Impact of Geomorphological Variables in Weighing the Lithological Influence on Geochemical Composition of Stream and Overbank Sediments: A Regression Model for the Žumberak Area (NW Croatia)

Abstract

The two multiple regression models were compared on the assumptionthat the geochemical composition of the alluvial material is basically originally derived from the bedrock lithology of a drainage basin of the Žumberak Area (NW Croatia). The latter was integrated with both stream sediment and overbank sediment geochemical data via the two essentially different approaches as regards the catchment basin geomorphological data: (1) as the relative area of influence representing a portion of the catchment basin occupied by a certain rock type; (2) as the relative “line” of influence representing a narrow tract of a certain rock type traversed by the majority of perennial streams which form the active stream network. The model comparisonwas accomplished on the basis of the goodness-of-fit test for both experimental designs and for the same set of data. The most important result of these experiments highlights the linear approach as the more appropriate model for ascertaining the lithological influence on the analyzed sample media. This can be explained by the stronger erosiveand transportational power of the water which flows in the well defined channel network in contrast to the unconcentrated surface runoff in the interfluvial area, coupled with the buffering effects of rich slope and riparian vegetation, which is characteristic of the Žumberak heartland.