Seok Soon Park

A water quality modeling study of the Nakdong River, Korea

A water quality modeling study was performed for water quality management of large river systems where autochthonous sources and denitrification play an important role in biochemical oxygen demand (BOD) and nitrogen dynamics. The model was based on the USEPAs QUAL2E and several modifications were made in the computer code to overcome limitations of QUAL2E. This paper outlines changes which were made in the model in addressing some of water quality problems and demonstrates the model application to the Nakdong River, Korea. The changes include the modification of computational structure and the addition of new constituent interactions, such as conversion of algal death to BOD, denitrification, and dissolved oxygen (DO) change caused by fixed plant. To validate the program modifications, both QUAL2K and QUAL2E were applied to the same reaches of river and the results were compared. The water quality parameters included in the model were DO, BOD, nitrogen and phosphorus series, and chlorophyll-a. Both QUAL2K and QUAL2E model represent the field data quite well except for some parameters of QUAL2E. In BOD, DO, and total nitrogen, there are significant discrepancies between the results of two models, where QUAL2K displayed better agreement with the field measurements than QUAL2E due to QUAL2Ks ability to simulate the conversion of algal death to BOD, fixed plant DO, and the denitrification.

Indirect influence of the summer monsoon on chlorophyll–total phosphorus models in reservoirs: a case study

Abstract This study examines how the Asian monsoon influences relationships between chlorophyll-a (Chl) and total phosphorus (TP), by means of a case study on Taechung Reservoir, Korea. A log–log regression model of Chl vs. TP was found to be quadratic relations, with Chl approaching an asymptote above 50 μg l−1 TP. This is similar to the pattern previously reported for temperate lakes in Europe and North America. However, viewing the data by season, a highly significant linear model was obtained during the pre- and post-monsoon periods (R2≥0.83), but not during the summer monsoon (R2=0.004). In the monsoon period, samples >50 μg l−1 TP (23% of the total observations) had fourfold lower Chl yields per unit TP (average=0.17) compared to samples from the same TP range in the other seasons (average=0.76) and were strongly correlated (r=0.97, n=17) to non-volatile suspended solids (NVSS). Yield of Chl per unit TP also increased significantly (P

N-Acetylglucosaminidase activities in wetlands: a global survey

AbstractA fluorogenic model substrate, methylumbelliferyl-N-acetylglucosamine was used to measure N-acetylglucosaminidase activities in wetland soils. The enzyme activity exhibited substrate saturation around 200 μM, and an approximate linearity for at least 90 min incubation time. The effects of temperature, pH, toluene, and γ-radiation on the enzyme were also determined. The method was applied to 32 different wetland samples from both freshwater wetlands and salt-water wetlands. Overall, the activities were the lowest in bogs and much higher in freshwater marshes and flooded grasslands. The variations of the activity were not explained by a single environmental variable. However, among peatland samples (e.g., bogs and fens) only, specific enzyme activity per organic matter exhibited a significant correlation with N-acetylglucosaminidase activity, suggesting the importance of the enzyme activity in organic matter dynamics in such systems.

Effective visualization for the spatiotemporal trend analysis of the water quality in the Nakdong River of Korea

Abstract Spatial and temporal trend analyses were performed to obtain more meaningful water quality information in table and three-dimensional graph forms. Using the statistical approaches of the Seasonal Mann–Kendall (SMK) and LOcally WEighted Scatter plot Smoother (LOWESS) methods, the trends of three water quality parameters, including Biochemical Oxygen Demand (BOD), Total Nitrogen (TN), and Total Phosphorus (TP) measured along the Nakdong River of Korea between 1992 and 2002 were analyzed. The trends of the slopes were calculated using the SMK method for two consecutive stations and years. These values are provided in the trend tables which indicate the extreme upward and downward trends. Also, three-dimensional graphs of the water quality in the Nakdong River were generated with respect to the distance from upstream of the river and time of month. From this study, it was concluded that these tables and three-dimensional maps could be used as a useful tool to provide the spatiotemporal trend information such as the hot spots/moments of improvement and deterioration in the water quality of the Nakdong River, with the present web-based information system.

Influence of seasonal monsoon on the trophic state deviation in an Asian reservoir

Trophic parameters including total nitrogen (TN), total phosphorus (TP), Secchi depth (SD), and chlorophyll-a (CHL) were analyzed to evaluate how the Asian monsoon influences the trophicstate of the Taechung Reservoir, Korea. By using conventional criteria, the trophic state of this system ranged from mesotrophic to hypertrophic with spatial and seasonal variationsdepending on landuse pattern and flow regime. Based on TP, CHL, and transparency, the overall trophic state declined from the headwaters to the dam. However, based on TN, the entire reservoir was hypereutrophic thoughout the year. Comparing nutrients and CHL as trophic parameters, large disparities of the trophic state have been observed in the headwaters during intensive monsoon. The trophic state was much greater when assessments were based on nutrients instead of CHL, indicating apotential trophic deviation. Using Carlsons (1990) twodimensional approach, deviations of the Trophic State Index(TSI), based on the relation between TSI (CHL) minus TSI(TP), and TSI (CHL) minus TSI (SD) during the intensivemonsoon indicated that factors other than phosphorus limitedalgal growth, and that non-algal particles affect lightattenuation. These findings were supported by high non-volatilesuspended solids (NVSS), short water residence time, and low CHL:TP ratios during monsoon. Such deviations, however, did not occur during weak monsoon. The trophic disparity during theintensive monsoon was considered to be a result of the shortwater retention time and reduced light availability throughdominance of inorganic suspended solids. Under these circumstances, trophic state assessments based only on nutrientloading may not be a useful indicator for water management.

An oxygen equivalent model for water quality dynamics in a macrophyte dominated river

Abstract A water quality modeling study was performed in a macrophyte dominated river. A computer model, MACRIV (macrophyte growing river) was formulated to incorporate diurnal dissolved oxygen variations and nutrient uptake/recycle caused by all aquatic plants, including macrophytes. In this model, the aquatic plant is represented as an equivalent amount of dissolved oxygen by reach, which varies diurnally as well as seasonally depending upon solar radiation, temperature, and nutrients. The solar radiation is computed in the model based on the latitude, Julian day, and real-time of day. The model simulates seven coupled state variables (BOD (CBOD or 5-day BOD), DO (daily average value or diurnal variation), organic nitrogen, ammonia nitrogen, nitrite/nitrate nitrogen, total organic phosphorus, dissolved inorganic phosphorus (DIP)) and two non-coupled variables (a first-order decay substance, and a conservative substance). Through a stoichiometric relationship between plant protoplasm and physiological processes including photosynthesis, respiration, and death, the water quality variables interacting with aquatic plants are computed in the model. The model was calibrated and verified against data collected from an impounded river in which macrophytes play an important role in defining water quality dynamics. There were reasonable agreements between model predictions and the field measurements both for steady-state water quality and diurnal dissolved oxygen. The overall study demonstrated that the developed MACRIV model can simulate the most important parameters involved in waste load allocation studies in macrophyte growing rivers, such as diurnal DO variation, BOD (autochtonous and allochtonous), ammonia toxicity, and nutrient dynamics.

Probabilistic prediction of cyanobacteria abundance in a Korean reservoir using a Bayesian Poisson model

There have been increasing reports of harmful algal blooms (HABs) worldwide. However, the factors that influence cyanobacteria dominance and HAB formation can be site-specific and idiosyncratic, making prediction challenging. The drivers of cyanobacteria blooms in Lake Paldang, South Korea, the summer climate of which is strongly affected by the East Asian monsoon, may differ from those in well-studied North American lakes. Using the observational data sampled during the growing season in 2007–2011, a Bayesian hurdle Poisson model was developed to predict cyanobacteria abundance in the lake. The model allowed cyanobacteria absence (zero count) and nonzero cyanobacteria counts to be modeled as functions of different environmental factors. The model predictions demonstrated that the principal factor that determines the success of cyanobacteria was temperature. Combined with high temperature, increased residence time indicated by low outflow rates appeared to increase the probability of cyanobacteria occurrence. A stable water column, represented by low suspended solids, and high temperature were the requirements for high abundance of cyanobacteria. Our model results had management implications; the model can be used to forecast cyanobacteria watch or alert levels probabilistically and develop mitigation strategies of cyanobacteria blooms.

A stoichiometric model for water quality interactions in macrophyte dominated water bodies

Abstract A computer model, SIREM1, which incorporates water quality interactions of aquatic plants including planktonic algae, periphyton, and macrophytes is presented in this paper. In this model, the total amount of aquatic plants is represented dynamically as an oxygen equivalent, dependent upon available solar radiation. Through the stoichiometric relationship between plant protoplasm and processes including photosynthesis, respiration, and death, nutrients and autochthonous organic matter are computed based on simulated oxygen equivalents. The model was applied to an impounded stream where macrophytes played an important role in water quality dynamics. There was good comparison between model prediction and actual observations. The results indicate that the time variable oxygen equivalent concept for aquatic plants could be a useful approach for simulating the function of aquatic plants in diurnal dissolved oxygen variations, nutrient uptake/recycle, and the generation of autochthonous organic matter.

The effect of sediment organic carbon content on bioavailability of hydrophobic compounds in aquatic ecosystems

Abstract The effect of sediment organic carbon content on bioavailability of hydrophobic compounds was investigated, using a numerical dynamic model capable of incorporating several major factors affecting bioconcentration. These included adsorption/desorption, metabolism, volatilization, and biochemical degradation. The model was validated against data obtained by exposing goldfish to two chlordane isomers in the presence of benthic sediments. Two sediments with differing organic matter content were used in the experiment: muck sediment with high organic matter and loam sediment with low organic matter. The bioconcentration factor was estimated from the water solubility and sediment partition coefficients ( K p ) measured in exposure experiment. There was good agreement between the model predictions and the experimental data for both chlordane isomers in two different sediments. In order to incorporate the organic content into the adsorption capacity of the sediment, the partition coefficients were normalized to organic carbon ( K oc ) by percentage of organic carbon content (%OC). Given different values of the partition coefficients computed from K oc and %OC as input conditions, the effect of sediment organic carbon on bioavailability was examined from the model results. It was shown that sediment organic carbon can cause a significant impact on bioavailability of hydrophobic compounds, especially sediment containing low organic carbon content, where small changes in organic carbon content produced large variations of chlordane concentration in organisms.

Comparison of Enzyme Activities in Vegetated and Nonvegetated Sediments

This study focuses on the effect of aquatic plants on the changes of enzyme activities in wetland sediments. Wetland plants play essential roles both as a carbon supplier for microbes which synthesize enzymes and as a regulator for enzyme activity by modifying hydrochemistry in the rhizosphere. Although numerous studies have been carried out on soil enzymes, little information is available on the vertical distribution and temporal variation of enzyme activities affected by the presence of plants in wetlands. Our results clearly show that sediments with wetland plants exhibit significantly higher enzyme activities of β -glucosidase, arylsulfatase, phosphatase, and N-acetylglucosaminidase (P<0.05) up to a depth of 15 cm throughout the year, whereas only lower values were observed even at the surface of sediments (0–3 cm) without plants. However, in the field, there were no statistically significant changes of enzyme activities associated with the changes of season and the vertical position along the depth (...