Table 2.
Oil concentration in soil (mg g−1); 0–20 cm depth (9 collected samples per plot).
| Plot | Year (Average values ± SD) | Wilcoxon test (2002–2006) | Wilcoxon test (2006–2014) | ||||
|---|---|---|---|---|---|---|---|
| 2002 | 2006 | 2014 | W | p-value | W | p-value | |
| 1 | 216.1 ± 25.3 | 72.2 ± 32.5 | 37.2 ± 18.9 | 20 | 0.02 | 15 | 0.25 |
| 2 (control) | 204.4 ± 35.0 | 176.1 ± 34.3 | 99.4 ± 17.9 | 17 | 0.10 | 19 | 0.03 |
| 3 | 199.4 ± 45.5 | 96.7 ± 38.2 | 91.7 ± 34.6 | 20 | 0.02 | 13.5 | 0.46 |
| 4 | 292.2 ± 40.3 | 83.3 ± 30.8 | 38.3 ± 25.2 | 20 | 0.02 | 17 | 0.11 |
| 5 | 243.9 ± 73.7 | 151.1 ± 73.1 | 110.0 ± 39.5 | 16 | 0.18 | 14 | 0.39 |
| 6 | 319.4 ± 58.0 | 83.9 ± 28.5 | 26.1 ± 21.6 | 20 | 0.02 | 20 | 0.02 |
| 7 | 228.9 ± 37.9 | 105 ± 11.7 | 65.6 ± 17.6 | 20 | 0.02 | 20 | 0.02 |
| 8 | 363.3 ± 66.1 | 191.7 ± 51.8 | 125 ± 23.3 | 20 | 0.02 | 17 | 0.10 |
| 9 | 305.6 ± 64.6 | 123.3 ± 47.8 | 30.6 ± 20.1 | 20 | 0.02 | 18 | 0.07 |
| Reference plot | 3.0 ± 0.1 | 2.9 ± 0.1 | 2.9 ± 0.1 | 11.5 | 0.80 | 9 | 0.90 |
SD denotes standard deviation; significant differences (p < 0.05) are bold.