The Relationship between Rainfall Pattern and Epilithic Diatoms in Four Streams of Central-Western Korea for Three Years (2013-2015).

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.

Physiological Response of the Freshwater Mussel Unio douglasiae in Microcystis aeruginosa Bloom Waters.

In the present study, we evaluated the effects of different environments on the filtering rate (FR), mortality, and biodeposition (BD) of the freshwater mussel Unio douglasiae in bloom waters containing the toxic cyanobacterium Microcystis aeruginosa. The mean FR of 19 selected individuals (shell length, 5.0-9.8 cm) was 0.30 ± 0.03 L g-1 h-1 (range = 0.24-0.35 L g-1 h-1). Shell length was strongly correlated with both net and gross BD of mussels (P < 0.0001). The mean FR was higher in river water (0.405 ± 0.052 L g-1 h-1) than in lake water (0.304 ± 0.051 L g-1 h-1). In contrast, the BD of mussels was higher in RW (0.671 ± 0.609 mg g-1 h-1) than in LW (0.275 ± 0.027 mg g-1 h-1). For algal species, the FR of mussels ranged from 0.114 ± 0.024 to 0.553 ± 0.019 L g-1 h-1. The FR of U. douglasiae was higher in river water (mainly diatoms), whereas BD was higher in lake water (mainly Microcystis). U. douglasiae did not prefer toxic M. aeruginosa, which was significantly accumulated in pseudofaeces and faeces. The maximum FR of U. douglasiae in algal bloom water was recorded at a water temperature of 25°C and water depth of 50 cm. Moreover, the in situ mortality of U. douglasiae was strongly affected by water temperature and nitrogen concentration. Overall, U. douglasiae can enhance water quality in eutrophic areas by removing dominant cyanobacteria, although its removal efficiency depends on environmental parameters and site of introduction.

Prediction of Geosmin at Different Depths of Lake Using Machine Learning Techniques.

Geosmin is a major concern in the management of water sources worldwide. Thus, we predicted concentration categories of geosmin at three different depths of lakes (i.e., surface, middle, and bottom), and analyzed relationships between geosmin concentration and factors such as phytoplankton abundance and environmental variables. Data were collected monthly from three major lakes (Uiam, Cheongpyeong, and Paldang lakes) in Korea from May 2014 to December 2015. Before predicting geosmin concentration, we categorized it into four groups based on the boxplot method, and multivariate adaptive regression splines, classification and regression trees, and random forest (RF) were applied to identify the most appropriate modelling to predict geosmin concentration. Overall, using environmental variables was more accurate than using phytoplankton abundance to predict the four categories of geosmin concentration based on AUC and accuracy in all three models as well as each layer. The RF model had the highest predictive power among the three SDMs. When predicting geosmin in the three water layers, the relative importance of environmental variables and phytoplankton abundance in the sensitivity analysis was different for each layer. Water temperature and abundance of Cyanophyceae were the most important factors for predicting geosmin concentration categories in the surface layer, whereas total abundance of phytoplankton exhibited relatively higher importance in the bottom layer.

Benthic Diatom Communities in Korean Estuaries: Species Appearances in Relation to Environmental Variables.

In the Korean Peninsula's southern estuaries, the distributive characteristics of epilithic diatoms and the important environmental factors predicting species occurrence were examined. The collection of diatoms and measurements of water quality and land-use were performed every May between 2009 and 2016, with no influence from the Asian monsoon and snow. Throughout the study, 564 diatoms were classified with first and second dominant species of Nitzschia inconspicua and N. perminuta. Based on diatom appearance and standing crops, the 512 sampling stations were divided into four groups by cluster analysis, and two regions, namely the West and East Sea. Geographically, G1, G2, G3, and G4 were located in the East Sea, Southeast Sea, West Sea, and Southwest Sea, respectively. Canonical correspondence analysis (CCA) results indicated that environmental factors, such as turbidity, electric conductivity (EC), and total phosphorus (TP), significantly influenced the distribution of epilithic diatoms. A random forest model showed that major environmental factors influencing the diatom species appearance included EC, salinity, turbidity, and total nitrogen. This study demonstrated that the spatial distribution of epilithic diatoms in the southern estuaries of the Korean Peninsula was determined by several factors, including a geographically higher tidal current-driven turbidity increase and higher industrial or anthropogenic nutrient-loading.

Accumulation of Microcystin (LR, RR and YR) in Three Freshwater Bivalves in Microcystis aeruginosa Bloom Using Dual Isotope Tracer.

Abstract: Stable isotope tracers were first applied to evaluate the Microcystis cell assimilation efficiency of Sinanodonta bivalves, since the past identification method has been limited to tracking the changes of each chl-a, clearity, and nutrient. The toxicity profile and accumulation of MC-LR, -RR and -YR in different organs (foot and digestive organs) from the three filter-feeders (Sinanodonta woodina, Sinanodonta arcaeformis, and Unio douglasiae) were assessed under the condition of toxigenic cyanobacteria (Microcystis aeruginosa) blooms through an in situ pond experiment using 13C and 15N dual isotope tracers. Chl-a concentration in the manipulated pond was dramatically decreased after the beginning of the second day, ranging from 217.5 to 15.6 µg·L-1. The highest amount of MCs was incorporated into muscle and gland tissues in U. douglasiae during the study period, at nearly 2 or 3 times higher than in S.woodiana and S. arcaeformis. In addition, the incorporated 13C and 15N atom % in the U. douglasiae bivalve showed lower values than in other bivalves. The results demonstrate that U. douglasiae has less capacity to assimilate toxic cyanobacteria derived from diet. However, the incorporated 13C and 15N atom % of S. arcaeformis showed a larger feeding capacity than U. douglasiae and S. wodiana. Our results therefore also indicate that S. arcaeformis can eliminate the toxin more rapidly than U. douglasiae, having a larger detoxification capacity.

Morphological and Molecular Phylogenetic Position of Prorocentrum micans sensu stricto and Description of Prorocentrum koreanum sp. nov. from Southern Coastal Waters in Korea and Japan.

Prorocentrum micans is an extremely variable dinoflagellate species, with many different local forms reported worldwide. Because of this morphological diversity, it is important to establish whether these various forms belong to P. micans sensu stricto. For this study, P. micans-like specimens were isolated from several localities in the southern coastal waters of Korea and Japan. The morphological characteristics and the molecular signatures of P. micans were re-examined. Moreover, a new Prorocentrum species, Prorocentrum koreanum sp. nov. was established through detailed light microscopy and scanning electron microscopy observations. Examination of the periflagellar platelets revealed that P. koreanum sp. nov. differs from P. micans. Furthermore, P. koreanum and P. micans exhibited different distribution patterns of trichocyst pores. Through molecular phylogeny analysis of small subunit (SSU) rRNA, internal transcribed spacer (ITS), and large subunit (LSU) rRNA sequence, we found P. koreanum to be more closely related to P. mexicanum and P. rhathymum than to P. micans. Additionally, ITS2 compensatory base changes also provide strong evidence to support P. koreanum and P. micans being separate species.

Water quality improvement by natural plant-mineral composites and field temperatures of a eutrophic lake in South Korea.

To improve the water quality of Shingal Reservoir, a eutrophic lake in South Korea, field tests were performed to assess the influence of water temperature on water quality improvement (WQI) ability of domestic plant-mineral composites (PMCs). Interestingly, Cyanobacterium was found to be dominant even in low-temperature seasons, especially winter leading to more effective for diatom growth. Factors such as phytoplankton, biological oxygen demand (BOD) and phosphorous showed high WQI over 70% at 20 degrees C, but declined to 40% at temperatures above 25 degrees C. WQI for Cyanobacteria decreased with increasing water temperature, whereas for diatoms WQI was 90% regardless of water temperature. Additionally, bacterial density and total nitrogen showed very low WQI without water temperature. Collectively, the results indicate that high water temperature decreased WQI ability of a PMC to control phytoplankton (Microcystis aeruginosa) and increased their ability to control diatoms.

Removal of cyanobacteria and microcystin by natural plant-mineral combinations in eutrophic waters.

The removal or mitigation of cyanobacterial bloom and cyanotoxins is a necessity to ensure safe drinking water and recreational water. As a feasible agent to control cyanobacterial bloom, a novel plant-mineral composite (PMC) was developed and optimized through laboratory and field testing over the past 3 years. Based on previous studies, we treated cyanobacterial bloom water (mainly Microcystis and Synechocystis) with 0.05 mg/L PMC at the small eutrophic reservoir; 2 h later, we collected samples and analyzed them in the laboratory. The intra-cellular (c-MC) and dissolved microcystin-LR (d-MC) were measured using an ELISA method. The PMC exhibited a remarkable removal of both c-MC (47.3 %) and d-MC (95.8 %) within 2 days. In addition, notable decreases (on average, 78 % of the control) in the chlorophyll-a, suspended solids, total phosphorus and biochemical oxygen demand values, in zooplankton and in the phytoplankton density (83.9 %) were verified after 48 h. These results indicate that the PMC is more effective in controlling d-MC than c-MC, suggesting a possible method to mitigate such hazardous chemicals as agrochemicals and endocrine disrupters in aquatic ecosystems.

Shift in nutrient and plankton community in eutrophic lake following introduction of a freshwater bivalve.

The impact of the freshwater bivalve Corbicula leana on plankton community dynamics was examined during a cyanobacterial bloom period. Nutrient and chlorophyll concentrations, primary productivity, and phytoplankton and zooplankton communities in the experimental enclosures were measured at 2-3 day intervals. The introduction of mussels reduced net primary productivity and phytoplankton and chlorophyll. Chlorophyll decreased immediately following addition of 100 mussels and then increased over time. After 600 mussels were added, chlorophyll decreased continuously from 87to 25 microg l(-1), approaching that in the mussel-free enclosure. Simultaneously, water transparency increased and concentrations of suspended solids and total phosphorus decreased. Mussel addition caused short-term increases in nutrient concentrations, especially following high-density treatment: phytoplankton density decreased, while cell density in the mussel-free enclosure increased. Zooplankton densities in the two enclosures were similar; however, carbon biomass in the mussel enclosure increased, associated with an increase in large zooplankton. The trophic relationship between phytoplankton and zooplankton was positive in the mussel-free enclosure and negative in the mussel-treatment enclosure, possibly reflecting effects of mussels on both consumer and resource control in the plankton community. Thus, filter feeding by Corbicula affects nutrient recycling and plankton community structure in a freshwater ecosystem through direct feeding and competition for food resources.

Effects of cyanobacterium Microcystis aeruginosa on the filtration rate and mortality of the freshwater bivalve Corbicula leana.

We compared filtering rates (FR) and mortalities between freshwater filter-feeding bivalve Corbicula leana acclimatized (AM) and non-acclimatized (NAM) to an cyanobacterial bloom (mainly Microcystis aeruginosa) over seven days. Both mussel populations were simultaneously stocked into mesocosms constructed in littoral zones of a eutrophic lake at a density of 740 ind. m(-2) for 16 days. NAMs decreased the concentration of chlorophyll-a 50% less than AMs. For the first seven days, the FRs (0.46-0.61) and mortality rate (slope = -30.2, r = -0.95) of NAMs were higher than those of AMs, possibly due to a sudden increase in unselective filtering. From the eighth day NAM mortality decreased rapidly and then stabilized, becoming similar to that of AMs through the end of the experiment. Stocking both AMs and NAMs increased the NH4-N concentration in the water, and the mortality rates of both mussel populations were correlated with NH4-N. In contrast, other nutrients and microcystin concentrations were not significantly associated with mussel mortality. These results indicate that although a sudden introduction of non-acclimatized C. leana may partially control phytoplankton biomass fora short period, previous short-term acclimatization is needed to minimize mussel mortality.

Relationship between cyanobacterial biomass and total microcystin-LR levels in drinking and recreational water.

Cyanobacterial biomass, chlorophyll-a, and microcystin-LR levels were monitored in drinking and recreational water in Seoul, South Korea and three satellite cities from Oct 2006 to Aug 2007. Total microcystin-LR was the sum of particulate and dissolved microcystin. Except during cold periods, toxic cyanobacteria, including Anabaena flos-aquae, were found at all sites. The total microcystin-LR levels were below guideline danger levels (<1.0 µg/L) except one time (1.27 µg/L in October), whereas chl-a (111.7 µg/L) and cell levels (2.6 × 105 cells/mL) were at 'vigilance' and 'alert' levels for drinking water and at 'guidance' level for recreational water, respectively. Discrepancies in these parameters may thus lead to frequent unnecessary alerts, thereby increasing water management costs.

Selective bactericidal potential of rice (Oryza sativa L. var. japonica) hull extract on Microcystis strains in comparison with green algae and zooplankton.

We examined the selective inhibitory potential of rice hull extract on the toxic cyanobacterium Microcystis aeruginosa, in comparison with inhibitory effects on two green algae (Ankistrodesmus convolutus and Scenedesmus quadricauda) and a zooplankton (Daphnia magna) species. The inhibitory effect of rice hull extract, measured by algal growth or zooplankton survival using four different concentrations of extract (1, 10, 100 and 1000 microg L(-1)), was highest on Microcystis strains (average: 98%, range: 95%-99%), followed by D. magna (average: 22%, range: 10%-47%), A. convolutus (average: 20%, range: 16%-24%), and S. quadricauda (average: 8%, range: 0%-15%). Rice hull extract had only a small effect on the growth of the green algae and Daphnia, particularly in the range 1-100 microg L(-1), and the inhibitory effect was somewhat diminished even at the 1,000 microg L(-1) level, at the end of the experimental period, especially for Daphnia. Our study indicates that rice hull extract has a strong specific algicide potential when used to combat M. aeruginosa.