Long-term variations of water quality and phosphorus loading in Lake Andong, Korea

概要

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Tropic state parameters were measured in a reservoir (Lake Andong, Korea) from 1993 to 2000. Phosphorus loading from the watershed was estimated by measuring total phosphorus concentration in the main inflowing stream (the Nakdong River). Phosphrus discharge of the pen-type fish farms was estimated from the amount of fish feed supplied annually and the rate of phosphrus excretion per feed weight. Minimum transparency in summer was only about 2.0m in 1993 and 1994, but it decreased to about 1.2m in 1997 and 1998, and recovered to about 2.3m in 1999 and 2000. TP increased from 11～30 mgP/m³ in 1993 to 18～42 mgP/m³ in 1998, but recovered to 8～13mgP/m³ in 2000, whereas TN decreased slightly from1.81～2.96mgN/L in 1993 to 1.17～1.80mgN/L in 2000. TN/TP ratio decreased from 82～281 in 1993 to 21～143 in 1998, but again increased to 101～209 in 2000 due to the decrease of TP. The average chlorophyll a concentration in growing season was in the range of 4.8-16.2mg/m³ from 1993 to 1997, but it decreased to 3.7-5.2 mg/m³ after 1998. The major cause of the trophic state recovery is thought to be the removal of fish farms in April 1998.
信州大学の論文
2004-02-28