74
modify the amount of infiltration and run off (Robertson and Sharp Jr. 2015), and in
the case of agricultural land, other parameters that may change are the amount of
water gained as irrigation returns, water lost as evapotranspiration, and discharges
that contribute salinity, phosphates, and nitrates among other contaminants present
in irrigation water return flows (Dávila Pórcel et al. 2014; Opazo et al. 2016).
The distribution of nitrate concentrations superimposed onto a land use map
helps visualize a possible relationship between them (see Fig. 4.7). Although higher
nitrate concentrations occur near areas of recent land use change, the occurrences of
contamination are not high enough as to show a clear relationship. Further monitoring is therefore needed to confirm a connection between the impacts of land use,
land cover, and groundwater resource (Scanlon et al. 2005). The contaminants As
and F exceeded the Mexican norms (25 μg As L
−1
, 1.5 mg F L
−1
) in 50% of the wells
for F and 30% of the wells for As (Fig. 4.6). Although As and F are natural geogenic
contaminants (Mahlknecht et al. 2008), excessive pumping may reach to deeper
parts of the aquifer where water is presumably richer in dissolved salts as well as in
As and F (Currell et al. 2011). Regarding pH, TDS, and TH, fewer wells exceeded
the norms, but a high WL drop rate could nevertheless pose a problem if the trends
for land use change and groundwater extraction continue. Nitrate high values correspond to agricultural areas or green areas within the city watered with reclaimed
water; however, this relationship is inconclusive due to the small number of data
(Yager and Heywood 2014). More measurements are needed to test this assumption
(see Fig. 4.7). The lowering of WL can also negatively affect biodiversity by altering the type and abundance of riparian vegetation, levels of water bodies, and spring
flows that sustain wildlife (Granados-Sánchez et al. 2011; Dávila Pórcel et al. 2014;
Opazo et al. 2016).
Conclusions
The aquifers were found at risk of losing balance based on (a) lowering of WL, (b)
land use change, and (c) water quality. Therefore, continued monitoring of these
indicators is recommended, a task that would greatly benefit from automated data
loggers to measure and record WL and water quality, especially if these data were
made available to all water users. Offering the proper incentives to farmers towards
the implementation of water-saving irrigation systems was identified as an action
that would greatly attenuate the projected depletion of these aquifers.
Other measures to reduce evaporation and increase artificial aquifer recharge
should be considered, as well as the promotion of sustainable actions such as the
planting of WL that are drought-resistant and to restrict fertilizer application to only
the amount needed by the plant. Injection of treated wastewater into the aquifer has
been mentioned as a viable alternative to recharge these aquifers; however, this
should be done with care and under high scientific scrutiny that this procedure is
safe and that it will not produce clogging that may affect the permeability nor the
groundwater quality in the long run, preferably testing at pilot scale first before
V. M. Reyes Gómez et al.
modify the amount of infiltration and run off (Robertson and Sharp Jr. 2015), and in
the case of agricultural land, other parameters that may change are the amount of
water gained as irrigation returns, water lost as evapotranspiration, and discharges
that contribute salinity, phosphates, and nitrates among other contaminants present
in irrigation water return flows (Dávila Pórcel et al. 2014; Opazo et al. 2016).
The distribution of nitrate concentrations superimposed onto a land use map
helps visualize a possible relationship between them (see Fig. 4.7). Although higher
nitrate concentrations occur near areas of recent land use change, the occurrences of
contamination are not high enough as to show a clear relationship. Further monitoring is therefore needed to confirm a connection between the impacts of land use,
land cover, and groundwater resource (Scanlon et al. 2005). The contaminants As
and F exceeded the Mexican norms (25 μg As L
−1
, 1.5 mg F L
−1
) in 50% of the wells
for F and 30% of the wells for As (Fig. 4.6). Although As and F are natural geogenic
contaminants (Mahlknecht et al. 2008), excessive pumping may reach to deeper
parts of the aquifer where water is presumably richer in dissolved salts as well as in
As and F (Currell et al. 2011). Regarding pH, TDS, and TH, fewer wells exceeded
the norms, but a high WL drop rate could nevertheless pose a problem if the trends
for land use change and groundwater extraction continue. Nitrate high values correspond to agricultural areas or green areas within the city watered with reclaimed
water; however, this relationship is inconclusive due to the small number of data
(Yager and Heywood 2014). More measurements are needed to test this assumption
(see Fig. 4.7). The lowering of WL can also negatively affect biodiversity by altering the type and abundance of riparian vegetation, levels of water bodies, and spring
flows that sustain wildlife (Granados-Sánchez et al. 2011; Dávila Pórcel et al. 2014;
Opazo et al. 2016).
Conclusions
The aquifers were found at risk of losing balance based on (a) lowering of WL, (b)
land use change, and (c) water quality. Therefore, continued monitoring of these
indicators is recommended, a task that would greatly benefit from automated data
loggers to measure and record WL and water quality, especially if these data were
made available to all water users. Offering the proper incentives to farmers towards
the implementation of water-saving irrigation systems was identified as an action
that would greatly attenuate the projected depletion of these aquifers.
Other measures to reduce evaporation and increase artificial aquifer recharge
should be considered, as well as the promotion of sustainable actions such as the
planting of WL that are drought-resistant and to restrict fertilizer application to only
the amount needed by the plant. Injection of treated wastewater into the aquifer has
been mentioned as a viable alternative to recharge these aquifers; however, this
should be done with care and under high scientific scrutiny that this procedure is
safe and that it will not produce clogging that may affect the permeability nor the
groundwater quality in the long run, preferably testing at pilot scale first before
V. M. Reyes Gómez et al.