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 <1,000,000 m 3 ), and most provide irrigation water for paddy farming. Characteristics of Korean agricultural reservoirs are high watershed-reservoir area ratios, shallow depth, unstable hydrodynamics, and eutrophic conditions. Many agricultural reservoirs are relatively old; 54% of all reservoirs were constructed more than 50 years ago. As a result, they have a considerable amount of organic matter accumulation on the sediment, which may contribute to the internal loading of nutrients. Deterioration of water quality and ecosystem health, resulting from cultural eutrophication and harmful algal blooms, are common problems in most Korean agricultural reservoirs. Environmental considerations about reservoirs, especially their ecological functions, have largely been ignored in past management plans. Limnology, the multidisciplinary study of lakes and reservoirs, can provide conceptual models of reservoirs and fundamental information needed to determine causes and potential solutions for environmental stresses. Problems prevailing in Korean reservoirs, such as cultural eutrophication and harmful algal blooms, are complicated ecosystem-level phenomena with many factors interacting with each other. Thus, limnological understanding is a prerequisite to identifying sound solutions and to making wise judgments about reservoir management and restoration. Cooperation with other related disciplines is necessary to establish the proper management plans and applications. Also, international cooperation is suggested to solve environmental problems in agricultural reservoirs, particularly among the countries with similar agricultural practices, climate, geology, and water uses.

A pilot study was performed in an experimental field at Konkuk University in Seoul, Korea, to examine the effect of treated sewage irrigation on paddy rice culture and its soil characteristics. Treated sewage irrigation did not adversely affect the growth or yield of rice; instead it resulted in about 10% (with dilution) or 50% (without dilution) greater yield than in controls. The strength of treated sewage was not a limiting factor and no lodging was observed in the rice culture even with a relatively high nitrogen concentration (up to 160 mg l − 1 ). The paddy soil also was not generally affected, although there was an indication of salt accumulation in the field irrigated with the highest strength of treated sewage. Overall, the treated sewage irrigation to paddy rice culture was thought to be an acceptable process for final sewage disposal as long as it is adequately treated and used as a supplemental source of irrigation. Copyright © 2001 John Wiley & Sons, Ltd.KEY WORDS: treated sewage; supplemental irrigation; paddy rice culture; water resources; paddy soil; sewage disposal RÉ SUMÉ Une étude-pilote a été menée dans un champ d'expérimentation à l'Université de Konkuk, à Séoul, en Corée du Sud pour examiner les effets de l'irrigation avec des eaux usées sur la culture du riz et sur les caractéristiques du sol. Cette méthode n'a pas provoqué d'effets négatifs; ni sur la croissance, ni sur le rendement du riz. Au contraire les rendements ont été supérieurs, soit de 10% (avec dilution), soit de 50% (sans dilution) à ceux du champ de contrô le. La dureté des eaux usées traitées n'était pas un facteur délimitant. En plus, aucun lodging n'a été observé au cours de la culture du riz même dans le cas d'une concentration de nitrogène relativement importante. Le sol non plus n'a pas été affecté même s'il y avait un signe d'accumulation de sel dans le champ irrigué avec des eaux usées les plus dures. En conclusion, l'irrigation avec des eaux usées pour la culture du riz pourrait être considérée comme une méthode acceptable pour le traitement final des eaux usées, tant que cette méthode est utilisée de manière adéquate et comme source supplémentaire d'irrigation.

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 BOD 5 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 BOD 5 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 1702 KWUN, YOON, AND KIMN efficiency decreased during low temperature period in winter, thus enhancement of the system applicable to all seasonal temperature ranges is recommended. The system performance was not significantly affected by the hydraulic loading up to 150 cm/day, which is far more than the loading limit of the sand filter systems.Maintenance requirement was minimal, and no problems with noise, odor, flies or sludge arose. Since the biofilter system can be operated at a distance, operation in remote rural area and multi-system connected to one control office might be advantageous to the rural area. Overall, considering the cost-effectiveness, stable performance, and minimum maintenance, the biofilter system was thought to be a competitive alternative to treat wastewater in Korean rural communities.

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 nonpoint 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.

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