초록 ▼

경상남도 고성군에 위치한 4개의 소하천(고성천, 배둔천, 마암천, 구만천)에서 하구둑이 생태계에 미치는 영향을 조사하였다. 폐쇄형(둑으로 막힌)과 자연형(둑이 없는) 하구에서 하상구배, 염분구조, 퇴적물특성 등을 파악하고, 이들 자료를 기초로 7개의 생태구역을 구분하였다. 구분된 각 생태구역에서 대형일차생산자와 소비자의 우점용, 생체량, 서식 면적 등 생태구조 지표와 자정능력, 오염물질분배, 제거 등의 생태 기능 지표의 차이를 알아보았다. 더불어 두 하구의 수산생태자원 기능 차이도 파악 하였다. 하구둑은 수층 유동 억제, 염분구조

경상남도 고성군에 위치한 4개의 소하천(고성천, 배둔천, 마암천, 구만천)에서 하구둑이 생태계에 미치는 영향을 조사하였다. 폐쇄형(둑으로 막힌)과 자연형(둑이 없는) 하구에서 하상구배, 염분구조, 퇴적물특성 등을 파악하고, 이들 자료를 기초로 7개의 생태구역을 구분하였다. 구분된 각 생태구역에서 대형일차생산자와 소비자의 우점용, 생체량, 서식 면적 등 생태구조 지표와 자정능력, 오염물질분배, 제거 등의 생태 기능 지표의 차이를 알아보았다. 더불어 두 하구의 수산생태자원 기능 차이도 파악 하였다. 하구둑은 수층 유동 억제, 염분구조 변화 등으로 생태계에 큰 영향을 주었고, 특히 오염물질의 배출을 저해하여 축적 및 농축을 야기하였다. 폐쇄형 하구에서는 기수 어종이 나타나지 않았다. 이들 자료는 해수유통이나 하구둑 제거 효과를 정량적으로 예측하는 도구가 될 것이다.

Abstract ▼

IV. Results
1. Characteristics of environment and Classification of ecological districts
가. Characteristics of sediment
o Surface sediment in natural estuary consisted of coarse grain sediment but closed estuary consisted of fine grain sediment. In cold season when rainfall is small both ty

IV. Results
1. Characteristics of environment and Classification of ecological districts
가. Characteristics of sediment
o Surface sediment in natural estuary consisted of coarse grain sediment but closed estuary consisted of fine grain sediment. In cold season when rainfall is small both type estuary consisted of fine grain sediment in winter.
o Fine grain sediment in rainy season has sustained at closed type but natural type where was provided coarse sediment consisted with coarse sediment.
나. Classification of ecological districts
o The estuarine habitats were classified into different ecological districts so as to the switch from one district to another district could be related to the environmental change due to the perturbations. Total 16 ecological districts was defined according to the presence of barrage, salinity and vegetation characteristics. The defined ecological districts were appHed to small estuaries in Goseong bay, south sea of Korea (Baedum, Guman, Maam, Goseong) to distinguish different regions which might have characteristics bottom topography, inclinations of river bottom, sediment characteristics, salinity structure and area of vegetation.
o Total 7 out of 16 ecological district was identified in this region;NFB(natural, fresh, bare),NHB (natural, high salinity, bare), NLV (natural, low salinity, vegetated) in natural (without barrage) estuaries and CFB(closed, fresh, bare), CFV(closed, fresh vegetated), CLV (closed, low salinity, vegetated), CRH (closed, high salinity, bare) in closed (with barrage) estuary.
A comparison of environmental factors and biota between CHB and CLV demonstrated the effect of barrage on estuarine ecosystem. The height and sediment characteristics of CHB and CLV were similar but the average salinity was lower in CLV than in GHB due to the barrage, which produced favorable condition for the Phragmites australis in CLV.
2. Structure of temperature and salinity and modelling
가. Structure of temperature and salinity
o The range of salt water intrusion was related considerably freshwater discharge and the tide depending on the season in natural estuary. Salt water intruded in high tide at lower altitudes than App.HHW(approximately highest high water), however, in summer it was slightly restricted by fresh-water discharge. Salt water intrusion in closed estuary was not related with altitude, it appear up to riverbed surveying sideline GO12.If Geo-san barrage was not exist, salt water might invade up to CO30 and wide areas of inner part of it might transfer to intertidal.
o Vertical salinity structure was consistent over 30 psu in Co-seong bay station 1~3 in dry season, whereas station 2~3 in rainy season was constant mean 20 on entire depth due to complete mixing of freshwater and seawateJ. Station 1 in rainy season showed about 15 psu difference between the surface and bottom layer. Freshwater layer transferring from each stream suggested to be most of surface of bay.
o The results of tidal harmonic analysis showed mean sea level(MSL) of T1 in rainy season with high outflow was 162cm, MSL in dry season with low outflow was 142cm. rainy and dry season showed about 20cm difference.
MSL of T2 in dry season was about 152cm, it was 10cm higher than T1 where located in the entrances to the bay, It seems to generate accumulation of innermost according to characteristic of one-Closed bay. Freshwater and seawater on opposite sides of the barrage happened to periodic form freshwater and seawater exchanage due to each water level and tide level difference.
나. Modelling
o To investigate the effect of tidal flow by Geo-san barrage, we performed numerical modelling using detail bottom topography observation and results of tidal survey. FVCOM model exploited the Finite-Volume Method and irregular grid.
o Result of current modeling development showed Geo-san barrage restricted the circulation of seawater and freshwater by blocking the connection with Go-seong stream and open sea. Especially, barrage might been factors of decline in the quality of water by trapping the water inside the barrage(CLV).
3. Structure and function of ecological constituent
가. Primary producer : Phragmites australis
o We found out survival condition of Phragmites australis from continuous measurement or water column and porewater salinity over the 17 days for the first time. Porewater in NLV area showed high salinity (8.48~28.74‰) due to the effects of tidal flow. Although high salinity in NLV area can inhibit the growth of P.australis, in the result of long term porewater salinity measurement, it comes out that P.australis can occur through being intermittently influenced by the fresh water during neap tide.
o Coverage area of P.australis Stands in the Gosung River Estuary (CFV+CLV) was about 40 times wider than Guman River Estuary(NLV) as well as Vertical height range of P.australis Stands was larger than Guman River Estuary. P.australis Stands in Gosung mostly occurred below 100cm more than Guman P.australis stands. These differences of distribution patterns indicate that decrease of salinity and flooding duration by dyke construction of Goseong river estuary (CLV) provide favorable condition for P.australis growth.
나. Consumer 1: Macrobenthos
o Macrobenthos were sampled at 29 stations in ecological districts in August, November in 2011 and February, June in 2012.
o The Macrobenthos was sampled at 29 stations showed 67-76 species, it was estimated that lower than in other subtidal tlat (300-400 species in Saemangeum intertidal flat; An et al., 2006). To consider two points that include tidal flat and relatively narrow study areas, it was difficult to estimate this result effect by Pollution.
o The number of species, density, biomass and species diversity were low in freshwater-dominated areas.
o The result of MDS(Non-metric Multi-Dimensional Scaling) analysis also shows that stations were divided by level of freshwater effect. Especially, stations in subtidal region were divided into natural and closed estuary when the freshwater highly discharged. However, the division was uncertain when the freshwater scarcely discharged.
o In two seasonal survey, when the freshwater discharged, number of species, biomass and species diversity were higher in natural than in closed estuary.
Especially, in C1(CLV), number of species was very lower than in other ecological districts, and although it were not appear in November 2011, benthos was appeared agaln in february 2012. The reason of reappearance in February 2012 was considered that benthic environment stabilized by low freshwater discharge and depletion of dissolved oxygen was not developed by law temperature in winter.
다. Consumer 2: Fish
o In natural estuary, primary freshwater fish, peripheral freshwater fish and brackishwater fish were collected. In NLV and NHB, the dominant species were Acentrogobius pflaumi, Gymnogobius castaneus and Favonigobius gymnauchen, which are commonly appeared in estuarine or coastal. In Ma-am stream, Gasterosteus aculeatus(anadromous fish) was collected.
o Primary freshwater fishes were only collected in CFB. Although there is no barrage in Baedun stream, Primary freshwater fishes were only collected like Gosung stream in natural estuary where freshwater discharge dominated, because the intrusion of sea water is limited by beam.
o In total of collected 28 species, 11 species that include Gymnogobius castaneus and Taridentiger brevispinis appeared only in Gu-man, Ma-am stream belong to natural estuary. These species may disappear if barrage is constructed.
o In CLV of closed estuary, primary freshwater fish or peripheral freshwater fish such as Zacco platypus, Tridentiger brevispinis, Mugil cephalus, Carassius auratus were collected. we suggest that result was caused by effects of the resticted water flow abd desalination by barrage construction.
라. Characteristics of purification in ecological district
o Mean salinity was simmilar between CLV and NLV, however, denitrification rate was higher in CLV. Because nutrient is accumulated inside the barrage due to restriction of normal tidal flushing, it is estimated that CLV has higher denitrification rate than NLV. Difference between light and dark treatment of sediment oxygen demand(SOD) showed a tendency to increase from summer(Aug) to winter(Feb).
o Sediment oxygen demand (SOD) showed obvious seasonal variation, SOD was highest in August and lowest in February. highest SOD in August is caused by vigorous respiration according to increase of temperature. On the contrary to this, lowest SOD in February is considered the effect by decrease of temperature. Denitrification rate showed obvious seasonal variation, denitrification bacteria, and lowest in February.
o In comparison between 2010 and 2011, denitrification rate on light treatment was much higher 2011 than 2010. This result was probably caused by facilitation of nitrification-denitrification coupling on the evidence of much lower ammonium efflux in 2011 compared with 2010.
4. Characteristics of Pollution in ecological district
가. Water column and sediments eutrophication
(1) Water column nutrients
o There is clear difference between natural and closed estuary on the characteristic of nutrient distribution. Nitrate, ammonium and phosphate were high in closed estuary. It is considered that nutrients are accumulated inside the barrage due to restriction of normal tidal flushing in closed stream. In case of ammonium associated with eutrophication, ammonium concentrations of CFB, CFV,CLV were 173.61 μM, 166.65 μM, 131.04 μM respectively, and closed stream showed very high ammonium concentration.
o Nitrate concentration was highest in highest then decrease toward spring and lowest in summer. Seasonal variation of ammonium and phosphate is unclear.
o Spatially, nitrate was highest in the upper region of stream and tends to decrease toward the sea. Upper region of stream is regarded as major source of nitrate. Ammonium and phosphate is high in the middle region of natural stream, however, ammonium and phosphate is high in the middle region of closed stream.
o After rain compared with before rain, nitrate concentration tended to increase in most streams. This trend is considered that porewater nitrate in surrounding inland region flow into the stream when the rain came down.
(2) Water content, Ignition Loss, Carbon content
o Water content and Ignition Loss were higher in closed stream than natural stream in all season. Maxunum value of water contents and Ignition Loss was 67.59% in CHB-Sub and 14.06% in CFB, respectively. High Water content and Ignition Loss in closed stream seems to be affected by fine-grained sediments in closed stream.
o Water content was high in winter, and Ignition Loss was high in summer.
(3) Biogenic Silica
o Relatively fine-grained and high organic content sediments was deposited in CLV where blocked by barragem and BSi content was low.
o CHB-int, where connected to the open sea, consisted of relatively course grain sediment, low organic matter and high BSI content.
o In CLV, Ignition Loss and coarse sediment contents in core sediment were changed suddenly in 80 to 60 cm layer, and were constant above the 55cm layeJ. It was considered that sudden change in environment caused by such as barrage construction during this time. BSi contents, However, There were no observable change.
나. Heavy metal
o Most heavy metal (Al, .Fe, Pb, Zn, Mn, V, Cu) had higher concentration in closed ecological districts than natural ecological districts.
o The concentration of Zn and Cu was exceed the ERL(Effects Range-Low) value in closed ecological districts. Zn and V had highest concentration at CFB and CFV, respectively in every season.
o The concentration of Pb, Cd, Ni exceeded the ERL value at all investigated stations, especially, the concentration of Pb exceeded the ERL value in NLV, CFB, CFV and CLV. The concentration of Cd was similar to the value of ERM in CFV on November 2011, Because surface sediment consist of fine sediment in closed estuary, heavy metal concentration is high. The reason of fine sediment in closed estuary is limited water movement, as a result accumulation of fine sediment.
다. organic pollutants
o We measured PBDEs at 11 stations in subtidal zone, 4 stations in Maam stream, 4 stations in Guman stream.
- Concentration of total 11 kinds of PBDEs(∑PBDF11) had a range of 0.06~3.53 ng/g dry wt. (average: 1.49 ng/g dry wt.) in stream sediments. Concentration of total 11 kinds of PBDEs(∑PBDE11) had a range of 0.03~1.78 ng/g(average:0.64 ng/ g) in subtidal zone sediments. Stream sediments have higher concentration than subtidal zone. (concentration decreased from upper stream to sea)
o Spatially, Guman stream, densely populated area, had higher concentration than other stream where has cultivated land.
o There were no differences between catural and closed estuaries, therefore we did not observe tendency that PBDEs accumulate inside the barrage (closed estuary)