The regional geochemical baseline soil survey of southern New Zealand: Design and initial interpretation

Abstract A multivariate geochemical baseline survey of soils from southern New Zealand has been completed. Soil samples were collected from 0 to 30 cm ‘A-depth’ and 50–70 cm ‘B-depth’ at 348 sites on an 8 km-spaced grid covering 40,000 km 2 of the Southland and southern Otago regions. The sub-180 μm fraction of all samples was analysed by inductively coupled plasma mass spectrometry following aqua regia (partial) digestion for 65 elements, and by Leco CS320 element analyser for total C and S. Sub-sets of the samples were analysed by XRF for 12 oxides/elements. Significant chemical variation in the soil samples can be linked to variations in source geology, soil type, climate and topography. Relatively high concentrations of certain elements (e.g. S, P, Pb, Hg, Cd), particularly in the A-depth, are attributed to anthropogenic sources such as fertilisers, paints, vehicle emissions or industrial emissions. Other elevated element concentrations, especially those in B-depth samples, are probably natural with high As, Bi, Sb and W reflecting proximity to Au mineralisation, Pt and Re near PGE mineralisation, and accumulation of heavy mineral-associated elements such as Cr in alluvium-derived soils related to the effects of both source material and hydraulic effects on flood plains. This study provides an important baseline that will benefit government, environmental, agricultural, forestry and mining sectors through improved regulatory guidelines and understanding of the regional geochemical landscape. This survey design, with minimal modification, is suitable for a national geochemical baseline survey for New Zealand.