• Korean Journal of Ecology and Environment
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• v.38 no.2 s.112
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• pp.160-180
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• 2005

Long-term data (Ministry of Environment Water Quality Monitoring data) of phytoplankton biomass (chlorophyll a) and water quality were analyzed to investigate trends in biomass of the primary producers and water quality for the estuarine systems in Korea: Sumjin River, Han River, Asan Lake- Bay, Youngsan River, Keum River and Nakdong River. The literatures were also reviewed to examine the characteristics of phytoplankton biomass and water quality in the estuarine systems. The Sumjin River estuary, the single estuary without a dike in Korea showed the characteristics similar to other typical estuarine systems. Phytoplankton biomass was high during the fall at transitional regions (5 ${\sim}$ 15 psu) after riverine freshwater inputs were increased in summer. Concentrations of the nitrate and silicate were increased with the high river discharge rates. Phytoplankton biomass and nutrient concentrations were high during spring at the lower regions in the Han River whereas phytoplankton biomass and nutrient concentrations were high during spring at the upper regions in the Youngsan River. Phytoplankton biomass was the highest in the Asan Lake and nutrient concentrations were high at the upper region of the lake. In Nakdong River, phytoplankton biomass was high during winter and the biomass was slightly higher at upper region than at lower region. Long-term trends showed that total nitrogen and total phosphorus were mostly increased in the river systems. Implications of these results relevant to the water quality management for the river systems were also discussed.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.3
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• pp.343-352
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• 1998

The relationship between summer hypoxia in bottom water layer and benthic community structure was discussed at forty sampling stations in semi-enclosed Youngsan River estuarine bay, Korea. The oxygen deficient layer less than $2.0 mg/\ell$ was widely developed in the inner estuarine stations in summer due to the summer stratification. A total of 141 species was occurred, with a mean density of $1,923 ind./m^2$ and biomass of $79.44\;g/m^2$ in summer season. The species number was significantly increased with the increment of the bottom dissolved oxygen, whereas density and biomass were partially correlated within the low oxygen level of $2.0\;mg/\ell$. These results imply that benthic community structures are affected by bottom oxygen depletion in summer. Cluster analysis showed that the benthic community could be classified into three station groups. These station groups from the species composition coincided with the groups based on the environmental factors. This fact suggests that the overall spatial distribution of macrozoobenthos in Youngsan River estuarine bay in summer should be controlled by the summer hypoxia and clay content of the area. Group-I was located the innermost estunrine bay from Mokpo Harbour to near the dike, where summer hypoxia was developed and one bivalve Theora fragilis, two polychaetes, Tharyx sp. and Lumbrineris longifolia were dominated. Group-II, the central transitory area of the estuarine bay between two another stational groups, where two bivalves Theora fragilis, Raetellops pulchella and a polychaete Tharyx sp. predominated with relatively low density compared to that of Group-I. Group-III, the mouth part of the estunrine bay exposed to the open sea, where a polychaetes Poecilochaetus johnsoni and a bivalve Yoldia Johanni predominated.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.3
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• pp.320-332
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• 1999

Investigations were made on the community structure of macrobenthos in the subtidal soft bottom around semi-enclosed Youngsan River estuarine bay, southwest coast of Korea during the period from April 1995 to February 1996. Three macrobenthos samples were collected at 40 stations using a van Veen grab(0.1 m^2) during the study period. A total of 206 species of macrobenthos was identified. Their mean density and biomass (wet-weight, wwt) were $1,137 ind./m^2$ and $65.28 gwwt/m^2$, respectively. Of these, there were 74 species of polychaetes ($36\%$), 60 molluscs ($39\%$), 51 crustaceans ($25\%$) and 21 miscellaneous taxa. Molluscs were represented as a density- and biomass-dominant faunal group with a mean density of $601 ind./m^2$($53\%$ of the total benthic animals) and biomass of $25.37 gwwt/m^2$($39\%$ of total biomass): It was followed by polychaetes with $405 ind./m^2$($40\%$ of the total density). Total number of species and diversity were Bow in the inner estuarine bay containing high mud content and organic matter, whereas they were high in the outer stations containing low mud content and organic matter. Major dominant species were one biralve, Theora fragilis and three Polychaetes, Tharyx sp., Poeciloceatus johnonni and Lumbrineris lontifolia whose mean densities were $490ind./m^2$, $96ind./m^2$, $74ind./m^2$and $52 ind./m^2$, respectively. Cluster analysis indicated that the study area could be divided into four station groups: two innermost station groups, a central bay and an outer station group. The species diversity increased from the inner station group toward the outer groups. These results were discussed in terms of both the environmental factors and distribution of benthic community.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.2
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• pp.169-176
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• 2000

This study was carried out to clarify the spatial and temporal patterns of macrobenthic assemblages on the subtidal area around Mokpo, southwest of Korea. A total of 238 species and 663 ind./$m^{2}$ were collected. Polychaetes were the most abundant faunal group that comprised 88 species and had a mean density of 389 ind./$m^{2}$. In the semi-enclosed Youngsan River estuarine bay and neighbouring Mokpo Port area were composed of fine sediments with high organic content, and revealed large seasonal variations in the salinity of surface water and bottom dissolved oxygen in contrast to little seasonal changes in those parameters in the outer area. The study area was classified into four station groups by the cluster analysis; the harbor area, the offshore area, and the inner and outer estuarine bay. Two estuarine bay areas showed different species composition; the dominant species of inner bay were Tharyx sp., Poecilochaetus johnsoni, Heteromastus filiformis and other opportunistic species whereas those in the outer bay were Ruditapes philippinarum, Corophium sinense. From the environmental data and species composition of benthic community, the inner bay was characterized to have unstable benthic faunal assemblages, especially under the seasonal disturbance and receiving large amount of organic matter input and intermittant discharge of fresh water. The coastal developments around Mokpo city also seem to have stressed the subtidal communities spatio-temporally.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.4
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• pp.254-267
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• 2011

In order to assess structure changes of marine benthic communities in the Youngsan River Estuarine Bay for this 10-year period, we sampled macrobenthos in 2006 using the van Veen grab at the same 40 stations where a previous benthic community survey was conducted in 1995. The number of species and mean density of macrobenthos in 2006 decreased significantly than those of 1995. There were no significant differences in both the number and the density of polychaetous species between the two sampling periods, while both number and den-sity of molluscan species decreased significantly. Although the first two density-dominant species, semelid bivalve Theora fragilis and polychaete Tharyx sp. occurred as most dominant species, but the density of T. fragilis decreased significantly in many stations between 1995 and 2006. However, polychaete Tharyx sp. showed increment in density and percentage composition within community. The area dominated by T. fragilis was replaced by Tharyx sp.. Also, polychaete Poecilochaetus johnsoni and bivalve Raetellops pulchella which were pre-dominant in 1995 decreased significantly by 2006. Bivalve Yoldia johanni decreased its density and reduced its distribution area by 2006. Species diversity and rarefaction curves also revealed that overall species richness decreased. These results confirmed that the dominant species and species diversity of macrobenthic communities in the area should be changed due to anthropogenic stresses during 10 years.