TABLE 2.
Effect of treatment on soil hydrocarbon loss, soil pH, dry weight, and soil biological parameters (mean or median values) during three summer seasonsa
| Season | No. of samplesb | Treatment | Hydrocarbon concn (μg g of soil−1) | pHc | Dry wt (%) | No. of heterotrophs (CFU g [dry wt] of soil−1)c | No. of oil degraders (CFU g [dry wt] of soil−1)c | Respiration (μg of CO2 g [dry wt] of soil−1 48 h−1) | Catalase activity (relative units)c | Lipase activity (relative units)c |
|---|---|---|---|---|---|---|---|---|---|---|
| 26 July to 22 September 1997 | 9 | Natural attenuation | 2,432 | 8.10 | 91.53 | 5.56 × 107 | 3.09 × 106 | 83 | 0.52 | 0.60 |
| Biostimulation | 1,899d | 7.90d | 91.37e | 1.87 × 108d | 1.27 × 107d | 223d | 5.53d | 2.60d | ||
| 5 June to 24 September 1998 | 18 | Natural attenuation | 1,873 | 7.45 | 90.82 | 3.29 × 107 | 6.26 × 106 | 99 | 1.12 | 0.36 |
| Biostimulation | 995d | 7.30d | 90.18e | 4.19 × 107e | 6.03 × 106e | 119e | 5.30d | 0.72d | ||
| 2 July to 23 September 1999 | 6 | Natural attenuation | 1,453 | 7.45 | 90.30 | 9.50 × 106 | 2.75 × 106 | 69 | 0.86 | 0.04 |
| Biostimulation | 910d | 7.45e | 90.30e | 1.50 × 107e | 1.60 × 106e | 104e | 3.25d | 0.42d |
All values obtained for each summer season were analyzed with the t test for independent samples (data with normal distribution) or with the Mann-Whitney two-sample U test (nonparametric data) to determine whether biostimulation had a significant effect (95% confidence level).
Three replicate lysimeters were used for each treatment and sampling date.
Nonparametric data (median values). All other values are means.
The value is significantly different from the natural attenuation value for the same season.
The value is not significantly different from the natural attenuation value for the same season.