Urban geochemical atlas of Dunedin City, New Zealand

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Turnbull, R.E.; Martin, A.P.; Rattenbury, M.S.; Rogers, K.M.; Strong, D.T.; Morgenstern, R. 2017 Urban geochemical atlas of Dunedin City, New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2017/31 187 p.; doi: 10.21420/G22P8N

Abstract: A geochemical atlas for Dunedin City, New Zealand is presented that highlights the variation in trace, minor and major element concentrations in surficial soil materials across the urban landscape. Sampling was undertaken at 83 sites across a 1 km grid, with a further 30 sites sampled within the grid from almost all primary, intermediate and secondary schools within the survey area. At each site, three samples were collected using a hand auger: an upper O-depth sample was taken from 0-2 cm, an A-depth sample was taken from 2-20 cm, and a lower Bdepth sample was taken from 50-70 cm depth. All samples were dried, sieved to <2 mm and split prior to analysis. All samples were analysed for a suite of 65 elements (Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, In, K, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, Pd, Pr, Pt, Rb, Re, S, Sb, Sc, Se, Sm, Sn, Sr, Ta, Tb, Te, Th, Ti, Tl, Tm, U, V, W, Y, Yb, Zn and Zr) using inductively coupled plasma mass spectrometry (ICP-MS) on aqua regia dilutions. Digestion by aqua regia was undertaken on the <2 mm grainsize on a 15 g sample size. Excluding the additional infill samples from Dunedin schools, 83 samples were also analysed for 12 elements - Si, Al, Fe, Ca, Mg, Na, K, Mn, Ti, P, Cr and Ba by X-ray fluorescence (XRF). Total C and total S were measured using a LECO analyser. Stable isotope measurements were made to determine δ13C and δ15N on a subset of A-depth samples. The analytical results have undergone comprehensive quality assurance and quality control, and are internally consistent and in line with typical worldwide concentration ranges of the analytes. Most analytes have all or most measured values above their analytical detection limit and these analytes show variation across the survey area consistent with both an anthropogenic (in particular for Pb, Bi, As, Sb, Hg) and geogenic influence. A reference split of each <2 mm sieved sample has been retained for future use. The baseline soil study is the first of its kind in New Zealand and provides a methodology for refining geochemical variation detail in Dunedin City and application to other New Zealand urban centres. Combined with regional soil geochemical surveys these urban surveys will provide a national understanding of geochemical variation and its causes. (auth)