SAMPLING REPRESENTATIVITY AND HOMOGENEITY OF RIVER SEDIMENTS

Statistical aspects of sediment sampling are discussed, Sampling sites at two selected rivers in East Germany were investigated using variou s sampling models. In the sediment samples the contents of 13 metals ( As, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Se and Zn) were analyzed b y means of atomic spectroscopy. Large differences in the contents of t he analyzed metals were already found at small distances. The applicat ion of an overall error analysis shows that independent of the analyze d grain size fraction, sampling is the main source of variance. Two-di mensional variance analysis and a geostatistical method were applied b ecause of homogeneity considerations. In contrast to the investigated longitudinal profiles, concentration gradients and spatial dependences of the metal contents were detected at the cross section. Finally, tw o approaches are described to determine the number of samples required for the representative assessment of loads. Weighting the result acco rding to a critical value is shown as a way to reduce the expenditure of sampling.