基于MODIS影像的洪泽湖水生植被覆盖时空变化特征及影响因素分析

Spatio-temporal Variations in Aquatic Vegetation Cover and the Potential Influencing Factors in Lake Hongze Based on MODIS Images

水生植被是湖泊生态系统的重要组成部分,在改善湖泊水质、维护生物多样性方面起到重要的作用.当前我国湖泊普遍面临富营养化和水生植被退化等问题,监测水生植被时空变化特征、探究主要影响因子,对于保护水生植被和修复富营养化湖泊生态系统具有重要意义.因此,本文选用2007~2017年中等分辨率卫星MODIS数据,引入植被频次法(vegetation present frequency,VPF)提取水生植被信息,结合气象因子和人类活动分析了洪泽湖近11 a水生植被的时空变化特征及潜在影响因素.结果表明,洪泽湖水生植被VPF存在着明显的季节和年际变化,VPF春夏显著高于秋冬(P <0. 05,one wayANOVA),最大值0. 43出现在6月,最小值0. 21出现在1月,4~10月生长期显著高于其他月份.年际上,洪泽湖北部湖区(Z1) VPF呈现显著降低的趋势(R2=0. 56,P <0. 01),由2008年的最高值0. 50下降到2016年最低值0. 27,下降了45. 8%,表明水生植被在该地区呈现快速退化趋势.空间上,洪泽湖水生植被VPF整体上由沿岸带向开敞水域递减,其中北部(Z1)和西部湖区(Z2)高于其他湖区(Z3~Z5).洪泽湖全湖VPF年际变化受年均气温、年降水量、年平均风速和年日照时数影响不显著(P> 0. 05),表明气候要素对洪泽湖水生植被年际变化影响较小.在采砂活动和水生植被共同存在的北部湖区,总悬浮物浓度与VPF存在显著负相关(R2=0. 48,P <0. 01),表明采砂导致的总悬浮物浓度增加是影响Z1区域水生植被退化的重要原因,又以采砂区附近表现尤为明显.

Aquatic vegetation is an important part of lake ecosystems and plays a vital role in improving water quality and maintaining biodiversity.At present,China’s lakes are facing eutrophication and the degradation of aquatic vegetation.The monitoring of temporal and spatial variations in aquatic vegetation and elucidating the main influencing factors are of great significance for protecting aquatic vegetation and restoring eutrophic lake ecosystems.Therefore,we introduced the Vegetation Present Frequency(VPF)method to extract data on aquatic vegetation and combined this with meteorological factors and human activities to analyze the temporal and spatial in Lake Hongze based on MODIS data from 2007 to 2017.The VPF of aquatic vegetation in Lake Hongze showed clear seasonal and interannual variations.The VPF was significantly higher in spring and summer than in autumn and winter(P<0.05,one wayANOVA).The maximum VPF of 0.43 occurred in June but the minimum VPF of 0.21 was recorded in January.The VPF from April to October,during the growing season of aquatic vegetation,was significantly higher than in other months.The annual mean VPF of the northern lake area(Z1)decreased significantly(R2=0.56,P<0.01),ranging from the highest value of 0.50 in 2008 to the lowest value of 0.27 in 2016(a decrease of 45.8%),indicating a significant loss of aquatic vegetation.Spatially,the VPF of Lake Hongze decreases from the coastal zone to the open water,and the VPF values of the northern(Z1)and western sub-lakes(Z2)are higher than that of other lakes segments(Z3-Z5).The interannual variation in VPF for the entire lake was not significantly affected by annual mean temperature,annual precipitation,annual mean wind speed,or annual sunshine duration(P>0.05),indicating that meteorological factors have little influence on interannual variation of aquatic vegetation in this lake.However,total suspended matter concentration was significantly negatively correlated with VPF in Z1 area(R2=0.48,P<0.01),with strong sand-mining activities occurring in this area.These results indicate that the increase of total suspended matter concentrations caused by sand mining is an important driving factor in the decline of aquatic vegetation in the Z1 segment.