Analysis Of Meteorological Factors Of The Formation Mechanism Of Algal Bloom And Algae-derived ’Hufan’ In Taihu Lake

It is difficult to obviously reduce the eutrophication degree of the water body of Taihu Lake within a short period of time. Under appropriate weather and climatic conditions, large-scale blooms of blue-green algae will come into being. A large quantity of algal blooms, driven by wind field, will accumulate, settle, perish and decompose ashore or in bays and shallow water areas, and form a phenomenon of black and odorous water masses (that is,’Hufan’) under specific meteorological conditions. Thus, it can be seen that weather and climatic conditions are one of key factors for the early warning of blooms of blue-green algae and algae-derived’Hufan’ caused by them. Weather and climatic conditions are predictable, so it is feasible to provide an early warning of the formation of blooms of blue-green algae and’Hufan’ according to weather and climatic conditions.When no control or change has been made to physiological and ecological environments of the algal growth of Taihu Lake, climatic conditions of high temperature and gentle breeze are one of important factors for the large-scale formation of blooms of blue-green algae. Moreover, in case of high temperature and gentle breeze, the superposition of local thermodynamic circulation as a result of temperature difference between the lake and land on weak background wind field will lead to the formation of the wind field diverging on the lake surface. Therefore, climatic conditions of high temperature and gentle breeze are not only conducive to the formation of blooms of blue-green algae, but also to the formation of the wind field diverging on the lake surface. At this time, it is obviously irrational to study the transportation and movement of the blooms of blue -green algae in the whole lake, by replacing the wind speed and wind direction of the whole lake surface with the wind speed and wind direction at a certain observational point on the lakeshore, and even a great deviation will occur to the results of this study. Therefore, it seems especially important to study the transportation and movement in the whole lake by integrating the mesoscale meteorological model with the hydrodynamic model as well as using the rotational, time-dependent highly-precise wind field on the lake surface exported by the meteorological model to drive the hydrodynamic model.Through this study, we have found out the correlation between weather phenomenon of high temperature & gentle breeze and the evolution of the occurrence and development of blooms of blue-green algae, demonstrated the importance of the impact of such a weather phenomenon on blooms of blue-green algae, as well as defined meteorologically early warning indexes of blooms of blue-green algae. In addition, we have confirmed the existence of lake/land wind and of the divergence of air current on the lake surface, provided the highly-precise method of simulating and forecasting this divergent wind field, and defined strength indexes for determining the occurrence of such a weather phenomenon. Based on this, this study has also improved the interface of upper boundary meteorological conditions of the hydrodynamic model of water quality, and applied highly-precise meteorological conditions to drive the hydrodynamic model of water quality, so as to make a study of hydrodynamic conditions for algal growth and transportation, thus enhancing the accuracy and reliability in the simulation and early warning of hydrological and aqueous environment. What’s more, against the crisis of drinking water happening in Wuxi in 2007, this study has clarified the dynamic mechanism by which black and odorous water masses and blooms of blue-green algae entered Gonghu Waterworks in May 2007, revealed meteorological factors of the formation mechanism of algae-derived ’Hufan’, established the early-warning mechanism of blooms of blue-green algae and ’Hufan’, and developed the visualized software for early warning purpose.Through this study, we have set up a platform for comprehensive analysis that can integrate such multiple sources of data as meteorology, water conservancy and environmental protection, as well as preliminarily actualized short-term early warning and long-term forecast of blooms of blue-green algae and algae-derived ’Hufan’. Furthermore, this study can help the decision-making department intuitively to judge characteristics of the aqueous environment of the lake to ensure the safety of drinking water of Tailhu Lake, and offer guidance and reference for the management over the aqueous ecology and the research into the early warning of large-scale lakes.