71
-1
0
1
2
3
4
2002
2004
2006
2008
2010
2012
2014
2016
2018
Sw
Years
pH
TDS
TH
As
F
Na
Cl
Series8
Series9
SO 4
NO 3
TA
-1
0
1
2
3
4
2002
2004
2006
2008
2010
2012
2014
2016
2018
Sw
Years
pH
TDS
TH
As
F
Na
Cl
Series8
Series9
SD
NO 3
SO 4
-1
0
1
2
3
4
2002
2004
2006
2008
2010
2012
2014
2016
2018
Sw
Years
pH
TDS
TH
As
F
Na
Cl
Series8
Series9
LH
NO 3
SO 4
Fig. 4.6 Water quality index (WQI) in wells for nine chemical parameters
4 Changes in the Vegetation Cover and Quality of Aquifers in the Drylands of Mexico…