Decadal trends and predictive insights into aquatic ecosystem health in the Namhan River, South Korea: Longitudinal analysis of hydro-environmental factors and stream health indices (2008-2022).

The main focus of this study is to explore the complex interactions between aquatic ecosystem health (AEH) and time-varying hydro-environmental factors. We measure AEH in the Namhan River of South Korea using stream health index (SHI) scores for the trophic diatom index (TDI), benthic macroinvertebrate index (BMI), and fish assessment index (FAI) for 2008 to 2022. Key hydro-environmental variables associated with AEH, including their time-lagged responses, are identified. Water quality parameters such as chemical oxygen demand (COD) are significantly and negatively correlated with TDI (r=-0.68), BMI (r=-0.87), and FAI (r=-0.70), highlighting the critical role of water quality in the sensitivities of diatoms, macroinvertebrates, and fish health. The apparent response lag of aquatic ecosystems to hydrological parameters, such as a one-year-lagged correlation of BMI with mean flow (r=0.74) and annual flow anomalies (r=0.73), suggests their potential use as predictors in AEH models. A longitudinal analysis of SHIs over a decade showed consistent changes in AEH from upstream to downstream, with notable trends in the deterioration and improvement of SHIs in different areas. The upstream TDI and BMI deteriorated, while the upstream FAI improved. A multiple-linear-regression-based predictive model demonstrated efficacy in predicting AEH under various hydro-environmental conditions, achieving R2 values up to 0.85 for BMI and also has the potential to simulate the impacts of anticipated climatic and hydrological changes.

Development of diagnostic systems for wide range and highly sensitive detection of two waterborne hepatitis viruses from groundwater using the conventional reverse transcription nested PCR assay.

Waterborne epidemics of human hepatitis virus A and E (HAV and HEV) have been reported worldwide. Molecular biology techniques, such as reverse transcription polymerase chain reaction (RT-PCR), have been widely used to detect the two hepatitis viruses. However, comparative studies of various types of samples are needed, and different environmental factors, including the low copy pathogens, presence of PCR inhibitors in the sample, unknown non-specific reaction with template, and sequence diversity leading to new variants in viruses, should be considered. In addition, standard positive material is required to determine the accuracy of the PCR and should be able to distinguish between false and real positives. In this study, we developed RT-PCR primer sets and optimised standard templates for HAV and HEV detection to address the above concerns associated with test sensitivity and possible PCR inhibition. Finally, previously reported diagnostic methods of HAV and HEV were compared and an applicability test using groundwater was performed. The nested RT-PCR developed in this study is expected to contribute to assess water safety by monitoring HAV and HEV in non-disinfected water, like groundwater.

Long-Term Monitoring of Noxious Bacteria for Construction of Assurance Management System of Water Resources in Natural Status of the Republic of Korea.

Climate change is expected to affect not only availability and quality of water, the valuable resource of human life on Earth, but also ultimately public health issue. A six-year monitoring (total 20 times) of Escherichia coli O157, Salmonella enterica, Legionella pneumophila, Shigella sonnei, Campylobacter jejuni, and Vibrio cholerae was conducted at five raw water sampling sites including two lakes, Hyundo region (Geum River) and two locations near Water Intake Plants of Han River (Guui region) and Nakdong River (Moolgeum region). A total 100 samples of 40 L water were tested. Most of the targeted bacteria were found in 77% of the samples and at least one of the target bacteria was detected (65%). Among all the detected bacteria, E. coli O157 were the most prevalent with a detection frequency of 22%, while S. sonnei was the least prevalent with a detection frequency of 2%. Nearly all the bacteria (except for S. sonnei) were present in samples from Lake Soyang, Lake Juam, and the Moolgeum region in Nakdong River, while C. jejuni was detected in those from the Guui region in Han River. During the six-year sampling period, individual targeted noxious bacteria in water samples exhibited seasonal patterns in their occurrence that were different from the indicator bacteria levels in the water samples. The fact that they were detected in the five Korea's representative water environments make it necessary to establish the chemical and biological analysis for noxious bacteria and sophisticated management systems in response to climate change.

Dynamic variation of toxic and non-toxic Microcystis proportion in the eutrophic Daechung Reservoir in Korea.

This study was conducted to determine the environmental factors affecting the level of potentially toxic Microcystis. The long-term tendencies of temperature, precipitation, and water quality factors were analyzed to determine the environmental characteristics of the Daechung Reservoir in Korea, and water samples were directly collected to analyze the dynamics of toxic and non-toxic Microcystis at weekly intervals from May to October 2012. Microcystis was the dominant genus during the study period, and it was composed of potentially toxic and non-toxic Microcystis. The fraction of potentially toxic Microcystis ranged from 6.0% to 61.1%. The amount of toxic Microcystis was highly related to the intracellular microcystin concentration (r = 0.760, P < 0.01). Therefore, the fraction of potentially toxic Microcystis is an important concern in Microcystis blooming because the intracellular microcystin concentration may reflect microcystin levels in the water. The prevalence of potentially toxic Microcystis was highly related to water temperature in Daechung Reservoir (r = 0.585, P < 0.01). Thus, temperature increase during Microcystis blooming may lead to more frequent toxic Microcystis blooms in eutrophic water bodies.