Morgenstern, R.; Martin, A.P.; Turnbull, R.E.; Norton, K.; Rattenbury, M.S.; Rogers, K.M. 2024 Urban geochemical atlas of Wellington, New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2024/01. 128 p.; doi: 10.21420/8ADH-F354
Abstract
The first geochemical atlas of Wellington – New Zealand’s third largest city and capital – is presented here. It shows the abundance and variability of element concentrations within surficial soil material across the study area. Sampling was undertaken between December 2022 and April 2023 at 151 sites across an area spanning from Paekakaririki and the Remutaka Road Summit to the southern coastline, and from the Remutaka Ranges to the western coastline. Highly urbanised land (domestic and commercial properties) was sampled, as well as a variety of other, more natural land use types (native regenerating park, native park, exotic park, exotic forest, agricultural pasture) for comparison. At each site, two samples were collected using a hand auger: the upper O-depth (0–2 cm) and a shallow A-depth (2–20 cm). Several deeper B-depth (50–70 cm) samples were also collected for statistical analysis. Samples were dried, sieved to <2 mm and split into 15 g sample sizes, before being 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 aqua regia digestion and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Most analytes have all or most measured values above their lower method detection limit and 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. Results from this study reveal that soil chemistry across the Wellington area is influenced by both natural factors (vegetation, environmental conditions) as well as anthropogenic activities (urbanisation). The relatively uniform geology of the area has minimal influence on the variability of soil geochemistry and no obvious visual correlations exist between analyte enrichment and soil order, beyond that which is controlled by land use and climate. Soils sampled from less disturbed, more natural vegetated environments (generally parks and forests) and soils sampled from areas with more anthropogenic land uses (residential and commercial) are observed to have distinct differences in their chemistry. Soils in residential and commercial areas, and proximal to major highways, show elevated levels of many heavy metals potentially harmful to human health (As, Cd, Cr, Cu, Hg, Pb, Zn), especially in the shallower soils. Other elements that visually correlate with high-density urbanisation in the study area are Ag, Au, Ba, P, Sb and Sn. Higher concentrations of these elements are particularly pronounced in Wellington City, surrounding Wellington Harbour and throughout the Hutt Valley, which are all locations that have a long history of European settlement and industrialisation dating back to 1839. We interpret elevated heavy metals in these soils to represent contamination as a direct result of human activities. Of the elements that potentially adversely affect human health, Pb, As and Cd exceeded the most restrictive category in the Ministry for the Environment soil contamination standards, at 23 sites (15% of survey sites). This included six samples (four sites) that exceeded the standards set for Pb and/or As in high-density residential areas. Median and average Pb, As and Zn values in the Wellington urban soils are above baseline values established for New Zealand and global soils but are below median values observed in Dunedin City. When comparing Wellington soils to those in the national atlas and soils in Dunedin and Auckland cities, Cd, Cr, Cu and Ni values are slightly lower on average while Zn values are higher than in Auckland City soils. Results from this survey serve as a tool that can be used by local and regional authorities to better identify potential localised health and societal impacts of pollutants and provide a reference for monitoring city-wide change in soil chemistry and potential related human health over time. This is especially important in the Wellington area where a projected 42% increase in population is expected by 2054, which will result in further urban densification and land use intensification. This survey provides a baseline and represents a significant step towards assessing the level of environmental contamination in one of New Zealand’s major urban centres. Together with other published urban, regional and national soil geochemical baselines, it will provide a greater understanding of geochemical soil variation and its causes across the New Zealand landscape (auths)
