Trace and major element contents, microbial communities, and enzymatic activities of urban soils of Marrakech city along an anthropization gradient

Abstract

Purpose

Due to their close proximity with the population, urban soils are extensively affected by human activities that release considerable technogenic inputs resulting in an overall soil degradation and leading to an increase of water-extractable fraction of trace elements. This work aimed to determine the influence of anthropization on trace and major element concentrations and to assess how it might also affect soil biochemical and microbiological parameters in an urban area of Marrakech city, Morocco.

Materials and methods

The work was carried out on nine topsoils located along an anthropogenic gradient from a suburban area to the city center. The percentage of technogenic fraction (TGF) (e.g., building material, plastic, wood, metallic material, bones, glass, paper, fabric) was used to quantify the degree of human interference in the different soils. Physicochemical parameters were measured: pH (in water solution), TOC (Anne method), TKN, and Olsen phosphorus. The total fraction of trace and major elements (ISO NF 11446) and their water-soluble fraction were analyzed with an ICP-OES. Enumeration of cultivable microorganisms (bacteria, fungi, actinomycetes) was conducted on culture media. Dehydrogenase, alkaline phosphatase, and urease activities were colorimetrically measured, and the structure and diversity of soil bacterial communities were determined by denaturing gradient gel electrophoresis (DGGE) technique.

Results and discussion

In general, trace and major element concentrations showed increasing levels along the anthropogenic gradient, except for Ca, Mg, B, and Cd. However, trace element concentrations remained below the standard international limits for soils. Total numbers of microorganisms (bacteria, fungi, and actinomycetes) varied significantly among sites, with bacterial counts directly related to the anthropogenic gradient, significantly increasing from suburban area to the city center. Dehydrogenase activity decreased throughout the anthropogenic gradient, while phosphatase and urease activities varied between sites independently of the gradient. DGGE profiles showed that bacterial diversity was higher in the most anthropized soils, where their community structure seemed to be influenced by the total concentrations of Zn, As, Cr, Cu, Ni, Pb, and the technogenic fraction.

Conclusions

Overall, trace and major element concentrations and the technogenic fraction were higher with increasing levels of urbanization. Microbiological and biochemical parameters appeared significantly influenced by the anthropogenic inputs without being systematically inhibited along the anthropogenic gradient. Dehydrogenase activity decreased along the anthropization gradient, and thus may be used as a proxy to assess the effect of anthropization on soil biological functions.

from Energy Ecology Environment Ambio via Terpsi Hori on Inoreader http://bit.ly/2R8Jpxn