R. Jimenez-Espinosa et al. : Time and Space Forecasting of Nitrate and Salinity Contents
75
In these layers, the analysis and evolution of salinization and pollution by nitrates
were the main goal of this work. The hydrogeochemical study of this area was
carried out using two seasonal surveys during the years 1988 to 1990, specifically,
a spring survey and an autumn one. In relation to salinization, layer 1 presents
parallel trends of pollution in the Aguadulce and Balanegra aquifers, but with a
high level of pollution in Aguadulce, restricted to the area of Sector III, a zone
highly overexploited, that has produced an important level of marine intrusion.
Moreover, the Balanegra reservoir has a natural barrier to oppose marine intrusion,
since the pollution is less than the other one. In the Balanegra aquifer the area
most affected by salinization is located in and around the Balanegra village and in
the zone of Guardias Viejas village. Layer 2, that involves Pliocene calcarenites
and AG and BM aquifers, appears more polluted in relation to the Aguadulce
aquifer, and again in the zone of Sector III.
On the other hand, the Balerma-Las Marinas aquifer is less polluted than the
previous one, but the area where values of conductivity are highest is located near
Sector III, indicating some kind of connection between aquifers. In the western
part of BM, a zone with smaller values appears. This disposition could suggest a
separation between the two parts, the most and the least polluted, and might
indicate a main fault. Layer 3, in relation to AG and BM and linked to Quaternary
lithologies presents similar values of salinization in both aquifers, but slightly
higher in the AG reservoir.
Most polluted areas in the Aguadulce aquifer are located around Roquetas village,
increasing towards the north and the coastal line with time. However, special care
must be taken because of the few points that exist. In the zone of Mojonera and
Las Marinas of the BM aquifer, the area of highest values appears restricted
around the Mojonera zone in 1988, and in 1989, a new polluted area arises in Las
Marinas. In general, an increase in conductivity values through time is evidenced
in this aquifer. In the zone of Balerma, one well presents a high value in
conductivity that produces a rich zone in the area of Guardias Viejas village. In
successive years a reduction in the value of this point is clear and produces a
diminution of the anomalous area and even its disappearance. However, another
high value appears in 1989 in the area of Balerma village, giving a zone of high
values.
In relation to nitrates, the behaviour of L1 in the two aquifers is parallel, and in this
case, the definition of a single layer for this lithology is fully justified. In general,
we can consider that this Ll layer is not greatly affected by nitrate pollution, but
the trend seems to be towards an increase in N0 3 concentrations. Therefore, special
care must be taken to preserve this layer from nitrification. Analysing the spatial
and temporal evolution of L2, a seasonal variation is observed on the maps, with
higher values in spring and lower ones in autumn.
In the Aguadulce aquifer, practically all wells have values greater than 50 mg/I, and
the whole area of this reservoir is affected by nitrate pollution. Moreover, there are
few points to explain the results satisfactorily. In the Balerma-Las Marinas, more
experimental data exist, and it is possible to establish a polluted area (> 50 mg/l),
located in the east of EI Ejido village. Towards the western part of this village,
values are very low « 20 mg/l).
75
In these layers, the analysis and evolution of salinization and pollution by nitrates
were the main goal of this work. The hydrogeochemical study of this area was
carried out using two seasonal surveys during the years 1988 to 1990, specifically,
a spring survey and an autumn one. In relation to salinization, layer 1 presents
parallel trends of pollution in the Aguadulce and Balanegra aquifers, but with a
high level of pollution in Aguadulce, restricted to the area of Sector III, a zone
highly overexploited, that has produced an important level of marine intrusion.
Moreover, the Balanegra reservoir has a natural barrier to oppose marine intrusion,
since the pollution is less than the other one. In the Balanegra aquifer the area
most affected by salinization is located in and around the Balanegra village and in
the zone of Guardias Viejas village. Layer 2, that involves Pliocene calcarenites
and AG and BM aquifers, appears more polluted in relation to the Aguadulce
aquifer, and again in the zone of Sector III.
On the other hand, the Balerma-Las Marinas aquifer is less polluted than the
previous one, but the area where values of conductivity are highest is located near
Sector III, indicating some kind of connection between aquifers. In the western
part of BM, a zone with smaller values appears. This disposition could suggest a
separation between the two parts, the most and the least polluted, and might
indicate a main fault. Layer 3, in relation to AG and BM and linked to Quaternary
lithologies presents similar values of salinization in both aquifers, but slightly
higher in the AG reservoir.
Most polluted areas in the Aguadulce aquifer are located around Roquetas village,
increasing towards the north and the coastal line with time. However, special care
must be taken because of the few points that exist. In the zone of Mojonera and
Las Marinas of the BM aquifer, the area of highest values appears restricted
around the Mojonera zone in 1988, and in 1989, a new polluted area arises in Las
Marinas. In general, an increase in conductivity values through time is evidenced
in this aquifer. In the zone of Balerma, one well presents a high value in
conductivity that produces a rich zone in the area of Guardias Viejas village. In
successive years a reduction in the value of this point is clear and produces a
diminution of the anomalous area and even its disappearance. However, another
high value appears in 1989 in the area of Balerma village, giving a zone of high
values.
In relation to nitrates, the behaviour of L1 in the two aquifers is parallel, and in this
case, the definition of a single layer for this lithology is fully justified. In general,
we can consider that this Ll layer is not greatly affected by nitrate pollution, but
the trend seems to be towards an increase in N0 3 concentrations. Therefore, special
care must be taken to preserve this layer from nitrification. Analysing the spatial
and temporal evolution of L2, a seasonal variation is observed on the maps, with
higher values in spring and lower ones in autumn.
In the Aguadulce aquifer, practically all wells have values greater than 50 mg/I, and
the whole area of this reservoir is affected by nitrate pollution. Moreover, there are
few points to explain the results satisfactorily. In the Balerma-Las Marinas, more
experimental data exist, and it is possible to establish a polluted area (> 50 mg/l),
located in the east of EI Ejido village. Towards the western part of this village,
values are very low « 20 mg/l).