Detection of temporal and spatial variation of Huangtai algae bloom using MODIS satellite data in Lake Ulansuhai from 2000 to 2010

Abstract

利用2000-2010年每年5-9月MODIS数据根据比值算法提取乌梁素海湖区黄苔的面积和空间分布信息并进行统计分析,探求乌梁素海黄苔产生的时空分布规律及特征,从而为黄苔的预防和治理提供支持.结果表明:(1)黄苔面积变化的年际和月际特征方面,2000、2001、2005、2006、2008、2010年黄苔面积超过了多年平均值(24 km²).5-7月份黄苔面积较小,保持在20 km²左右;8月黄苔面积迅速增长(约28 km²),9月黄苔面积最大,达到40 km²左右.(2)黄苔发生频率方面,2001年黄苔的规模和频率最高,发生频率达到0.58;2005、2006、2010年次之,发生频率在0.25附近波动(多年年均黄苔暴发频率为0.19);其他年份黄苔的发生频率处于低于0.10的水平.黄苔发生规模较大、次数较多的月份集中在8、9月,发生频率分别达到0.27、0.52,超过多年月均黄苔暴发频率0.19;其他月份黄苔的发生频率处于低于0.10的水平.(3)黄苔出现的空间分布方面,西大滩为东大滩的北部至中部,以及乌梁素海南部明水区排干口附近的西部沿岸是黄苔出现频率较高的区域.(4)2个月前的日均温度、降雨和营养盐浓度及当月风速与黄苔的产生具有极显著相关性;营养盐含量(TN、TP)的空间分布与黄苔的空间分布表现出较好的相关性.乌梁素海黄苔面积的年际变化受人类活动特别是生态补水的影响明显.;Understanding the temporal-spatial distribution characteristics of Huangtai algae bloom can provide support decisionmaking for prevention and control of Huangtai algae bloom in Lake Ulansuhai, China. Cloud-free images shot by MODIS sensor from May to September and from 2000 to 2010 were utilized to extract algae bloom area and spatial distribution by means of Normalized Difference Vegetation Index. According to the analysis, conclusions are as below:(1) as for area variation, Lake Ulansuhai had a severe situation of Huangtai algae bloom in 2000, 2001, 2005, 2006, 2008 and 2010, more than the average of the whole period (24 km²). In regard to monthly variation, Huangtai algal areas in May, June, July remained low around 20 km². Yet Lake Ulansuhai have larger Huangtai algal areas in August and September, around 28 km² and 40 km², respectively. (2) As for occurrence frequency, the highest frequency of Huangtai algae bloom occurred in 2001 (0.58), followed by 2005, 2006 and 2010 fluctuating around 0.25 (higher than the average of 11 a, 0.19); occurrence frequency in other years kept a low level around 0.10. In the aspect of monthly variation, occurrence frequency in May, June, July kept a low level around 0.10. The times of Huangtai algal bloom experienced a more rapid increase and a larger scale of outbreak frequency in August and September, 0.27 and 0.52, respectively, higher than the average of 5 months (0.19). (3) Huangtai algae blooms mostly lied in the region called Xidatan, the north coast and middle of the region called Dongdatan, and along the west coast of south Lake Ulansuhai, where local agricultural irrigation drainage water flows into the lake and thus the most striking algal blooms emerge there. (4) Daily average temperature, precipitation and nutrient concentrations (total nitrogen and total phosphorus) in two months ago have a significant correlation relationship with Huangtai algae's occurrence. Additionally, synchronous wind speed has a significant correlation relationship with Huangtai algae's occurrence. The spatial distribution of nutrient (TN, TP) is well consistent with the distribution of Huangtai algae's occurrence. Human activities, especially artificial supplement for water in Lake Ulansuhai, have great impact on the variation of Huangtai algae occurrences.