基于时序NDVI的东平湖菹草(Potamogeton crispus L.)遥感提取及时空格局

东平湖是国家南水北调东线工程的重要枢纽.但近年来，东平湖菹草（Potamogeton crispus L.）大量繁殖引起河道阻塞、鱼类死亡等事件频发，导致湖区面临很多生态风险.为维护区域生态安全，迫切需要了解菹草群落在东平湖的时空演变特征及驱动因素.利用MODIS植被指数时序数据结合野外调研，建立菹草群落独特的物候曲线，并结合Landsat数据进行了1985-2017年东平湖菹草识别分析.结果表明：32年间菹草群落不断扩张，生境由1991年前零星分布于湖岸发展到2013年蔓延至全湖且连片式分布.菹草群落的增长分为3个阶段：1996年之前，面积增长缓慢，1996年其面积仅10.34 km²；1996-2001年菹草呈暴发式增长，菹草变为区域优势种；2001-2017年，菹草面积继续增长，到2017年达49.07 km²，约占湖区水域面积的40%.经Spearman秩相关分析，菹草面积与湖水营养化水平显著正相关.南水北调东线工程的通水虽使水质有所改善，但东平湖菹草群落仍呈增长态势，应引起足够重视.

Spatio-temporal pattern of Potamogeton crispus L. in Lake Dongping based on NDVI time series

Lake Dongping is the second largest freshwater lake in Shandong Province. It is also an important junction on the east route of south to north water transfer project and on the route of the west to east water transfer. However, Potamogeton crispus L. community''s expansion has caused a series of ecological issues, including the waterway blocking and a large number of fish death. In order to maintain the ecological environment security in Lake Dongping, there is an urgent need to understand the spatial and temporal characteristic and the inducements of P. crispus community''s expansion. We employed moderate-resolution imaging spectroradiometer (MODIS) NDVI data and the field investigation to extract the phenological characteristic curve of P. crispus. According to the P. crispus growth characteristics, the Landsat images at P. crispus flowering phase and decline phase in eight different years during 1985 and 2017 were used to extract and analyze the P. crispus distribution characteristics. The results showed that P. crispus community expanded continuously in the past 32 years. Its habitat changed from the scattered distribution in near shore in 1991 to the continuous distribution in whole lake in 2013. The period of P. crispus community growth was divided into three stages. Before 1996, it is a slow growth, with 10.34 km². During 1996-2001, it was an explosive growth feature and P. crispus has become the dominant species in Lake Dongping. During 2001-2017, the area continues to increase to 49.07 km² in 2017, accounting for 40% of the water area of Lake Dongping. Spearman rank correlation analysis showed that there was a significant correlation between P. crispus area and lake eutrophication level. Although with the opening of east route of south to north water transfer project and increased management for Lake Dongping, P. crispus community still shows continuous growth and the ecological risk caused by P. crispus is still not solved. The managers should pay more attention to this issue.