蓝藻越冬对河道型水库沉积物界面微环境与磷再生及迁移的影响

Eutrophication and outbreaks of algal bloom, caused by the retention of biogenic elements in river damming, is a major problem in the reservoir in China. The contribution of the recruitment of overwintering cyanobacteria to the formation of algal bloom in the reservoir has raised great concern. However, the response of the regeneration and migration patterns of phosphorus in the sediments to the growth of overwintering cyanobacteria, on which very inadequate research has been carried out. In this investigation, the large river-type reservoir Caojie in the Jialing jiang river served as the study area. The relationship between the characteristics of phosphorus in the sediments of different ecological areas and the composition of the overwintering algae was studied through field investigations with the help of the technologies such as 31P-nuclear magnetic resonance (31P-NMR), enzymatic hydrolysis, and a sequential extraction procedure. On the contrary, a multi-parameter system for sediment micro-interface measurement and real-time sampling methods, such as Rhizon and Peeper, were used to analyze the influence of overwintering cyanobacteria growth on the physico-chemical and bacterial property alteration of sediment-water interface and suspended particle solids-water interface. This was done through laboratory simulation and in-situ trials. The results of this study could help reveal the mechanism of sediment phosphorus (especially organophosphorus) regenerative capacity and migration rules in sediments under the effect of cyanobacteria overwintering. This knowledge is of great significance to further understand the formation mechanism of cyanobacterial bloom, the cycle process of phosphorus, and the release of internal phosphorus in the reservoir.

河流筑坝对生源物质的滞留引起水体富营养化及藻类水华是我国水库水环境保护中的重大环境问题。越冬蓝藻的复苏对水库水华形成的贡献已引起人们的关注，然而蓝藻越冬对水库沉积物关键生源要素磷的利用，影响其再生及迁移转化能力的研究尚未被关注。本项目以嘉陵江典型河道型水库—草街水库为研究对象，基于野外调查、室内模拟和原位模拟实验，应用沉积物微界面多参数测量、31P核磁共振（NMR）、酶水解及磷化学形态提取等技术，借助Rhizon和Peeper等实时微界面取样手段，弄清水库不同生态类型区沉积物磷赋存特征与沉积物微藻组成的关系，分析蓝藻越冬影响下水库沉积物（悬浮颗粒物）-水界面微环境物理、化学和生物特性的变化，揭示越冬过程对沉积物磷、尤其是有机磷再生能力及迁移规律的内在影响机制，对于深入理解水库蓝藻水华形成机理、水库磷素的循环过程以及内源磷释放等问题具有十分重要的意义。

河流筑坝对生源物质的滞留引起水体富营养化及藻类水华是我国水库水环境保护中的重大环境问题。蓝藻细胞在环境条件不利的季节会下沉至沉积物中越冬，它们保持有一定的生理活性，沉积物此时是越冬藻细胞生源物质的主要供给源；另一方面，越冬蓝藻细胞的生长或死亡可能会改变沉积物界面pH、Eh和微生物等微环境，进而影响沉积物中生源物质的赋存形态，影响其迁移、转化能力。本项目以嘉陵江典型河道型升钟水库为研究对象，开展了为期1年的逐月调查分析，探索该水库沉积物中藻类组成与磷形态时空分布特征及二者之间的联系；通过室内和原位模拟实验解析沉积物界面pH、Eh、微生物群落、磷赋存特征等环境因子对蓝藻越冬的响应，同时利用薄膜梯度扩散装置（DGT）监测间隙水中磷的高分辨垂向分布特征并定量水-沉积物界面磷交换通量。研究结果表明，周年沉积物中的藻类主要由绿藻、硅藻和蓝藻组成，分别占藻类物种数的41%、25.7%和19.2%，且具有较明显的时空分布特征。蓝藻占沉积物中藻类总数的比例由春季的23.0%逐渐上升至冬季的73.8%，并呈现河流区向湖泊区演变的趋势。沉积物中总磷（TP）的含量在278.4～1140.3 mg/kg之间，而生物可利用性磷比例较低。虽然随着春季至冬季，沉积物中TP含量较高的区域会逐渐从河流区移至湖泊区，但并未发现沉积物中磷形态与藻类组成的明显关系，室内和原位模拟实验也发现类似结果。但是，蓝藻越冬初期对水-沉积物界面的pH、Eh值有一定的提升，并诱发了Bacillales、Micrococcales丰度的增加而Steroidobacterales、Rhizobiales、Mcrotrichales丰度的减少，抑制了沉积物向间隙水溶出正磷酸盐（SRP）的量，进而减少了水-沉积物界面磷的释放通量。该研究结果说明在模拟的越冬蓝藻密度添加背景下，沉积物中磷的赋存特征并未被明显改变，但释放能力受到了抑制。这于深入理解水库越冬蓝藻介导下水库磷素的循环过程以及内源磷释放等问题具有十分重要的意义。