Capturing the rapid intra-day change of cyanobacteria bloom by land-based hyperspectral remote sensing in Lake Taihu

Abstract

受蓝藻自身垂直迁移和频繁风浪扰动影响，太湖蓝藻水华漂浮混合和迁移堆积等变化迅速，在传统的湖面定位和断面监测中总感觉蓝藻水华有些来无影、去无踪，限制了对其形成过程、驱动机制和防控治理的深入认识.卫星遥感可以实现蓝藻水华空间分布同步观测，但由于观测频次的限制很难捕捉蓝藻水华快速动态变化过程.本文利用与杭州海康威视数字技术股份有限公司联合自主研发的陆基（地基、岸基或者平台、船舶、桩基等能固定安装的均可）高光谱多参数水质遥感监测仪，架设于中国科学院太湖湖泊生态系统研究站（简称太湖站）水上观测场，通过对叶绿素a浓度及其他关键水质参数秒-分钟级的连续观测，有效捕捉了一天内蓝藻水华短期突然和快速变化过程.研究结果显示，在微风和小风条件下蓝藻容易在表层水体漂浮，盛行西北风驱动湖面开敞水域蓝藻水华快速漂浮集聚到太湖站岸边，短短半小时内表层水体叶绿素a浓度可以由10 μg/L快速攀升到100 μg/L以上，一天内会出现多个叶绿素a峰值，清晰展示了蓝藻快速日内动态变化过程.受蓝藻快速日内变化影响，透明度、总氮、总磷和高锰酸盐指数等水质参数也呈现出快速日内变化，叶绿素a浓度与透明度存在极显著负相关，与总氮、总磷和高锰酸盐指数存在极显著正相关，叶绿素a能解释总氮、总磷80%以上的变化，说明蓝藻短期内的漂浮和集聚深刻影响到湖泊水质.;Due to the vertical migration of cyanobacteria and frequent wind waves disturbance, the floating, mixing, migration and accumulation of cyanobacteria bloom in Lake Taihu occur rapidly. It is very difficult to accurately capture cyanobacteria bloom occurrence and appearance using the traditional lake positioning and cross-section monitoring due to low temporal and spatial observation frequency and resolution, which limits the in-depth understanding of cyanobacteria bloom formation process, driving mechanism, prevention and control. Satellite remote sensing can realize the synchronous observation of the spatial distribution of cyanobacteria bloom, but it is difficult to capture the rapid dynamics of cyanobacteria bloom due to the limitation of observation frequency. Using independently developed land-based (ground-based, shore-based, or fixed on the platform, ship and pile foundation) hyperspectral water quality remote sensing instrument by the Hangzhou Hikvision Digital Technology Co., Ltd and Nanjing Zhongke Deep Insight Technology Research Institute Co., Ltd installed in Taihu Laboratory for Lake Ecosystem Research (TLLER) of Chinese Academy of Sciences, the short-term sudden and rapid cyanobacteria bloom dynamics in a day was effectively captured through the continuous observation of chlorophyll-a concentration and other key water quality parameters at the second-minute level. The results show that cyanobacteria are easy to float in the surface water under the conditions of breeze and light wind, and the prevailing northwest wind drives the cyanobacteria bloom in the open water area of the lake to float and accumulate to the shore of TLLER quickly. Chlorophyll-a concentration in surface water can rapidly rise from 10 μg/L to more than 100 μg/L in just half an hour. Several chlorophyll-a peaks are recorded in a day from 8:30 to 18:30. All these results clearly show that cyanobacteria have a rapid hourly dynamic change process. Affected by the rapid hourly variations of cyanobacteria, water quality parameters such as secchi disc depth, total nitrogen, total phosphorus and chemical oxygen demand also show rapid hourly variations. Significantly negative relationship between chlorophyll-a and secchi disc depth but significantly positive relationships between chlorophyll-a and total nitrogen, total phosphorus, chemical oxygen demand are found, which indicate short-term floating and gathering of cyanobacteria have a profound impact on the water quality of lakes.