Simulations Of Sediment Resuspension And Water Temperature Under Different Meteorological Conditions In Taihu Lake

The sediment resuspension and water temperature have important ecological significance on the outbreak of algal blooms in Taihu Lake, but recent studies have mainly concentrated on the flume experiments and individual site observation analysis, whereas the continuous temporal and spatial distribution driven by the real meteorological conditions has been scarcely studied. In this paper, with initial fields provided by Weather Research and Forecasting model (WRF) and Simulating WAves Nearshore (SWAN) model respectively, the spatial distributions of sediment resuspension and water temperature in Taihu Lake were simulated under different meteorological conditions by using Finite Volume Coastal Ocean Model (FVCOM). Meanwhile, the impact factors of the euphotic depth which are closely related to the sediment resuspension were also discussed. The major results are summarized as follows:(1) Firstly, the distributions of convergence and subsidence regions driven by the wind fields are closely related to the spatial distribution of sediment in Taihu Lake, deriving from statistic analysis on 16 current fields simulated by FVCOM model which is driven by annual average wind speed and specified different wind directions.(2) Secondly, under the real meteorological conditions (temperature, pressure, humidity, wind etc.) and the wave action, the simulation result of the sediment resuspension by the FVCOM model is in agreement with the satellite retrieval result, which has a greater improvement than the previous studies. In addition, the sensitivity experiments show that at the same wind speed, not only the dominant winds (northwest and southeast wind directions) play an important role in the sediment resuspension, meanwhile, but also the effect of the non-dominant winds (northeast and southwest wind directions) cannot be ignored. Under different wind conditions, the sediment concentration is always larger in the center and southwest of Taihu Lake due to the fact that although the sediment thickness is small in the center, the flow fields are helpful for the surrounding suspended solids to transport to the central area, while the sediment is thick in the southwest where it is easier to be resuspended by the wave and current. (3) Thirdly, investigation is also conducted on the effects of the absorption and scattering coefficients, which are closely related to the sediment concentration, as well as the solar elevation angle on the euphotic depth. The theoretical relationship among them, which is validated by the point observation data, is revealed as follows:the ratio of scattering to absorption coefficients (b/a) is the key factor to determine the extent of the solar elevation angle impacting on the euphotic depth, which would be smaller or even be neglected if the ratio (b/a) is reaching to 15 or larger. The change of euphotic depth is larger when the solar elevation angle varied between 10 to 70°.(4) Finally, driven by the simulated meteorological and wave data, the water temperature and the vertical temperature difference were simulated by the optimized FVCOM model in Taihu Lake, which was verified by the in situ data. Based on the above, the sensitivity experiments of vertical temperature difference to the wind speed, temperature, evaporation, solar radiation and precipitation were also conducted. The results show that the wind speed and solar radiation are the main meteorological factors affecting the vertical temperature difference in the lake.