1999～2007年天津湿地景观格局及水鸟生境变化

Changes of Wetland Landscape Pattern and Water Birds'Habitat in Tianjin during 1999-2007

天津市湿地是亚洲东部候鸟南北迁徙的重要驿站,有大量属国家一、二级保护的鸟类。近几十年来,受人类活动和自然因素变化影响,天津市湿地景观结构发生巨大变化,对湿地鸟类栖息地环境和鸟类迁徙、繁殖产生了不利影响。在遥感和地理信息系统技术的支持下,以天津市1999年、2003年和2007年3期TM影像为数据源,采用目视解译分类方法,并结合其他非遥感以及高清晰影像作为辅助资料,获得了天津市湿地基本信息;在此基础上,将天津市湿地分成2大类12小类;利用ArcMap软件,分析了3个时期湿地面积的变化;利用Frag-stats3.0软件和Excel软件,得到天津市湿地景观格局的动态变化。研究结果表明,天津市湿地总面积从1999年的312088.73hm2增加到2007年的328133.61hm2,面积增加了4.89%;湿地面积增加的主要原因是人工湿地盐田面积大幅增加,人工湿地8年间共增加了24043hm2,其中,盐田面积增加了25699.57hm2,但天然湿地面积减少了7.38%。天津市湿地景观的破碎化程度在一直加剧,斑块类型更加多样化,湿地景观中没有明显的优势类型,且各斑块类型在景观中均匀分布。湿地类型转化的基本规律表现为天然湿地向人工湿地、人工湿地向农林用地、农用地向建设用地转换,人类的开发活动已经转向一些人为干扰较少的潮间带、滩涂区以及河流河口水域、浅海水域、湖泊和沼泽等地区。将各种驱动因素加以组合,归纳为2大类和20个变量指标,建立湿地景观变化驱动因素指标体系。分析表明,人口和经济因素对湿地景观格局变化有显著影响。随着经济发展水平的提高,天津市产业结构并未得到改善,尤其是第二产业仍然占较大比重;城市人口急剧增长,快速城市化导致的城市实体扩张占用大量农田和湿地;在农业因子中,粮食产量的提高与通过占用湿地来扩大种植面积有直接关系。1999～2007年间,天津湿地水鸟生境发生了明显变化,深积水区面积和斑块数量逐年增加;无隐蔽物的湿地面积和人工建筑物的面积大幅增加,重干扰区的面积增加;水鸟的水生动物性食物增多,谷物草籽等植物性食物减少。人类活动已对天津湿地水鸟生存环境构成严重威胁。总体上,天津湿地水鸟生境质量在下降。

The wetlands in Tianjin are of local,regional and international significance for south-north migratory birds in eastern Asia,a large number among which are listed in the Red Book of China.However,in recent decades due to human activities and natural factors,the changes of wetland landscape pattern have caused distinct ecological effects on water birds＇habitat,migration and propagation.Supported by the technique of remote sensing and geographical information system,this research used TM images of Tianjin city in 1999,2003 and 2007 as the data source to acquire the data of wetlands.The main classification and mapping method is traditional visual interpretation in combination with non-remote sensing images and other materials with high resolutions.According to the condition of study area,the wetlands were divided into 2 major categories and 12 sub-classes.The patch changes during 3 periods were analyzed by ArcMap software and the change of wetland landscape pattern was processed by using softwares of Fragstats 3.0 and Excel.The result showed that the total area of wetlands increased 4.89%,from 312 088.73 ha in 1999 to 328 133.61 ha in 2007,mainly attributing to the increase of constructed wetlands,especially salt fields.The salt fields increased significantly from 24 043 ha in 1999 to 25 699.57 ha in 2007,while natural wetlands lost 7.38% on the contrary.Some important landscape pattern indices calculated showed that in the spatial distribution the degree of the wetland landscape fragmentation was aggravated.Wetland types were getting more diversified,evenly distributed in the research area without apparent advantage ones.The transition rule of main wetland type is natural wetlands to constructed ones,then to agricultural fields and forests,finally to human development areas.Human development activities have shifted to inter-tidal zone,tide silt beach,river estuary,shallow sea,swamps and reservoir which were less disturbed before.The paper selected 20 variables for indices system of driving factors,and divided them into 2 types：social and natural ones.Among the social driving factors,demographic and economic factors have significant impact on the change of wetland landscape pattern.Further analysis explained that,with fast economic development,the industrial structure did not improve,especially the large proportion of secondary industry.Population factor reflected that associated with the urban population growth,rapid urbanization has led to urban physical expansion of intensive agricultural fields and wetlands.Food production increase was achieved via expanding the farmland to wetlands,and new agricultural technology improvement could help wetland landscape pattern.Wetland landscape pattern change has an important impact on waterfowl habitats.The analysis with water,food,hidden object and interference factors showed that the habitat of water birds changed obviously.Considering the water bird species and migration character,and interference factor as the origin for the other factors,the quality of water bird habitats in Tianjin declined dramatically.