Soil biogeochemical properties of Angren industrial area, Uzbekistan

Background, aim, and scope The present study examined air pollution effects on soil health applying microbiological parameters. It was carried out near the Angren heavy industry complex in a semiarid region of Uzbekistan. This area was selected in order to establish a national monitoring program for assessing environmental condition of areas remote but downwind from greater emission sources. Moreover, little information exists about how air pollution affects microbiological functioning of soils in semiarid and arid regions of the world, and especially those of Central Asia. Materials and methods Soil samples were collected in May 2005 along a 20-km NE-SW river valley transect downwind from the industrial complex. Soil chemical analyses included electrical conductivity, pH, water soluble Na, Ca, and K, total soluble nitrogen, and mineralizable nitrogen content upon a 1:2 digestion by deionized water. Major elements and heavy metal inventory in solids was measured by X-ray fluorescence and atomic absorption spectrometry. Microbiological ecosystem properties were assessed by biological indicators such as basal respiration (R _B), microbial biomass related C and N contents, and microbial community functioning coefficients like the metabolic quotient qCO₂. Results There was a significant spatial dependence and differences for all soil chemical and microbiological parameters tested. The highest contents were found for the relatively volatile metals Zn (≤1,136 mg/kg) and Pb (≤373 mg/kg) in upper soil layers near the power station suggesting that the metal pollutants are derived from local stack emissions. Soil microflora was obviously affected by heavy metals. Significant positive correlations (p∈≤0.001) were found between the metal content, R _B, and qCO₂, while a negative one was found for the mineralizable N and C _mic/C _org ratio. A high total number of nematodes was found only most distant from the industrial emission sources. Discussion: The results disclosed remarkable spatial dependence not only of the heavy metal impact onto the soil but also of microbiological soil properties in the study area. The latter suggests bioavailability of the anthropogenic metals in the soil affecting the soil microbial community. This is suggested by less biomass formation and higher qCO₂ values in heavy metal-contaminated compared to less-polluted soil plots. Conclusions: Knowledge of these spatial ecosystem functioning patterns and dependence could be very useful in determining and delineating specific land use and management programs that would be suited and feasible for the highly polluted area. Results of this study can be utilized to develop a monitoring program that may quantify harmful effects on the soil health and impact of any future remediation activities. Recommendations and perspectives: Studies on the relationship between soil biota and pollution levels have raised the question regarding the status of natural soil microbial health, stressing the importance of background data of environmental conditions, and elucidating the importance of this environmental monitoring approach even in semiarid and arid regions. Soil microbiological parameters, in particular the metabolic quotient qCO₂ as one of the most sensitive bioindicators identified for that region, should clearly become part of the national environmental monitoring program.