SPATIAL DISTRIBUTION CHARACTERISTICS OF HEAVY METALS IN THE SEDIMENTS OF CHANGJIANG RIVER SYSTEM ——SPATIAL AUTOCORRELATION AND FRACTAL METHODS
Zhang Chaosheng Zhang Shen He Jianbang (LREIS, Institute of Geography, Chinese Academy of Scienes, Beijing 100101)
The spatial distribution characteristics of 11 heavy metals (Cu, Pb, Zn, Cd, Hg, Co, Ni, As, Cr, Mn and Fe) in the sediments of the Changjiang River system were studied with methods of spatial autocorrelation and fractal. Moran's I indices were calculated to quantitatively describe the significance and the directional characteristics of their spatial autocorrelations, and spatial correlograms were drawn to show the variation of spatial autocorrelation along with the changes of distance. Fractal dimensions were calculated to reveal the complication degrees of the spatial distributions. Significant spatial autocorrelations are detected for all of the elements studied. The spatial autocorrelations of heavy metals in fine grained sediments are better than those in raw sediments. The positive autocorrelations extend to about 500 km, which is consistent with the sizes of patches in the distribution maps. Fractals exist in about less than 1 000 km , and fractal dimensions are around 2.76~2.95. The variation of fractal dimension among elements has negative trend against Moran's I, which shows consistence of the two indices. Most of the elements have relatively good autocorrelations in the directions of NE SW or NW SE, which are consistent with the results from variogram method.