1973-2013年黄河三角洲湿地景观演变驱动力

1973-2013年间,日益加剧的人类活动和愈发严峻的自然环境对黄河三角洲湿地景观形成巨大威胁。人与自然双重影响下黄河三角洲湿地发生了怎样的变化,哪些因素、多大程度上导致了这种变化的发生,科学解答这些问题对于加强黄河三角洲湿地保护具有重要意义。以Landsat卫星1973-2013年40a的9期影像为数据源,利用人工目视解译方法构建研究区景观数据库,在分析研究区景观特征的基础上,通过主客观相结合的方法,构建了能够反映黄河三角洲地区景观湿地化和人工化状态的表面湿地-人工状态指数(SWCSI)。结合黄河入海水沙、区域降水以及地方生产总值(GDP)、水产品产量和原盐产量,分别从区域尺度和像元尺度上,定量分析了过去40年黄河三角洲湿地景观演变的驱动力及其空间差异。研究表明:(1)过去40年来,黄河三角洲自然湿地面积不断萎缩,人工湿地增加,湿地总面积减小,黄河三角洲整体上呈现出人工化或湿地退化趋势,同时也存在明显的空间异质性:滨海地区以人工化和湿地退化趋势为主,黄河入海口地区以湿地化趋势为主,中西部和西南部传统农耕区基本无变化。(2)黄河三角洲湿地景观的人工化或湿地退化趋势是过去40年来黄河水沙减少、人类活动加剧共同作用的结果。区域尺度上,人类社会经济活动对黄河三角洲湿地景观演变起主导作用,黄河径流量和输沙量的作用明显弱于社会经济因素。像元尺度上,驱动因素的空间异质性是导致黄河三角洲湿地景观演变空间异质性的原因。湿地的发展主要归因于自然因素,以黄河水沙作用最为关键;湿地的人工化或退化过程以人类社会经济活动的强制改造为主导,但是否伴随黄河水沙变化的潜在影响,对特定区域而言应是确定的,但仍很难从像元尺度进行量化。

Quantitative analysis of the factors driving evolution in the Yellow River Delta Wetland in the past 40 years

The Yellow River delta is one of the most active regions in the world, where wetlands play a significant role in balancing the regional eco-environment. However, in past decades, it has been subjected to severe disturbance by nature and by humans. Thus, it is critical to figure out what changes have occurred during this period and what could be done in this region now to protect the local wetland system. Therefore, in this study, we took Landsat satellite imagery from 9 years (1973, 1979, 1985, 1992, 1995, 2000, 2005, 2010, and 2013) as data sources to build wetland thematic databases using the method of visual interpretation. Based on these databases, a Surface Wetland and Construction State Index (SWCSI) was constructed to indicate the state of the land cover. These were combined with Yellow River runoff and sediment data, regional precipitation, local GDP, aquatic product output, and crude salt output. Then, the driving forces and corresponding spatial heterogeneity of wetland variations in the past 40 years in regions of the Yellow River delta were quantitatively analyzed at regional and pixel scales. From this research, we concluded that the area of wetland in the Yellow River Delta declined during the years 1973-2013, accompanied by large-scale conversion of natural wetlands to artificial wetlands and non-wetland. In the past 40 years, the area of natural wetlands decreased by 42.67% (annual reduction of 30.58 km²). In contrast, the area of artificial wetlands increased by 490.52% (annual increase of 24.47 km²). As a result, the total wetland area was reduced by 7.99% (annual reduction of 6.13 km²). The variations of wetland in the Yellow River delta showed high spatial heterogeneities. Wetlands in coastal regions experienced artificial enhancement or wetland degradation, while those in estuarine regions experienced wetland construction and development; however, there were no changes in the western and southwestern traditional farming districts. On the regional scale, GDP was the dominant driving force for wetland variation in the Yellow River Delta. In the past 40 years, intensifying human activities and decreasing Yellow River runoff and sediment made a number of important changes (decreases in natural wetlands, increase in artificial wetlands, and degradation of regional wetlands) more serious. In contrast, a large area of natural wetland was constructed and developed in the estuary of the Yellow River because of the continuous runoff and sediment supply, although there has been an overall decline in these factors during the past 40 years. Therefore, the Yellow River runoff and sediment still played an important role in the evolution of wetlands in the Yellow River Delta, but this role was not very significant because these influences were regionally limited. The influence of regional precipitation on wetland evolution was extremely limited. This was perhaps due to the severe dependence of the regional wetlands on runoff. At the pixel scale, the driving factors of evolution of the Yellow River delta wetlands showed obvious spatial heterogeneity. This was mainly due to the spatial heterogeneity of driving force factors themselves.