DOI: 10.5176/2251-189X_SEES13.78
Authors: Kwang-Seuk Jeong, Dong-Gyun Hong
Abstract:
Abstract—The lower Nakdong River system is one of regulated river system, whose flow is extensively controlled by upriver dams and an estuarine barrage. Since the completion of the estuarine barrage construction, the river experienced summer cyanobacterial and winter diatom proliferations frequently. A Long-Term Ecological Research (LTER) for plankton dynamics revealed that hydrological control is one of key issue in excessive development of phytoplankton in the river. Flow control caused elongation of water residence time in the river, which might provide chances for the phytoplankton to grow in relatively more stable water environment, on the basis of sufficient nutrient loadings. From the LTER data analysis, we found evidence explaining that wise control of water flow could suppress phytoplankton proliferations in the river system. Dam discharge had almost six-year periodicity during the study period, and the river flow responded well to the changes of dam discharge. Chlorophyll a concentration also fluctuated responding to the changes of hydrology, and during the years with serious summer drought (i.e. 1994-1992), excessive increase of phytoplankton was observed (mainly by Microcystis aeruginosa). Interestingly, similar pattern of hydrological drought recurred in 2001, however, chlorophyll a concentration did not increase to the level of previous dry years. In depth researching to discover relationship between hydrology and phytoplankton species dynamics in the river, rainfall quantity in two or three consecutive years determined the pattern of artificial flow regulation, and serious phytoplankton proliferation occurred when summer drought occurred in more than two consecutive years. Recently a huge construction effort was applied for two years, throughout the river system, which tremendously altered morphology of the river, including installation of eight moving weirs. Appropriate direction of flow management to increase ecological health of the Nakdong River should be adapted (e.g. flusing or dilution of phytoplankton), and this type of strategy should be researched on the basis of ecological and hydrological interdisciplinary collaboratio
Keywords: Regulated rivers; the Nakdong River; phytoplankton proliferation; water quality
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