Author(s): Gwo-Wen Hwang; Hsin-Hua Yang
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Abstract: The aim of this study is to explore the characteristics of flow and salinity affected by tidal gates for Mortonagrion hirosei habitating. The population of Mortonagrion hirosei, one species of Odonata emerging in brackish water area, living in the reeds of the tidal wetland. In 2005, it is the first time to find Mortonagrion hirosei which is near threatened species in the International Union for Conservation of Nature (IUCN) Red List in Wu-ku wetland of Tanshui River, Taiwan. The Society of Wilderness incessantly monitor the species and then detect that the number of Mortonagrion hirosei rapidly decreased from 2006 to 2014. Flow condition and salinity are considered the crucial factor of the habitat destruction and responsible for the loss of species. Therefore, this study conducted a tidal current investigation on January 4,2022, from 7 o'clock to 19 o'clock (about one tidal cycle), using Acoustic Doppler Current Profiler (ADCP) -River Surveyor M9 for velocity and flow measurements. According to the results of tidal current investigation, the tidal cycle of the Wu-ku wetland is similar to the mouth of the Er-chong floodway. The variations of tidal range and salinity are affected by tidal gates of the Er-chong floodway. According to this study, the ecohydraulic characteristics of the habitat of Mortonagrion hirosei are analyzed, and the regulation mechanism of the tidal gates was established. The results of this study may enhance the comprehensive understanding of the tidal gates effects on flow and salinity characteristics and may also provide some guidance for restoration of Mortonagrion hirosei.
Year: 2022