Eutrophication of reservoirs in South Korea

Abstract

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.

Eco-hydraulic Modelling of Eutrophication for Reservoir Management

“…The Chl-a concentration in the surface layer also shows a decrease over ). The pattern of seasonal variation of phytoplankton in upstream Korean reservoirs (which are usually deep) generally shows that water blooms occur just after the monsoon storm mnoff in August or September, coinciding with increased phosphorus concentration in the surface layer (Kim et al, 2001) Figure 6.5, w suggests that in that year there had been relatively long rainfalls and runoffs as mentioned already in the previous section.…”

“…Agricultural ninoff is one of the main causes of mrbidity in many reservoirs during the rainy season (Meybeck et a/., 1992;Kim et al, 2001). The main constituents of turbidity in the Yongdam resei"voir are solids suspended from agricultural lamoff from the farming area of 139 km^ occupying about 15% of the total basin area (see Figure 6.2).…”

“…These con^espond to the periods with long residence time that makes it possible for algal biomass to accumulate. Because zooplankton is washed out during the monsoon and has not become established in high numbers, algae are able to respond strongly once hydrologie conditions are suitable (Kim et al, 2001). …”

Heterogeneidade espacial e a qualidade das águas superficiais do Reservatório Guarapiranga (São Paulo-SP-Brasil)

“…Como exposto anteriormente, no período das cheias a vazão é aumentada e o tempo de residência da água tende a ser menor, assim os materiais que entram no reservatório tornam-se menos disponíveis à utilização pela biota, não ocorrendo aumento significativo das concentrações de clorofila 'a', fator este contribuinte na avaliação do estado trófico (KIM et al, 2001;AMARASINGHE & VIJVERBERG, 2002;LEITE & ESPÍNDOLA, 2004;LAMPARELLI, 2004).…”

“…Segundo parecer técnico n° 01/97/ER/DA/DD, elaborado pela Cetesb (1997) apud Matsuzaki (2007) Matsuzaki (2007) sugere que a transposição das águas do braço Taquacetuba possa influenciar a qualidade das águas da represa Guarapiranga, especialmente em relação às concentrações de nutrientes e densidades de cianobactérias potencialmente tóxicas. Embora funcionários da Sabesp, em comunicação pessoal, aleguem que nos períodos de reversão a qualidade das águas da represa Guarapiranga sofra melhoras.…”