Soon-Jin Hwang

Characterizing effects of landscape and morphometric factors on water quality of reservoirs using a self-organizing map

Understanding the pattern of reservoir water quality in relation to morphometry and other landscape characteristics can provide insight into water quality management. We investigated the water quality of 302 reservoirs distributed nationwide in Korea by classifying them using a self-organizing map (SOM), examining how hydrogeomorphometry variables are related to reservoir water quality, and evaluating the effects of variables at different categories including geology, land cover, hydromorphology, and physicochemistry on reservoir water quality through a theoretical path model. The SOM classified the reservoirs into six clusters, from least to most polluted, with differences in physicochemical and hydrogeomorphometry variables between clusters. Water quality exhibits strong relationships with the proportions of urban, agricultural, and forest land cover types in the watersheds. Finally, our results revealed that hydrogeomorphometry of reservoirs and percentages of land cover types within watersheds have a considerable impact on the water quality of adjacent aquatic ecosystems. Water quality of agricultural reservoirs was characterized with variables in multiple spatial scales.SOM classified 302 agricultural reservoirs into six different clusters based on water quality.The water quality also has strong relations with the proportions of land cover types in watersheds.The hydrogeomorphometry of reservoirs have a considerable impact on the water quality of adjacent aquatic ecosystems.

A Multimetric Benthic Macroinvertebrate Index for the Assessment of Stream Biotic Integrity in Korea

At a time when anthropogenic activities are increasingly disturbing the overall ecological integrity of freshwater ecosystems, monitoring of biological communities is central to assessing the health and function of streams. This study aimed to use a large nation-wide database to develop a multimetric index (the Korean Benthic macroinvertebrate Index of Biological Integrity—KB-IBI) applicable to the biological assessment of Korean streams. Reference and impaired conditions were determined based on watershed, chemical and physical criteria. Eight of an initial 34 candidate metrics were selected using a stepwise procedure that evaluated metric variability, redundancy, sensitivity and responsiveness to environmental gradients. The selected metrics were number of taxa, percent Ephemeroptera-Plecoptera-Trichoptera (EPT) individuals, percent of a dominant taxon, percent taxa abundance without Chironomidae, Shannon’s diversity index, percent gatherer individuals, ratio of filterers and scrapers, and the Korean saprobic index. Our multimetric index successfully distinguished reference from impaired conditions. A scoring system was established for each core metric using its quartile range and response to anthropogenic disturbances. The multimetric index was classified by aggregating the individual metric ..scores and the value range was quadrisected to provide a narrative criterion (Poor, Fair, Good and Excellent) to describe the biological integrity of the streams in the study. A validation procedure showed that the index is an effective method for evaluating stream conditions, and thus is appropriate for use in future studies measuring the long-term status of streams, and the effectiveness of restoration methods.

Response of Fish Communities to Various Environmental Variables across Multiple Spatial Scales

A better understanding of the relative importance of different spatial scale determinants on fish communities will eventually increase the accuracy and precision of their bioassessments. Many studies have described the influence of environmental variables on fish communities on multiple spatial scales. However, there is very limited information available on this topic for the East Asian monsoon region, including Korea. In this study, we evaluated the relationship between fish communities and environmental variables at multiple spatial scales using self-organizing map (SOM), random forest, and theoretical path models. The SOM explored differences among fish communities, reflecting environmental gradients, such as a longitudinal gradient from upstream to downstream, and differences in land cover types and water quality. The random forest model for predicting fish community patterns that used all 14 environmental variables was more powerful than a model using any single variable or other combination of environmental variables, and the random forest model was effective at predicting the occurrence of species and evaluating the contribution of environmental variables to that prediction. The theoretical path model described the responses of different species to their environment at multiple spatial scales, showing the importance of altitude, forest, and water quality factors to fish assemblages.

Predicting potential impacts of climate change on freshwater fish in Korea

Abstract Climate change is expected to have profound effects on the distribution and phenology of species and the productivity of aquatic ecosystem. In this study, we projected the impacts of climate change on the distributions of 22 endemic fish species in Korea with climatic and geographical variables by using species distribution models (SDMs). Six different SDMs – linear discriminant analysis, generalized linear model, classification and regression trees, random forest, support vector machine, and multivariate adaptive regression splines – were implemented for the prediction, and compared for their prediction capacity. The results showed that the random forest displayed the highest predictive power for the prediction of current species distributions. Therefore, the random forest was used to assess the potential impacts of climate change on the distributions of 22 endemic fish species. The results revealed that five species (Acheilognathus yamatsutae, Sarcocheilichthys variegatus wakiyae, Squalidus japonicus coreanus, Microphysogobio longidorsalis, and Liobagrus andersoni) have a high probability of becoming extinct in their respective habitable sub-watersheds by the 2080s due to climate change. The sensitivity analysis of the model showed that geo-hydrological variables such as stream order and altitude and temperature-related variables such as mean temperature in January and difference between the minimum and maximum temperatures exhibited relatively higher importance in their contributions for the prediction of species occurrence than that other variables. The decline of endemic fish species richness, and their occurrence probability due to climate change, would lead to poleward and upward shifts, as well as extinctions of species. Finally, we believe that our projections are useful for understanding how climate change affects the distribution range of endemic species in Korea, while also providing the necessary information to develop preservation and conservation strategies for maintaining endemic fish.

Nutrients and chlorophyll-a dynamics in a temperate reservoir influenced by Asian monsoon along with in situ nutrient enrichment bioassays

Long-term nutrients and chlorophyll-a dynamics during 1993–2000 were analyzed in a temperate reservoir influenced by the Asian monsoon. Nonparametric Mann–Kendall tests and seasonal trend analyses indicated that there were no long-term annual increasing or decreasing trends in major trophic parameters over 8 years, but the monsoon seasonality was evident. Seasonality in chlorophyll (CHL) and total phosphorus (TP) showed a mono-modal pattern, which was closely associated with the monsoon season of July–August, and the magnitude of the mono-modal peak was greater in the headwater zone than in the downlake zone. Such temporal patterns fluctuated interannually over the study period, and the magnitude of the variation was directly controlled by the intensity of the monsoon rain. Empirical models of annual mean CHL–TP were developed supporting the view that phytoplankton in lentic ecosystems responds to P enrichment and that annual mean TP may provide a reliable basis for predicting the average algal abundance. Ambient nutrient analyses, N:P ratios and in situ nutrient enrichment bioassay experiments (NEBs) in premonsoon and postmonsoon supported the P limitation for phytoplankton growth. Ambient nutrients and non-volatile suspended solid (NVSS) data on CHL in the intense monsoon year, however, showed the possibility of light limitation, even though the NEBs did not show the direct evidence. These findings were confirmed by two-dimensional graphic approaches of trophic state index deviations (TSIDs).

Seasonal performance of constructed wetland and winter storage pond for sewage treatment in Korea.

Abstract A pilot study was performed from July 1998 to December 2002 to examine the feasibility of a constructed wetland system for sewage treatment in small communities of Korea. To maintain treatment performance during the winter period, an intermittent-discharge pond was connected to the wetland; its effects were evaluated from December 2001 to April 2003. The subsurface flow (SSF) wetland was satisfactory for treating sewage with good removal efficiency even during the winter period. The wetland effluent concentrations of BOD5 and TSS were often higher in winter than in the growing season, but this was explained by the higher loading rates, rather than lower removal efficiency. The relatively poor-quality wetland effluent was further polished during winter in the pond. The upper layer of the pond water column became remarkably clear immediately after ice melt. Overall, the wetland system was found to be adequate for treating sewage with stable removal efficiency, and the intermittent-discharge pond was found to be effective for further polishing if necessary. Therefore, a wetland and subsequent pond system is recommended as a practical alternative for treating sewage in small communities in Korea, and partial discharge of pond water in March is suggested.

Longitudinal Difference in Zooplankton Grazing on Phyto- andBacterioplankton in the Nakdong River (Korea)

Microzooplankton (35‐157 µm, rotifers and nauplii) and macrozooplankton (>157 µm, cladocerans and copepods) grazing on bacteria and phytoplankton were evaluated at two stations along the Nakdong River. The lower site was more eutrophic with much higher chlorophyll a concentration and total zooplankton biomass (105 µg C L ‐1 ) than the upper site (13.2 µg C L ‐1 ). At both sites bacterial carbon was lower than phytoplankton carbon and mean microzooplankton biomass was higher than macrozooplankton biomass. However, biomass specific clearance rates were higher for the macrozooplankton in contrast to the community clearance rates which were higher for the microzooplankton. Carbon ingestion rates were about ten times higher for the lower station (up to 40 µg C L ‐1 d ‐1 for phytoplankton and 5 µg C L ‐1 d ‐1 for bacteria). Here a mean community clearance rate for the microzooplankton of 44.6% d ‐1 was reached.

Fatty acid biomarkers to verify cyanobacteria feeding abilities of herbivorous consumers

To search useful fatty acid biomarkers for cyanobacteria feeding abilities of control organisms, we compared fatty acid composition of six cultured algal species in four taxonomic groups (Cryptophyceae, Bacillariophyceae, Chlorophyceae, and Cyanophyceae) and evaluated several fatty acid biomarkers using data from three lakes that varied in trophic status. In addition, a laboratory feeding experiment was conducted to verify fatty acid markers for cyanobacteria using Selenastrum capricornutum (Chlorophyceae) and Microcystis aeruginosa (Cyanophyceae). Two strains of M. aeruginosa had the highest content of 18:3ω6 while Anabaena sp. had a relatively high content of 18:1ω7 among the six species. Both 18:1ω7 and 18:3ω6 (γ-linolenic acid, GLA) concentrations showed significant linear relationships with cyanobacteria biomass in natural systems. In the laboratory feeding experiment, a principal component analysis score plot indicate that fatty acid composition of Branchinella kugenumaensis fed with M. aeruginosa became similar to that of the cyanobacterial population. In S-plot of partial least square discriminant analysis, 18:3ω6 and 18:1ω7 were selected for fairy shrimps feeding on M. aeruginosa, whereas 18:3ω3 (ALA, α-linolenic acid) and 18:1ω9 were selected for those feeding on S. capricornutum. 18:3ω6 content of B. kugenumaensis fed with M. aeruginosa significantly increased after the third day and 18:1ω7 content was significantly different from the other feeding group after six days. In particular, 18:3ω6 appeared to be a useful fatty acid biomarker for M. aeruginosa in tracing trophic relations of herbivorous organisms in freshwater ecosystems.

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

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 woodiana, 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. woodiana. Our results therefore also indicate that S. arcaeformis can eliminate the toxin more rapidly than U. douglasiae, having a larger detoxification capacity.

Ecological conservation and the restoration of freshwater environments in Korea

Freshwater ecosystems worldwide are subjected to a variety of anthropogenic threats (Malmqvist and Rundle 2002). Inappropriate land use practices, pollutants, overexploitation, and overpopulation have simplified/fragmented aquatic habitats and degraded biodiversity and water quality. In fluvial systems, human threats result from relatively slight use, such as, sports activities (e.g., canoeing and rafting), to severe pollution of water quality (inflow of nutrient-enriched sewage and a large amount of nonpoint source pollution loads), and damage to stream morphology (e.g., channelization and straightening) and the flow continuum (e.g., impoundment by large dams and weirs). Thus, conserving and reviving freshwater health and biodiversity are increasingly becoming global aims to ensure ecosystem integrity and freshwater ecosystem sustainability. Freshwater is a crucial resource for nature and man, and a biodiversity hotspot, which supports almost 10 % of all known animal species (Strayer and Dudgeon 2010), but they are much more vulnerable to disturbances than other ecosystems (Cushing and Allan 2001). Nevertheless, despite global attention on biodiversity imperilment in freshwater ecosystems for decades, increasing human pressures will accelerate species loss. Dudgeon et al. (2006) apprehended the extinction of freshwater animal species at a rate of 4 % per decade in North America, which exceeded by several fold that is expected of terrestrial species. In the case of Korean freshwater fishes, 63 of the 215 species (29.3 %) are endemic and 26 (12.1 %) are designated as ‘Critically Endangered,’ ‘Endangered,’ or ‘Vulnerable’ based on the IUCN (International Union for the Conservation of Nature and Natural Resources) red list, which portends a consistent decrease in their numbers (MOE/NIBR 2012). Intensive human-centered land use practices, such as, agricultural activities and urbanization, over decades have severely altered most stream and river ecosystems in Korea through excessive water use, which threatens water security and biodiversity (Jeong et al. 2010). Consequently, very few Korean streams and rivers remain undisturbed, and currently these compose only 5 % of reference streams listed in the National Aquatic Ecological Monitoring Program (NAEMP) database (Jun et al. 2012). ‘‘Restoration of the ecological integrity of the nation’s water’’ is one of the most important objectives of legislation concerning water environment management and conservation and related policies in many countries (e.g., US EPA 2011). This is also the case in Korea, where the Water Quality and Aquatic Ecosystem Conservation Act, and water environment management programs declare the importance of the health and integrity of aquatic ecosystems (MOE 2007). Given the implementation of national investment in water infrastructure and regulation, much work has been done to restore aquatic ecosystems, particularly rivers and streams. However, although major water quality improvements have been achieved (e.g., BOD) over the past three decades, many environmental challenges remain, such as, loss and destruction of habitat, altered S.-J. Hwang (&) Department of Environmental Health Science, Konkuk University, Seoul 143-701, Republic of Korea e-mail: sjhwang@konkuk.ac.kr