Spatial-temporal distribution and limiting factor variation of algal growth: three-dimensional simulation to enhance drinking water reservoir management

Although algal growth in drinking water reservoirs has attracted worldwide attention, its spatial-temporal distribution and limiting factor variation are still not well described. In this study, three-dimensional environmental fluid dynamic code of Miyun reservoir had been established and numerical simulation was conducted to reveal the detailed temporal-spatial variation and interrelationship of temperature, total nitrogen, total phosphorous, chlorophyll a at specific time points and locations in a drinking water reservoir in China. The limiting effect of light, temperature, nitrogen and phosphorus on algae growth was also quantified throughout the year. The results suggested that thermal stratification and internal sources of nutrients played an important role in the algal bloom development; the surface layer of shallow regions was identified as the originating algal habitat. The dominant controlling factors for algal growth varied throughout the year. Temperature was the main limiting factor before May 4 and after November 25, while total phosphorous became the dominant limiting factor from May 4 to November 25. Variation of chlorophyll a and phosphorous concentration was closely related during the phosphorous limiting period. This study suggests that comprehensive measures, including external nutrient reduction, internal nutrient reduction and mixing condition improvement, should be implemented to reduce algal bloom events.