鄱阳湖采砂南移扩大影响范围——多源遥感的证据

Abstract

采砂是一项具有巨大生态影响的经济活动。利用多源遥感影像描述鄱阳湖中部的采砂分布,分析其对悬浮泥沙浓度的影响。2011年7月28日的Landsat Thematic Mapper (TM) 5用于采砂相关船只的识别,2009-2011年7-8月的Terra卫星中分辨率成像光谱仪(MODIS)影像用于悬浮泥沙浓度的反演,(Before-after-control-impact,BACI)方法用于采砂影响评价。Landsat TM 5影像解译结果发现鄱阳湖中部的两个采砂区和90余艘船只,MODIS Terra反演结果显示在采砂区及其下游区域悬浮泥沙浓度剧增,BACI评价结果揭示采砂是导致此区域悬浮泥沙浓度增加的主要因素。平衡经济发展与生态保护之间的关系,将因采砂而造成的负面影响降到最低,使鄱阳湖的各种生态功能全面发挥是紧要的。;Lakes provide multiple functions to society through commerce, aesthetics, tourism, recreation and biodiversity conservation. Dredging occurs frequently in many lakes, rivers, harbors, or coastal areas to maintain adequate water depths for navigation, provide sand and gravel for construction and reclamation projects, or to remove contaminated sediment to improve water quality and restore the health of aquatic ecosystems. However, long-term and intensive dredging can also cause disturbances to aquatic ecosystems with adverse impacts. Dredging stirs up sediment, increases suspended sediment concentration and reduces water clarity. Thus, dredging alters the physical, chemical and biological properties of the aquatic environment, and further might affect the provision of lake functions. Dredging in Poyang Lake started in 2001. After the activity was banned from the Yangtze River, it increased in Poyang Lake because of the rapidly rising demand for sand in order to support construction in the lower Yangtze River economic zone. The benefits to the local economy are likely to further have persuaded the local government to allow and possibly promote dredging in this lake. Dredging in Poyang Lake was focused at the north of Songmen Mountain before 2010, while the activity has moved to the central parts of Poyang Lake during the most recent two years. However, the distribution of dredging in central Poyang Lake and its impact zone and intensity are not clear. This study, using multi-remote sensing images, aimed to describe the distribution of dredging activities in central Poyang Lake, and further analyze its impact on suspended sediment concentrations (SSC). The Landsat Thematic Mapper (TM) 5 captured on July 28, 2011 was employed to identify the dredging-related vessels through visual interpretation. Moderate resolution imaging spectroradiometer (MODIS) images from the Terra satellite taken over the months July-August for three years (2009-2011) combined with a regression model were applied to retrieve the SSC in Poyang Lake, and the before-after-control-impact (BACI) method with three evaluated regions was used to assess the impact of dredging on SSC. Two dredging regions and more than 90 vessels were observed from the TM 5 image in the central Poyang Lake. The MODIS-based SSC values indicated that the SSC increased in the dredging regions and their downstream impact zones from < 10 mg/L before dredging to > 50 mg/L after the start of dredging. The BACI analyses confirmed that dredging increased the SSC in Poyang Lake by comparing an impacted region with a non-impacted region. Currently, many lakes around the world are suffering a number of problems caused by natural and/or human factors, which may hamper the sustainable developments of multiple lake functions. Remote sensing techniques may provide methods to obtain the spatio-temporal variations of these problems, which will help managers or researchers to analyze and understand the processes and mechanisms in lakes and make sound decisions for lake management. Poyang Lake is an important habitat for several rare or endangered species, such as the baiji (<em>Lipotes vexillifer</em>), Chinese sturgeon (<em>Acipenser sinensis),</em> white sturgeon (<em>Acipenser transmontanus</em>), and Yangtze finless porpoise (<em>Neophocaena phocaenoides</em>). The lake is reputed to be the most important habitat for wintering waterfowl in East Asia, and more than 95% of the Siberian crane (<em>Grus leucogeranus</em>) population winters here. Dredging has seriously affected directly or indirectly the survival of these rare or endangered species. There is an urgent need to balance the relationship between economic development and ecological conservation, minimize the negative effects of dredging and preserve the various productive, environmental and ecological functions provided by Poyang Lake.