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The Total Maximum Daily Load (TMDL) program is an integrated process of watershed assessment and management to address surface water quality impairment. The management of organic contaminants and nutrients is a primary concern in conserving surface water bodies. Watershed-scale pollutant loads simulation can assist stakeholders and watershed planners in making decisions on immediate and long-term land use schemes to improve water quality. However, the behavior of contaminants in a watershed needs to be characterized prior to such model applications. The objectives of this study were to characterize point and nonpoint pollutants runoff at a watershed scale and to develop a Pollutant Load Calculation Model (PLCM), which facilitates the estimation of pollutant delivery to a watershed outlet. The developed model was applied for the six sub-watersheds of the Saemangeum estuarine watershed in Korea, where a large tidal reclamation project has been underway. Two years stream flow and water quality data were used for the model calibration, while 1 year data were utilized for the model validation. The model calibration resulted in the R 2 values of 0.58, 0.53, and 0.35 for BOD, TN, and TP, respectively. Overall performance for the validation period was similar with that for the calibration period although the R 2 values were slightly decreased. The PLCM tends to substantially under or overestimate delivery pollutants loads during the summer rainy seasons when most rainfall events occur. This is probably because once-a-month-measured water quality data, which might not represent appropriately monthly water quality, particularly, for rainy seasons, were used for the loads calculation. Thus, more frequently monitored water quality data should be used for the delivery loads estimation at least for a rainy season in order to improve the PLCM performance. Nevertheless, the developed model took the pollutant reduction process into account, which is not allowed with the conventional unit loading method, and furthermore temporal variations of pollutant loads based on stream flows were also incorporated into the pollutant loads estimation. The developed PLCM can be a useful tool to assess pollutants delivery loads at a watershed scale and thus assist decision makers in developing watershed pollution management schemes.

South Korea is located in the Asian monsoon region, and paddy rice farming is one of the important agricultural activities, which may contribute to the non-point source pollution of inland water bodies along with rainfall runoff. The status of water quality in rural streams located throughout South Korea was examined in this study by water quality monitoring and statistical analysis. Totally six surveys were conducted in 2003 and 2005 to monitor 300 streams located in rural subwatersheds; these streams are affected by agricultural activities and water supply for agricultural practices. The monitoring was performed at the terminal point of each subwatershed. In each study year, the streams were monitored in the three hydrological periods (April, July, and October) to observe differences in the impacts of agricultural activity and rainfall pattern. During the surveys, 15 water quality parameters were measured and interpreted using multivariate statistical methods including factor analysis and cluster analysis. Results show that the water quality of the rural streams monitored in this study appeared to meet the Korean water quality criteria for agricultural use, which are 8.0 and 100 mg/L for biochemical oxygen demand and suspended solids, respectively. In terms of organic contamination and suspended solids, the best stream water quality was observed in October compared to other periods. This can be attributed to the fact that October follows the rice-harvesting period and has low rainfall; thus the streams are probably less affected by agricultural activities and surface runoff. The three hydrological periods did not show much variation in the nitrogen and phosphorus parameters related to stream water nutrient conditions. Factor analysis indicates that the first five factors for April explained about 67% of the total sample variance. In July, the first four factors explained about 60% of the total variance, while the first four factors for October explained about 65%. Cluster analysis reveals that the streams could be divided into four groups in April and October and five groups in July. The box-and-whisker plots of the physicochemical variables indicate that Group A had the best water quality among the groups. This study demonstrates that the rural stream water quality of South Korea in the Asian monsoon region can be greatly affected by agricultural activities such as paddy rice farming and rainfall patterns.

We investigated the applicability of a dredged pool formed at the inlet of a reservoir for pollution control. To quantify the effect of a dredged pool on the water quality of a reservoir, we monitored the water quality of the Masan Reservoir, located in the city of Asan, Choongnam Province, Korea, before and after dredging. In addition, a completely mixed box model was applied to simulate the water quality of the dredged pool and reservoir. The model included a water balance equation and chemical mass balance equation, into which several interactions among water quality components, such as phytoplankton, total nitrogen (T-N), total phosphorus (T-P), dissolved oxygen, and chemical oxygen demand (COD), were incorporated. The water quality monitoring and modeling results indicated that reservoir water quality was greatly affected by the dredged pool. The loads of T-N and T-P into the reservoir were reduced by the dredged pool, which may have induced the removal of nutrients by settling. However, the dredged pool may have had a negative effect on the reservoir in terms of COD and chlorophyll-a because of the internal production of organic matter and/or algae with water detention. Therefore, a dredged pool may be used for pollution control in a reservoir, as long as it is combined with measures to reduce concentrations of organic matter and/or algae.

This study was performed to evaluate the need for heating wastewater to enhance treatment efficiency of organic matter (BOD, SS) during cold winter in newly developed Absorbent Biofilter System (ABS) which was established in the Suwon Campus of the Seoul National University. Treatments consisted of non-heating (2000 year) and heating(2001, 2002 year), and sampled data were analyzed during cold winter period as well as post winter period to investigate the influence of heating after winter season. Even the average air temperature showed only difference between two experimental years, the difference in the average effluent temperature during cold winter period between heating and non-heating experiment was approximately . The average effluent concentration of organic matter in non-heating treatment exceeded the Korean standards for water quality of discharged effluent in riparian area (BOD and SS 10 mg/L); however, the standards were met in case of heating treatment during both winter and post winter period. Therefore, the need fur heating wastewater during cold winter season in ABS was justified. On the other hand, there was no improvement of treatment efficiency in T-N and T-p, but we observed the more activated nitrification as increasing the wastewater temperature. Because the average underground temperature was higher than the average air temperature during cold winter period, we recommend that the ABS can be established in the underground rather than on-ground for saving the heating cost.

An Absorbent Biofilter System (ABS) combined with the recirculation process was investigated for the feasible application in additional removing of organics (BOD, SS) as well as nutrients (TN, TP) from small Community wastewater in Korea. Polyurethane biofilter media with high porosity and large surface area were /used for the aerobic system. A part of treated wastewater was recirculated into the anoxic septic tank to promote removal of nutrients. The concentrations of BOD and SS of treated wastewater satisfied the regulations for small on-site wastewater treatment facility (10 mg/L) during the overall experimental period. The effluent concentrations of BOD and SS were decreased with enhancement of removal efficiencies of 95.7 and . The nitrogen and phosphorus removal efficiencies by the recirculation increased to in average during the overall experimental period, respectively. With the improvement, these values were increased as much as additional 42 and compared with those of non-recirculation. The rates of nitrification and denitrification were enhanced showing , respectively. The described process modification is a low cost and effective method of enhancing nitrogen and phosphorus removal, especially on existing systems without changing major design components of a treatment facility.

In this study, on-site sewage treatment tests were conducted using the Absorbent Biofilter System (ABS) under different hydraulic loading rates to examine its treatment characteristics and efficiencies and to determine its feasibility as a small on-site sewage treatment system in a rural area. Results showed that the removal rates of BOD and SS were satisfactory at hydraulic loading rates of 100~150 cm/day, meeting the Korean effluent water quality standards for the riparian zone (10 mg/L). In the case of nutrients (N, P), however, the system did not perform well, necessitating further improvement for nutrient removal. A comparative analysis indicated that as a small on-site sewage treatment system, the ABS would be more suitable than other treatment systems in terms of performance stability, maintenance requirement, and cost-effectiveness and could be applied as an alternative treatment system in Korean rural areas.

Reservoirs are the predominant type of lentic ecosystem in Korea, and they account for a considerable proportion (~59%) of the agricultural water uses. There are 18,797 reservoirs in Korea; most (~90%) are small (storage capacity

The objective of this study was to know the qualities of soil and shallow groundwater in plastic film house fields around Central Part of Korea. The study was conducted at 11 sites in Suweon, Hwasung, Pyungtaek, Yongin and Chuncheon through May to August in 1999. Soil textures of plastic films house were mainly sandy loam or loam. Electric conductivity and organic matter content of surface soils mostly exceeded the critical levels for crop production. Average concentration of in the sha]low groundwater was 19.1 mg/L, and it reached almost the limiting level of agricultural groundwater quality (20 mg/L). Moreover about 36% of survey sites exceeded the limiting level of agricultural groundwater quality. Sulfate concentrations also at some sites exceeded agricultural groundwater quality limit level (50 mg/L). Nitrate-N, one of the most important factors in the groundwater quality, had positive correlations with other ions in foundwater.

A pilot study was performed to examine the feasibility of using a constructed wetland system for treatment of sewage in a Korean rural community. The treatment system was a subsurface flow wetland with a loading rate and hydraulic residence time of 6.3 cm/day and 3.5 days, respectively. The wetland system was highly effective in treating the sewage; median removal efficiencies of BOD5 (biological oxygen demand) and TSS (total suspended solids) were about 70.0%, with median effluent concentrations of 24 and 13 mg/L, respectively, for these constituents. However, BOD5 and TSS did often exceed the effluent water quality standards of 20 mg/L. Removal of TN (total nitrogen) and TP (total phosphorus) was relatively less effective and median effluent concentrations were approximately 81 and 8 mg/L, respectively. The treatment system did not experience any clogging or accumulation of organic and inorganic solids during the study, and during winter a substantial amount of removal of BOD5 and TSS continued to occur. Overall, the constructed wetland was judged to be an effective sewage treatment system, but not sufficient by itself to attain regional water quality standards. Therefore, treatment of rural sewage by a wetland system should be followed by another process such as use of the effluent for irrigation of agricultural crops (e.g., rice).

The feasibility of an absorbent biofilter system was examined for rural wastewater treatment in Korea. Hydraulic loading rates varied from 50 to 250 cm/day. Effluent of the septic tank was fed into the absorbent biofilter, and small ventilation fan was provided to supply air at the rate of 250 L/min to aerate the biofilter. The biofilter system demonstrated high removal rates for BOD5 and TSS at the loading rate of 150 cm/day, generally meeting the Korean effluent water quality standard of 20 mg/L applicable to both. The nutrient removal was less satisfactory than the results of BOD5 and TSS, but it was within the expected range of biological treatment processes. Considering the abnormally high influent concentration of nutrients during the experiment, better performance results could have been obtained if ordinary domestic wastewater was used. The treatment efficiency decreased during low temperature period in winter, thus enhancement of the system applicable to all seasonal temperature ranges i...

This study focused on estimating a methane (CH4) inventory and developing mitigation options in South Korea, and was performed jointly in an integrated national research program on CH4 from rice fields conducted by three National Agricultural Research Institutes, under the Rural Development Administration during 1993-1997. Methane emissions were measured by a closed chamber method, in rice plots at three locations (Suwon, Iksan, and Milyang) with the single rice cropping system. All experimental data from 5 years of study were summarized and used for calculating nation-wide CH4 emissions. Temperature, soil type, cultural practices, water management, organic matter management, and cultivar selection significantly affected the fluctuations of CH4 emissions. The two most promising mitigation options for reducing emissions were altered water management, in particular mid-season aeration by short-term drainage, and improved organic matter management, by promotion of aerobic degradation through composing or soil incorporation. Annual total CH4 emission in Korea changed from 410Gg in 1990 to 339Gg in 2000, due mainly to a decrease in the cultivated area of paddy rice. If we convert annual CH4 emission to Global Warming Potential as CO2 equivalent, it amounts to 7.1 M CO2 t yr(-1) of greenhouse gas emitted to the atmosphere in 2000 from the rice fields in Korea, which is just 5.3% of the annual CO2 emission from the industry and energy sector. More importantly, the balance between CO2 uptake by photosynthesis and CO2 emission is positive (a net sink), so that rice culture actually has net benefits for the global atmospheric carbon issue. Further reductions in emission amounts, by following recommendations in this article, could make these benefits even greater.

A bench-scale absorbent biofilter system combined with a conventional anoxic process was investigated in regard to its feasibility for removing organic as well as nutrient materials from small community wastewater in Korea. A polyurethane biofilter medium with high porosity and a large surface area were used for the aerobic system. Part of treated wastewater was recirculated into the anoxic process to promote removal rate of nutrients. At three different ratios of recirculation, the BOD and SS of treated wastewater satisfied standard regulations for a small wastewater treatment facility (10 mg/l) during the overall experimental period. The system reduced the concentration of BOD from approximately 130 mg/l to 6.1 (removal rate of 95.2%) and 1.7 mg/l (removal rate of 98.7%). These results correspond to recirculation ratios of 1 and 2, respectively. A further increase of the recirculation ratio did not significantly improve the removal rate or further reduce effluent BOD concentration. Nutrients such as nitrogen and phosphorus also were removed effectively, with maximum removal rates of 65.3 and 84.1% for nitrogen and phosphorus, respectively. The recirculation ratio for optimum nitrogen removal was 2, while the removal of phosphorus continued to increase across the entire range of recirculation ratios tested. With a recirculation ratio of 2, the total phosphorous removal rate increased dramatically as initial ammonium concentration increased, while nitrogen removal was not affected in this manner. During the experimental period of 2 years, the system was quite stable, requiring the minimum amount of maintenance and a relatively low cost compared to other utility expenses. Based on the experimental data, the proposed anoxic-biofilter aerobic recirculation system might be used as a new alternative technology for wastewater treatment in small communities in Korea.

A feasibility study was performed to examine the agronomic application of the treated sewage on paddy rice culture through field experiment. The domestic sewage was treated using a constructed wetland system, a subsurface flow type consisting of sand and macrophyte. The effluent of the wetland system was diluted to maintain the total nitrogen concentration below 25 mg/L and was used as irrigation water. Addition of the treated sewage to the irrigation water showed no adverse effect on the paddy rice culture; in fact some enhancement was noticed in both growth and yield. Irrigation with the treated sewage after the concentration was adjusted accompanied by conventional fertilization showed a better result, with the yield exceeding that of the control where clean water was used, thus suggesting that reuse of the treated sewage as supplemental irrigation water could be a feasible and practical alternative. For a full-scale application, however, further study is recommended on the specific guideline for controlling the major water quality components in the treated sewage.