64
apparent vegetation, whereas the opposite change was used to identify areas of
recovered vegetation cover. The losses in vegetation cover were identified when the
original classification represented different types of vegetation cover: Temperate
forest, desert scrub, grasslands, or other types of vegetation were transformed to
land uses such as agriculture, urban areas, bodies of water or areas without apparent
vegetation. With inverse transitions it was possible to detect the surface recovered
by the vegetation cover. Finally, the dynamics of change from a condition of primary to secondary succession in the vegetation cover allowed identifying processes
of degradation of vegetation cover.
Water Quality
Water quality was determined from chemical analyses of water samples collected in
2004, 2007, 2010, 2011, and 2015. In 2015, 20 new wells were added to the original
ten in order to expand and improve data coverage, as well as to have a better view
of temporal variations (Table 4.2). The 2015 samples were collected in spring, summer, and fall and analyzed for hardness, electrical conductivity, and potential contaminants As, F, Na, and nitrate.
In order to determine the chemical quality of the water in wells, a water quality
index (WQI) was considered that contemplates the maximum permissible limits
(MPL) according to Mexican guidelines (NOM 127 SSA1 1994 mod. 2005). For
each of the parameters examined, the WQI was determined by dividing the current
concentration over the NML concentration, the result reflects wells with pollution
Table 4.2 Chemical parameters analyzed of water samples
Parameter
Recommended limits
Analytical methods
Mexican norm NOM 127 SSA1 1994
mod. 2005 (NOM); World Health
Organization (WHO)
Mexican norm
NOM-230SSA1–2002
Arsenic, As
10 ppb WHO; 25 ppb NOM
ICP-MS spectrometer
Fluoride, F
1.5 mg L
−1 NOM, WHO
Ion selective
electrode
Calcium, magnesium,
potassium, sodium
(Ca, Mg, K, Na)
Na 200 mg L
−1 NOM
ICP-MS spectrometer
Nitrate, N-NO 3
10 mg L
−1 NOM
HACH spectrometer,
method 8171
Sulfate, SO 4
400 mg L
−1 NOM
HACH spectrometer,
method 8051
Total dissolved solids, TDS 1000 mg L
−1 NOM
Calculated from EC
Chloride, Cl
250 mg L
−1 NOM
Titration
pH
6.5–8.5 NOM
pH meter
Total hardness, TH
500 mg CaCO 3 L
−1 NOM
Titration
Salinity
3.32 g L
−1 NOM
Calculated from EC
V. M. Reyes Gómez et al.
apparent vegetation, whereas the opposite change was used to identify areas of
recovered vegetation cover. The losses in vegetation cover were identified when the
original classification represented different types of vegetation cover: Temperate
forest, desert scrub, grasslands, or other types of vegetation were transformed to
land uses such as agriculture, urban areas, bodies of water or areas without apparent
vegetation. With inverse transitions it was possible to detect the surface recovered
by the vegetation cover. Finally, the dynamics of change from a condition of primary to secondary succession in the vegetation cover allowed identifying processes
of degradation of vegetation cover.
Water Quality
Water quality was determined from chemical analyses of water samples collected in
2004, 2007, 2010, 2011, and 2015. In 2015, 20 new wells were added to the original
ten in order to expand and improve data coverage, as well as to have a better view
of temporal variations (Table 4.2). The 2015 samples were collected in spring, summer, and fall and analyzed for hardness, electrical conductivity, and potential contaminants As, F, Na, and nitrate.
In order to determine the chemical quality of the water in wells, a water quality
index (WQI) was considered that contemplates the maximum permissible limits
(MPL) according to Mexican guidelines (NOM 127 SSA1 1994 mod. 2005). For
each of the parameters examined, the WQI was determined by dividing the current
concentration over the NML concentration, the result reflects wells with pollution
Table 4.2 Chemical parameters analyzed of water samples
Parameter
Recommended limits
Analytical methods
Mexican norm NOM 127 SSA1 1994
mod. 2005 (NOM); World Health
Organization (WHO)
Mexican norm
NOM-230SSA1–2002
Arsenic, As
10 ppb WHO; 25 ppb NOM
ICP-MS spectrometer
Fluoride, F
1.5 mg L
−1 NOM, WHO
Ion selective
electrode
Calcium, magnesium,
potassium, sodium
(Ca, Mg, K, Na)
Na 200 mg L
−1 NOM
ICP-MS spectrometer
Nitrate, N-NO 3
10 mg L
−1 NOM
HACH spectrometer,
method 8171
Sulfate, SO 4
400 mg L
−1 NOM
HACH spectrometer,
method 8051
Total dissolved solids, TDS 1000 mg L
−1 NOM
Calculated from EC
Chloride, Cl
250 mg L
−1 NOM
Titration
pH
6.5–8.5 NOM
pH meter
Total hardness, TH
500 mg CaCO 3 L
−1 NOM
Titration
Salinity
3.32 g L
−1 NOM
Calculated from EC
V. M. Reyes Gómez et al.