作为山东第一大湖和南水北调东线工程的必经路线,近年来,南四湖菹草泛滥严重,引发水质污染和河道阻塞等生态问题,对南水北调工程构成季节性威胁。因此,科学地提取湖区中的菹草,明确其时空变化特征对后续治理工作具有重大意义。基于MODIS MOD13Q1 16d合成数据提取的南四湖不同地类的NDVI时序曲线的特征差异及物候信息,结合Landsat系列数据监督分类的结果,借助决策树及遥感动态监测手工阈值设定方法,对多年间湖区菹草群落分别进行提取,探究菹草群落的时空分布特征。研究结果表明,自2000年起,南四湖菹草群落面积呈大幅增长趋势,由1988年的25.22km ²上升至2018年的171.46km ²,且由湖岸地区蔓延至湖心,占湖区面积比由3.61%上升至24.55%,尤其是微山湖最为明显。年际尺度上,菹草已由普通优势种演变为湖区绝对优势种。经过Spearman秩相关分析和Pearson相关分析发现,菹草面积与湖区营养盐和富营养化程度等指标的相关系数均显著高于0.8(P<0.05),相关性显著。南四湖菹草的泛滥现状对南四湖生态治理提出了更高的要求,应加大治理力度以防其对南水北调水质造成影响。

Nansi Lake is the largest lake in Shandong province and one of the largest freshwater lakes in China.In recent years,Nansi Lake has been threatened by the serious flooding of Potamogeton crispus L. From April to May, P.crispus grows vigorously in the lake area,becoming the only dominant species in the submerged plant area.In June, P.crispus declines rapidly,which not only causes severe ecological problems such as water pollution and waterway blocking,but also becomes seasonal threats to the water quality of the South-to-North Water Transfer Project.Based on the characteristics and phenological information shown by the NDVI time-series curves of different typical landscape extracted from MODIS MOD13Q1 16d that are combined with Landsat data,the community of P.crispus in Nansi Lake was extracted and visualized as the distribution maps.The results showed that from the beginning of 21st century,the area of P.crispus in Nansi Lake increased from 25.22 km ² in 1980s to 171.46 km ²in 2018,and that the distribution range of P.crispus had been expanded from the lakeside to the centre of the lake from past 30 years,with the ratio increasing from 3.61% to 24.55%.On inter-annual scales, P.crispus developed from an ordinary dominant species into an absolute dominant species in the lake.Additionally,the Pearson Correlation and the Spearman Rank Correlation Analysis were used to reveal the correlations between the area of P.crispus and lake eutrophication level or water quality.Results revealed that there was no correlation between the area of P.crispus and water quality,but the correlations were significantly positive between the area of P.crispus and the other three related factors.Specifically,the correlation coefficients are higher than 0.8,which means a significantly positive correlation.The current situation of the P.crispus in Nansi Lake ask a higher requirements for the management in Nansi Lake.Departments should strengthen the control of P.crispus in order to prevent further extension in Nansi Lake.