[pp.101-108]

Estimation of Environmental Impact for Water Quality in Lakes with Regard to Entropy Index

Hideki TATSUMOTO, Yoshimasa AMANO, Motoi MACHIDA, Dennis GEORGE and Kazuo TAKI （Chiba University / Tennessee Technological University / Chiba Institute of Technology）

Abstract:
In eutrophic lakes, the excessive growth of phytoplankton as water blooms makes a diversity state for water quality. In this study, entropy model was established to quantify the disordered state caused by the growth of water blooms. As a case study, the entropy change according to the transition of solar energy by Microcystis aeruginosa blooms as a function of TN/TP mass ratio (TN/TP ratio) and water temperature was estimated through the culture experiment and through the data analysis of actual lakes. The results were obtained as follows: The value of entropy change was differed by the various origins of lakes. The mean value of entropy change for all dammed lakes investigated was 7.74 J/(Kl), that for tectonic lakes was 6.93 J/(Kl), coastal lakes was 6.32 J/(Kl) and volcanic lakes was 0.78 J/(Kl). The entropy value was significantly affected by TN/TP ratio rather than water temperature in lakes. Therefore, the control of TN/TP ratio for lakes purification and/or control of nutrient salts from lake basin would be needed for the reduction of entropy change.

Key Word:
entropy, evaluation, eutrophic lake, water blooms, photosynthesis

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