This comprehensive review explores the escalating challenge of nutrient enrichment in aquatic ecosystems, spotlighting the dire ecological threats posed by harmful algal blooms (HABs) and excessive particulate organic matter (POM). Investigating recent advancements in water treatment technologies and management strategies, the study emphasizes the critical need for a multifaceted approach that incorporates physical, chemical, and biological methods to effectively address these issues. By conducting detailed comparative analyses across diverse aquatic environments, it highlights the complexities of mitigating HABs and underscores the importance of environment-specific strategies. The paper advocates for sustainable, innovative solutions and international cooperation to enhance global water quality and ecosystem health. It calls for ongoing advancement, regular monitoring, and comprehensive research to adapt to emerging challenges, thus ensuring the preservation of aquatic biodiversity and the protection of communities reliant on these vital resources. The necessity of integrating technological innovation, ecological understanding, and global cooperation to safeguard aquatic ecosystems for future generations is paramount.

Two new benthic freshwater species belonging to the genus Achnanthidium were found in Korea. Achnanthidium ovale sp. nov. and A. cavitatum sp. nov. are described as new species based on light and scanning electron microscopy observations and molecular analyses. Both species are compared with the type material of morphologically similar taxa. Achnanthidium ovale differs from other species belonging to the A. pyrenaicum complex in outline, striation pattern, raphe central endings, and freestanding areolae at the apices. Achnanthidium cavitatum differs from other species in the A. minutissimum complex in outline, broad axial central area in the raphel ess valve, and slit-like areolae near the axial central area. We assessed their molecular characteristics by analyzing nuclear small subunit (SSU) rRNA and chloroplast-encoded rbcL gene sequences. Both the morphological comparison and the SSU and rbcL sequence analyses provide strong evidence to support the recognition of A. ovale and A. cavitatum as new species.

This study investigates the ecological effects of weirs on water quality and phytoplankton communities in the South Han River (SHR) over a two-year period. By focusing on three key weirs—Kangcheon Weir, Yeoju Weir, and Ipo Weir—the research examines how artificial structures influence river hydrodynamics, nutrient cycles, and algal growth patterns. Utilizing water quality measurements, phytoplankton analysis, and environmental factor assessments, the study identifies significant fluctuations in water quality parameters and phytoplankton abundance across the surveyed points. The analysis reveals a direct correlation between environmental conditions such as temperature, flow rates, and nutrient concentrations, particularly nitrogen and phosphorus, and the proliferation of harmful cyanobacteria, notably Microcystis. This research highlights the critical role of comprehensive management strategies that consider hydraulic residence time, nutrient balance, and temperature regulation to mitigate the impacts of weirs on river ecosystems and improve water quality in the SHR.

To study the effect of rainfall patterns on diatom communities in four major central western streams on the Korean Peninsula during the monsoon seasons of 2013 through 2015, we measured precipitation, environmental factors, and epilithic diatoms at 42 sites before (May) and after (August and September) each monsoon. The Mangyeonggang river and Sapgyocheon stream (SS) had a high percentage of low-permeability soil, and the stream had the highest proportion (49.1%) of surrounding land in urban areas. Precipitation and precipitation frequency was closely correlated with electrical conductivity and nutrients, and this was particularly evident in SS. Epilithic diatom abundance for the most abundant species as, Navicula minima, decreased in the stream in 2013 and 2014 and increased in 2015 when precipitation and precipitation frequency were low. This was not clearly distinguishable in the ecological characteristics of each watercourse’s indicator species, except in SS. The dynamic community index was highest in 2015 (ca. 5.50), and the annual changes in the index were clearly shown in SS. The precipitation pattern and the dynamic community index were negatively correlated (r = −0.026~−0.385), and the precipitation within 2 weeks (r = −0.480 for SS) before the second sampling and the frequency of 10 mm of precipitation were closely correlated in the stream (r = −0.450 for SS). The distribution of epilithic diatoms in the four watercourses is therefore affected by monsoon precipitation and precipitation frequency, and the dynamic community index is determined by soil characteristics and land use.

In January 2019, epilithic diatoms were collected from two streams on Mount Gumdan and Mount Yongma near Lake Paldang in central South Korea. A total of 16 diatoms were isolated and classified by molecular and morphological analysis. Morphology was studied by LM and SEM, while the molecular study focused on small subunit (SSU) rRNA and ribulose bisphosphate carboxylase (rbcL) genes. Molecular analysis showed that the three species had clear differences in phylogenetic distance. Based on these findings, we studied the ultrastructure of three species. Among the morphological characteristics, Hannaea librata is longer but narrower and always has conical spines, while the similar species H. pamirensis has bifurcated spines in the central region and conical spines near the pole. Gomphonema seminulum is wider in the axial–central area than G. pumilium. Nitzschia inclinata has a bended valve apex, while N. oligotraphenta has a straight apex.

This paper reviews the evolution and integration of diatom-based water quality assessments with environmental DNA (eDNA) techniques for advancing river ecosystem health evaluations. Traditional methods, relying on microscopy and diatom indices, have significantly contributed to our understanding of aquatic ecosystems but face challenges such as the need for taxonomic expertise and the labor-intensive nature of sample collection. Recent advancements in molecular biology, particularly eDNA analysis, offer opportunities to overcome these limitations, providing more accurate and comprehensive assessments. This study highlights the benefits of combining traditional microscopy with modern molecular techniques, enhancing the precision and efficiency of water quality evaluations. By addressing the challenges of standardizing methods and improving species identification through comprehensive reference libraries and advanced bioinformatics tools, this integrated approach aims to refine and advance the effectiveness of diatom-based strategies in monitoring and managing river health amidst environmental changes.