Abstract: Soil quality monitoring is a science-based soil
management tool that assesses soil ecosystem health.
A soil monitoring program in Auckland, New Zealand’s largest
city extends from 1995 to the present. The objective of this study was
to firstly determine changes in soil parameters (basic soil properties
and heavy metals) that were assessed from rural land in 1995-2000
and repeated in 2008-2012. The second objective was to determine
differences in soil parameters across various land uses including
native bush, rural (horticulture, pasture and plantation forestry) and
urban land uses using soil data collected in more recent years (2009-
2013).
Across rural land, mean concentrations of Olsen P had
significantly increased in the second sampling period and was
identified as the indicator of most concern, followed by soil
macroporosity, particularly for horticultural and pastoral land. Mean
concentrations of Cd were also greatest for pastoral and horticultural
land and a positive correlation existed between these two parameters,
which highlights the importance of analysing basic soil parameters in
conjunction with heavy metals. In contrast, mean concentrations of
As, Cr, Pb, Ni and Zn were greatest for urban sites. Native bush sites
had the lowest concentrations of heavy metals and were used to
calculate a ‘pollution index’ (PI). The mean PI was classified as high
(PI > 3) for Cd and Ni and moderate for Pb, Zn, Cr, Cu, As and Hg,
indicating high levels of heavy metal pollution across both rural and
urban soils. From a land use perspective, the mean ‘integrated
pollution index’ was highest for urban sites at 2.9 followed by
pasture, horticulture and plantation forests at 2.7, 2.6 and 0.9,
respectively.
It is recommended that soil sampling continues over time because
a longer spanning record will allow further identification of where
soil problems exist and where resources need to be targeted in the
future. Findings from this study will also inform policy and science
direction in regional councils.