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The role of wind-induced flow velocities in destratification
发布人:lyp    发布时间:2018-09-05 15:14    访问次数:

ABSTRACT
Wind induced flow velocity patterns and associated thermal destratification can drive to hypoxia reduction in large shallow lakes. The effects of wind induced hydrodynamic changes on destratification and hypoxia reduction were investigated at the Meiliang Bay (N 31° 22' 56.4", E 120° 9' 38.3") of Lake Taihu, China. Vertical flow velocity profile analysis showed surface flow velocities consistency with the wind field. Lower flow velocity profiles were also found consistent (but with delay response time) with a wind speed of more than 6.2 m/s. Wind field and temperature were found the control parameters for hypoxia reduction and for water quality conditions at the surface and bottom profiles of the lake. The critical temperature for hypoxia reduction at the surface and the bottom profile was ≤24.1°C (below which hypoxic conditions were found reduced). Strong prevailing wind field (onshore wind directions ESE, SE, SSE and E, wind speed ranges of 2.4-9.1 m/s) reduced the temperature in the range of 22°C to 24.1°C, which caused reduction of hypoxia at the near surface with a rise in water levels whereas, low to medium prevailing wind field did not supported destratification which increased temperature resulting in increased hypoxia. Non-prevailing wind directions (offshore) were not supportive for the reduction of hypoxia in study area due to less variable wind field.  Daytime wind field was more variable (as compared to night-time) which increased the thermal destratification during daytime and was found supportive for destratification and hypoxia reduction. The second order exponential correlation was found between surface temperature and Chlorophyll-a (R2: 0.2858, RMSE: 4.395), Dissolved Oxygen (R2: 0.596, RMSE: 0.3042) concentrations. The findings of the present study reveal the driving mechanism of wind-induced thermal destratification and hypoxic conditions, which may further help to evaluate the wind role in eutrophication process and algal blooms formation in shallow water environments.
Outcome: Wind is the key control factor for thermal destratification, hypoxia reduction and 24.1°C is the threshold temperature value for hypoxia, Chl-a and NH3-N concentrations at Lake Taihu. 
Keywords: Hypoxia; Thermal destratification; Wind field; Anoxia; Vertical velocity.

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