太湖藻华释磷潜力时空差异性研究

In view of the phenomenon that cyanobacteria blooms in Lake Taihu is still large scale and the total phosphorus concentration in water bodies abnormally increased in summer, on the basis of analyzing the spatiotemporal differences of cyanobacterial bloom density in Lake Taihu, the potential of in situ phosphorus release from cyanobacterial blooms in different lake areas of Lake Taihu and its correlation with meteorological and hydrological environmental factors are studied to reveal the spatiotemporal differences in the phosphorus release potential in Lake Taihu. Through the analysis of enzyme activity and epiphytic bacterial activity during cyanobacterial blooms by means of molecular biology, the phenomena of aerobic phosphorus uptake-anaerobic phosphorus release and apoptosis phosphorus release will be studied, and then the biological mechanism of phosphorus release of cyanobacterial blooms is proposed. This project will explore the effects of zooplankton, fish and macrophytes on the phosphorus release of cyanobacterial blooms, and evaluate the influence strength and way of organisms in different trophic levels of aquatic ecosystems on the potential of phosphorus release of cyanobacterial blooms. The effects of different environmental factors such as water temperature, pH, organic matters, sediment and hydraulic disturbance on the release of phosphorus from cyanobacterial blooms also are studied through laboratory simulation methods. The environmental chemical behavior of phosphorus release from cyanobacterial blooms is clarified and the key environmental factors that drive this process are determined too. The spatial distribution map of potential phosphorus release of cyanobacterial blooms in Lake Taihu in different seasons is finally drawn to reveal the potential characteristics of phosphorus release from cyanobacterial blooms in different lake areas of Lake Taihu. The research enriches the content of phosphorus biogeochemical cycle in lakes and provides the theoretical basis for clarifying the outbreak mechanism of cyanobacterial bloom.

本项目针对近年太湖蓝藻水华仍然大面积暴发和夏季水体总磷浓度异常升高的现象，在分析太湖藻华密度分布时空差异性的基础上，开展太湖不同湖区藻华原位释磷潜力以及与气象、水文环境因素之间相关性研究，揭示太湖藻华释磷潜力时空差异性；通过分子生物学手段分析藻华释磷过程中酶活变化和附生细菌活性，研究藻华颗粒好氧吸磷厌氧放磷和凋亡释磷的现象，提出藻华释磷的生物学机理；探索浮游动物、鱼类和大型水生植物等对湖泊藻华释磷的效应，评价水生态系统不同营养级生物对湖泊藻华释磷潜力的影响强度和方式；通过室内模拟研究水温、pH、有机物、沉积物和水力扰动等不同环境因素影响藻华释磷程度，明晰藻华释磷的环境生物化学行为，确定驱动藻华释磷的关键环境因素。最终绘制太湖不同季节藻华释磷潜力空间分布图，揭示太湖不同湖区藻华释磷的潜力格局特征，丰富湖泊磷生物地球化学循环的内容，为阐明藻华暴发机制提供理论依据。

2016年以来，太湖水体总磷浓度和蓝藻水华面积处于高位波动状态。为了揭示太湖蓝藻水华暴发与总磷浓度相互关系，采用野外原位测定和室内定量模拟相结合的方法，研究太湖水华蓝藻释磷时空差异性以及生物和非生物环境因子对其影响，并探索蓝藻释磷的分子生物学机制，从“磷-藻”互为因果关系角度出发，阐明太湖水华蓝藻释磷时空差异性对湖体总磷浓度的影响。重要研究结果如下：在不同季节和太湖不同湖区，水华蓝藻释磷潜力各异，盛行风和湖流作用下的水华蓝藻分布及其环境因素导致的藻生理状态差异直接影响太湖水华蓝藻释磷潜力时空差异性。夏季太湖高温、高pH和高紫外线辐射等不利环境因素一方面改变水华蓝藻生理状态及颗粒内部理化环境，加速藻华颗粒分解释磷，另一方面改变藻华颗粒附生细菌群落结构组成，显著提高具有溶藻功能的芽孢杆菌和假单胞菌数量，加速有机碎屑的分解以及有机磷向无机磷的转化，促进蓝藻磷释放。此外，太湖不同营养级生物通过竞争或食物链影响藻华释磷，夏季水生动植物生物量高，蓝藻释磷潜力大。高温、高紫外线、高pH等不利环境因子促进水华蓝藻有机磷水解基因、多聚磷酸盐降解基因和碱性磷酸酶基因表达上调，加速了蓝藻凋亡释磷。太湖上游地区年降水量影响入湖总磷通量，湖区藻华积聚促进沉积物“铁轮”驱动的磷释放，导致蓝藻水华暴发。夏季水华蓝藻为了减轻高温、高pH和高强度紫外线等不利环境条件对其胁迫，合成聚磷而导致过量吸磷，加剧蓝藻水华暴发。水华蓝藻在太湖不同湖区积聚，发生衰亡或通过食物链作用而释磷，太湖水华蓝藻的运移加剧了蓝藻释磷潜力时空差异性，显著提升了夏季太湖西北部区和冬季南部与东部湖区总磷浓度。因此，除磷外源输入影响外，“磷多藻多，藻多磷多”的磷与蓝藻互为因果关系决定了太湖总磷浓度高低及蓝藻水华释磷时空格局特征，揭示了太湖近年了蓝藻水华暴发与总磷浓度高位波动的生态学机制，丰富了湖泊磷生物地球化学循环过程。