盐城淤泥质潮滩湿地潮沟发育及其对米草扩张的影响

Effection of tidal creek system on the expansion of the invasive Spartina in the coastal wetland of Yancheng

潮沟是潮滩上发育典型的地貌因子,是潮滩演变的重要标志。米草植被的发育与扩张,改变了潮流的动力特征和滩面物质组成,从而形成了特殊的米草潮沟系统。采用实地调查与遥感影像相结合的方法,分析了湿地潮沟的整体形态特征,并重点对米草潮沟系统的形态特征及成因进行了系统分析。结果表明:①受潮流和地形作用的控制,本区并无大型潮沟分布,潮沟规模从北至南依次增大,发育高程为0—1.8 m。盐沼和光滩上潮沟形态截然不同。②米草潮沟系统具有独特特征:潮沟多窄而深、密度大、分级多、侧向迁移小于纵向迁移、宽深比较小;潮沟两侧发育高度不等的不对称性的沿岸堤;盐沼边缘发育有陡坎和冲沟,并贯穿整个米草带。③潮沟的发育是影响米草向内陆碱蓬区扩张的因素之一,起着非常重要的引领作用,而米草陆向扩张的宽度和幅度取决于所在区域潮沟的发育程度。同时,随米草扩张速度的降低,光滩上潮沟的活动性有所放缓。

Wetland ecosystems are landscapes of the highest biodiversity in nature and one of the most important environmental resources for human welfares. Their important ecosystem functions sometimes are regarded as ＂the earth＇s filtration system＂. Yancheng coastal wetland now remains a typical mudflat by frequent tidal reaction. A more complex, changing creek system is formed by the mudflat development with a process of tidal movement. The creek system as a typical geomorphologic factor has formed at mudflat and become a pivotal pathway to continuously exchange matter, energy and information within and outside of the system. It is also important for distribution of the tidal water and sediment supply. And creek system development has a direct impact on the wetland ecologically environmental change and spatial distribution of vegetation. Therefore it has become an important indicator for the evolution of the mudflat. Spartina is a salt, flooded tolerant and perennial plant growing in a vast intertidal zone. It is growing at low tide with well-developed root system, and it could strongly intercept sediment. Accompanied with the formation of Spartina, hydrodynamic force and sediment transport conditions change in its mudflat surface, caused by changes of tidal flat sedimentm~~ characteristics and topography, thereby affecting the development of trenches. And Spartina tidal trenches are specially established. Yancheng coastal wetland was chosen as the study area. Based on the remote sensing images of 1996--2012, using GIS techniques and field survey, we extract tidal creek system in this study. And a 16-year trend was analyzed on the mutual relations of Spartina expansion and tidal creek system development between 1996 and 2012 of Yancheng coastal wetland. Research results show that： Under the control of the tidal and terrain, no large-scale distribution of trenches present in this study area. The size of the trenches gradually increased from north to south. Their elevation is 0--1.8m. Distinct morphology exists in salt marsh and bare mudflat. Trenches covered by Spartina indicate a unique feature, which present narrow and deep; Trenches are very dense with covering of 1539rn/km2; They reach up to 4--5 grades; And lateral movement is less than longitudinal. The trenches are wide and deep, the main trenches are generally about 17m and branches between 3--9m. The trenches are becoming deep at low grade ; both sides of the edges of the trenches often development in asymmetry coastal embankment with ranging different height. The edges of the salt marsh have developed scarps and gullies with stretches throughout the Spartina zone. Inside the salt marsh, tidal creek development leads to Spartina inland expansion, expansion of the width and amplitude largely depends on the density and size of the tidal creek areas ; Outside of the salt marsh, creeks activity in bare tidal will slow down with the reduction of the rate of expansion of Spartina. The wetlands microrelief variation has been further understand with this study. The baseline information greatly supports the Yancheng coastal wetlands and management, and benefits regional s6cial and economic development in an effective manner.