Natural lakes in South Korea are limited in number and generally quite small. As a result, reservoirs and regulated rivers are the major sources of freshwater for society. About 18 000 reservoirs have been constructed in South Korea, and they are particularly important for domestic water supply. Thirteen of the major reservoirs were surveyed in this general assessment of the trophic state of South Korean reservoirs. Ten reservoirs were from the upper or middle reaches of rivers (including eight of the ten largest reservoirs in Korea), and three were estuarine reservoirs. Reservoirs in the mountainous district of South Korea were usually mesotrophic, whereas the estuarine reservoirs were highly eutrophic. Because total nitrogen to total phosphorus ratios were always between 18 and 163, phosphorus was probably more limiting than nitrogen for algal growth. However, hydraulic residence time and light penetration may be limiting in the nutrient-enriched downstream reservoirs. In winter, algal density was lowest in deep reservoirs, perhaps due to deep mixing. During the same season, algal density was high in shallow reservoirs, perhaps due to a favorable hydraulic residence time. Factors contributing to the observed eutrophication patterns, including nutrient runoff from agriculture, animal farms, fish aquaculture, and urban areas, are discussed. According to the national budget of phosphorus, fertilizer and livestock manure are major source of phosphorus, contributing 133 400 and 73 700 tons of phosphorus per year, respectively, while human excretion discharges 30 000 tons P year Ϫ1 . Reduction of the application of fertilizer, proper treatment of manure, and conservation of topsoil may be the most practical and effective measures to prevent further lake eutrophication.

The genus of leafy green algae, Prasiola Meneghini, includes marine, terrestrial, and freshwater species. A total of 11 species and one variety have been identified in China, Korea, and Japan. In Korea, Prasiola formosana var. coreana has been reported in Muncheon, North Korea, while a different type of Prasiola species has been reported in South Korea. The South Korean species has been found growing along a small stream originating from Chodanggul Cave, a limestone cave in Samcheok, Gangwon Province. Here, we revised the morphological characteristics of the South Korean Prasiola species and analyzed plastid rbcL, psaB, and tufA genes to clarify its identity. Although the external and anatomical morphologies varied among individuals, our results were very similar to previous reports. Plastid three genes sequences of the South Korean specimens were identical to those of P. japonica collected from Japan as well as to published sequences of P. yunnanica from China. A short rbcL-3P sequence (196 bp) from P. formosana var. coreana, which was identified in the type specimen, was also identical to a sequence from P. japonica. These Prasiola species and variety from Korea, Japan, and China are all distributed in areas characterized by limestone bedrock. Based on morphological, phylogenetic, and distributional features, the South Korean Prasiola species is regarded herein as P. japonica. Here, we also propose to synonymize P. formosana var. coreana and P. yunnanica with P. japonica.

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