This study was focused on estimating instream flow, and its optimal alternative for securing the required total amount of instream flow was also researched in order to restore ecosystems and riverine aesthetics of the Mugeo Stream, the first tributary of the Taewha River flowing through the center of Ulsan. In this study the hydraulic and hydrologic conditions and water quality were investigated at specific channel reaches and representative stations of the Mugeo Stream to determine a proper estimate of instream flow. And riverine functions, such as the minimum flow, water quality conservation, fish habitat, and recreation, were considered to restore the environmental functions of the stream. As a result, the total amount of 11,500㎥/day was set as the target instream flow for the Mugeo Stream. It was chosen as the optimal alternative for securing the total external supply of 10,000㎥/day which have to be transfered from the riverbed flow diverted through the Taewha Main river at upstream of Samho bridge. The water quality throughout the Mugeo Stream channels will be improved considerably to 3-4 mg/l of BOD standard if the target instream flow is supplied and sewage is intercepted by the sanitary sewage system.

Large scale of fish kills by red tides has been occurred every year in coastal water fisheries of Korea. To suppress red tide spreading out over the south coastal water of the Korean Peninsula large amount of loess has been applied every year because loess is known to be effective in removing red tide organisms. Effects of loess application in ecosystem of underwater near sea shore were investigated with some physical characteristics of loess. Loess used for the red tide reduction consisted of very fine particles, of which size was mostly less than 0.1㎜. Particles of loess blocked light penetration, which is essential for the underwater ecosystem. Loess also pushed pH down by the hydrolysis activities of aluminium and iron. It was found that underwater ecosystems where loess was applied near sea shore were devastated. Sea plants such as sea weeds were gone leaving only their roots. Clams and snails were dead under the loess dust blanket. And fishes were not found at all where loess has been sprayed for long time. It was found that even if loess has some capacity to reduce red tide temporarily, loess application should be stopped to protect underwater ecosystems.

The eco-hydrodynamic model was used to estimate the environmental capacity in Gamak Bay. It is composed of the three-dimensional hydrodynamic model for the simulation of water flow and ecosystem model for the simulation of phytoplankton. As the results of three-dimensional hydrodynamic simulation, the computed tidal currents are toward the inner part of bay through Yeosu Harbor and the southern mouth of the bay during the flood tide, and being in the opposite direction during the ebb tide. The computed residual currents were dominated southward flow at Yeosu Harbor and sea flow at mouth of bay. The comparison between the simulated and observed tidal ellipses at three station showed fairly good agreement. The distributions of COD in the Gamak bay were simulated and reproduced by an ecosystem model. The simulated results of COD were fairly good coincided with the observed values within relative error of 1.93%, correlation coefficient(r) of 0.88. In order to estimate the environmental capacity in Gamak bay, the simulations were performed by controlling quantitatively the pollution loads with an ecosystem model. In case the pollution loads including streams become 10 times as high as the present loads, the results showed the concentration of COD to be 1.33～4.74㎎/ℓ(mean 2.28㎎/ℓ), which is the third class criterion of Korean standards for marine water quality. In case the pollution loads including streams become 30 times as high as the present loads, the results showed the concentration of COD to be 1.38～7.87㎎/ℓ(mean 2.97㎎/ℓ), which is the third class criterion of Korean standards for marine water quality. In case the pollution loads including streams become 50 times as high as the present loads, the results showed the concentration of COD to be 1.44～9.80㎎/ℓ(mean 3.56㎎/ℓ), which is the third class criterion of Korean standards for marine water quality.

The emergy concept was used to valuate the contributions of a tidal flat ecosystem included in the fourth stage reclamation plan for the Youngsan River area to the Korean economy. Emergy contributions of the ecosystem were compared with those of economic valuations performed on the same ecosystem. The tidal flat ecosystem contributed 3.55 million Em\/ha annually. This, however, cannot be compared directly with those of the economic valuations because both methodologies approach the valuation of ecosystems in different perspectives. The emergy methodology is a donor-based valuation in which what goes into making a product or service is measured, while the economic valuation is a receiver-based approach in which human receivers determine the value of an ecosystem product or service. An emergy valuation was conducted for the three ecosystem functions included in the economic valuations to compare the results of both methodologies on the same basis. Fishery production and pollutants removal contributed 9.86 million Em\/ha/yr and 0.88 million Em\/ha/yr, respective1y. The conservation value of the tidal flat ecosystem was 3.55 million Em\/ha/yr. Overall, the emergy valuation that try to include works of both human and nature on the same basis resulted in higher economic contribution of the tidal flat ecosystem than that calculated by the economic methodologies in which only human works are measured based on the willingness-to-pay of people. This study showed that the emergy concept could provide an alternative tool for policy decision-making regarding utilization and conservation of ecosystems by approaching the ecosystem valuation from a different perspective than that of economic methodologies.

The three-dimensional eco-hydrodynamic model was applied to estimate the physical process in terms of COD (chemical oxygen demand) and net supply(or decomposition) rate of COD in Kamak Bay to find proper management plan for oxygen demanding organic matters. The estimation results of the physical process in terms of COD showed that transportation of COD is dominant in surface level while accumulation of COD is dominant in bottom level. In the case of surface level, the net supply rate of COD was 0～0.50 mg/m2/day. The net decomposition rate of COD was 0～0.04 mg/m2/day in middle level(3～6m) and 0.05～0.15 mg/m2/day in bottom level(6m～bottom). These results indicates that the biological decomposition and physical accumulation of COD are occurred predominantly at the northern part of bottom level. Therefore, it is important to consider both allochthonous and autochthonous oxygen demanding organic matters in the region.

A three-dimensional ecological model (EMT-3D) was applied to Nonylphenol in Tokyo Bay. EMT-3D was calibrated with data obtained in the study area. The simulated results of dissolved Nonylphenol were in good agreement with the observed values, with a correlation coefficient(R) of 0.7707 and a coefficient of determination (R2) of 0.5940. The results of sensitivity analysis showed that biodegradation rate and bioconcentration factor are most important factors for dissolved Nonylphenol and Nonylphenol in phytoplankton, respectively. In the case of Nonylphenol in particulate organic carbon, biodegradation rate and partition coefficient were important factors. Therefore, the parameters must be carefully considered in the modeling. The mass balance results showed that standing stocks of Nonylphenol in water, in particulate organic carbon and in phytoplankton are 8.60×105 g, 2.19×102 g and 3.78×100 g, respectively. With respect to the flux of dissolved Nonylphenol, biodegradation in the water column, effluent to the open sea and partition to particulate organic carbon were 6.02×103 g/day, 6.02×102 g/day and 1.02×101 g/ day, respectively.

The three-dimensional eco-hydrodynamic model was applied to estimate the physical process in terms of nutrients and net uptake(or regeneration) rate of nutrients in Kamak Bay for scenario analysis to find proper management plan. The estimation results of the physical process in terms of nutrients showed that transportation of nutrients is dominant in surface level while accumulation of nutrients is dominant in bottom level. In the case of dissolved inorganic nitrogen, the results showed that the net uptake rate was 0～60 mg/m2/day in surface level(0～3m), and the net regeneration rate was 0.0～10.0 mg/m2/day in middle level(3～6m) and above 10 mg/m2/day in bottom level(6m～below). In the case of dissolved inorganic phosphorus, the net uptake rate was 0.0～3.0 mg/m2/day in surface level, and the net regeneration rate was 0.5～1.5 mg/m2/day in middle level and 1.0～3.0 mg/m2/day in bottom level. These results indicates that net uptake and transport of nutrients are occurred predominantly at the surface level and the net generation and accumulation are dominant at bottom level. Therefore, it is important to consider the re-supplement of nutrients due to regeneration of bottom water.

Jindong bay at the northwestern part of Jinhae bay suffers from the occurrence of red tides in summer every year. In order to study the management methods of coastal environments, an ecological numerical model has been developed. The model experiments was forecasted that the load of nutrients from the land and field concentration will be cut down per 10% each. When we cut down 57.2% nitrogen load in the inner bay and 38.4% phosphorous load in the outer bay of bottom layer of the nutrients load from land and field concentration, the seawater quality standard levels up first grade. When we cut down 86.5% nutrients in the inner bay and 93.0% nutrients in the outer bay, the concentration of chlorophyll a decreases below 3.2(an individual concentration of phytoplankton : 10,000cell/ml), i.e. the red tides do not occur.

From the environmental aspects, primary productivity of phytoplankton plays the most important role in enhancement of marine culture oyster production. This study may be divided into two branches; one is estimation of maximum oyster meat production per unit facility(Carrying Capacity) under the present environmental conditions in Kamak Bay, the other is improvement of carrying capacity from increase of primary productivity by changing the environmental conditions that cause not to form an unfavorable environment such as the formation of oxygen deficient water mass using the eco-hydrodynamic model. By simulation of three-dimensional hydrodynamic model and ecosystem model, the comparison between observed and computed data showed good agreement. The results of sensitivity analysis showed that phytoplankton maximum growth rate was the most important parameter for phytoplankton and dissolved oxygen. The estimation of mean primary productivity of Wonpo, Kamak, Pyongsa, and Kunnae culture grounds in Kamak Bay during culturing period were 3.73gC/㎡/d, 2.12gC/㎡/d, 1.98gC/㎡/d, and 1.26gC/㎡/d, respectively. Under condition not to form the oxygen deficient water mass, four times increasing of pollutants loading as much as the present loading from river increased mean primary productivity of whole culture grounds to 4.02gC/㎡/d. Sediment N, P fluxes that allowed for 35% increasing from the present conditions increased mean primary productivity of whole culture grounds to 3.65gC/㎡/d. Finally, ten times increasing of boundary loadings from the present conditions increased mean primary productivity of whole culture grounds to 3.95gC/㎡/d. The maximum oyster meat production per year and that of unit facility in actual oyster culture grounds under the present conditions were 6,929ton and 0.93ton, respectively. This 0.93ton/unit facility is considered to be the carrying capacity in study area, and if the primary productivity is increased by changing the environmental conditions, oyster production can be increased.

A three-dimensional ecosystem model is applied to the Suyoung Bay, located at the southeastern part of Korea, to study of the material distribution in the time scale of several tens days. The model has included of the DIN(Dissolved Inorganic Nitrogen), DIP(Dissolved Inorganic Phosphate), phytoplankton, zooplankton and detritus, and also was coupled with the physical processes. The spatial distribution of chlorophyll-a and primary productivity in the model is determined by the physical and chemical-biological parameters. The horizontal distributions of the DIN, DIP and chlorophyll-a are decreased from the coast to the off-shore, though the nutrients show some more complicated pattern than the chlorophyll-a. The nutrient contents in the off shore are low, and thus a relatively low productivity(chlorophyll-a) are presented. On the whole, the distribution of the results of model are smoother than the observed ones and some small scale variation in the observed data cannot be reproduced by the model due to the resolution limits of model. However, the basic pattern and the quantitavities has been reproduced by the model well.

Masan bay is one of the polluted enclosed bays, which has red tides problem and the formation of oxygen deficient water in the bottom layer. Most important factors that cause eutrophication and red tide is nutrient materials containing nitrogen and phosphorus which stem from terrestrial sources and nutrients released from sediment. Therefore, to improve of water quality, reduction of these nutrient loads should be indispensible. At this study, the three-dimensional numerical hydrodynamic and eutrophication model, which were developed by Institute for Resources and Environment of Japan, were applied to analyze the processes affecting the phytoplankton production and also to evaluate the effect of water quality improvement plans on phytoplankton production. in field survey, the range of concentrations of chlorophyll -a at surface area was found to be 29.17 - 212.5㎎/㎥, which were exceeding eutrophication criteria. The constant currents defined by integrating the simulated tidal currents over 1 tidal cycle showed the counterclockwise eddies in the southern part of Budo. The general directions of constant currents were found to be southward at surface and northward at bottom over all the bay. The eutrophicatior model was calibrated with the data surveyed in the field of the study area in June, 1993 The calculated results are in fairly good agreement with the observed values within relative error of 30%. The pollutantI load from the sources such as the input from terrestrial sources and release from the sediment was reduced by the rate of 50, 70, 90, 98% to evaluate the effect of phytoplankeon production. Phytoplankton production was reduced to 50% in case of the 90% reduction of the input loads from terrestrial sources and 8% in case of the 90% reduction of the load from sediment.