基于近湖面定点遥感连续监测藻类水华的研究

Continuous Monitoring of Algal Blooms Based on Near Surface Remote Sensing Technique

全球湖泊富营养化问题日益突出,而基于数码相机的近湖面遥感可以连续、高频地监测藻类状况。该文于2019年3-10月采用数码相机在太湖4个生态功能区的站点(梅梁湾2、避风港、小雷山和平台山)对水体相对绿度指数开展连续和高频的原位观测,并同步观测气象要素和太阳辐射。研究藻类水华的时空变化特征和单次藻华的动态演变,并分析气象因子和热带气旋事件的影响。结果表明:(1)4个站点在观测期间相对绿度指数的平均值分别为0.355、0.348、0.347和0.344。处于太湖北部藻型湖区的梅梁湾2站点相对绿度指数明显高于其他站点,蓝藻水华较为严重;太湖西南部的小雷山站和东南部的避风港站相对绿度指数发生频率处于中间水平,而处于湖心位置的平台山站则相对绿度指数普遍较低。(2)关于藻华暴发之前的天气过程,在观测时段内13次典型的藻类水华事件中,有11次水华事件在之前的3 d经历了明显降水过程,其余2次藻华过程的前期天气为冷空气过境和晴热高温天气。特别地,暴雨过后的10 h左右就有可能发生水华事件。说明强烈降水过程之后的晴朗天气,有利于藻华暴发。(3)热带气旋会使得全湖相对绿度指数降低,但是之后的水温分层和晴好天气,则有利于形成严重水华并持续一段时间。近湖面遥感方法能为水体藻类动态监测及影响机制研究提供新的数据支持和技术支撑。

Eutrophication is a prominent problem for many lakes across the world.near-surface remote sensing based on digital cameras can be used to monitor the status of algae continuously with high frequency.In this paper,the green chromatic coordinate of Lake Taihu was monitored with high temporal frequency at the sites Meiliangwan 2,Bifengang,Xiaoleishan and Pingtaishan located in four different ecological regions from March to October in 2019,with meteorological variables and solar radiation observed simultaneously.The spatial pattern and temporal variability of algae bloom,and dynamics of individual bloom event were investigated.The impact of meteorological variables and tropical cyclone event were also analyzed.The results indicated that the average of the green chromatic coordinate index at the four sites during the observation periods were 0.355,0.348,0.347 and 0.344,respectively.The green chromatic coordinate index at the Meiliangwan 2 site located in the algae type zone in the north of Lake Taihu was higher than the other sites,indicating that the algae bloom occurred severer.The green chromatic coordinate was at an intermediate level at the Xiaoleishan and Bifenggang sites located in the southwest and southeast of the Lake,and lowest at the Pingtaishan in the center of the Lake.Regarding the weather process during the three days before 13 typical algae bloom events,there were obvious precipitation before 11 algae bloom events,and cold air transit before 1 event,and clear and hot day before the other event.Especially,algae bloom can occur only10 hours following a rainstorm for one case,indicating that clear day after strong precipitation events was favourable to algae bloom.Tropical cyclone reduced green chromatic coordinate,after then algae bloom occurred severely and lasted for a while due to water temperature stratification and sunny weather.Near-surface remote sensing can provide technical support and data reference for the investigations on lake algae dynamic monitoring and controlling mechanisms.