• Journal of Korean Society on Water Environment
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• v.33 no.6
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• pp.696-714
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• 2017

Simple material budget models were developed to predict the spring season (March ~ May) water quality for a river-type reservoir Paldang, in the Republic of Korea. These models are available at mixed water bodies whose light intensity is negligible at the bottom. The calculated data from the models fit quite well with field data collected for 30 years, from 1988 to 2017. The apparent settling velocity of total phosphorus was estimated to be $110m\;d^{-1}$. The critical hydraulic load that determines the usability of phosphorus for algal production appeared to be about $2.0m\;d^{-1}$. When a hydraulic load was larger than the critical value, the concentrations of chlorophyll ${\alpha}$ ($Chl.{\alpha}$), chemical oxygen demand (COD), and 5-day biochemical oxygen demand BOD in the reservoir water became insensitive to internal algal reactions. The model analysis showed that the allochthonous COD continued to increase while the allochthonous BOD slightly decreased after 1999. The decrease of allochthonous BOD is due to the expansion of sewage and wastewater treatment plants in the watershed. The increase of allochthonous COD seems to result from the increase in anthropogenic non-point sources as well as the increase in the discharge of natural organic matters due to climate change. Organic matter of algal origin continued to increase until the mid-2000s, but recently it has decreased as the phosphorus concentration has decreased. The COD and BOD of algal origin increased from 35 % and 27 % during 1988 ~ 1994 to 43 % and 40 % during 2000 ~ 2010, respectively, and then decreased to 25 % and 28 % during 2011 ~ 2017.

• Journal of Korean Society on Water Environment
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• v.34 no.5
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• pp.470-486
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• 2018

This study is to investigate the allochthonous load and water quality of a typical river-reservoir, Paldang during spring (March ~ May) of 17 years (2001 ~ 2017). Phosphorus loading from point sources seems to have been reduced by 74 % in the 2010s. As a result, trophic state of the Paldang reservoir, eutrophic during the 2000s, has returned to the lmesotrophic state. Along with decrease in phosphorus concentration, standing crops of algae (Chl.a) decreased, and concentration of biodegradable organic material decreased to the past level. Concentration of total suspended solids has decreased, and it is due to the decrease of phytoplankton standing crops since the mid-2000s. As transparency increased, it is estimated that euphotic area increased by 22 % and euphotic capacity expanded by 27 %. In the river/transition zone of Paldang, concentration of organic matter increases slightly due to algal growth, but concentration of all water quality items decreases in the lacustrine zone. Although algal growth rate revealed positive correlation with concentration of phosphorus, it was insignificant. Algal growth appeared to be dependent on renewal of phosphorus by flow, than either flow rate or phosphorus concentration. The empirical model including inflow phytoplankton concentration fit well with observed values, and indicates the Paldang reservoir is greatly influenced by allochthonous loads.

• Journal of Korean Society on Water Environment
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• v.26 no.3
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• pp.420-431
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• 2010

Simple material budget models were developed to predict the dry season water quality for a river-type reservoir in Paldang, Republic of Korea. Of specific interest were the total phosphorus (TP), chlorophyll ${\alpha}$ (Chl. ${\alpha}$), 5-day biochemical oxygen demand (BOD), and chemical oxygen demand (COD). The models fit quite well with field data collected for 20 years and have enabled the identification of the origins of organic materials in the reservoir. The critical hydraulic load that determines the usability of phosphorus for algal production appeared to be about $1.5m\;d^{-1}$. When a hydraulic load was smaller than the critical value, the concentrations of $Chl.{\alpha}$, COD, and BOD in the reservoir water became sensitive to internal algal reactions such as growth, degradation, and settling. In spite of the recent intensive efforts for organic pollutant removal from major point sources by central and local governments, the water quality in the reservoir had not been improved. Instead, the concentration of COD increased. The model analysis indicated that this finding could be attributed to the continuing increase of the algal production in the reservoir and the allochthonous load from non-point sources. In particular, the concentrations of COD and BOD of algal origin during 2000~2007, each of which is comprised of approximately one half of the total, were approximately 2.5 times higher than those observed during 1988~1994 and approximately 1.3 times higher than those between 1995~1999. The results of this study suggested that it is necessary to reduce the algal bloom so as to improve the water quality of the reservoir.