Kwang-Seuk Jeong

Prediction and elucidation of phytoplankton dynamics in the Nakdong River (Korea) by means of a recurrent artificial neural network

A recurrent artificial neural network was used for time series modelling of phytoplankton dynamics in the hypertrophic Nakdong River system. The model considered meteorological, hydrological and limnological parameters as input variables and chl. a concentration as output variable. It was trained and validated by means of a complex database measured from 1994 to 1998 at a study site 27 km upstream of the river mouth. The validation results for 1994 indicated that the recurrent training algorithm and a 3 days time lag of input data predict reasonably accurate the timing and magnitudes of chl. a. A comprehensive sensitivity analysis of the model revealed relationships between seasons, specific input variables and chl. a that correspond well with theoretical assumptions and literature findings.

Modelling Microcystis aeruginosa bloom dynamics in the Nakdong River by means of evolutionary computation and statistical approach

Dynamics of a bloom-forming cyanobacteria (Microcystis aeruginosa ) in a eutrophic river � /reservoir hybrid system were modelled using a genetic programming (GP) algorithm and multivariate linear regression (MLR). The lower Nakdong River has been influenced by cultural eutrophication since construction of an estuarine barrage in 1987. During 1994 � /1998, the average concentrations of nutrients and phytoplankton were: NO3 � /N, 2.7 mg l � 1 ;N H 4 � /N, 0.6 mg l � 1 ;P O 4� � /P, 34.7 m gl � 1 ; and chlorophyll a , 50.2 m gl � 1 . Blooms of M. aeruginosa occurred in summers when there were droughts. Using data from 1995 to 1998, GP and MLR were used to construct equation models for predicting the occurrence of M. aeruginosa . Validation of the model was done using data from 1994, a year when there were severe summer blooms. GP model was very successful in predicting the temporal dynamics and magnitude of blooms while MLR resulted rather insufficient predictability. The lower Nakdong River exhibits reservoir-like ecological dynamics rather than riverine, and for this reason a previous river mechanistic model failed to describe uncertainty and complexity. Results of this study suggest that an inductive-empirical approach is more suitable for modelling the dynamics of bloom-forming algal species in a river � /reservoir transitional system. # 2002 Elsevier Science B.V. All rights reserved.

Application of DNA barcoding for identification of freshwater carnivorous fish diets: Is number of prey items dependent on size class for Micropterus salmoides?

Understanding predator–prey interactions is a major challenge in ecological studies. In particular, the accurate identification of prey is a fundamental requirement in elucidating food-web structure. This study took a molecular approach in determining the species identity of consumed prey items of a freshwater carnivorous fish (largemouth bass, Micropterus salmoides), according to their size class. Thirty randomly selected gut samples were categorized into three size classes, based on the total length of the bass. Using the universal primer for the mtDNA cytochrome oxidase I (COI) region, polymerase chain reaction (PCR) amplification was performed on unidentified gut contents and then sequenced after cloning. Two gut samples were completely empty, and DNA materials from 27 of 28 gut samples were successfully amplified by PCR (success rate: 96.4%). Sequence database navigation yielded a total of 308 clones, containing DNA from 26 prey items. They comprised four phyla, including seven classes, 12 orders, and 12 families based on BLAST and BOLD database searches. The results indicate that largemouth bass show selective preferences in prey item consumption as they mature. These results corroborate a hypothesis, presence of ontogenetic diet shift, derived through other methodological approaches. Despite the practical limitations inherent in DNA barcoding analysis, high-resolution (i.e., species level) identification was possible, and the predation patterns of predators of different sizes were identifiable. The utilization of this method is strongly recommended for determining specific predator–prey relationships in complex freshwater ecosystems.

Vertical distribution of Microcystis population in the regulated Nakdong River, Korea

Abstract The vertical distribution of a bloom-forming Microcystis population was studied based on the relevant limnological parameters obtained from the lower Nakdong River (Mulgum) during the summer of 1994. Over three months (late June to late September), a high abundance of Microcystis population (mean ± SD, 2.9 ± 8.4 × 105 cells ml−1, n = 40) and algal biomass (mean ± SD, chlorophyll a, 131 ± 346 μg l−1, n = 31) was persistent throughout the entire water column (0–5 m, n = 11). The vertical distribution of carbon content was uneven, with a high concentration near the surface zone (mean ± SD, total, 7.9 ± 7.8; Microcystis, 5.2 ± 8.3 μg C ml−1, n = 15). Incorporating limnological and meteorological factors, a diel study of the vertical distribution of Microcystis showed that the chlorophyll a concentration was highest near the surface zone on a calm night (wind velocity, <2 m s−1, 2300–700) but was evenly distributed on a windy day (>4 m s−1, 1100–1900). Among many possible factors, wind velocity may have played an important role in controlling the vertical distribution of Microcystis in the lower Nakdong River.

The Current Status of the Distribution of Introduced Fish in Large River Systems of South Korea

A nation-wide survey of introduced fish fauna in large river systems (>4th order streams, 28 sites, 9 river systems, total area 75,000 km 2 ) was conducted from July 1999 to January 2000 in South Korea. A total of 62 fish species (12,317 individuals, 16 families) were collected from two sampling programs. These included 32% of 194 known freshwater ichthyofauna of S. Korea. Dominant and subdominant species were Zacco platypus (16.2% relative abundance), Acheilognathus intermedia (10.6%), A. rhombea (7.2%), Opsariichthys bidens (7.1%), and Carassius auratus (6.9%). Fifteen exotic fish species have been introduced in S. Korea for food sources and about 120 species for aquarium use since the 1950s. In this study, five of the introduced food species were collected (Carassius cuvieri, 24 sites; Micropterus salmoides, 13 sites; Lepomis macrochirus, 7 sites; Oreochromis niloticus and Cyprinus carpio, 3 sites). C. cuvieri and M. salmoides were common (subdominant at 5 sites) and followed by L. macrochirus. These species were spread widely (93%; 26 sites) over all the study sites. Future research must consider the impacts of these exotic fish on natural ecosystem structure and function.

Community changes in carabid beetles (Coleoptera: Carabidae) through ecological succession in abandoned paddy fields

Carabid beetle community changes in paddy fields, abandoned paddy fields, and mountains were investigated to un derstand differences in species diversity and composition of different habitat types in small agricultural landscapes in South Korea. A total of 2,938 individuals from 37 species were identified and classified from the studied habitats. Di versity in the mountains was higher than that in abandoned paddy fields. As the number of years since abandonment increased, the diversity and stability of the carabid beetle community also increased. Abandoned paddy fields in some paddy field areas and adjoining mountainous areas, left with preconditions for management and control, have provided the opportunity to improve the diversity and habitat of small agricultural landscapes. Species composition changed continuously from the paddy fields to the mountains, in accordance with individual species habitat preferences. Aban doned paddy fields in small agricultural landscapes are believed to play an important role as transitional buffer zones between paddy fields and the adjacent mountainous areas.

Population Growth of the Cladoceran, Daphnia magna: A Quantitative Analysis of the Effects of Different Algal Food

In this study, we examined the effects of two phytoplankton species, Chlorella vulgaris and Stephanodiscus hantzschii, on growth of the zooplankton Daphnia magna. Our experimental approach utilized stable isotopes to determine the contribution of food algae to offspring characteristics and to the size of adult D. magna individuals. When equal amounts of food algae were provided (in terms of carbon content), the size of individuals, adult zooplankton, and their offspring increased significantly following the provision of S. hantzschii, but not after the provision of C. vulgaris or of a combination of the two species. Offspring size was unaffected when C. vulgaris or a mixture of the two algal species was delivered, whereas providing only S. hantzschii increased the production of larger-sized offspring. Stable isotope analysis revealed significant assimilation of diatom-derived materials that was important for the growth of D. magna populations. Our results confirm the applicability of stable isotope approaches for clarifying the contribution of different food algae and elucidate the importance of food quality for growth of D. magna individuals and populations. Furthermore, we expect that stable isotope analysis will help to further precisely examine the contribution of prey to predators or grazers in controlled experiments.

Remedial strategy of algal proliferation in a regulated river system by integrated hydrological control: an evolutionary modelling framework

We simulated water-quality measures in a regulated river system (the lower Nakdong River) under simultaneous discharge control at upriver dams and an estuarine barrage with the goal of reducing phytoplankton biomass (chlorophyll a concentration). We used genetic programming (GP) to create a rule-set-based predictive model for the chlorophyll a concentration based on 16 years (1994–2009) of meteorological, hydrological, and limnological data. The rule-set model used eight variables, including water temperature, dam and estuarine barrage discharge, phosphate and silica concentrations, and accurately predicted the phytoplankton biomass (determination coefficients, r2, for training and test data were 0.52 and 0.45, respectively). According to sensitivity and scenario analyses, a larger water volume resulting from increased discharge from upriver dams and decreased discharge from an estuarine barrage would reduce chlorophyll a concentrations at the study site. This result provided ample evidence that simultaneous manipulation of dam and estuarine discharge rates could effectively increase river flow and flush aggregated algal populations downstream. Additionally, we considered that even small increases in river flow could play a role in diluting phytoplankton biomass during the dry winter season when estuarine discharge remains low. These two hydrological mechanisms could be used as selective strategies for water-resource management.

Longitudinal patterns in limnological characteristics based on long-term ecological research in the Nakdong River

In 2004, the Korean Ministry of Environment initiated the National Long Term Ecological Research (LTER) program. We have attempted to analyze longitudinal patterns in limnological aspects based on LTER monitoring data collected from June 1994 to May 2008 in the Nakdong River, a regulated river ecosystem. Factor analysis, a multivariate ordination statistical method, was employed. Relationships among measured parameters were evaluated at different sites of the river. Overall, the trophic state of the Nakdong River was hyper-trophic (total nitrogen, 3.5-4.8 mg/L; total phosphorous, 57-95 μg/L; chlorophyll a, 15.2-38.5 μg/L). Among the three study sites, recurrent algal blooms consistently appeared in the lower reaches of the river. Extracted factors revealed different patterns, particularly for chlorophyll a concentration, and a rigid separation of limnological patterns was found at site 3 (Mulgeum) based on the factor analysis. From the results, more sustained observations through LTER will be helpful to manage and conserve ecosystems in the future. Furthermore, recent issues regarding ecosystem dynamics such as water quality with respect to global climate change require long-term datasets. Information collected by the LTER approach is hereby indispensable for ecological characterization.

Search of optimal locations for species- or group-specific primer design in DNA sequences: Non-dominated Sorting Genetic Algorithm II (NSGA-II)

Abstract In this study, we applied Non-dominated Sorting Genetic Algorithm II (NSGA-II) to the problem of identifying appropriate locations in cytochrome oxidase I (COI) gene for species- or group-specific primer design. As concerns about ecological management grow, quantification of predator-prey interaction has become a central issue in ecology. Recently, improved techniques have allowed for the extensive use of genomic DNA barcoding for qualitative analysis. However, quantification of DNA barcoding results is important and still needs to be resolved. Even though species- or group-specific primers that can be used for samples containing multiple species are difficult to design, species- or group-specific primers are a practical solution for quantification in the current era. To resolve this issue, we present here an efficient method for discovering the regions of a DNA sequence that have the highest inter-species variability by applying the NSGA-II algorithm. DNA sequence information for the COI gene region was obtained for 24 species from Jo et al. (2014). These sequences were transformed into binary data, either 0 (not different) or 1 (different), to reflect sequence conservation at each base for all combinations of two species. These data were analyzed by two objective functions, the average and standard deviation of the difference, which were used in the NSGA-II algorithm to search for appropriate DNA locations for species-specific primer design. The NSGA-II program identified four solutions (possible primer binding sites); consequently NSGA-II is believed to be a suitable algorithm for species-specific primer design, and is expected to make this difficult and time-consuming process more efficient.