• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.6
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• pp.708-720
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• 2021

As hypoxia adversely affects the marine environment in northwestern Gamak Bay every summer, the present study determined its comprehensive occurrence mechanisms using the Multiple Regression Analysis (MRA) and suggested management directions based on the primary MRA factors. The first hypoxia occurred by thermocline related to weather conditions, with organic matter deposited inside the bay on 26^th June, 2017. Additionally, on 12^th July, halocline was also developed by increased rainfall, and the hypoxia was most expanded horizontally and vertically. The primary factors were the stratification and deposited organic matter. In contrast, the hypoxia correlated to phytoplankton growth and deposited organic matter on 8^th August was diminished with remarkably less precipitation. However, the stable halocline was caused by massive precipitation, and the reproduced phytoplankton re-generated the expanded hypoxia on 16^th August despite a short sampling interval. Subsequently, the hypoxia influenced by the deposited organic matter spread shallowly along the seafloor on 13^th September as the extinction period. These results suggest that stratification alleviation technologies, and the improvement and removal of the organic matter deposited on the surface sediment are necessary.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.3
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• pp.47-57
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• 2022

We carried out studies on prediction in concentration of dissolved oxygen (DO) with LSTM model and prediction in occurrence of hypoxia water mass (HWM) with decision tree. As results of study on prediction in DO concentration, a large number of Hidden node caused high complexity of model and required enough Epoch. And it was high accuracy in long Sequence length as prediction time step increased. The results of prediction in occurrence of HWM showed that the accuracy of nonHWM case was 66.1% in 30 day prediction, it was higher than 37.5% of HWM case. The reason is that the decision tree might overestimate DO concentration.

• Journal of the Korean Society of Marine Environment & Safety
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• v.16 no.3
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• pp.241-248
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• 2010

Hypoxic(oxygen-deficient) water masses are a key threat to the ecosystem of shallow marine coastal areas worldwide. The phenomena of hypoxia occurred at Gamak Bay, on the southeast coast of Korea, in late June 2007. In this paper, the physicochemical characteristics of seawater were surveyed for a period of hypoxic water mass disappearance. The hypoxic water mass was located between Sunso and the northwestern area of the inner bay. The dissolved oxygen(DO) concentrations of surface and bottom water were $1.3mgL^{-1}$ and less than $2mgL^{-1}$, respectively, in the hypoxic water masses, and $4.5{\sim}6.8mgL^{-1}$ and $3.8{\sim}6.0mgL^{-1}$ at the other oxygen-rich sample sites, respectively. Chlorophyll a concentrations were $4.9{\sim}25.3{\mu}gL^{-1}$ at the surface, $2.3{\sim}23.1{\mu}gL^{-1}$ in the middle, and $1.9{\sim}9.0{\mu}gL^{-1}$ at the bottom of the hypoxic water masses. When the hypoxic water mass appeared in Gamak Bay, it formed three different vertical types. The first type occurred throughout the water depth around Sunso. The second type developed from the bottom. The third type of hypoxic water mass was formed in the middle water layer when the inversion of water temperature occurred. The third type of phenomena appeared at only St. 9, St. 14 and St. 21 sites near the Hodo coast. Aquatic surface respiration of bottom-dwelling fishes such as the oriental goby(Acanthogobius flavimanus) was observed and many crustaceans were seen along the adjacent shore of the hypoxic water mass area. About 3,000 oriental gobies as well as many crustaceans died due to this event in Gamak Bay. The results of this study could provide fundamental data for the mechanism of hypoxic water masses in Gamak Bay.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.15 no.3
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• pp.115-123
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• 2010

The occurrence and variation of oxygen deficient water mass (ODW) in Namdae stream estuary, Yangyang were studied. Field observations for water properties and sediment environments were conducted at 5 stations of the estuary from April 2008 to November 2008. The coastal sandbar is developed at the estuary mouth, and there is a pool between the estuary mouth and about 2.3 km upstream of the estuary. The pool is relatively deep and narrow compared to riverbed of the estuary. The ODW was observed continuously in the pool from May to October. The ODW extends vertically up to 2 m depth in August, and maximum length of the ODW were about 2.3 km. Mean concentration of ignition loss (IL) and acid volatile sulfide (AVS) of sediment was 7.5~9.0%, $0.282{\sim}1.106\;mg/g{\cdot}dry$ wt, respectively. Ammonium concentration in the bottom layer during formation period of the halocline and the ODW was 4~23 times higher than that of surface layer. ODW was initiated by the introduction of seawater into bottom of the estuary pool to make a strong halocline, and then decomposition of organic matter within sediment accelerated the formation of the ODW.

• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.4
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• pp.216-224
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• 2006

To clarify the formation process and characteristics of oxygen deficient water mass in Gamak Bay, oxygen deficiency was weekly observed from 17 June to 12 September 2005. Surface water temperature was significantly lower in the outer bay than in the inner bay, whereas the bottom water temperature was higher in the central area of bay than in the outer and inner bay. The vertical stratification of water mass was strongly formed during the period, and thermocline was observed between 3 and 5m deep. The oxygen deficiency in the bottom layer began to appear at early July in the inner bay and gradually spread to the center area of the bay in early August. The mean transparency and light attenuation coefficient($K_d$) in water mass was 4.0m and 0.47, respectively. Average concentrations of nutrient and chlorophyll ${\alpha}$ in the bottom layer were significantly higher than those in surface, and those concentrations were significantly higher in the inner bay than in the outer bay. During the formation of oxygen deficiency in the bottom layer, oxygen penetration depth in the bottom sediment were extremely shallow, and oxygen consumption rate in the bottom sediment were lower than that in the area where oxygen deficient water mass disappeared. Dissolved oxygen concentrations in the bottom layer are negatively correlated with nutrient concentrations, whereas those in the surface layer did not show a significant relationship with nutrient concentrations. Elevated loss of oxygen in the bottom water mass was attributed to the increase of the oxygen consumption rates in sediments and the decomposition of organic matter by microorganism.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 1993.10a
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• pp.24-24
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• 1993

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.41-50
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• 2010

This study established a 3D ecosystem model composed of stratification considering the topographic heat accumulation effect and river outflow, and then applied this model to Jinhae, Masan Bay. Specifically, it reenacted the formation and developmental process of ODW according to the stratification by calculating the kinematic eddy viscosity and eddy diffusion coefficient of the stratification model. The results were used as input data for the ecosystem model and compared with DO, COD, I-N, and I-P, which is the standard index of ocean water quality. As a result, it was determined that COD and T-N are third grade and T-P is second grade standards for a natural environment.

• Journal of the Korean Society of Marine Environment & Safety
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• v.16 no.4
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• pp.339-344
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• 2010

Oxygen depleted water mass can damage aquatic animals not only in direct way but also in indirect way by generating toxic substances including occurrence of hydrogen sulfide and ammonia which are also highly detrimental to animal life in the water mass. An oxygen dissolution device was developed, which makes turnover of the oxygen rich (over 20 mg/L) surface water down to the bottom where hypoxia is evident and tested the device in terms of oxygen recovery in the oxygen depleted bottom water. the device with turnover rates of $3.6\;m^2$/min at the liquid oxygen injection rate of 48~26.3 L/min could recover dissolved oxygen level to 7~25 mg/L at depth 7 m to lead to the dissolution level of over 90% by the supply of liquid oxygen. The running advantage of the device is that it does not require any auxiliary tank and higher energy for operation. Therefore, it can be highly useful device to relieve damages to the farmed animals in the oxygen depleted waters.

• Journal of Ocean Engineering and Technology
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• v.22 no.5
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• pp.75-82
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• 2008

As a basic study for establishing a countermeasure for an oxygen deficient water mass (ODW), we investigated the variation of ODW volume according to the enforced total pollution load management in Jinhae Bay. This study estimated the inflowing pollutant loads into Jinhae Bay and predicted the reduction in ODW by using a sediment-water ecological model (SWEM). The result obtained in this study are summarized as follows: 1) The daily average pollutant loads of COD, SS, TN, TP, DIN, and DIP inflowing into Jinhae bay in 2005 were estimated to be about 12,218 kg-COD/day, 91,884 kg-SS/day, 5,292 kg-TN/day, 182 kg-TP/day, 4,236 kg-DIN/day, and 130 kg-DIP/day. 2) The calculated results of the tidal current by the hydrodynamic model showed good agreement with the observed currents. Also, an ecological model well reproduced the spatial distribution of the water quality in the bay. 3) This study defined the ODWDI (ODW decreasing index) in order to estimate the ODW decreasing volume caused by a reduction in the inflowing pollutant loads. As a result, the ODWDI was predicted to be about 0.91 (COD 30% reduction), 0.87 (COD 50% reduction), 0.79 (COD 70% reduction), 0.85 (ALL 30% reduction), 0.66 (ALL 50% reduction), and 0.45 (ALL 70% reduction). The ODW volume was decreased 1.5 $\sim$ 2.6 times with a reduction in the COD, TN, and TP inflowing pollutant loads compared to a reduction in just the COD inflowing pollutant load. Therefore, it is necessary to enforce total pollution load management, not only for COD, but also fm TN and TP.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2008.09a
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• pp.92-95
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• 2008