Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, Hohai University, Nanjing, 210098, China; College of Environment, Hohai University, Nanjing, 210098, China.
Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, Hohai University, Nanjing, 210098, China; College of Environment, Hohai University, Nanjing, 210098, China.
Environ Pollut. 2018 Jan;232:591-602. doi: 10.1016/j.envpol.2017.09.095. Epub 2017 Oct 8.
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 Meiling 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 and lower flow velocity profiles were also consistent (but with delay response time) when the wind speed was higher than 6.2 m/s. Wind field and temperature found the control parameters for hypoxia reduction and for water quality conditions at the surface and bottom profiles of lake. The critical temperature for hypoxia reduction at the surface and the bottom profile was ≤24.1C° (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 (22C° to 24.1C°) 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 found supportive for the reduction of hypoxia in study area due to less variable wind field. Daytime wind field found more variable (as compared to night time) which increased the thermal destratification during daytime and found supportive for destratification and hypoxia reduction. The second order exponential correlation found between surface temperature and Chlorophyll-a (R: 0.2858, Adjusted R-square: 0.2144 RMSE: 4.395), Dissolved Oxygen (R: 0.596, Adjusted R-square: 0.5942, 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.
Wind field is the key control factor for thermal destratification and hypoxia reduction. 24.1C° is the critical/threshold temperature for hypoxia, Chlorophyll-a and NH-N concentrations of the shallow freshwater lake.
风引起的流速模式和相关的热分层可以减少大型浅湖的缺氧。本研究在中国太湖梅岭湾（N 31°22'56.4″，E 120°9'38.3″）调查了风引起的水动力变化对分层和缺氧减少的影响。垂直流速剖面分析表明，表面流速与风场一致，当风速高于 6.2 m/s 时，较低的流速剖面也一致（但响应时间滞后）。风场和温度是缺氧减少和湖泊表面及底部剖面水质条件的控制参数。表面和底部剖面缺氧减少的临界温度为≤24.1°C（低于该温度时缺氧状况减少）。强盛行风场（东南风、南风、东南风和东风，风速范围为 2.4-9.1 m/s）降低了温度（22°C 至 24.1°C），导致近表面缺氧减少，水位上升，而低至中盛行风场不支持分层，导致温度升高，缺氧增加。由于风场变化较小，非盛行风向（沿海岸方向）在研究区域内不利于缺氧减少。白天的风场比夜间更具变化性，白天增加了热分层，有利于分层和缺氧减少。发现表面温度与叶绿素-a（R：0.2858，调整 R 平方：0.2144，RMSE：4.395）和溶解氧（R：0.596，调整 R 平方：0.5942，RMSE：0.3042）浓度之间存在二阶指数相关性。本研究的结果揭示了风引起的热分层和缺氧条件的驱动机制，这可能进一步有助于评估风在浅水富营养化过程和藻类大量繁殖形成中的作用。
风场是热分层和缺氧减少的关键控制因素。24.1°C 是浅淡水湖泊缺氧、叶绿素-a 和 NH-N 浓度的临界/阈值温度。
