Spatial variability of eight hazardous heavy metals in agricultural topsoils: a case study from Xuzhou area, Jiangsu, China

Figures & data

Figure 1. (a) The map of China, with the red star showing the location of the Xuzhou area. (b) Sample locations in the Xuzhou area. (c) An example of the distribution of samples with the background of a satellite image

Table 1. Summary of statistical parameters of topsoil heavy metals (unit: mg/kg)

Element	Cu	Zn	Ni	Pb	Cr	Hg	As	Cd
Minimum	2.74	37.22	15.45	4.98	15.12	0.01	3.73	0.00
Maximum	245.9	398.30	57.12	125.46	229.65	0.20	18.80	0.74
Median	18.40	64.41	28.12	21.43	57.45	0.09	8.80	0.10
Mean	22.38	71.29	30.15	24.65	57.60	0.08	9.39	0.13
S.D.	21.73	36.62	7.60	13.01	20.56	0.05	2.85	0.11
C.V.	0.97	0.51	0.25	0.53	0.36	0.59	0.30	0.83
Skewness	8.81	6.23	1.19	4.46	4.38	0.04	1.13	3.23
Kurtosis	90.23	51.84	1.46	28.69	35.45	1.26	1.98	12.80
K–S test	0.24	0.20	0.13	0.18	0.14	0.13	0.13	0.20
K–S p	0.00	0.00	0.023	0.00	0.00	0.02	0.012	0.00
n	127	127	127	137	137	137	137	135
Distribution	lognormal	lognormal	lognormal	lognormal	lognormal	lognormal	lognormal	lognormal
Xuzhou background	12.61	91.10	32.80	16.30	55.50	0.03	11.20	0.29
China Mean	20.00	69.96	25.04	18.80	57.77	0.08	6.16	0.15
GB15618–2018	100	300	190	170	250	1.0	20	0.6

p < 0.05, S.D. = standard deviation, C.V. = coefficient of variation.

Table 2. Pearson correlation coefficients of topsoil heavy metals

	Cu	Zn	Ni	Cr	Hg	As	Cd	Pb
Cu	1
Zn	0.531**	1
Ni	0.308**	0.291**	1
Cr	0.215*	0.451**	0.475**	1
Hg	0.145	−0.038	0.316**	−0.035	1
As	0.241**	0.361**	0.584**	0.456**	0.038	1
Cd	0.212*	0.576**	0.249**	0.325**	–0.149	0.262**	1
Pb	0.524**	0.709**	0.389**	0.347**	–0.079	0.230**	0.298**	1

* Correlation is significant at the 0.05 level; ** Correlation is significant at the 0.01 level.

Table 3. Semivariogram parameters and models of topsoil heavy metals

Heavy medal	Model	Nugget (C0)	Sill (C+ C0)	Nugget/Sill C0/(C+ C0)	Range (km)
Hg	Exponential	0.247	0.591	41.8%	0.807
Cd	Linear	0.327	0.339	96.4%	1.0859
As	Spherical	0.0001	0.0902	0.1%	0.0902
Cr	Gaussian	0.0262	0.104	25.1%	0.0849
Cu	Exponential	0.0227	0.192	11.8%	0.099
Ni	Gaussian	0.0001	0.0552	0.2%	0.0901
Pb	Exponential	0.013	0.147	8.8%	0.204
Zn	Linear	0.0827	0.0827	100%	1.0844

Figure 2. Semivariograms of topsoil heavy metals

Figure 3. The spatial distribution maps of the eight heavy metal contents. unit: mg/kg