| 摘要: |
| 面积是湖库蓝藻水华强度的重要表征指标之一，其变化受水体营养物质状况、水文气象条件及食物链结构等多种因素综合影响。揭示蓝藻水华面积与环境因子的关系对于科学评估蓝藻水华强度、制定防控措施具有重要意义。本研究基于太湖2003~2023年2332幅卫星遥感影像提取的蓝藻水华面积数据，结合同期湖体营养盐及水文气象观测数据，探讨了影响太湖蓝藻水华面积的主要环境因子及其年内变化。结果发现，2003年至2023年，太湖蓝藻水华年平均面积总体呈现周期性波动，多年均值为159 km2，其中水华季（5~9月）的多年均值为223 km2。蓝藻水华面积与水体叶绿素a及微囊藻生物量均呈显著相关关系，相关系数分别为0.47及0.48，表明遥感获得的蓝藻水华面积能够较好指征蓝藻水华强度变化情况。2005~2023年太湖水体总氮（TN）、溶解性总氮（DTN）浓度下降显著，2023年TN均值较2005年下降61%，DTN下降65%，总磷（TP）、溶解性总磷（DTP）也呈现出波动下降趋势。随机森林分析表明，蓝藻水华面积的影响因子随季节变化而变化，春季的主导因素是水温、TP与风速；而夏季的主导因素依次是风速、DTN和水位；秋季的主导因素是风速、TN和水位；冬季的主导因素是风速、DTN和DTP；具体到月尺度上，蓝藻水华面积的影响因子也呈现月间差异。基于蓝藻水华面积与水体TN、TP的统计关系，若要大概率控制太湖处于无明显水华状况（月均蓝藻水华面积小于103 km2，约为湖泊面积的5%），则建议冬春季TN和TP的浓度控制阈值分别为1.35 mg/L和0.054 mg/L，或DTN为1.03 mg/L及DTP为0.018 mg/L；夏秋季TN和TP控制阈值分别为1.00 mg/L和0.059 mg/L，或DTN为0.62 mg/L、DTP为0.015 mg/L。研究表明，遥感影像提取获得的蓝藻水华面积总体能够较好指示大型湖泊的蓝藻水华强度状况；太湖蓝藻水华面积在夏秋季节受风速变化的影响较大，但氮、磷等营养盐水平也是影响蓝藻水华面积变化的重要因子，其中冬春季磷的影响大，而夏秋季氮的影响大；从控制策略上，实施氮磷双控是有效降低蓝藻水华风险的根本途径。 |
| 关键词: 浅水湖泊 蓝藻水华 气象条件 季节变化 氮磷双控 |
| DOI： |
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| 基金项目:国家自然科学基金国际合作项目（42220104010）、江苏省自然科学基金（BK20220041）、中国科学院南京地理与湖泊研究所自主部署项目（NIGLAS2022GS03） |
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| Control factors of cyanobacterial bloom area in Lake Taihu, China （2003-2023） |
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YANG Zhi-xuan1, LI Yun-xiang1, ZHU Guang-wei2, KANG Li-juan2, LI Na2, ZHANG Yun-lin2, QIN Bo-qiang2
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1.College of Environmental Science and Engineering,China West Normal University,Nanchong;2.Nanjing Institute of Geography and Limnology,Chinese Academy of Sciences
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| Abstract: |
| Surface area is one of the important indicators of the intensity of cyanobacterial blooms in lakes and reservoirs, and its changes are affected by a combination of factors such as the nutrient status of the water body, hydrometeorological conditions and the structure of the food chain. Revealing the relationship between the area of cyanobacterial bloom and environmental factors is of great significance for the scientific assessment of the intensity of cyanobacterial bloom and the formulation of preventive and control measures. Based on the cyanobacterial bloom area data inverted from 2332 satellite remote sensing images of Lake Taihu from 2003 to 2023, combined with the nutrient salts of the lake and hydrometeorological observation data during the same period, this study explored the main environmental factors affecting the area of cyanobacterial bloom and their intra-annual changes in Lake Taihu. The results showed that the annual mean cyanobacterial bloom area of Lake Tai was 159 km2 from 2003 to 2023, of which the multi-year mean value of the bloom season (May to September) was 223 km2, with the peak occurring in 2017, when the annual mean area of the bloom reached 291 km2, and the mean area of the bloom season was 363 km2. The area of the cyanobacterial bloom was significantly correlated with the chlorophyll a and microcystin biomass in the same period, with correlation coefficients of 0.47 and 0.48, respectively, indicating that the area of the cyanobacterial bloom obtained from remote sensing can better characterise the overall situation of the intensity of the cyanobacterial bloom. The annual average area of cyanobacterial blooms in Lake Taihu from 2003 to 2023 generally showed cyclic fluctuations, which could be roughly divided into four stages, (1) The area of cyanobacterial bloom firstly increased and then decreased from 2003 to 2008, with large fluctuation; (2) The overall area of cyanobacterial bloom from 2009 to 2015 was low, with small change; (3) The area of cyanobacterial bloom from 2016 to 2020 was obviously increased, with high fluctuation; (4) The area of cyanobacterial bloom from 2021 to 2023 showed a rapid decreasing trend, in which the annual mean area of bloom in 2023 will be 77 km2, and the mean area of the bloom season will be 116 km2 , which is the lowest value in the study period. The concentrations of total nitrogen (TN) and dissolved total nitrogen (DTN) in the water body of Lake Taihu from 2005 to 2023 declined significantly, with the average value of TN decreasing by 61% and DTN decreasing by 65% in 2023 compared with that of 2005, and total phosphorus (TP) and dissolved total phosphorus (DTP) also showed fluctuating downward trends. Random forest analysis showed that the environmental factors affecting the area of cyanobacterial blooms varied seasonally, with the dominant factor in spring being water temperature, followed by TP and wind speed; whereas in summer, the dominant factor was wind speed, followed by DTN and water level; in autumn, the dominant factor was wind speed, followed by TN and water level; and in winter, the dominant factor was wind speed, followed by DTN and DTP, and, specifically, on the monthly scale, the area of cyanobacterial blooms factors also showed inter-monthly differences. Based on the relationship between the area of cyanobacterial bloom and the TN and TP of the water body, if we want to control Lake Taihu to be in the condition of no obvious bloom with high probability (monthly average cyanobacterial bloom area is less than about 5 per cent of the lake area, set at less than 103 km2 for Lake Taihu), it is recommended that the control thresholds for TN and TP in winter and spring should be 1.35 mg/L and 0.054 mg/L, respectively, or DTN 1.03 mg/L and DTP 0.018 mg/L; the control thresholds for TN and TP in summer and autumn are 1.00 mg/L and 0.059 mg/L, respectively, corresponding to 0.62 mg/L for DTN and 0.015 mg/L for DTP. The study shows that the area of cyanobacterial bloom obtained from remote sensing image inversion can be a good indicator of the intensity of cyanobacterial bloom in large lakes; the area of cyanobacterial bloom in Lake Taihu is greatly affected by the change of wind speed in summer and autumn seasons, but the level of nitrogen, phosphorus and other nutrient is also an important factor affecting the change of the area of cyanobacterial bloom, among which the effect of phosphorus is large in winter and spring, and the effect of nitrogen is large in summer and autumn; the implementation of nitrogen-phosphorus dual-control is the fundamental way of effectively reducing the risk of cyanobacterial bloom in the control strategy. The implementation of dual control of nitrogen and phosphorus is a fundamental way to reduce the risk of cyanobacterial bloom. |
| Key words: Shallow lake cyanobacterial blooms meteorological condition seasonal variation dual control of nitrogen and phosphorus |
