SPATIAL VARIATION OF POTAMOGETON CRISPUS TURION AND ITS CAUSES OF FORMATION IN XUANWU LAKE OF NANJING

In order to investigate the spatial distribution of the Potamogeton crispus turion in Xuanwu Lake, a total of 52 samples were collected by the grid method. In each sampling site positioned by GPS, four samples of P. crispus turion from 15cm depth under surface sediment were collected, summing the data to represent turion density of the site. MSpatial variation of P. crispus turion density in the Lake was studied by using the geostatistical component of ArcGIS. Compared with traditional statistical methods, the geostatistic method took directivity, distance and location of sampling points into account. Semivariogram is the specific theory of the method, it can be used to research the spatial correlation and the spatial pattern by determining differences of regional variable among equidistant sampling sites. The survey data converted by Log function were close to nomal distribution and could be discussed by semivariogram. Theortical model and curve graph of regional variable were derived respectively after calculating semivariogram of all possible distance interval, and spatial variation patten about regional variable could be analyzed quantitatively by model parameters such as nugget, sill, range, fractal dimension etc.. Furthmore, the spatial variation map of P. crispus turion was drawn by the method of Kriging interpolation. The results showed: ① The semivariogram of P. crispus turion density fitted spherical model and exhibited an intense special aggregation. ② Spatial heterogeneity of Potamogeton crispus turion density existed obviously, that is, an average density of P. crispus turion in the North-east Lake and the North-west was 30.5 and 10 ind./m2 respectively; Omnidirectional, elliptic semi-major axis and elliptic semi-minor axis fractal dimension decreased; ③ Mowing and differences of population size, water depth, substrate leaded to spatial variability of the density; ④ The scale size of spatial auto correlation of the density was bigger than distance of the tuition fallout itself, which showed flowing water played an important role in the turion diffusion.