西南山区河道型水库藻类水华的水动力学阈值研究

Eutrophication is a vital water environment issue drawing intentness world-wide. In recent years, outbreak of algae bloom has been reportedly more frequent in the channel-type reservoirs in mountainous Southwest. Research on hydrodynamics, the influential factor, is still at its initial stage. By the methodology of combination of laboratory experiment, site investigation and numerical simulation, the study is focusing on the dominating types of algae in the channel-type reservoirs in mountainous Southwest and lays systematic research upon their corresponding flow field and state. In the laboratory, the sunlight, temperature and substance are set to the optimal levels for algae growing. Afterwards, the courses of growing and decaying of the algae are closely monitored under circumstances of different fluid speed and turbulence. Through the foresaid, a model is established with the relationship between algae biological indicators and hydraulics indicators. Through monitoring time and spatial distributions of algae presence in typical lakes under different hydrodynamics conditions, the principle of influence of hydrodynamics over outbreak and decay of algae is then supplemented and tested. On the basis of the hydro-model of vertical bi-dimensional hydraulics, water temperature and quality, the module of algae growth influenced by hydrodynamics is built in to establish a sophisticated bi-dimensional non-stationary bio-hydrodynamics model that is suitable for the channel-type reservoirs. The modeled results are calibrated, optimized and validated against the observed data. The ultimate goal is to form a threshold value system of hydrodynamics on algae bloom in reservoirs. This research is of great significance in theory and application for evaluating, forecasting, alarming and preventing outbreak of algae bloom, and diversifying and developing the theories of eutrophication.

富营养化是世界关注的重大水环境问题。近年来西南山区河道型水库水华暴发的报道日趋频繁，水动力过程的改变作为其重要影响因素，相关研究尚处于起步阶段。本项目采用室内试验、原型观测与数值模拟相结合的方法，针对西南山区河道型水库水华优势藻类，系统开展其优势流场、流态研究。通过在室内将光照、温度、营养盐等控制于藻类生长最适水平，监测不同流速、紊动强度下的藻类生消过程，建立藻类生物学指标与水动力学表征指标之间的关系模型；选择典型水库开展藻类时空分布与水动力条件的多点监测，对藻类生消的水动力学规律予以补充、验证；在立面二维水力学、水温、水质模型的基础上，引入水动力影响下的藻类生长模型，开发适宜于河道型水库的二维非稳态生态动力学模型，并用实验成果与原观数据进行参数率定、优化与校验；最终建立水库藻华的水动力学阈值体系。本研究对于评价、预测、预警和防控水华，丰富和发展富营养化理论，具有重要的科学意义和应用价值。

藻类水华频发于西南山区河道型水库，对区域水资源与生态环境安全构成严重威胁。水动力作为主要驱动力影响水库环境系统的关键过程，可主导藻类消长与分布。水华过程的水动力影响规律与作用机制是目前水环境与生态水利研究领域的重点与难点。本项目针对西南山区河道型水库水华优势藻类，采用以室内试验为主的方法，结合典型水库原型观测、数值模拟等手段，系统研究水动力条件对藻类生消动态的影响。主要工作及成果包括：（1）研究对象以西南山区河道型水库常见水华藻种铜绿微囊藻为主，拟多甲藻、小环藻等为辅，通过在室内将光照、温度、营养盐等控制于藻类生长最适水平，监测不同流动与紊动条件下的藻类生消过程，跟踪检测指标包括藻类自身的生长特性（含生物量、光合作用强度、营养盐消耗、脂质过氧化水平及抗氧化酶活性、微观形貌变化等）与外界水质指标（含pH、溶解氧、浊度、总磷、总氮）变化，由此建立了一系列藻类生物学指标与水动力学表征指标之间的关系模型，发现组间差异显著，水动力条件对藻类普遍存在低促高抑影响，但阈值与作用方式各有不同；（2）选择具有连续藻华发生史的代表性水库——紫坪铺水库，开展了为期21个月的藻类时空分布与水动力条件的多点监测，对水库典型藻类生消的水动力学规律予以了补充、验证；（3）在立面二维及三维水动力-水温-水质耦合模型的基础上，引入水动力影响下的藻类生长模型，初步建立了适宜于河道型水库的藻类生态动力学模型，并用实验成果与原观数据进行了参数率定、优化与校验；（4）针对典型藻华优势种（以铜绿微囊藻为主）的生消过程，建立了包括流速、紊动强度、紊动耗散率、剪切力等在内的水动力学阈值体系，初步揭示了典型藻类生长的优势与抑制流场特性。本研究有益于揭示西南山区河道型水华形成与发展的基本规律，成果有助于揭示藻类水华的生消规律与内在作用机制，并可为后续开展水库水华的水力调控提供关键数据与技术支持。