal flats (Table 7). All the species represented in the commercial catch are typical inhabitants of such inshore waters where water is relatively turbid and seasonal variation of water temperature is great.主として昭和33 ，34年度農林省農林漁業試験研究費によっ

富栄養海域における新生沈殿物量とその性状からみたリンの動態

湖沼に比べて海域でのリン沈積速度の実測例は多くない。浅海の海水・底土間のリン循環を検討するため,潜水作業を要しない沈降物捕集装置(Fig.1)を考案し,瀬戸内海備後灘で1975年4月～1977年1月の約2年間にわたって沈積速度(1日1cm2当りの乾重量(DW)および粒子態リン(PP)の沈降量)を測定した。捕集された沈降物の性状(リン含有率, chl.a含有率など)を同時に採取した海水中懸濁物(セストン)および底土最表層部の性状と比較し,また水中懸濁量と沈積量とを比較して,リンの動態を考察した。 1. 特別に高い捕集値を除くと,沈降量の平均は,DWでは,水深の浅い岸寄りのSt.2で0.98,沖側のSt.BG-1で0.42㎎/cm2/dayとなった。PPではそれぞれ0.64,0.33μg/cm2/dayであった(Table2)。 2. 季節別にみると,沈降量は概ね5～10月の高水温期に大きく,11～4月の低水温期に小さい。両期におけるDWの平均沈降量はSt.2で1.26および0.60㎎/cm2/day, St.BG-1で0.83および0.11㎎/cm2/dayで,低水温期のSt.BG-1で特に低かった。これらは,水柱中での粒子態有機物生産や,流入陸水が搬入する陸源の土粒子量などの季節変化を反映したものと考えられた(Table2)。 3. 水中懸濁物のリン含有率(乾重比)に比べ,沈降物のそれは格段に低いことが特微であり,平均で,0.21%対0.072%であった。従って,水中懸濁物は,沈降物(いわゆる新生堆積物)として捕集されるまでの過程で,7割近いリンを溶存態として海水中に放出していたことになる(Fig.3)。 4. 底土最表層部の試料は,5～65日間の沈降量に相当する厚さを採取して用いたが,そのリン含有率は沈降物と差がなく,両者のリン含有率の季節変化もほぼ一致した(Fig.2, Table3)。一方,chl.a含有率は底土最表層よりも沈降物で高かった(Fig.3)。 5. 水柱中の懸濁量に対する1日間沈降量の割合は,平均で,リンの場合7.3(St.2)および25%(St.BG-1)であった。DWの場合には地点間の差が大きく,25.1(St.2)および6.3%(St.BG-1)であり,St.2ではDW沈降量が懸濁物に対して顕著に高い割合を示した(Table2)。 6. 水中懸濁物のリン含有率の鉛直的変化,沈降物のリン・chl.a含有率,捕集物の予備的検鏡結果などから,PPの沈積には,デトリタス状物質の凝集大型化および動物プランクトン等による糞塊生成作用が重要な役割りを果すと推測された。 7. 水柱中の懸濁物が新生堆積物となるまでに海水中に放出するリン量(即ち沈降過程における粒子態リンから溶存態リンへの移行量)を上記の3と5の結果から計算し,St.2で0.43～5.3,St.BG-1で0.07～0.3μgP/ cm2/dayの値を得た(Fig.4)。 8. 上記1の平均値にもとずき,一定の仮定を設けて堆積速度を厚さで試算したところ,St.2で10.6mm/yr, St.BG-1で4.6mm/yrとなった。実際には,捕集器中への再懸濁物の混入,堆積後の溶出を多少とも見込む必要があるので長期的に見た底土の堆積速度はこれをやや下まわると推定される。Precipitation rates of particulate matter, as expressed in terms of dry weight and particulate phosphrus, were measured on 11 occasions at each of Sts. 2 and BG-1 in the central part of the Seto Inland Sea (water depths ea. 7 and 24 m, and 2 and 10 km from shore, respectively) during April 1975 - January 1977 with a sedimentation trap that does not require diving operations (collecting area 107.5 cm2; exposure period 1 or 2 days). On the overall average, 0.98 and 0.42 mg of dry matter and 0.64 and 0.33µg of P were found to precipitate onto each cm2 of collecting area per day at the respective stations. The foregoing daily precipitation corresponded on the average to 25.1 and 6.3% in terms of dry weight (7.3 and 2.5% in terms of particulate phosphorus) of the seston crop simultaneously present in the overlying water column at the respective stations. P content of the precipitates collected in the trap averaged 0.072%, or only 1/3 of the average P content of the seston. The loose uppermost layer of muddy sediment showed the P content similar to, and the chlorophyll a content lower than the precipitates in the trap. It was preliminarily estimated that the bottom sediment augments in thickness by 10.6 and 4.6 mm per year at the respective stations. Geographical and seasonal variation in the precipitation rates and the possibility of resuspended sediment particles to be collected in the trap were discussed.This study was supported partly by the Grant in Aid for Fundamental Scientific Research of the Ministry of Education and partly by the Research Fund on the Ecosystem under contract with the Fisheries Agency, Ministry of Agriculture and Forestry

Crystal structure and thermoelectric properties of chimney–ladder compounds in the Ru2Si3–Mn4Si7 pseudobinary system

Phase relationships of manganese-substituted ruthenium sesquisilicide alloys have been investigated by using X-ray powder diffraction and scanning and transmission electron microscopy. A series of chimney–ladder phases Ru1−xMnxSiy (0.14 less-than-or-equals, slant x less-than-or-equals, slant 0.97, 1.584 less-than-or-equals, slant y less-than-or-equals, slant 1.741) are formed over a wide compositional range between Ru2Si3 and Mn4Si7. The compositions of these chimney–ladder compounds deviate slightly from the composition line connecting Ru2Si3 and Mn4Si7, which corresponds to the ideal composition line satisfying VEC (valence electron counting) = 14 rule. The occurrence of this compositional deviation is discussed in terms of the VEC rule and the atomic packing. The thermoelectric properties of the directionally solidified Ru1−xMnxSiy alloys (0.55 less-than-or-equals, slant x less-than-or-equals, slant 0.90) have also been investigated as a function of the Mn content and temperature. The dimensionless figure of merit (ZT) for those alloys with a high Mn content (x greater-or-equal, slanted 0.75) increased with the increase in Mn content. The ZT value for a crystal with x = 0.90 was as high as 0.76 at 874 K

富栄養沿岸海域におけるリンの存在様式とその季節変動

瀬戸内海の備後灘北部の2定点において,1972年4月から約2年間,リンの基本的変動様式を知るために,約1カ月間隔で,海水中のリンを懸濁態リン(particulate phosphorus, PP),溶存態無機リン(dissolved inorganic phosphorus, DIP),溶存態有機リン(dissolved organic phosphorus, DOP)の3態に分別して定量した。結果を要約すると次のとおりである。 1. 本海域における海水中のリンの季節変動の一つの特長として,海水中のchlorophyllα濃度が高い暖季(5～10月,水温15℃以上)にPPの濃度が寒季におけるよりも,顕著に高かった。chlorophyllαとPPの間の高い相関などから,懸濁態リンの主部分は植物プランクトンに含まれていたと推定された。富栄養化の進んだ測点で,chlorophyllαが20㎎/m3以上の赤潮状態を呈した場合PPは1.0μg-at/l前後の高い値を示した。 2. DIPの変動にはいくつかの要因が考えられるが,全リン(total phosphorus, TP)中に占めるDIPとPPの割合が逆の変動を示したことは,DIPの減少が,PPの主体をなす植物プランクトンの生産に強く支配されていたことを示唆する。事実,植物プランクトン現存量が大きく,3態中でPPの割合が卓越している場合にはDIPの濃度はしばしば著しく低下した。 また,DIPの濃度は9月から12月にかけて高かったが,これは夏季に流入陸水および底泥から補給されたリンの影響が残存する時期に,植物プランクトンの生産が低下したためと考えられた。 3. DOPが海水中のリンに占める割合は周年かなり高かった。DOPの濃度は比較的季節変化に乏しかったが,その増減はPP濃度の変化と同時に,あるいは多少の遅れを伴って生じた。この結果は,DOPの主体が植物プランクトンおよびその他生物の代謝・分解産物から成る,との考えと矛盾しない。 4. 海水中の各態リン濃度の季節変化は,各態相互間の変換によっているだけではなく,3態の和である全リン(TP)も季節変化を示した。そのさい,リンの補給経路としては,夏季底泥からの溶出,および陸水の流入が指摘された。海水の成層期には光合成層ではTPの増加分にほぼ比例してPPが増加した。 5. これらの結果から,本海域におけるリンのサイクルには植物プランクトンの生産とその分解過程が極めて重要な位置を占めていると考えられる。Field observations were made during two years on the seasonal variation and the balance of three forms of phosphorus (particulate phosphorus, PP; dissolved inorganic phosphorus, DIP; and dissolved organic phosphorus, DOP) in the water column at two stations situated in the eutrophicated coastal region of the Seto Inland Sea, Japan. In the high temperature season concentration of PP was definitely higher than in the low temperature season. High correlation between the concentrations of PP and chlorophyll a suggested that PP was mostly composed of the phosphorus contained in the phytoplankton, especially at high PP levels. Maximal PP values were observed in dense phytoplankton blooms, and were as high as 0.91－1.06µg-at/l. Proportion of DOP in the total phosphorus of seawater was considerably high throughout the year, averaging 38.7 and 41.7% at each station. An increase of DOP in the water column coincided with, or followed with a short delay, an increase of PP. DIP was consumed in the course of the growth of phytoplankton in upper layers during stratification period. There was indication that DIP was supplied to the water column from the outside during September through October. The influx of land water and the liberation of dissolved phosphorus from the bottom sediments were suggested as two main routes of phosphorus supply to the water column. In conclusion, then, it appears that in this sea region the production and decomposition of phytoplankton played an important role in the annual cycle of phosphorus