近20年白洋淀湿地水文连通性及空间形态演变

水文连通性是表征湿地格局和功能稳定性的重要指标,连通性的降低通常意味着湿地生态功能的退化,内部能量流动和养分循环的扰乱。选取京津冀最具典型性的白洋淀湿地为案例,将形态学空间格局分析模型(MSPA,Morphological Spatial Pattern Analysis)与连通性指数(IIC,Integral Index of Connectivity;PC,Probability of Connectivity)相结合,从时空两方面分析了白洋淀湿地水文连通性的变化,总结出水文连通性变化的空间形态演变规律。结果表明,1990—2015年间,白洋淀湿地整体连通性较差,以2005年为节点呈现先降低后逐步恢复的趋势;根据MSPA功能类型的变化,将白洋淀湿地空间形态演变分为消退期与恢复期两个阶段。消退期主要表现为核心斑块逐步分裂为分支、环岛、桥接、孤岛等细碎斑块,然后逐渐消退的过程;恢复期各类型主要表现为核心湿地面积逐渐增加,分支向桥接转变的过程。其中核心湿地的面积由1990年的8974.90 hm2,最低下降到2005年2092.97 hm2,到2015年又恢复到4122.14 hm2。整体而言,核心湿地的变化对白洋淀湿地水文连通性变化起主导作用。白洋淀湿地水文连通性降低的影响因素主要有上游补给水量的多少,土地利用变化以及气候变化等因素。研究将MSPA模型与连通性指数相结合的方法,能较好揭示湿地水文连通性变化过程中水文形态组织和运行变化的规律,可为其他地区湿地相关研究提供方法上的借鉴。

Changes in hydrological connectivity and spatial morphology of Baiyangdian wetland over the last 20 years

Hydrological connectivity is an important stability indicator of the pattern and function of wetlands. A decrease in hydrological connectivity of wetlands usually indicates the degradation of ecological functions, and the disruption of internal energy flow and nutrient circulation. Baiyangdian Lake is the most typical and representative wetland in Beijing, Tianjin, and Hebei provinces. Based on morphological spatial pattern analysis (MSPA) and connectivity indices, we chose Baiyangdian Lake as a study case for analyzing the changes in its hydrological connectivity at the spatial and temporal scales, and for summarizing the morphological and spatial processes. The results show that the hydrological connectivity of the Baiyangdian wetland was generally weak from 1990 to 2015, which reduced between 1990 and 2005, but gradually recovered thereafter. The mechanism of spatial and temporal evolution of the Baiyangdian wetland can be divided into two stages according to the changes in landscape function type of the MSPA: the period of degradation between 1990 and 2005, and the period of recovery between 2005 and 2015. During the period of degradation, the core wetlands were partly divided into fine patches such as branches, loops, bridges, and islets, and then disappeared gradually. During the recovery period, the core wetlands extended, whereas the branches converted to bridges. The core wetland area decreased from 9974.90 hm² in 1990 to 2209.97 hm² in 2005 and increased thereafter to 4122.14 hm² in 2015. The changes in area and morphology of core wetlands dominated the changes in hydrological connectivity of the Baiyangdian wetland. The driving factors for the decrease of hydrological connectivity in Baiyangdian wetland are mainly the amount of upstream recharge water, land use changes, and climate change. The present study shows that the MSPA model combined with connectivity indices can explain the organization and operation mechanism of wetland hydrological connectivity well, which would provide essential background for other related studies.