**3. Results**

#### *3.1. Bulk Chemical Analyses of Surface Soil*

Substantial variability in the concentrations of major elements and basic soil properties (Table 1), including potential trace element contaminants (Table 2), was observed in surface soils at Smith's Lake and Charles Veryard Reserves. In most cases, the maximum concentrations were at least five times the minima. Much greater variability was observed for calcium (Ca, maximum/minimum ≈ 108); cadmium (Cd), copper (Cu), magnesium

(Mg), manganese (Mn), neodymium (Nd), nickel (Ni), phosphorus (P), lead (Pb), sulfur (S), strontium (Sr), and zinc (Zn) all had maximum/minimum ratios between 20 and 90. Soluble salt content measured by EC showed a maximum/minimum ratio of ≈29, and there was a relatively large, ≈3.4 units range in pH across the Reserves. Except for zinc, which exceeded the interim Ecological Investigation Level (EIL; National Environment Protection Council, 1999) in three samples, no other soil thresholds were exceeded by any element (Table 2).

**Table 1.** Summary of pH, EC, and major element concentrations in surface (0–10 cm) soil and in vertical soil profile samples at Smith's Lake and Charles Veryard Reserves. EC and pH were measured in 1:5 solid: deionised water suspensions; element concentrations were measured using *aqua regia* digestion followed by ICP-OES.


**Table 2.** Summary of minor/trace element concentrations in surface (0–10 cm) soil and in vertical soil profile samples at Smith's Lake and Charles Veryard Reserves. Element concentrations were measured using *aqua regia* digestion followed by ICP-OES.


1 Health Investigation Level C (Recreational) [36]; 3 Ecological Investigation Level (interim urban) [37].

#### *3.2. Spatial Distributions in Surface Soil*

The measurements of primary interest (pH, EC, Al, As, Ca, Cu, Fe, Pb, Zn) generally showed significant overall spatial patterns across the study area, shown by *p* values ≤ 0.05 for Global Moran's I. The exceptions were Al, Ca, Cr, and Ni for which the Global Moran's

I values were close to zero (Table 3). The spatial patterns and clusters of points with significant local autocorrelation are shown in Figures 3–6, and summarised in Table 3.

**Table 3.** Global Moran's I, *p*-values simulated by Monte-Carlo randomization, and information on local spatial autocorrelation for the variables of principal interest in surface soil at Smith's Lake and Charles Veryard Reserves. Variables except pH were log10-transformed before calculation. IPI is integrated pollution index (Equation (1)).


a CVR is Charles Veryard Reserve; SLR is Smiths Lake Reserve; NE is north-east; NW is north-west; SE is south-east; SW is south-west; N is north; S is south; E is east; b not associated with main CVR-SE cluster.

**Figure 3.** Spatial distributions of (**a**) As and (**b**) Cu in soil across Smith's Lake and Charles Veryard Reserves, interpolated by inverse distance weighting with significant local spatial autocorrelations (Local Moran's I ≤ 0.05) indicated with filled symbols. All sample points shown by + symbols.

**Figure 4.** Spatial distributions of (**a**) Cr and (**b**) Ni in soil across Smith's Lake and Charles Veryard Reserves, interpolated by inverse distance weighting with significant local spatial autocorrelations (Local Moran's I ≤ 0.05) indicated with filled symbols. All sample points shown by + symbols.

**Figure 5.** Spatial distributions of (**a**) Pb and (**b**) Zn in soil across Smith's Lake and Charles Veryard Reserves, interpolated by inverse distance weighting with significant local spatial autocorrelations (Local Moran's I ≤ 0.05) indicated with filled symbols. All sample points shown by + symbols.

**Figure 6.** Spatial distributions of (**a**) pH and (**b**) Integrated Pollution Index (IPI) in soil across Smith's Lake and Charles Veryard Reserves, interpolated by inverse distance weighting with significant local spatial autocorrelations (Local Moran's I ≤ 0.05) indicated with filled symbols. All sample points shown by + symbols.

Arsenic (As) showed a broad concentration peak in soil in the south-east of Charles Veryard Reserve, with scattered local maxima in a few other locations (Figure 3). The As peak in the south-east of Charles Veryard Reserve was co-located with samples having significant (*p* ≤ 0.05) high-high local Moran's I. Two points in Smith's Lake Reserve had significant low-high local Moran's I (i.e., isolated low As concentrations).

Copper (Cu) showed peaks in the north-east and south-east of Charles Veryard Reserve, with no other obvious maxima (Figure 3). Samples in both peaks in Cu concentration were significantly spatially autocorrelated (high-high, local Moran's I *p* ≤ 0.05). One point in north-west Charles Veryard Reserve had significant low-high local Moran's I (i.e., an isolated low Cu concentrations).

Lead (Pb) showed peaks in concentration in soil in the south-east of Charles Veryard Reserve and the north of Smith's Lake Reserve, with scattered local maxima in Pb concentration in a few other locations (Figure 5). The Pb peak in the south-east of Charles Veryard Reserve was co-located with samples having significant (*p* ≤ 0.05) high-high local Moran's I. A broad area of low Pb concentrations in Smith's Lake Reserve coincided with significant (*p* ≤ 0.05) low-low local Moran's I, and instances of significant high-low and low-high local Moran's I values represented isolated high and low Pb concentrations.

Zinc (Zn) showed peaks in the north-east and south-east of Charles Veryard Reserve, with a few other subtle maxima (Figure 5). Samples in both clear peaks in Zn concentration were significantly spatially autocorrelated (high-high, local Moran's I *p* ≤ 0.05). An area of low Zn concentrations in Smith's Lake Reserve coincided with significant (*p* ≤ 0.05) low-low local Moran's I. Similar to Pb, instances of significant high-low and low-high local Moran's I values in Smith's Lake Reserve represented isolated high and low Zn.

Soil pH showed a cluster of lower values in the north-west of Charles Veryard Reserve with significant low-low spatial autocorrelation (Moran's I *p* ≤ 0.05). In contrast, significant clusters of higher pH values were present in the west of Charles Veryard Reserve, the south-east of Charles Veryard Reserve, and the south of Smith's Lake Reserve (Figure 6).

Finally, the derived Integrated Pollution Index (IPI) had a maximum in the south-east of Charles Veryard Reserve, with a minor maximum in the north-east (Figure 6). A cluster of samples in the south-east IPI peak were significantly spatially autocorrelated (high-high, local Moran's I *p* ≤ 0.05). An isolated low IPI value (low-high local Moran's I, *p* ≤ 0.05) was present to the east of Smith's Lake.

A comparison of mean values of the variables of interest between samples from the different zones in Figure 2 reinforced the qualitative results from spatial interpolation (Table 4). The highest mean values for several potential contaminants (As, Cr, Cu, and Pb) were observed in the south-east of Charles Veryard Reserve (no significant effect of sampling zone was found for Ni or Zn).

**Table 4.** Comparison of pH, EC (1:5 soil: water extract), element concentrations, and IPI in distinct Zones of Smith's Lake (SLR) and Charles Veryard (CVR) Reserves. Mean values in a *row* are different if no superscript letters are shared (*p* ≤ 0.05, Conover's pairwise test with Holm's correction).


1 Overall *p*-values from Kruskal-Wallis test; 2 CVR is Charles Veryard Reserve; SLR is Smiths Lake Reserve; NE north-east; NW north-west; SE south-east; SW south-west; N north; S south.

#### *3.3. Relationships between Soil Elements*

Several significant positive correlations existed between elements across the soil data from Charles Veryard and Smith's Lake Reserves (Table S1, Supplementary Material). Calcium, Mg and Sr were very highly correlated (r = 0.80–0.96), and Ca and Sr were the only elements significantly correlated (r = 0.66) with pH. The major elements Na, K, and Mg were all highly correlated (r ≥ 0.7), as were P, K, Mn, and S. High correlations also existed between iron (Fe) and As, Ba, Cu, Pb, and V. Many potential contaminants were also highly correlated with one another, e.g.,: Cu with Ba, Pb, and Zn; Pb with Cd, Cu, and Zn; Cr with V.

Principal components analysis (Figure 7) showed grouping of Cu, Pb, and Zn in PC1- PC2 space, associated with some of the samples from north-east and south-east where peak concentrations of these elements were observed (Figures 3 and 5). Arsenic plots at similar values of PC2, but has an association with Fe and Cr at small positive PC1 values. No obvious element associations were observed using PCA for Ni. The principal components analysis also identifies an association of Ca with Sr and Ba, an association of nutrient elements (S, P, K) with the central Charles Veryard Reserve samples, and clustering of rareearth and related elements (Ce, Gd, La, Nd, Y). Additional results derived from principal components analysis are available in Tables S2–S4 in the Supplementary Materials.

**Figure 7.** Principal components biplot for the first two principal components based on elemental composition in surface soil at Charles Veryard and Smith's Lake Reserves. Observation scores are identified by sampling Zone (see Figure 2). Concentrations were transformed using centered log-ratios before PCA, to avoid spurious effects of compositional closure.

In surface soil, there was a weak negative relationship between lead and vanadium concentrations and minimum (Euclidean) distance from any road surrounding or bisecting the reserves (Figure 8). No other contaminant of primary interest showed a significant trend in relation to distance from roads.

**Figure 8.** Weak trends in (**a**) Pb and (**b**) V concentrations in surface soil with distance from roads in Charles Veryard and Smith's Lake Reserves. Solid blue lines are log-linear models.

#### *3.4. Depth Distributions of As, Cr, Cu, Ni, Pb, and Zn*

Depth profile plots for As, Cr, Cu, Ni, Pb, and Zn are presented in Figures 9–11. Depth profiles of As, Cr, Cu, Ni, Pb, and Zn frequently showed maximum concentrations in subsurface soil samples. High maximum concentrations of Pb (376 mg/kg) and Zn (1155 mg/kg) were measured at 30–40 cm in core 4.2 (Figure 11), on the eastern side of Charles Veryard Reserve south of the Macedonia Place car park. Core 3.2 also contained 568 mg/kg Pb at 50–60 cm. Core 4.2 also contained the maximum concentration of As (14 mg/kg at 20–30 cm), Cd, Mn, and Ni. The greatest concentration of Cu (356 mg/kg) was observed in the adjacent core 4.1 (Figure 9).

**Figure 9.** Depth profiles of (**a**) arsenic (As) and (**b**) copper (Cu) in soil cores collected from Smith's Lake and Charles Veryard Reserves, City of Vincent, Western Australia. Core locations from Figure 1. Ecological investigation limits (EIL) are shown as vertical dashed lines where relevant.

**Figure 10.** Depth profiles of (**a**) chromium (Cr) and (**b**) nickel (Ni) in soil cores collected from Smith's Lake and Charles Veryard Reserves, City of Vincent, Western Australia. Core locations from Figure 1.

**Figure 11.** Depth profiles of (**a**) lead (Pb) and (**b**) zinc (Zn) in soil cores collected from Smith's Lake and Charles Veryard Reserves, City of Vincent, Western Australia. Core locations from Figure 1. Ecological investigation limits (EIL) are shown as vertical dashed lines where relevant.

There was a tendency for pH to increase with increasing depth, and EC to decrease with increasing depth, and the trends in Fe with depth were very similar to those for As (Figure S1, Supplementary Material).
