Topography And Its Impact On The Landscape Differentiation In The Coastal Wetland Of Yancheng

Terrain is the basic data of primitive wetland protection and management, and at the same time, influences the structure of wetland landscape and the evolution of spatial structure. Yancheng coastal wetland is one of the typical Primitive wetlands. In the past, limited to the wetland’s objective conditions, there has been no complete height measurement for the silt mass coastal wetland, which makes terrain’s study become "the blank area of the wetland". Terrain, which serves as an important factor of landscape structure and spatial pattern, not only provides a basis for the formation of landscape pattern, but also affect the evolution of landscape. The 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. Accompanied with the formation of Spartina, hydrodynamic force and sediment transport conditions change in its mudflat surface, caused by changes of tidal flat sedimentary characteristics and topography, thereby affecting the development of trenches. And Spartina tidal trenches are specially established. As the result, Yancheng coastal wetland was chosen as the study area in this study. Based on the remote sensing images, using GIS techniques and methods of landscape ecology, we use two kinds of different thought interpolation methods--Kriging and TIN--to research DEM construction and accuracy evaluation and analyze the relationship between landscape types and terrain factors and reveal the response characteristics of terrain factors on the distribution and evolution and analyze on the mutual relations of Spartina expansion and tidal creek system development. Research results show that:(1) Constructing DEM and Assessing its Accuracy. Two kinds of methods--Kriging and TIN--are able to better simulate wetland terrain. Grid-DEM is far higher than TIN-DEM in terms of accuracy. But from the perspective of DEM surface integral smoothness, Grid-DEM is superior to the TIN-DEM. Meanwhile, the use of waterline to build the DEM of outer edge, the accuracy is greatly improved.(2) Influences of topographic features on the distribution and evolution of landscape. Spartina wetland mainly distributes in0.9-1.5m, Suaeda wetland mainly distributes in1.5-2.1m, and Reed wetland in the2.1-2.7m. We found that the relationship between the characteristics of wetland landscape spatial distribution and the topography is more obvious. Where the space distribution of Spartina wetland space evolving at the range of0.6-1.2m, shows strong expansion trend to low altitude interval. At the same time, with terrain increasing, Suaeda wetland distribution range shows downward trend generally. In the higher terrain, the distribution index of Reed wetland rapidly, whose advantage distribution range is extended to2.1-3.0m.(3) Scour and deposition evolution along the mudflats. Between1996and2002, reclaimed lands at0m slowly deposited towards the sea at a speed of0.59km2/a. Waterline at average0m pushed43m/a toward to the sea. This proved wetlands in this period remain stable and sedimentation presented a natural condition. Waterline at0m rapidly pushed average106m/a toward to the sea, which demonstrated the sedimentation significantly speeded up. And the stability of coastal wetlands was largely impacted and they are presenting an abnormal sedimentation.(4) Effection of tidal creek system on the expansion of the invasive Spartina. 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 is0-1.8m. Trenches covered by Spartina indicate a unique feature, which present narrow and deep; And lateral movement is less than longitudinal. The trenches are wide and deep.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.