Geochemical mapping in Oxfordshire: a comparison of stream sediment and soil sampling

Abstract

Summary352 stream sediments and 429 topsoils were sampled from 1000 km2 of SW Oxfordshire. These were analysed by direct reading emission spectrometry, and simple geochemical maps were prepared for ten elements (Ca, Sr, Ba, V, Cr, Mn, Fe, Co, Cu and Pb). The maps showed that (i) the unsmoothed data were very ‘noisy’, (ii) there was a weak overall similarity between stream sediment and soil maps for some elements (Ca, Cu, Fe, Mn, Sr and Co) but little if any for the others; and (iii) removing some of the short‐range (less than 3 km) variability from the data by smoothing increased the overall similarity in some cases, but not in others.Stream sediment and soil maps based on a more detailed sampling (topsoil and subsoil) of the area covered by map sheet SP30 did not show better agreement. The stream sediment maps generally agreed better with the subsoil maps than with the topsoil maps. Of the elements studied, Ca consistently showed the best agreement between stream sediment maps and soils. The agreement shown by the other elements was variable and unpredictable so that stream sediment data are unlikely to be useful for predicting local element concentrations in soils of areas without mineralization such as Oxfordshire.