• Journal of Korean Society of Water and Wastewater
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• v.35 no.4
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• pp.259-275
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• 2021

This study explored the usefulness and implications of the Bayesian hyperparameter optimization in developing species distribution models (SDMs). A variety of machine learning (ML) algorithms, namely, support vector machine (SVM), random forest (RF), boosted regression tree (BRT), XGBoost (XGB), and Multilayer perceptron (MLP) were used for predicting the occurrence of four benthic macroinvertebrate species. The Bayesian optimization method successfully tuned model hyperparameters, with all ML models resulting an area under the curve (AUC) > 0.7. Also, hyperparameter search ranges that generally clustered around the optimal values suggest the efficiency of the Bayesian optimization in finding optimal sets of hyperparameters. Tree based ensemble algorithms (BRT, RF, and XGB) tended to show higher performances than SVM and MLP. Important hyperparameters and optimal values differed by species and ML model, indicating the necessity of hyperparameter tuning for improving individual model performances. The optimization results demonstrate that for all macroinvertebrate species SVM and RF required fewer numbers of trials until obtaining optimal hyperparameter sets, leading to reduced computational cost compared to other ML algorithms. The results of this study suggest that the Bayesian optimization is an efficient method for hyperparameter optimization of machine learning algorithms.

• Korean Journal of Ecology and Environment
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• v.45 no.1
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• pp.72-81
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• 2012

We investigated the effects of acid mine drainage (AMD) from abandoned coal mines on benthic macroinvertebrate communities in the upper reaches of the Nakdong River from May to October in 2009. Qualitative and quantitative sampling (Surber sampler: $50{\times}50$ cm; mesh size, 0.2 mm) was conducted at 7 study sites and 3 control sites in the study area. We thus sampled 117 species belonging to 53 families, 15 orders, 6 classes, and 5 phyla; the Ephemeroptera, Plecoptera, and Trichoptera group (EPT-group) represented the majority of the benthic macroinvertebrate community (71 species; 64.5%). In the quantitative sampling, a total of 11,575 individuals belonging to 58 species of benthic maroinvertebrates were sampled from the study sites (Sites 1-7), whereas 2,844 individuals belonging to 79 species were sampled from the control sites (Sites A-C). Tolerant species such as oligochaetes, $Epeorus$ $pellucidus$, $Baetis$ $fuscatus$, Hydropsychidae species, and Chironomidae species were predominant in the study sites. The community indices for the study sites, such as MacNaughton's dominance index (DI) (mean${\pm}$SD, $0.52{\pm}0.21$; range, 0.33-0.85) and the Shannon diversity index ($H^{\prime}$) ($2.06{\pm}0.60$; 1.06-2.57), were different from those for the control sites (DI: $0.29{\pm}0.07$, 0.22-0.35; $H^{\prime}$: $3.13{\pm}0.14$; 3.03-3.30). In the study sites, shredders and scrapers were scarce, whereas gathering-collectors (mainly Chironomidae species) were relatively abundant, as were clingers and burrowers. The detrended correspondence analysis (DCA) and similarity analyses showed that benthic macroinvertebrate communities in the study sites were clearly separated from those of the control sites, with the greatest dissimilarity being noted at the uppermost study site (Site 1), which is located close to an abandoned coal mine. The Korean saprobic index (KSI) and the ecological score using benthic macroinvertebrates (ESB) showed that the uppermost study site (Site 1) was ${\alpha}$-mesosaprobic or heavily polluted, whereas other study sites were in a fair or relatively good condition.

• Korean Journal of Ecology and Environment
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• v.43 no.2
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• pp.190-198
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• 2010

This study was conducted to examine the effects of dams on benthic macroinvertebrate communities in Korean streams and rivers. Four low-head dams and three large dams were studied throughout South Korea. Sampling was taken at immediately upper (impoundment), lower (riffle area), and control (riffle area) sites from the dams during 2004-2007. The upper sites, of which substrate heterogeneity and velocity were relatively low, showed a lower degree of species richness, density, and diversity indices, which is very different from the lower and control sites. Heavily polluted streams showed a lesser degree of community differences between the upper and lower sites. In the large dams, the upper and lower sites showed very low values of species diversity indices and very high values of dominance indices compared to the control sites. In the low-head dams, however, the difference of degree of the values was relatively smaller. Compositions of the functional feeding groups and the habitat orientation groups were relatively simpler at the upper sites than at the lower sites and the degree of difference was greater in the large dams. Species richness and community indices of benthic macroinvertebrates were more significantly affected by habitat characteristics than water quality at the upper sites; however, those were more significantly related with water quality at the lower sites. In conclusion, large and low-head dams could simplify stream habitats particularly at the upper sites (impoundment), and they negatively affected on the benthic macroinvertebrate communities inhabited the habitats. The impact was larger in the large dams than in the low-head dams.

• Journal of Environmental Impact Assessment
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• v.27 no.6
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• pp.685-694
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• 2018

We measured ecological niche space (ENS) using carbon and nitrogen stable isotope ratios of benthic macroinvertebrates to estimate its applicability for large river assessment. In particular, we compared ENSs of selected macroinvertebrates between upper and lower area of Seungchon Weir in Yeongsan River to estimate the impact of weir on biological community. We also measured basic water quality and community indices including benthic macroinvertebrates index (BMI) to estimate their correlations with calculated ENS. ENS was calculated using the Bayesian Stable Isotope in R statistics (package "SIBER"). The results showed that seasonal variations in water quality and community indices were found, but there was no apparent tendency between upper and lower area of the Seungchon Weir in June (before rainy season) and August (after rainy season). However, ENS of benthic macroinvertebrates markedly decreased across the weir in both June and August regardless of changes in water quality. This means the physical change of the stream due to the weir cause decrease of ecological isotopic niche space of benthic macroinvertebrates regardless of water quality, suggesting physical modification by the weir can affect the interaction between habitat condition and macroinvertebrates. Therefore, the ecological isotopic niche space can be a useful supplementary indicator for the river ecosystem assessment.

• Korean Journal of Ecology and Environment
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• v.54 no.1
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• pp.24-38
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• 2021

Microhabitat In the upper stream is created by various environment variables such as the bottom substrate and the physicochemical factors, and may influence the distribution of benthic macroinvertebrates. We investigated the bottom substrate and environmental variables influencing the distribution of benthic macroinvertebrate in 26 stream-type waterways established at upper reaches of Geum River. During study period, total 85 families, 160 species, 9305 individuals of benthic macroinvertebrates were recorded. The stream-type waterways, where the bottom substrates consist mainly of pebble (16~64 mm) and cobble (64~256 mm) or with rapid water velocity (more than 0.2 m/s) and high dissolved oxygen (more than 120%), were supported by high species diversity of benthic macroinvertebrate. Hierological cluster analysis and the nonparametric multidimensional scale (NMDS) divided 26 stream-type waterways into a total of three clusters. In Cluster 1, the invertebrate species, such as Branchiura sowerbyi, Cloeon dipterum, Ischnura asiatica, Paracercion calamorum, and Radix auricularia, closely related to aquatic macrophytes, and Chironomidae spp., Limnodrilus gotoi, and Tanypodinae sp. were abundant in waterways, with high coverage of silt and clay as well as high turbidity and total nitrogen. The benthic macroinvertebrate species (Cheumatopsyche brevilineata, Drunella ishiyamana, Dugesia japonica, Ephemera orientalis, Gumaga KUa, Macrostemum radiatum, Potamanthus formosus, Semisulcospira libertine, Stenelmis vulgaris, and Teloganopsis punctisetae) included in Cluster 2 were dominated in sites with high cover rates of pebble and gravel. Cluster 3 was predominantly covered by the Cobbles, was supported by Simulium sp. Such a clear distinction in the study sites means that each stream-type waterways is governed by a clear habitat environment. In the case of some sites with low species diversity, improvement measures are required to restore nature, such as improving the function of inflows and outflows, creating meandering channel, and inducing the settlement of littoral vegetation.

• Korean Journal of Ecology and Environment
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• v.57 no.1
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• pp.1-16
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• 2024

Most wetlands worldwide have suffered from extensive human exploitation. Unfortunately they have been less explored compared to river and lake ecosystems despite their ecological importance and economic values. This is the same case in Korea. This study was aimed to estimate the assemblage attributes and distribution characteristics of benthic macroinvertebrates for fifty wetlands distributed throughout subtropical Jeju Island in 2021. A total of 133 taxa were identified during survey periods belonging to 53 families, 19 orders, 5 classes and 3 phyla. Taxa richness ranged from 4 to 31 taxa per wetland with an average of 17.5 taxa. Taxa richness and abundance of predatory insect groups such as Odonata, Hemiptera and Coleoptera respectively accounted for 67.7% and 68.2% of the total. Among them Coleoptera were the most diverse and abundant. Taxa richness and abundance did not significantly differ from each wetland type classified in accordance with the National Wetland Classification System. There were three endangered species (Clithon retropictum, Lethocerus deyrolli and Cybister (Cybister) chinensis) and several restrictively distributed species only in Jeju Island. Cluster analysis based on the similarity in the benthic macroinvertebrate composition largely classified 50 wetlands into two major clusters: small wetlands located in lowland areas and medium-sized wetlands in middle mountainous regions. All cluster groups displayed significant differences in wetland area, long axis, percentage of fine particles and macrophyte composition ratio. Indicator Species Analysis selected 19 important indicators with the highest indicator value of Ceriagrion melanurum at 63%, followed by Noterus japonicus (59%) and Polypylis hemisphaerula (58%). Our results are expected to provide fundamental information on the biodiversity and habitat environments for benthic macroinvertebrates in wetland ecosystems, consequently helping to establish conservation and restoration plans for small wetlands relatively vulnerable to human disturbance.

• Korean Journal of Ecology and Environment
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• v.55 no.4
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• pp.352-359
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• 2022

Recently, with the development of genetic technology, interest in environmental DNA (eDNA) to study biodiversity according to molecular biological approaches is increasing. Environmental DNA has many advantages over traditional research methods for biological communities distributed in the environment but highly depends on the established base sequence database. This study conducted a comprehensive analysis of the habitat status and classification at the genus level, which is mainly used in eDNA (12S rRNA, 16S rRNA, 18S rRNA, COI, and CYTB), focusing on Korean registration taxon groups (phytoplankton, zooplankton, macroinvertebrates, and fish). As a result, phytoplankton and zooplankton showed the highest taxa proportion in 18S rRNA, and macroinvertebrates observed the highest ratio in the nucleotide sequence database in COI. In fish, all genes except 18S rRNA showed a high taxon ratio. Based on the Korean registration taxon group, the gene construction of the top 20 genera according to bio density observed that most of the phytoplankton were registered in 18S rRNA, and the most significant number of COI nucleotide sequences were established in macroinvertebrates. In addition, it was confirmed that there is a nucleotide sequence for the top 20 genera in 12S rRNA, 16S rRNA, and CYTB in fish. These results provided comprehensive information on the genes suitable for eDNA research for each taxon group.

• Korean Journal of Environment and Ecology
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• v.30 no.6
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• pp.996-1008
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• 2016

Effects of substrate types (bedrock and boulder habitat) on the community structures of benthic biota (macroalgae, macrobenthos) were monthly examined at Sinheung in Jeju Island, Korea, from Feb. to Nov. 2015. Species diversity of seaweeds and macrobenthos was greater at bedrock sites with 57 and 102 species than at boulder sites having 42 seaweeds and 67 macrobenthos. Average annual biomass of seaweeds was $1,601.13g\;wet\;wt./m^2$ at bedrock site and $448.85g\;wet\;wt./m^2$ at boulder site. Ecklonia cava was the most dominant species, occupying 62.64% ($1,002.93g/m^2$)of total biomass at bedrock. Amphiroa anceps was the most dominant species and subdominant species was Ecklonia cava, Grateloupia angusta, Peyssonnelia capensis and Meristotheca papulosa at boulder site. Density and biomass of macrobenthos were estimated to be $106.9indivi./m^2$ and $871.93g/m^2$, respectively at bedrock site and they were $64.6indivi./m^2$ and $984.28g/m^2$ at boulder site. The dominant macrobenthos species based on biomass were Turbo comutus (36.40%), Astralium haematragum (19.18%) and Anthocidaria crassispina (13.61%) at bedrock site and they were Alveopora japonica (54.13%) and Psammocora profundacella (24.28%) at boulder site.

• Korean Journal of Environmental Biology
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• v.31 no.3
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• pp.225-231
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• 2013

To study the characteristics of rocky intertidal invertebrate fauna on the coastal areas of the East Sea, seven regions including Dokdo, Ulleungdo, Gyeongju, Pohang, Yeongdeok, Uljin, and Gangwondo, the common species ratio (%) and similarity index using Bray-Curtis similarity matrix were calculated. The contributed species for dissimilarity between Dokdo and the other East Sea's coastal areas were selected by using SIMPER. The common species ratio and the cluster analysis showed that Ulleungdo presented the highest similarity. However, Yeongdeok showed the highest similarity in the eastern costal areas, and Gangwondo showed the lowest one. However the cluster analysis revealed the discrimination of the rocky intertidal invertebrate community on Dokdo with others region caused by the particularity of rocky shores exposed to strong wave action and by the particular distribution of rocky intertidal invertebrate fauna in Dokdo.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.4
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• pp.346-356
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• 2000

This study was carried out to investigate the distribution pattern of macrobenthos in the subtidal sandy bottoms of the east coast of Korea, and seasonal samplings were performed from April 1993 to February 1994. The species number of macrobenthos was in the range from 70 in winter to 109 in spring season. Polychaete worms were the most dominant faunal group in species richness and abundance, but mollusks showed the highest biomass. The mean density of macrobenthos fluctuated from 631 individuals/m$^2$ in autumn to 1,995 individuals/m$^2$ in summer. The major macrofauna in abundance were polychaetes, Spiophanes bombyx which occurred all seasons with top rank and Prionospio sp. and a mollusk, Alvenius ojianus, and crustaceans, Wecomedon sp. and Urothoidae spp. were also numerically dominant macrobenthic fauna. The macrobenthos in the study area were classified into two assemblages by water depth. However, they showed a different community structure near small rivers in autumn and winter seasons.