Hydro-geomorphological changes in an artificial modified lake-catchment system inferred from lacustrine sediments of Ri-Yue Tan (Sun Moon Lake), central Taiwan.

Sedimentary records of Ri-Yue Tang (Sun Moon Lake), which is the largest lake in Taiwan, provide valuable hydro-environmental information during the past 15,000 years. From the viewpoint of hydro-geomorphological conditions, the interval is roughly divided into four stages: (i) high water level with large artificial water inflow (1934 AD–present), (ii) low water level with a comparatively large catchment area (1919 AD–ca. 2800 years BP), (iii) frequent high water level with a small catchment area (ca. 2800–ca. 13,500 years BP), and (iv) low water level with a comparatively large catchment area (ca. 13,500–15,000 years BP). The changes in the conditions are mainly shown in the physical properties. A small mineral grain size and large grain density suggest enough water with high water level while large grain size and small density imply low water level and limited water discharge. Dam construction (1919–1934 AD) for more water supplies to the newly established power station greatly influences the hydro-geomorphological and environmental conditions in the Ri-Yue Tan lake-catchment system. Additional artificial water inflow with mineral material through the waterway from the Wujie Reservoir has transported more sediments (roughly twice) after the dam construction. The increase in water level due to the dam construction caused water-area enlargement and catchment-area shrinkage, resulting in changes in material production (erosion), transportation, and sedimentation in the original system. The increase in water amount supplied from the reservoir is also printed in the physical properties (small mineral grain size and large grain density) and chemical properties (organic, HCl soluble, and bi-SiO₂ contents) of lacustrine sediments. [ABSTRACT FROM AUTHOR]