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

Abstract

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.