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This study investigated the effects of sediment removal on water quality and phytoplankton development by setting up mesocosms at Uiam Lake, South Korea, and analyzing the environmental parameters and phytoplankton communities between June and October 2015. The comparison between testbed without sediment removal (TB-1) and testbed after sediment removal (TB-2) gave similar values for water temperature, pH, dissolved oxygen (DO), and electrical conductivity. Nevertheless, the average electrical conductivities of the two testbeds were 139 µS/cm and 135 µS/cm, which were lower than the value obtained from the external control point (TB-con; 154 µS/cm). The small difference in total phosphorus (TP) and total nitrogen (TN) concentrations between the two testbeds implied that sediment removal did not greatly reduce nutrients; however, the phytoplankton cell count had decreased by approximately 37% in TB-2 (average 1,663 cells/mL) compared to TB-1 (average 2,625 cells/mL). Compared to TB-con, the phosphorus and nitrogen concentrations of the two testbeds had decreased by 39% and 30%, respectively, whereas the phytoplankton abundance had decreased by up to 73%, perhaps because of the blocked inflow of nutrients and the stabilized body of water caused by the installation of the mesocosm. The concentration of geosmin was lower in testbeds than in the external point, because installation of the structures had reduced the cyanobacteria biomass.
This study was carried out in the Bukhan River in the summer of 2014 and 2015, to identify the relationship between geosmin and the morphological changes in Anabaena. Identification of Anabaena was conducted using morphological and molecular analyses. Anabaena in this study was similar to Anabaena circinalis, A. crass, and A. spiroides with regard to regular coils, vegetative cell, akinete shape, and size, hoever, it was distinguishabl from A. crass and A. spiroides because of its larger trichome coil size. Additionally, the sequences of phycocyanin (PC) gene from Anabaena showed a 99% genetic similarity with A. circinalis NIES-1647 strain. The coil diameter of trichome ranged from 106 to 899 μm, and the diameter and abundance showed an insignificant positive correlation (r=0.544, p<0.05). The result of relationship between the coil diameter and the cell number per 360-degree rotation was kept at 33.8±5.2 cells per 100 μm diameter despite variable diameter. The average geosmin concentrations in 2014 and 2015 were investigated to be 99 ng/L and 35 ng/L, respectively. A. circinalis cell density contributed considerably to the change in geosmin and was positively correlated with geosmin concentration (2014; r=0.599, p<0.01, 2015; r=0.559, p<0.01). Our results suggest that geosmin and coil diameter could be estimated with the help of cell density.
The objective of this study was to investigate the relationship between the biomass of cyanobacteria and the concentration of 2-methylisoborneol (2-MIB) in the lower Gongji stream. The investigation was done using a field study that was conducted from 2015 to 2017. The 2-MIB concentration in the lower Gongji stream ranged from 0 to 153 ng/L, while the upper stream had 0 2-MIB concentration. 3 genera (Oscillatoria, Phormidium, Pseudanabaena) of cyanobacteria were detected in the lower Gongji stream with 2-MIB concentration. Among these 3 genera, an increase in Phormidium, Pseudanabaena biomass was associated with an increase in 2-MIB concentration. Accordingly, Phormidium, Pseudanabaena were regarded as the biological source of 2-MIB in that area. In October 2017, although planktonic cyanobacteria occurred less frequently, many benthic cyanobacteria mats were observed on the surface of the water body. Therefore, the high 2-MIB concentration, which exceeded 110 ng/L, can likely be attributed to the benthic cyanobacteria. In a laboratory experiment, individual Oscillatoria filaments were aggregated to form a colony with a higher density. This colony tended to float on the water surface. Cyanobacteria mats after floating aggregated mats were distributed in a net shape on the bottom.
An experiment to study the effect of temperature, light, and dredging on release of nutrients downstream from Gongjicheon in the Uiam reservoir was carried out in the laboratory using sediments from different depths. At various water temperatures, dissolved total nitrogen was not released, but the average nutrient flux of dissolved total phosphorus was increased (0.034 at 15°C, 0.005 at 20°C, 0.154 at 25°C, 0.592 mg/m2/d at 30°C). Dissolved total phosphorous was released in controlled darkness. In contrast, in controlled light, the concentrations of dissolved total phosphorous and dissolved total nitrogen in the overlying water steadily decreased during the study period (70 d), because they were continuously consumed by the growth of photosynthetic algae. However, there was no significant relationship between water nutrient concentration, nutrient release, and the depth of the sediment. We concluded that the dredging of sediment would not affect the nutrient release rate of the sediment, because there were no significant differences in the nutrient concentrations released from the sediment. When the sediment was removed from the surface to 20 cm in depth , the nutrients were not transferred to the water body, implying that the sediment removal had little effect on secondary pollution.
윤석제 ( Seok Jea Youn ),김헌년 ( Hun Nyun Kim ),임종권 ( Jong Kwon Im ),김용진 ( Yong-jin Kim ),백준수 ( Jun-soo Baek ),이수웅 ( Su-woong Lee ),이은정 ( Eun Jeong Lee ),유순주 ( Soon Ju Yu ) 한국환경과학회 2017 한국환경과학회지 Vol.26 No.8
Phytoplankton populations were examined at three sites in Lake Cheongpyeong, South Korea from March 2008 to December 2016, including measurement of phytoplankton communities and their dominant species, abundance and environmental factors. The annual average ranges of water temperature, dissolved oxygen and conductivity were 15.2-18.8℃, 10.3-12.2 mg/L, 86-140 μS/cm, respectively, with similar values at all studied sites. The highest phytoplankton cell density was observed in spring and fall, and it subsequently decreased rapidly during heavy rainfall. Diatoms were dominant in spring (mainly Stephanodiscus hantzschii, Asterionella formosa) and fall (mainly Aulacoseira granulata), while greenalgae and cyanobacteria had high appearance in early-summer and summer, respectively, indicating that water temperature is the most important factor influencing their growth. Stephanodiscus hantzschii and Asterionella formosa frequently occurred at low water temperature (4.5-15.0℃ and 5.4-21.6℃, respectively) while Aulacoseira granulata and Anabaena spp. were favored by high water temperature (8.6-28.4 and 14.9-26.2℃, respectively) and phosphorus. Additionally, Fragilaria crotonensis occurred at low nutrient conditions. Rhodomonas spp. frequently appeared year-round.
춘천호의 2014~2015년 평균 강수량은 800 mm 이하였으나, 2016~2017년에는 1,200 mm 이상으로 나타났다. 수온의 범위는 17.0~21.1°C, COD는 연평균 농도가 2.7~4.2 mg L-1였고, 2015년에 가장 높았으며 적은 강수량으로 체류시간이 증가하여 다른 해에 비해 높은 농도가 나타난 것으로 판단된다. TP와 TN의 연평균 농도는 각각 0.012~0.019 mg L-1와 1.272~1.922 mg L-1로 나타났으며 TN은 2014년부터 지속된 갈수현상으로 2015년이 다른 년도에 비해 높았다. 식물플랑크톤의 종 다양성 지수는 2014~2015년에 2.0 이하로 다른 년도에 비해 낮았으며, 강수량과 환경요인과의 상관 분석 결과 수온, TP 및 Chl. a가 높게 나타났다. 식물플랑크톤의 세포수는 CC3 (상류) 지점이 CC1 (하류)과 CC2 (중류) 지점보다 상대적으로 많았으며 그 이유는 갈수현상으로 수체의 안정 및 유기물이 농축되어 남조류를 포함한 식물플랑크톤이 성장하기 유리한 조건이 되었을 것으로 판단된다. 수온에 따른 식물플랑크톤의 분류군별 상관관계 결과 규조류는 음의 상관관계, 녹조류와 남조류는 양의 상관관계를 보였다. 춘천호의 식물플랑크톤은 온대호수의 천이 형태를 보이고 있으나 강우에 따라 식물플랑크톤의 종 다양성 및 발생량과 수질환경요인이 다르게 나타났을 것으로 판단된다. 본 연구는 춘천호의 수질 및 식물플랑크톤의 장기변화를 조사한 최초의 결과이며 향후 추가 연구를 위한 선행자료로 제공하고자 한다. Effects of environmental factors on phytoplankton succession and community structure were studied in Lake Chuncheon located in Bukhan River, South Korea. The data were sampled at three sites such as CC1 (lower side), CC2 (middle side), and CC3 (upper side of Lake Chuncheon) from 2014 to 2017. The annual average precipitation in Lake Chuncheon was 992 mm during the study period (2014~2017), and the annual precipitation was lower than 800 mm in 2014 and 2015. The annual average water temperature, total phosphorus (TP), and total nitrogen (TN) ranged from 17.0 to 21.1°C, 0.012 to 0.019 mg L-1, and 1.272 to 1.922 mg L-1, respectively. The TN concentration was relatively high in 2015 compared with the other study years, as a drought continued from 2014 to 2015. When comparing the correlation between precipitation and environmental factors, water temperature (p<0.01) and TP (p<0.05) showed positive correlations with rainfall. The average numbers of phytoplankton cells by branch were 2,094, 2,182, and 3,108 cells mL-1 in CC1 , CC2, and CC3, respectively. CC3 is considered advantageous for phytoplankton growth, even in small pollution sources due to low water depth. As a result of analyzing the relationship between precipitation and phytoplankton, the correlation between the two was shown to be high for 2016 (p<0.01) and 2017 (p<0.05), which is when precipitation was high. However, the correlation was not clear to 2014 and 2015. The relationship between water temperature and phytoplankton indicated a negative correlation with diatoms (p<0.01), yet positive correlations with green algae (p<0.01) and cyanobacteria (p<0.01). Diatoms increased in spring and autumn, which are characterized by low water temperature, and green algae and cyanobacteria increased in summer, when the water temperature is high. Our findings provide a scientific basis for characteristics of phytoplankton and water quality and management at the Lake Chuncheon.