Inland Plains Of Freshwater Wetlands Microrelief Quantitative Extraction Technology And Methods

Geomorphic feature plays a leading role to control pattern of ecosystem structure. It also has effect on energy flow, material flow and human disturbance. In a certain degree, geomorphic factors control the distribution and variation of other ecological or environmental factors. Micro-topographies restrict water status in different area; thereby affect the variation of plant community. Micro-topographies are the important foundation for the study of wetland classification and wetland habitat conditions, and the basis for the analysis of environmental change and the wetland protection. The digital characterizing definition of wetland micro-topography is premise of quantitative analysis for environmental information of wetland complex micro-topography and for the wetland habitat change. According to the shape and distributing feature of wetland micro-topography and hydrological information, the study confirm micro-topography types and partitioning standards of freshwater wetland with small watershed scale, and bring forward the relatively complete division system of wetland micro-topography types. On the basis of geomorphic morphology methods, the study makes digital definitions of each wetland micro-topography types.Within this study, Honghe National Nature Reserve (HNNR) was selected as the study area for such research experiments of automatic delineation of wetland micro-topographies in Heilongjiang Province, Northeast China. From a grid DEM of 5 meter resolution-extracted vector on the 1:10000 relief maps with the Hydro Arc tools on ArcGIS-as fundamental information source, researchers attempted some digital definitions of three major geomorphic units-hill land, depression area and flooding flat area-as the micro geomorphic types and six geomorphic units-platform, slope, lacustrine bog, shallow sink, riverside bank and flat area-as six subtypes. Various methods of spatial analyses based on the DEM were carried out to delineate these wetland micro-landforms. Primarily, researchers defined micro topography types of mound, depression area and flooding water bank. Secondly, researchers integrated with some spatial analysis methods, including a new improved hydrologic analysis method to extract two geomorphic units as follow:a threshold value of sink filling is defined by the elevation range of the watershed of every sink point. And then, the depression area will be delineated by using map algebraic subtraction between the original DEM and the sink-filled DEM; by comprehensive application of a reversed DEM, coupling with a hydrologic analysis method, researchers conformed the threshold and the difference of the sink-filled DEM and the original DEM, three micro geographic types of hill land, depression area and flooding flat area have been extracted digitally. On this basis, combined with RS data, six subtypes have been extracted. This study also gives further discussions on the morphological characteristics and spatial distribution of the geomorphologic types after the digital delineation. We extracted 224 depression areas and 67 hill land totally in this study. The classification accuracy is 71.76%, with the GPS and RS testing methods. This research result shows the digital method can be potentially application in various aspects of digital theory and methodology. It will improve the efficiency of hard work on manual delineation of the topographies of fresh water wetlands. And this digital terrain analysis method will be integrated with the traditional ecological study of wetland science.