engleski

Assessment of soil Cu concentration and background threshold value in Terra rossa of Dalmatia

The aims of this study were (i) to assess soil Cu concentration in the mineral A horizon and cambic Bw horizon, (ii) to determine the background threshold value (BTV), and (iii) to quantify the differences between the horizons in Terra rossa soil from Dalmatia. A total of 128 samples collected from 64 soil profiles located on terrains used for non-agricultural purposes, were analysed for aqua regia soluble Cu concentration. The soils were classified according to the Croatian Soil Classification System and World Reference Base for Soil Resources as Terra rossa soil and Chromic and Rhodic Cambisols. The median value of Cu concentration in A horizon (CuA) and cambic Bw horizon (CuB) were 34.9 and 36.1 mg/kg, respectively, and ranged between 16.2 and 69.5 mg/kg in the CuA and from 17.0 to 73.0 mg/kg in the CuB horizon. Both CuA and CuB samples had a small interquartile range and slightly spread out of data. The estimated BTV for CuA varied between 43.6 and 58.4 mg/kg depending on the calculation method applied. The Kolmogorov-Smirnov test (KS) demonstrated that the distribution functions of samples CuA and CuB are equal. The median ratio CuA/CuB of 0.96 was close to identical and amounted to 0.91 and 1.02 for the first quartile (Q1), and third quartile (Q3), respectively. The Wilcoxon matched pairs signed rank test showed that the median difference in Cu concentration between the matched pair samples is significantly different from zero but provided no straightforward estimate of the magnitude of the difference. The median difference between paired samples established by the Hodges-Lehmann estimator was very small (-1.78 mg/kg) and its 95% confidence interval is likely to be between -2.65 to -0.91 mg/kg. These results indicate that the established differences in the concentration of Cu between compared A and Bw horizon have no practical meaning. Mentioned statistical evidence on the small differences in Cu concentration between the horizons suggests that Cu concentrations measured in the Bw horizon can be considered a “local background” for the samples collected in A horizon and its utilization in screening Terra rossa soil contamination can be suggested.

background threshold value, cambic horizon, matched pair testing

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