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Sediment resuspension plays an important role to provide nutrient release for algal growth in large shallow lakes. The settling velocity (w ) is the key parameter for understanding the suspended sediment transport. In this paper, acoustic Doppler velocimeter (ADV) and optical backscatter sensor (OBS) instruments were used to measure in situ velocities and suspended sediment concentration (SSC) simultaneously without affecting the ambient turbulence in the bottom layer of Lake Taihu. The results showed that (1) ADV echo intensity (EI) could be transferred into SSC successfully by using a simple logarithmic relationship with a strong correlation of 0.87. (2) Three methods from a balance of settling and diffusive flux gradients for calculating settling velocities were applied, including Reynolds concentration flux, estimation of eddy diffusivity using the von-Karman Prandtl equation, and Kwon's power equation. The average settling velocity during the observation period was 0.11 mm/s for Lake Taihu. (3) The fitted power function, w = 1.85 × 10 C , could be used to estimate w according to SSC. (4) Settling velocity changes with SSC, vertical velocities, and wind speed, which describes suspended sediment instantaneous and continuous motions. This paper provides an effective approach for estimating the settling velocity, provides a reference value of settling velocity for hydrodynamic model, and supports a better understanding of sediment transport process and nutrient release in large shallow lakes.

Synthesis of photocatalysts with high charge separation and transfer efficiency are of huge significance in the photocatalytic waste water treatment technology. Herein, we report the phase transformation of bismuth oxyiodide through the facile calcination of BiOI microsphere at different temperatures. Different phases including BiOI, Bi 4 O 5 I 2 and Bi 5 O 7 I were obtained as confirmed by different characterization techniques studied. The synthesized photocatalysts depicted high visible light absorption efficiency in a range of ∼ 655 to 420 nm. The photo-catalytic activity of the synthesized photocatalyst were studied on the reduction of the highly carcinogenic and toxic hexavalent chromium as the representative heavy metal in waste water. Bi 4 O 5 I 2 depicted high photocatalytic activity (k = 0.0366 min À 1 ) which was ascribed to high charge separation and transfer as evidenced in PL, photocurrent response and EIS. This study may furnish a new concept in designing a series of phases that are more advantageous in solar energy conversion.

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