A novel flushing strategy for diatom bloom prevention in the lower-middle Hanjiang River

There are many concerns over the environmental consequences of river regulation in China, such as the Three Gorges Project and the South-to-North Water Diversion Project (SNWDP). In this study, however, we attempted to find the positive role of these constructions in solving environmental problems. We explored the possibility for preventing downstream diatom blooms by using the water storage in the Danjiangkou Reservoir. And we developed a flushing strategy accessing the proper flushing time and water quantity to control the diatom growth. First, we set up a Generalized Additive Model (GAM) to analyze the dynamics of the bloom-formation species, Stephanodiscus hantzschii, in response to the environmental variation. The model took into account the time lags between the biovolume and the environmental parameters. The model indicated that, air temperature explained the most variance in biovolume, followed by soluble reactive silicon (SRSi), turbidity, TP, dam release, PAR, pH and total nitrogen (GAM, R(2) = 0.759). Afterwards, we applied the model to a new predictive dataset, in which values were simulated according to the assumed dam release and air temperature. The GAM predicted fewer releases for flushing by using this dataset than the measured data, implying a prospect of saving water when using this strategy. Finally, we drew a contour map to present the operating procedure of this strategy. Our flushing strategy is to regulate the dam release above a critical value dependent on the air temperatures predicted over the following few days.