• Journal of Korean Society on Water Environment
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• v.22 no.2
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• pp.342-348
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• 2006

Changes in water quality and algal growth according to the differences in the inflow volume were investigated in the Daecheong Lake from 1998 to 2001. Until year 2000, inflow volume considerably depended on the rainfall throughout the basin. However, the correlation was low since 2001 when water storage in the upstream Yongdam Lake was started. According to inflow volume-TP relationship analyses, significant correlation was found at up- and middle-stream sites, excluding down-stream site of the Daechong Lake. For chlorophyll-a, correlation was found with flow volume at all sites except for Choo-So. In a dry year, although nutrients loads were relatively lower than those in rainy years, there were higher concentrations of chlorophyll-a and massive bloom of Microcystis. Limiting factors for algal growth seems to be not the volume of nutrients load but retention time and physical disturbance of the water body influenced by inflow volume. Thus, in the Daecheong lake, it would be more important to focus on the management of eutrophication in dry years than in rainy ones.

• Journal of Korean Society on Water Environment
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• v.23 no.6
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• pp.863-871
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• 2007

Spectroscopic characteristics of river water from four major watersheds in the Ulsan area were measured to examine their potential for estimating water quality parameters. The total 176 river samples were collected from 44 sites of small streams within the watersheds during the year 2006. Spectroscopic characteristics investigated included protein-like fluorescence (FLF) intensity, fulvic-like fluorescence (FLF) intensity, terrestrial humic-like fluorescence (TLF) intensity, UV absorbance at 254 nm, and UV absorbance difference at 220 nm and 254 nm. Protein-like fluorescence intensity showed linear relationships with biochemical oxygen demand (BOD), chemical oxygen demand (COD), total phosphorous (TP) concentrations of the samples with the correlation of 0.784, 0.779, and 0.733, respectively. Due to the UV absorption characteristics of nitrate at 220 nm, UV absorbance difference at 220 nm and 254 nm was selected to represent total nitrogen (TN) concentration. Exclusion of some samples with PLF intensity higher than 5.0 improved the correlation between the UV absorbance difference and TN as demonstrated by the increase of the correlation coefficient from 0.392 to 0.784. Instead, for the samples with PLF intensity lower than 5.0, the highest correlation of TN was achieved with UV absorbance at 254 nm. The results suggest that PLF intensity could be used as the estimation index for BOD, COD, and TP concentration of river water, and as the primary screening index for the prediction of TN using UV absorbance difference. Some BOD-based water quality levels among the river water were statistically discriminated by the PLF intensity. Low p-values were obtained from the t-tests on the samples with the first level and the second level (p=0.0003) and the samples with the second and the third levels (p=0.0413). Our combined results demonstrated that the selected spectroscopic characteristics of river water could be utilized as a tool for on-site real-time monitoring and/or the primary estimation of water quality.

• Journal of Microbiology and Biotechnology
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• v.30 no.9
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• pp.1355-1366
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• 2020

Sediment bacterial communities are critical to the biogeochemical cycle in river ecosystems, but our understanding of the relationship between sediment bacterial communities and their specific input streams in rivers remains insufficient. In this study, we analyzed the sediment bacterial community structure in a local river receiving discharge of urban domestic sewage by applying Illumina MiSeq high-throughput sequencing. The results showed that the bacterial communities of sediments samples of different pollution types had similar dominant phyla, mainly Proteobacteria, Actinobacteria, Chloroflexi and Firmicutes, but their relative abundances were different. Moreover, there were great differences at the genus level. For example, the genus Bacillus showed statistically significant differences in the hotel site. The clustering of bacterial communities at various sites and the dominant families (i.e., Nocardioidaceae, and Sphingomonadaceae) observed in the residential quarter differed from other sites. This result suggested that environmentally induced species sorting greatly influenced the sediment bacterial community composition. The bacterial co-occurrence patterns showed that the river bacteria had a nonrandom modular structure. Microbial taxonomy from the same module had strong ecological links (such as the nitrogenium cycle and degradation of organic pollutants). Additionally, PICRUSt metabolic inference analysis showed the most important function of river bacterial communities under the influence of different types of domestic sewage was metabolism (e.g., genes related to xenobiotic degradation predominated in residential quarter samples). In general, our results emphasize that the adaptive changes and interactions in the bacterial community structure of river sediment represent responses to different exogenous pollution sources.

• Journal of Korean Society on Water Environment
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• v.39 no.2
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• pp.131-141
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• 2023

In this study, the relationship between organic carbon distribution characteristics and decomposition rate classified according to the particle size and biological degradation characteristics in water was investigated for the Nam river and Geumho river. The average concentrations of TOC in the Nam river and Geumho river were 2.7±1.2 mg/L and 5.0±1.2 mg/L, respectively, but the composition ratios for each type of organic carbon were similar. An average value of 80.9% of TOC was present as DOC and 72.8% of DOC consisted of Refractory-DOC (RDOC). In addition, the change in the RDOC composition ratio according to temporal and spatial distribution was the smallest. There was no difference in the decomposition rate of organic carbon except for TOC by the site (p≥0.108, one-way ANOVA), and the decomposition rates of Labile-POC (LPOC) and LDOC were similar at 0.139±0.102 and 0.137±0.149 day^-1, respectively (p=0.110, paired t-test). The coefficient of variation (CV) of the decomposition rate of DOC (average 8.1%), which had the smallest composition ratio of organic carbon, was 1.1, showing the largest temporal variation. The TOC, POC, and DOC decomposition rates showed a significant correlation with the ratio of the initial concentration to the concentration after 25 days of decomposition (OC₂₅/OC₀) (r²=0.89~0.94, p<0.001), and the decomposition rates of LPOC and LDOC were significantly correlated with the ratio of the initial concentration to the concentration after 5 days of decomposition (LOC₅/LOC₀) (r²=0.67~0.75). This suggests that it is possible to estimate the decomposition rate through the concentration of each type of organic carbon.

• Korean Journal of Environmental Biology
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• v.24 no.2 s.62
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• pp.172-178
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• 2006

The dynamics of bacterial populations belonging to $\alpha\;\beta\;\gamma-subclass$ proteobacteria, Cytophaga-Flavobacterium (CF) group and sulfate reducing bacteria (SRB) in water column of the middle reaches of Nakdong River depending on sediment harvesting were analyzed by fluorescent in situ hybridization (FISH) at sediment harvesting site (near the Seongju bridge) and non-sediment harvesting site (near the Gumi bridge). In addition, some physico-chemical parameters such as temperature, pH, $chi-\alpha$ and electrical conductivity were measured. Regarding the number of total cell counts, cells stained by DAPI, there were no substantial quantitative differences between both sites, but those fluctuation at sediment Harvesting site was greater. And also the ratios of CFgroup and SRB to total cell counts tend to increase at sediment harvesting site with higher $chl-\alpha$, maybe due to the resuspension of sediment into water column. But the total proportion of all determined bacterial populations to total cell counts were greater at non-sediment harvesting site, compared with those at sediment harvesting site. Since the detectibility of bacteria by FISH depends on their metabolic activity, those lower proportion at the sediment harvesting site implies that sediment harvesting may lead to malfunction of those bacteria respect to nutrient recycling and subsequently negative effects on microbial food web.

• Journal of Ecology and Environment
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• v.47 no.4
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• pp.228-240
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• 2023

Growing complexity in ecosystem structure and functions, under impacts of climate and land-use changes, requires interdisciplinary understandings of processes and the whole-system, and accurate estimates of the changing functions. In the last three decades, observation networks for biodiversity, ecosystems, and ecosystem functions under climate change, have been developed by interested scientists, research institutions and universities. In this paper we will review (1) the development and on-going activities of those observation networks, (2) some outcomes from forest carbon cycle studies at our super-site "Takayama site" in Japan, and (3) a few ideas how we connect in-situ and satellite observations as well as fill observation gaps in the Asia-Oceania region. There have been many intensive research and networking efforts to promote investigations for ecosystem change and functions (e.g., Long-Term Ecological Research Network), measurements of greenhouse gas, heat, and water fluxes (flux network), and biodiversity from genetic to ecosystem level (Biodiversity Observation Network). Combining those in-situ field research data with modeling analysis and satellite remote sensing allows the research communities to up-scale spatially from local to global, and temporally from the past to future. These observation networks oftern use different methodologies and target different scientific disciplines. However growing needs for comprehensive observations to understand the response of biodiversity and ecosystem functions to climate and societal changes at local, national, regional, and global scales are providing opportunities and expectations to network these networks. Among the challenges to produce and share integrated knowledge on climate, ecosystem functions and biodiversity, filling scale-gaps in space and time among the phenomena is crucial. To showcase such efforts, interdisciplinary research at 'Takayama super-site' was reviewed by focusing on studies on forest carbon cycle and phenology. A key approach to respond to multidisciplinary questions is to integrate in-situ field research, ecosystem modeling, and satellite remote sensing by developing cross-scale methodologies at long-term observation field sites called "super-sites". The research approach at 'Takayama site' in Japan showcases this response to the needs of multidisciplinary questions and further development of terrestrial ecosystem research to address environmental change issues from local to national, regional and global scales.

• Journal of Korean Society on Water Environment
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• v.35 no.6
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• pp.557-566
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• 2019

Paldang is a river reservoir in the Midwest of Korea, which is a drinking water source for the metropolitan area. Since the Paldang Reservoir is shallow, and has a short hydraulic residence time, its water quality is directly impacted by two incoming rivers, the north Han River (NHR) and the south Han River (SHR). The NHR has different seasonal patterns of water temperature from the SHR because the NHR is greatly impacted by the discharge water from upstream dams. The electrical conductivity (EC) and other material concentrations of the SHR are usually higher than those of the NHR because its basin is limestone-based. The difference in water temperature in the two rivers causes density flow, and the distribution of the EC within the reservoir can be an indicator for monitoring density flow. From the vertical gradient of the EC at the dam site, from spring to fall, it was confirmed that the SHR flowed into the upper layer, and the NHR flowed into the lower layer, and vice versa at other times. The relative difference (RD) of the EC between the upper layer and the lower layer at the dam site was used as an indicator for density flow. The RD of the EC showed a very significant correlation with the RD of total organic carbon (r = 0.70, p < 0.001) and the RD of total nitrogen (r = 0.58, p < 0.01). This relationship is based on the assumption that the difference in electrical conductivity and water quality between the SHR and the NHR is constant. However, in many cases this assumption is inconsistent. Thus, further study is needed on more suitable indicators to evaluate the impact of density flow on water quality.

• Korean Journal of Environmental Biology
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• v.28 no.2
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• pp.56-63
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• 2010

In order to clarify the ecological properties of phytoplankton community, the distribution of phytoplankton and the relation of water temperature and size-fractionation measurements were studied from November 2004 to August 2005 in Youngsan River, Korea. A total of 265 phytoplankton species was identified. It consists of 48 genera and 123 species (46%) of Chlorophyceae, 27 genera and 89 species (34%) of Bacillariophyceae, 12 genera and 25 species (9%) of Cyanophyceae, respectively. From size fractionation analysis, nanophytoplankton (2~20 ${\mu}m$) dominated from early spring to early summer, and microphytoplankton (20~200 ${\mu}m$) from summer to winter. The relationship between chl-a and nanophytoplankton showed high correlation coefficient value ($r^2$=0.93) from Najudaegyo site. The correlation coefficient values between water temperature and nanophytoplankton were low except Dongkangdaegyo site which showed high value ($r^2$=0.73).

• Water for future
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• v.15 no.3
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• pp.23-36
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• 1982

The stochastic variations and structures of time series data on water quality were examined by employing the techniques of autocorrelation function, variance spectrum, Fourier series, autoregressive model and ARIMA model. These time series included hourly and daily observation on DO, turbidity, conductivity pH and water temperature. The measurement was made by automatic recording instrument at Noryangjin and Dook-do located in the downstream part of Han River during 1975 and 1976. Hourly water quality time series varied with the dominant 24-hour periodicity, and the 12-hour periodicity was also observed. An important factor affecting 24-hour periodic variation of DO is believed to be photosynthesis by algae. These phenomena might be attributable to periodic discharges of municipal sewage. Noryangjin site showed the more distinct 12-hour periodicity than Dook-do site did, and tidal effect might be responsible for the difference. The water quality, as measured by DO and turbidity, was better in the afternoon compared with the quality in the morning. This change can be explained by the periodic variation of DO, temperature and the amount of municipal wewage discharge. It was also observed that the water temperature at Noryangjin was higher than the temperature at Dook-do. This difference might have been caused by the pollutants that were added to the section between two sites. The correlation coefficients between some of the variables were fairly high. For example, the coefficient was -0.88 between DO and water temperature, 0.75 between turbidity and river flow, and 0.957 between water temperature and air temperature. The lag time of heat transfer from the air to the water was estimated as 24 days. The first order auto-regressive model was appropriate for explaning standardized hourly DO time series. The ARIMA model of (1, 0, 0) type provided relatively satisfactory results for daily DO time series after the removal of significant harmonic value.

• Journal of Korea Water Resources Association
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• v.42 no.6
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• pp.481-491
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• 2009

In this study, a comprehensive field monitoring was conducted to understand habitat conditions of fish species in the upper Geum river. Based on the monitoring data, riverine health conditions such as composition ratio of fish species, richness and dominance indexes, bio-diversity (dominance index, diversity, evenness and richness), and index of biological integrity were assessed, and optimal ecological flowrates were estimated using the habitat suitability indexes established for three fish species Coreoleuciscus splendidus, Zacco platypus and Pseudopungtungia nigra selected as icon species using the physical habitat simulation system (PHABSIM). The total number of species sampled was 20 species, and two sensitive species of C. splendidus (22.4%) and Z. platypus (22.0%) dominated the fish community. The estimated IBI values ranged from 34 to 42 with average being 38 out of 50, rendering the site ecologically fair to good health conditions. An optimal ecological flowrate of 9.0 cms was recommended for the representative fish species at the site.