Soil organic matter as sole indicator of soil degradation

Triad-based screening risk assessment of the agricultural area exposed to the long-term PAHs contamination

The aim of the study was ecological risk assessment (ERA) of the agricultural soils located in the vicinity of the highly industrialized area and exposed to different emission sources of polycyclic aromatic hydrocarbons (PAHs). In this study, we demonstrated the combination of generic and site-specific ERA approach for screening assessment and delineation of the area of a high ecological risk. Generic approach was based on a hazard quotient and indicated that 62% of the research area needs further assessment. For site-specific evaluation, the Triad approach was utilized. Information from three lines of evidence (LoE): chemical, ecotoxicological and ecological, was integrated into one environmental risk (EnvRI) index. The chemical risk was derived from toxic pressure coefficients based on the total PAHs concentration. The ecotoxicological LoE included an acute toxicity testing: the luminescent bacteria Aliivibrio fischeri activity in both liquid- and solid-phase samples and the ability of crustacean Thamnocephalus platyurus to food uptake. The ecological LoE comprised microbial parameters related to soil respiration and enzymatic activity. Integrated EnvRI index ranged from 0.44 to 0.94 and was mainly influenced by high values of chemical LoE risk, while the ecotoxicological and ecological LoE indicated no or low risk. Due to the relatively high uncertainty associated with the contradictory information given by LoEs, there is the need to confirm potential risk in a tier 2 analysis.

Long-Term Effects of Crude Oil Spillage on Selected Physicochemical Properties Including Heavy Metal Contents of Sandy Tropical Soil

Crude oil spillage effects on the environment often wane with time, making late remediation of affected soils look irrelevant. Physicochemical quality of a sandy soil under 9-year-old spillage was compared with that of adjacent unaffected site in southern Nigeria. Soil bulk density and equilibrated water content were higher in affected than unaffected site, but permeability did not change. The spillage increased soil pH, organic carbon, total nitrogen and available phosphorus by about 7%, 1700%, 133% and - 16%, respectively. It lowered divalent exchangeable bases/acidity but raised base saturation. It increased total petroleum hydrocarbon (PHC_t) and micronutrients/heavy metals (Fe, Mn, Zn, Cd and Pb), all of which were below their critical limits in soils by regulatory bodies. Soil pH, organic carbon and PHC_t correlated positively with all five micronutrients/heavy metals; total nitrogen did so with Zn and Pb. Nine-year period may be insufficient for spillage effects in sandy soils to cease to be evident. Such effects for PHC_t and heavy metals, however, are deemed tolerable for ecological safety.

Erodibility of calcareous soils as influenced by land use and intrinsic soil properties in a semiarid region of central Iran

The most important properties affecting the soil loss and runoff were investigated, and the effects of land use on the soil properties, together with the erodibility indices in a semiarid zone, central Iran, were evaluated. The locations of 100 positions were acquired by cLHS and 0-5-cm surface soil layer samples were used for laboratory analyses from the Borujen Region, Chaharmahal-Va-Bakhtiari Province, central Iran. To measure in situ runoff and soil erodibility of three different land uses comprising dryland, irrigated farming, and rangeland, a portable rainfall simulator was used. The results showed that the high variations (coefficient of variation, CV) were obtained for electrical conductivity (EC), mean weight diameter (MWD), soil organic carbon (SOC), and soil erodibility indices including runoff volume, soil loss, and sediment concentration (CV ~ 43.6-77.4%). Soil erodibility indices showed positive and significant correlations with bulk density and negative correlations with SOC, MWD, clay content, and soil shear strength in the area under investigation. The values of runoff in the dryland, irrigated farming, and rangeland were found 1.5, 28.9, and 58.7 cm³; soil loss in the dryland, irrigated farming, and rangeland were observed 0.25, 2.96, and 76.8 g; and the amount of sediment concentration in the dryland, irrigated farming, and rangeland were found 0.01, 0.11, and 0.15 g cm^-3. It is suggested that further investigations should be carried out on soil erodibility and the potential of sediment yield in various land uses with varying topography and soil properties in semiarid regions of Iran facing the high risk of soil loss.