洞庭湖景观格局变化及其对水文调蓄功能的影响

景观格局影响并决定着湿地水文调蓄过程和功能。基于洞庭湖区1980、1990、2000和2005年的景观格局数据和相应4年的水文实测数据,利用灰色关联分析,探讨了洞庭湖景观格局变化对水文调蓄功能的影响及其作用机制。结果表明,洞庭湖区景观格局指数与调蓄功能存在不同程度的相关性,其中调蓄量与最大斑块指数和聚合度指数关联度最大,分别为0.77和0.75,说明景观中的优势斑块大小以及同质斑块间的连通性有利于湖区调蓄能力的增加。泥沙沉积率与斑块数、形状指数、多样性指数和均匀度指数关联度也较大,变化于0.7—0.78之间,说明景观的破碎化程度,多样性,形状复杂度的增大会加大湖区泥沙沉积率。分流比、分沙比与景观格局指数的关联度均较小。景观类型指数与调蓄量的关联度分析表明,水田、林地和水体的最大斑块指数和聚合度指数与调蓄量关联度均较高,说明水田、林地和水体最大斑块面积和聚合度的增大有效增大了湖区调蓄能力。

Analysis on the responses of flood storage capacity of Dongting Lake to the changes of landscape patterns in Dongting Lake area

Dongting Lake is an important ecological barrier along the Yangtze River and is also important for social and sustainable economic development. An ecosystem services assessment of Dongting Lake shows flood control and floodwater storage is its most important ecological function. However, we know little about the factors controlling the evolution of the Dongting Lake flood storage function. We especially lack an analysis of the mechanisms of interaction between the landscape structure and flood storage conditions. Any landscape pattern is the result of various combined natural and human factors at different spatial and temporal scales. At Dongting Lake, these factors have had a profound influence and determine the hydrological procession of the wetlands storage capacity of the lake. Exploring the relationship between the structure-procession-function of the Dongting Lake area by studying the landscape patterns with specific ecological functions is very important. This study, based on landscape ecology and hydrology, uses landscape data from the Land TM satellite imagery from the Dongting Lake area from 1980, 1990, 2000, and 2005. Combined with the hydrological measurement data for these four years, the landscape and hydrological data were analyzed by using gray connection analysis, to discuss the influence and mechanisms of the landscape pattern and structure on the lake's flood storage capacity. The results show the landscape pattern of Dongting Lake area changed significantly from 1980 to 2005. The paddy fields, dry land, and human settlement areas changed the most dramatically, while the beaches changed less and forests, grassland and water changed the least. Numbers of patches (NP) of each land type and shape index (LSI) had similar trends, showing a surge between 1980 and 1990, stabilizing from 1990 to 2000, and then decreasing from 2000 to 2005. The aggregation of the various land types and the largest patch index (LPI) changed in different ways. The aggregation index (AI) and LPI of the paddy fields, forest and water changed in similar ways. The value of these indices gradually dropped from 1980 to 2000, and then increased from 2000 to 2005. The AI of the dry lands, grasslands, beaches and villages, and other types have contrasting changes when compared with the paddy fields; these increased from 1980 to 2000 and then decreased from 2000 to 2005. Flood storage capacity of the Dongting Lake area decreased in the first part of the study period and then increased later. This corresponded to the landscape pattern changes. Gray connection analysis showed there was clear relationship between the landscape patterns and flood storage capacity. The correlation was largest between the flood retention amount and the indices of LPI and AI, with correlation values of 0.77 and 0.75, respectively. This shows the obvious relationship between dominant patch size and the aggregation of homogeneous patches with flood storage capacity. The correlation is also pronounced between the silt deposition ratio and the NP and LSI indices, whose correlation values were 0.7 and 0.78, respectively. This illustrates the positive correlation between the silt deposition ratio and the scale of landscape fragmentation, diversity and shape complexity. The correlation was small between the landscape pattern indices and the flow diversion and sediments diversion ratios. The landscape indices and storage capacity correlation analysis revealed a high correlation between the flood retention capacity and the LPI and AI indices of paddy fields, woodlands, and water area. In conclusion, an increase of the LPI and AI of the paddy fields, woodlands, and water area would be helpful in increasing the flood storage function of Dongting Lake.