基于淤积量的崇明东滩促淤围垦合理性评价

摘要

精准围垦的生态预警研究,需要从较短的时间尺度上和较集中的空间尺度上及时精准地监测滩涂的淤积量和淤积位置,这是滩涂围垦工程规划和实施的参考依据.以崇明东滩为例,结合滩涂湿地淤积量的直接测定和滩涂微地貌调查,尝试基于淤积量长期累积的相对高程评价促淤围垦的合理性.淤积量的测定结果表明:①微地形下的植被群落分带差异大到足以掩盖高程逐渐下降的梯度趋势;②潮间带和高潮滩的年均淤积速度均不足1 cm,而低潮滩的年均淤积速度达到了7 cm左右;③微地貌高程与淤积量之间呈极显著的负相关关系,呈现出两种不同的淤积机制.在此基础上,对目前以"生物促淤+物理围垦"的模式治理互花米草外来种入侵的促淤围垦进行了评价:①在快速淤涨的崇明东滩湿地中,生态系统工程师效应起着重要作用;②尽管在本研究实验区的围垦边界高程选择是合理的,但在实验区以外的围垦边界高程甚至延展到了0 m线以下,这是滩涂湿地过度围垦的直接证据之一;③与过去几次大围垦所不同的是,本次围垦范围选择的留一半、围一半的模式,一方面可以有效治理互花米草,另一方面可以预留足够的生态栖息地保留区.总之,淤积量的长期定点观测,为长江三角洲滩涂资源的动态管理和科学围垦提供了参考依据,可更客观地协调滩涂湿地保护和开发利用之间的矛盾.%Ecological early-warning of targeted reclamation needs to accurately and timely monitor the volume and position of sediment at a short time scale and a compact spatial scale, which was the basis for tideland reclamation planning and implementation. The east beach of Chongming island was take as a case study, in which direct measurements of sediment volume and the micro-topography survey in the tidal wetlands were considered together to assess the appropriateness of siltation promotion through reclamation based on relative depth of the accumulated sedimentation. The rate of sediment accumulation in the intertidal and high tide zones presents was less than 1 cm each year, but the rate in the low tide beach was nearly 7 cm. Moreover, micro-topography elevation based on vegetation community zoning showed a significant negative correlation with sediment volume. The model of "biological siltation promotion + physical reclamation" for the control of invasive plant Spartina alterniflora was evaluated. The elevation of the boundary of reclamation within the study sites was set properly, but outside the study sites the elevation extended to below 0 m, providing a direct evidence of excessive reclamation of mudflat. However, different from practices in the past, the recent reclamation only reclaims a half range of the wetlands, leaving another half as natural. By doing so, the invasive plant Spartina alterniflora could be controlled effectively on one hand, leaving su?cient area for habitat reserve on the other hand. In addition, long-term regular observation on sedimentation volume provides a basis for dynamic management of the tidal flat resources and scientific reclamation in the Yangtze River delta. This also harmonizes the contradiction between wetlands protection and mudflats utilization more objectively.