小網代湾湾央部において, 未撹乱推積物コアを現場条件下で培養する方法により, 水-推積物間の酸素と窒素化合物のフラックス(全フラックス)を2月, 4月, 8月及び11月の4回測定した。同時に, 界面近傍における酸素と窒素化合物の濃度プロファイルを測定し, 濃度勾配と分子拡散係数からフラックス(拡散フラックス)を計算した。堆積物表面0～5mm層の有機物含量は, 4月に一時的な増加が見られた。酸素の全フラックスの向きは年間を通して上層水から堆積物に取り込まれており, 春から夏にかけて増加する明瞭な季節変化を示したが, 有機物含量の季節変化とは対応しておらず, 温度と有意な正の相関を示した。アンモニア態窒素の全フラックスの向きは年間を通して堆積物から溶出しており, 酸素の全フラックスと同様の季節変化を示したが, 有機物含量や温度との相関はなかった。全フラックスと拡散フラックスの比較から, 水-堆積物間の酸素やアンモニア態窒素の輸送過程として, 年間を通して分子拡散が重要であると考えられた。また, 酸素とアンモニア態窒素の全フラックスの比から, 堆積物中で無機化されている有機物のC/N比として5.2という値が推定された。

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水深の浅い沿岸域では, 堆積物による酸素消費や堆積物からの栄養塩溶出が富栄養化の原因となっている. 本研究では酸素・窒素・炭素の共役循環 (coupled cycle) の鉛直微細構造を表現できる堆積物表層物質循環モデル (生態系モデル) を開発した. 開発したモデルを堆積物コアデータに適用した結果, 良好な現況再現が得られモデルの妥当性が示された. また, 生物・化学・物理過程の鉛直微細構造が明確化され, 酸素消費, アンモニア生成, 脱窒の速度やメカニズムが表現された. 本研究で開発したモデルは, 沿岸生態系全体に与える堆積物の寄与や, 覆砂・浚深などの施策効果を定量的・機構的に評価する基盤となる.

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Tributyltin (TBT) is a biocidal chemical that has been used primarily as an antifouling agent incorporated into antifouling paints for vessel hulls. However. TBT was found In affect non-target organisms, which led lo the global restrictinn on its use. As a result, organometallic substances, pesticides and other chemicals have been used as alternatives to TBT. These include zinc pyrithione (ZnPT). copper pyrithione (CuPT). pyridine-triphenylborane (PK), SeaNine211, Diuron (DCMU) and Irgarol 1051. Although TBT alternatives have been used for ship hulls, fishing nets and other fishing equipment, they have been mainly used as antifouling paints for ship hulls. Antifouling paints are used for commercial vessels, fishing boats and pleasure boats. Taking total areas of ship hulls into account, we considered only commercial vessels as discharge sources of TBT alternatives. As a result of our surveys, it was found that CuPT was the one used on commercial vessels as a TBT alternative. We conducted literature review on the toxicity of CuPT on aquatic organisms and its uncertainty. As a result, we selected 1.8 μg/L. which was the lowest acute toxicity, as a criteria toxicity data for risk assessment, and concluded that 100 was appropriate　as its uncertainty factor. Ecological risk assessment can be conducted using these toxicity data and uncertainty factor and　estimated environmental concentrations nf CuPT.

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Routine analytical method of organic carbon and nitrogen in marine sediments were de scribed, and results of the method were compared with those of acid wash-out method. Samples were treated with UCl to remove carbonate within ceramic sample boats, by drop ping UCl using microsyringe, and organic carbon and nitrogen were determined with Yanaco MT-5 CHN analyser. The method were applied to sand of tidal flat, silt of estuary, sediment trap particles and coralline samples. Precision (CV%) were 4-8% for organic carbon and 8-14% for nitrogen. 10 -30% of organic carbon and nitrogen were lost by wash-out acid treatment.

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Changes in the benthic community structure, relating to a decline in bottom dissolved oxygen concentration in the shallow muddy bottom of Mikawa Bay, were observed throughout a 50 days period during the early summer of 1996. Water mass movements related to tides and winds were largely responsible for changes in the bottom oxygen concentration. During the observation period, the dissolved oxygen deficiency tended to progress as the water temperature increased, which probably caused an increase in decomposition of organic matter on the bottom. An increase in the apparent dissolved oxygen consumption rate was mainly due to decomposition of newly deposited organic matter from water column rather than that of existing bottom sediment. Biomass of bacteria increased during the early stage of the dissolved oxygen deficiency, but decreased in the later stage, resulting in an increase of undecomoposed detritus in the sediment. Benthic chlorophyll fluctuated mainly with changes in sunlight intensity, but decreased when severe dissolved oxygen deficiency conditions prevailed. Differeces in the ability to tolerate the oxygen deficiency amongst meio-and macro-benthos species were observed. Almost all benthos species, however, decreased during the severe oxygen deficiency period, except for subsurface deposit feeders.

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干潟における栄養塩の季節変化に関する定期調査と干潟と周辺海域におけるDO濃度の時間変化について現地観測を行った.その結果, 干潟上で観測された貧酸素水塊は周辺海域から輸送されているものではなく, 干潟上での酸素消費過程によって形成されると推察された.また, 和白干潟のような過栄養海域に位置する干潟では, 日中の日射量が高ければ, 6月においても赤潮が発生し, 夜間に貧酸素水塊が形成されることが示唆された.さらに, 鉛直一次元の解析を行った結果, 和白干潟上の水柱0.5mにおいて貧酸素水塊を形成させないためには, 平均的な底泥の酸素消費速度を145mg/m2/h以下に抑える必要があることが明らかとなった.

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干潟域の水質変動に寄与する要素, つまり底泥生態系と海水中のプランクトン等による酸素消費速度および底泥生態系による栄養塩溶出速度を個別に計測し, 物質収支について検討した.底泥生態系による酸素消費速度と栄養塩溶出速度は水温の上昇に伴って増加する.酸素消費については底泥の寄与の方がホソウミニナより大きく, アンモニア態窒素の溶出速度についてはホソウミニナによる寄与の方が大きいことを示し, 実験によって得られた底泥生態系による酸素消費およびアンモニア態窒素の溶出速度は観測によるこれらの値の30～50%であった.現地観測結果と実験結果に基づいて物質収支を評価した結果, 両者の間には大きな差異が認められた.

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We have developed a prototype model that can estimate the concentration of hazardous substance coplanar polychlorinated biphenyls (co-PCBs) in marine organisms and used it to estimate the concentration that target species of a basic and specific food chain had accumulated in Tokyo Bay. This model based on three models: a 3D-hydrodynamic model (Horiguchi et al. 2001). an ecological model (Taguchi et al, 1999) and a chemical fate model (Kobayashi. 2004). The model could reproduce, both temporally and spatially, the actual concentrations of co-PCBs found in fish, of Tokyo Bay.

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In order to reproduce changes of the dissolved oxygen concentration in summer in the vicinity of the Nanko thermal power plant, located in the inner part of Osaka Bay, a numerical simulation model was developed. According to the model results, daily fluctuation of dissolved oxygen concentration in the surface layer is high in June, the early stratification period, because of instability of stratification and after July. The dissolved oxygen concentration gradually decreases from a level of 6 to 17 mg/L in June to a level of 6 to 9 mg/L in July in the vicinity of the Nanko thermal power plant. Both the observations and model values near the depth of the thermal power plant outlet are 3 to 5 mg/L, which is considered not to affect the water quality of dissolved oxygen. Our simulation model should be able to reproduce the characteristics of dissolved oxygen concentration during the stratification period in the vicinity of the Nanko thermal power plant.

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The bottom sediment, benthic community, fish and larvae of commercial shellfish species were investigated at an artificial tidal flat in Mikawa Bay, Japan. Differences between low and high tidal flat areas were investigated. The central area of the development was comprised of fine sand, whereas fine sand and coarse sand were present in the original bottom of the tidal flat. Organic matter content was high in the waterway and the marginal area of the development. The water purification rate, in terms of macrobenthic biomass, was high in the central and marginal areas of the development. In contrast, biodiversity in terms of macrobenthos species abundance was low in the central area of the development. Thus the distributions in the water purification rate and biodiversity were different. Mactra chinensis, Mactra veneriformis, and Ruditapes philippinarum dominated the commercial bivalve species at different heights of the tidal flat. Platichthys bicoloratus dominated the fish larvae of commercial species, and distribution across defferent depths varied according to body length. The marginal area of the development was important for settling larvae. As distributions of dominant species and functions of the tidal flat are different, we suggest that it is important to ensure a range of consecutive depths when creating an artificial tidal flat.

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We targeted Tokyo Bay to study the risk trade-off of substituting Copper pyrithione (CuPT) for Tri-butyltin (TBT) as an antifoulant. We estimated the ecological risk by assessing calcification of giant Pacific oysters (Crassostrea gigas). We estimated the environmental concentrations of TBT and CuPT using chemical fate model (FATE model). The risk assessment was used the uncertainty factor (UF) and margin of exposure ( MOE) method. For TBT. the ecological risk was estimated by the no observed effect concentration (NOEC:0.001 μg・L^-1 : calcification of giant Pacific oysters) and the UF (10). As a result, a high risk level was shown for all sea areas of Tokyo Bay. For CuPT. the ecological risk was estimated by the no observed effect concentration (NOEC:0.25 μg •L^-1: Growth Reduction of Skeleionema costatum) and the UF (100). There is a high risk for the ports areas, but the risk was not of concern for other sea areas of the Bay. Regarding calcification of giant Pacific oysters, the risk was low for CuPT(EC50 11 μg・L^-1: UF10) though it was high for TBT (NOEC:0.001 μ• L＾-1:UF1) in all sea areas. It was suggested that the ecological risk to C. gigas in Tokyo Bay would greatly reduce by substituting TBT with CuPT. The risk evaluation of development inhibition of Bafununi　Hemiceiurotuspulcherrimus) from CuPT　NOEC: 1.0 μg. UF 10) was done for February 2007. which is the spawning season. The results show that the risk is low in all　ea areas.

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In food webs between usual zooplankton and phytoplankton, an ecosystem model, which con tains a microbial loop between bacteria and zooplankton, was developed. Numerical simulations of the ecosystem in Tokyo Bay were carried out for 1 year using this model. The observation result for the time series fluctuation of 3 stations of the phytoplankton concen tration in the bay was compared with the calculation result. The fluctuating range of simulated values is smaller than that of observed values in winter. Simulated results are in good agreement with order of phytoplankton cycle throughout 1 year the observations. Primary production in Tokyo Bay from June 1995 to May 1996 is estimated at 1,600 tonC/y from the simulations. Dia toms are about 1.4 times dinoflagellate in terms of biomass. This indicates that diatom accounts for about 58% of phytoplankton standing stock in Tokyo Bay. Carbon flow fluxes to zooplankton from phytoplankton are 550 tonC/y, and carbon flow fluxes to zooplankton from bacteria through protozoa are 990 tonC/y, and microbial loop are about 1.8 times grazing food webs. In addition, nitrogen flow fluxes to phytoplankton from nitrogen pool are 156 tonN/y, and nitrogen flow fluxes to bacteria from nitrogen pool are 480 tonN/y,and microbial loop are about 3 times grazing food webs. Thus results suggest that the role was great and very important in carbon and nitrogen cycle. The horizontal distribution of phytoplankton in the summer season from the classical type of the ecosystem model showed the stabilized distribution. However, daily variations of horizon tal distributions of diatom concentration in the present model are revealed. It is considered that the effect by the advection is strong for the change of the horizontal distribution of phytoplankton.

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In order to analyze the water quality, especially COD, T-P and T-N of Tokyo Bay in summer, the hydrodynamical and ecosystem coupled model we have developed was applied. The stationary state results could be obtained over 100 days time integration. For the phytoplankton abundance, COD,T-P, T-N, and inorganic nitrogen concentrations, the model could reproduce the realistic values except an inorganic phosphrous concentration whenwe adopted phytoplankton cellcomposition ratio (N/P ratio by weightin the model) to be 14in place of 8. The discrepancy could not be improved, even if we gave 10times larger phosphrous relaese rate from the sea bottom than standard rate. It maybe improved if weconsider the cell quota mechanism or different decomposition rate of organic matter for nitrogenand phosphrous. The DOC concentrations in the model showed lower values than the ones in the observations. It was implied that when the lowerdecomposition rates of DOCand POC, and changing the POC/DOC ratio in the loading from land were considered, the discrepancy could be reduced. The zooplanktonbiomass distribution showed the influence of fresh water distribution, that is, theinfluence of zero value attheriver boundary. The dominance of physical processes such as diffusion and advection compared to biological processes such as zooplankton growth rate couldbe plausible reason. In phytoplankton case, suchproblem does not occur because of biological processes dominance (high turnover rate).

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