INVESTIGADORES
JOBBAGY GAMPEL Esteban Gabriel
artículos
Título:
Water and nitrate exchange between cultivated ecosystems and groundwater in the Rolling Pampas.
Autor/es:
PORTELA SI; ANDRIULO AE; JOBBAGY, EG; SASAL MC
Revista:
AGRICULTURE, ECOSYSTEMS AND ENVIRONMENT
Editorial:
ELSEVIER SCIENCE BV
Referencias:
Año: 2009 vol. 134 p. 277 - 286
ISSN:
0167-8809
Resumen:
Understanding nitrogen (N) exchange between cultivated ecosystems and groundwater becomes crucial
in the Rolling Pampas where high and variable water table levels are accompanied by increasing Nfertilization
rates. Field monitoring of crops, soils and groundwater was combined with modeling to
evaluate bidirectional flows (from terrestrial ecosystems to aquifers and vice versa) of water and N
throughout a 10-year period (19982007) of highly variable precipitation (7601506 mm year1) and
water table depths (6.5 to <1 m). Piezometers at three topographic positions (upland: UP, mid slope: MS,
and toe slope: TS; 1740 and 510 mapart) were used to monitor water table depth and phreatic (<14 m),
intermediate (35 m) and bottom of the aquifer (45 m) water chemistry. Crop production and soil water
and nitrate content were monitored in two agricultural plots (wheat/soybeancorn rotation) where MS
and TS piezometers were located. Nitrate concentration in phreatic groundwater was relatively stable
and low at UP and MS (<10 mg l1) but increased sharply at TS (>45 mg l1) during periods of high water
table levels (<3 m deep). Groundwater chloride concentrations increased with depth in piezometers at
UP and MS, but showed the opposite trend at TS during periods of high water table levels, suggesting
evaporative discharge at this position. The lateral hydraulic gradient (moving energy) between MS and
TS ranged from 0.1 to 0.4% and was negatively correlated with water table depth at TS (R2 = 0.23,1) and
water table depths (6.5 to <1 m). Piezometers at three topographic positions (upland: UP, mid slope: MS,
and toe slope: TS; 1740 and 510 mapart) were used to monitor water table depth and phreatic (<14 m),
intermediate (35 m) and bottom of the aquifer (45 m) water chemistry. Crop production and soil water
and nitrate content were monitored in two agricultural plots (wheat/soybeancorn rotation) where MS
and TS piezometers were located. Nitrate concentration in phreatic groundwater was relatively stable
and low at UP and MS (<10 mg l1) but increased sharply at TS (>45 mg l1) during periods of high water
table levels (<3 m deep). Groundwater chloride concentrations increased with depth in piezometers at
UP and MS, but showed the opposite trend at TS during periods of high water table levels, suggesting
evaporative discharge at this position. The lateral hydraulic gradient (moving energy) between MS and
TS ranged from 0.1 to 0.4% and was negatively correlated with water table depth at TS (R2 = 0.23,<1 m). Piezometers at three topographic positions (upland: UP, mid slope: MS,
and toe slope: TS; 1740 and 510 mapart) were used to monitor water table depth and phreatic (<14 m),
intermediate (35 m) and bottom of the aquifer (45 m) water chemistry. Crop production and soil water
and nitrate content were monitored in two agricultural plots (wheat/soybeancorn rotation) where MS
and TS piezometers were located. Nitrate concentration in phreatic groundwater was relatively stable
and low at UP and MS (<10 mg l1) but increased sharply at TS (>45 mg l1) during periods of high water
table levels (<3 m deep). Groundwater chloride concentrations increased with depth in piezometers at
UP and MS, but showed the opposite trend at TS during periods of high water table levels, suggesting
evaporative discharge at this position. The lateral hydraulic gradient (moving energy) between MS and
TS ranged from 0.1 to 0.4% and was negatively correlated with water table depth at TS (R2 = 0.23,<14 m),
intermediate (35 m) and bottom of the aquifer (45 m) water chemistry. Crop production and soil water
and nitrate content were monitored in two agricultural plots (wheat/soybeancorn rotation) where MS
and TS piezometers were located. Nitrate concentration in phreatic groundwater was relatively stable
and low at UP and MS (<10 mg l1) but increased sharply at TS (>45 mg l1) during periods of high water
table levels (<3 m deep). Groundwater chloride concentrations increased with depth in piezometers at
UP and MS, but showed the opposite trend at TS during periods of high water table levels, suggesting
evaporative discharge at this position. The lateral hydraulic gradient (moving energy) between MS and
TS ranged from 0.1 to 0.4% and was negatively correlated with water table depth at TS (R2 = 0.23,<10 mg l1) but increased sharply at TS (>45 mg l1) during periods of high water
table levels (<3 m deep). Groundwater chloride concentrations increased with depth in piezometers at
UP and MS, but showed the opposite trend at TS during periods of high water table levels, suggesting
evaporative discharge at this position. The lateral hydraulic gradient (moving energy) between MS and
TS ranged from 0.1 to 0.4% and was negatively correlated with water table depth at TS (R2 = 0.23,<3 m deep). Groundwater chloride concentrations increased with depth in piezometers at
UP and MS, but showed the opposite trend at TS during periods of high water table levels, suggesting
evaporative discharge at this position. The lateral hydraulic gradient (moving energy) between MS and
TS ranged from 0.1 to 0.4% and was negatively correlated with water table depth at TS (R2 = 0.23,R2 = 0.23,
p < 0.001, n = 79) indicating that groundwater flow towards TS increased as the water table level rose. A
capillary transportmodel (UPFLOW) suggested that at TS groundwater supplied an important amount of
water and solutes to crops with corn obtaining approximately half of its water needs (228413 mm) and
one fourth of its N requirement (3876 kg ha1) from groundwater. Water and N supply from
groundwater may have explained the higher biomass and grain yield in the lower positions of each plot
with regard to the rest of the area. Our results suggest that the Rolling Pampas landscapes can switch
from a typical recharge behavior to a rechargedischarge one following extended rainy periods that rise
water table levels and hydraulic gradients, favoring water and solute transport towards the lower
positions of the landscape and local concentration of solutes by groundwater consumption,
simultaneously affecting groundwater quality.< 0.001, n = 79) indicating that groundwater flow towards TS increased as the water table level rose. A
capillary transportmodel (UPFLOW) suggested that at TS groundwater supplied an important amount of
water and solutes to crops with corn obtaining approximately half of its water needs (228413 mm) and
one fourth of its N requirement (3876 kg ha1) from groundwater. Water and N supply from
groundwater may have explained the higher biomass and grain yield in the lower positions of each plot
with regard to the rest of the area. Our results suggest that the Rolling Pampas landscapes can switch
from a typical recharge behavior to a rechargedischarge one following extended rainy periods that rise
water table levels and hydraulic gradients, favoring water and solute transport towards the lower
positions of the landscape and local concentration of solutes by groundwater consumption,
simultaneously affecting groundwater quality.1) from groundwater. Water and N supply from
groundwater may have explained the higher biomass and grain yield in the lower positions of each plot
with regard to the rest of the area. Our results suggest that the Rolling Pampas landscapes can switch
from a typical recharge behavior to a rechargedischarge one following extended rainy periods that rise
water table levels and hydraulic gradients, favoring water and solute transport towards the lower
positions of the landscape and local concentration of solutes by groundwater consumption,
simultaneously affecting groundwater quality.