Evaluation of aggregate stability as influenced by petroleum compounds in texturally different soils

Oil pollutants are inevitable consequence of rapid population growth and the process of industrialization. Their spread in soil can affect many soil properties, especially aggregate stability. Particle size distribution and aggregate stability are of the main physical and hydraulic characteristics of soil that study of these indices are the basis of soil conservation strategies and are very important parameters in identifying the status of soil structure. Iran is an oil-rich country and the effect of different petroleum compounds on aggregate stability and stability indices including mean weight diameter and geometric mean diameter of aggregates in soils of different textures have not been studied so far. Therefore, this study aimed to investigate the effect of different levels of crude oil, kerosene, and gasoline as the three high-consumption petroleum products on the stability of aggregates in three soils with clay loam, sandy loam, and loamy sand textures.

In this study, the effect of 0, 1.5, 3.5, and 4.5% levels of crude oil, kerosene, and gasoline on the stability of aggregates in clay loam, loamy sand, and sandy loam soils was investigated in a factorial completely randomized design experiment. Studied stability indices were the mean weight diameter and geometric mean diameter of aggregates deterimined using both dry and wet sieving approaches. Finally, the results of the research were analyzed using EXCEL and SAS statistical softwares and the means of each separate treatment as well as their interactions compared using the Duncan's multiple range test at the 5% level.

The results showed that the mean dry weight of aggregate diameters in the loamy sand and sandy loam soils were significantly lower than that of the clay loam soil by nearly 72% and 56%, respectively. The reductions were about 78% and 69% for the dry geometric mean diameter of aggregates. Furthermore, the dry mean weight diameter of aggregates in the soils treated by kerosene and gasoline were more than that of the crude oil- treated soils by nearly 17% and 25%, respectively. The mentioned increaments were about 22% and 35% for the dry geometric mean diameter. The wet mean weight diameter of aggregates in the loamy sand soils was significantly higher than that of the clay loam and sandy loam soils by nearly 20% and 35%, respectively. Furthermore, the wet geometric mean diameter of aggregates in the loamy sand soils was significantly higher than that of the clay loam and sandy loam soils by nearly 91% and 12%, respectively. The wet mean weight diameter of aggregates in the soils treated by kerosene and gasoline was significantly lower than that of the crude oil- treated soils by nearly 32% and 8%, respectively. Furthermore, the wet geometric mean diameter of aggregates in the soils treated by kerosene and gasoline was significantly lower than that of the crude oil- treated soils by nearly 34% and 14%, respectively.

Generally, results indicated that the application of low levels of petroleum products significantly increased the wet and dry mean weight diameter of aggregates and geometric mean diameter of aggregates; whereas, high levels reduced the above-mentioned attributes. The results of this study can be used in both aspects of identifying and monitoring the properties of oil-contaminated soils for their remediation and making appropriate management decisions, as well as conservation of soils against the destructive erosion phenomenon.