[1] Most sedimentary plains occupied by semiarid woody ecosystems have low groundwater recharge rates and high vadose zone salt accumulation. Their cultivation has often led to drainage of water below root zone, displacement of solutes, and rising water tables, affecting, in most extreme cases, long-term viability of agriculture. To explore this possibility in semiarid plains of South America, we characterized vadose flow using chloride data in dry forests of central Argentina, in an area that has been subject to intense deforestation and agricultural expansion during the last century. We selected five paired stands under natural dry forests and dryland agriculture (sites deforested ≥30 years ago) and sampled sediments (n = 3 boreholes) down to 6 m depth. Profiles were consistently dry and salty in forest stands with chloride inventories (0-6 m) of 150 g/m 2 to 9 × 10 3 g/m 2 . Under cultivation 78% to 99% of the chloride stock was leached, and total water storage was ≥30% higher than in the dry forest, with soil water content close to field capacity. Estimates of groundwater recharge rates based on residual moisture flux approach (cumulative chloride versus cumulative water curves) suggested maximum values of 0.33 to 128.4 mm/yr for dry forest and agriculture, respectively. At agricultural stands recharge was also estimated using chloride front displacement, yielding minimum values ≥5.3 mm/yr. While the long-term impact of cultivation on regional groundwater hydrology is still unclear in the region, our findings suggest that land salinization processes are possible and need careful monitoring in areas with high agricultural expansion.

In a semiarid sedimentary catchment of central Argentina, we describe a recent process of landscape dissection, abrupt canyon and watercourse formation and soil salinization. We link these adverse hydrological and geomorphological transformations to three potentially important drivers: precipitation increase, seismic activity and deforestation. Remote sensing imagery in the last 48 years showed an exponential increase in the length of streams, with drainage density values tripling to reach 0.22 km km2. During the same period, forest area declined from 47% to 10%, at the expense of agriculture expansion. A 3.4‐fold expansion of surface water bodies and water table level raise of 0.15 m y−1 over the last 35 years was observed. Discharge of a new stream at the middle of the basin ranged between 0.25 and 0.45 m3 s−1 accompanied by a large and stable load of salts (~0.7 g l−1). Nil recharge and large vadose accumulation of salts in dry forests stands contrasted with recharge rates of ~16 mm y−1 and salt‐leached profiles under agriculture. Although the process of landscape dissection occurred during decades of higher than average precipitation, extreme rainfall events and seismic activity were not exceptional in that period. Results suggest that the replacement of forests by annual crops played a more important role, reducing evapotranspiration, triggering the onset of groundwater recharge and favouring subsurface through piping/sapping processes. The abrupt landscape dissection shows no signs of stabilization at the present and may only be ameliorated through changes in vegetation that restore the original non‐flow condition of the forest. Copyright © 2012 John Wiley & Sons, Ltd.

Abstract. Conversions of natural woodlands to agriculture can alter the hydrologic balance, aquifer recharge, and salinity of soils and groundwater in ways that influence productivity and sustainable land use. Using a land-use change chronosequence in semiarid woodlands of Argentina's Espinal province, we examined the distribution of moisture and solutes and estimated recharge rates on adjacent plots of native woodlands and rain-fed agriculture converted 6-90 years previously. Soil coring and geoelectrical profiling confirmed the presence of spatially extensive salt accumulations in dry woodlands and pervasive salt losses in areas converted to agriculture. A 1.1-km-long electrical resistivity transect traversing woodland, 70-year-old agriculture, and woodland, for instance, revealed a low-resistivity (high-salinity) horizon between ;3 m and 13 m depth in the woodlands that was virtually absent in the agricultural site because of leaching. Nine-meter-deep soil profiles indicated a 53% increase in soil water storage after 30 or more years of cultivation. Conservative groundwater-recharge estimates based on chloride tracer methods in agricultural plots ranged from ;12 to 45 mm/yr, a substantial increase from the ,1 mm/yr recharge in dry woodlands. The onset of deep soil moisture drainage and increased recharge led to .95% loss of sulfate and chloride ions from the shallow vadose zone in most agriculture plots. These losses correspond to over 100 Mg of sulfate and chloride salts potentially released to the region's groundwater aquifers through time with each hectare of deforestation, including a capacity to increase groundwater salinity to .4000 mg/L from these ions alone. Similarities between our findings and those of the dryland salinity problems of deforested woodlands in Australia suggest an important warning about the potential ecohydrological risks brought by the current wave of deforestation in the Espinal and other regions of South America and the world.

Effects resulting from the use of reclaimed waters on mandarins and grapefruits are evaluated by measuring the spectral responses of their canopies and the anatomy and the chlorophyll content of their leaves against control trees irrigated with waters provided by an interbasin transfer. Spectral responses from the red (R) and near-infrared (NIR) wavelength bands, and its normalized ratio (NDVI), were acquired from a hyperspatial flight conducted after a low-moderate exposition to reclaimed waters. Chlorophyll and leaf and palisade/spongy ratio thicknesses were analyzed after a moderate-high exposition. Significant differences between controls and treatments were detected in mandarins in R and leaf chlorophyll, but not in grapefruits, likely because of their higher tolerance to saline waters. Reused waters did not affect either NIR-NDVI or anatomy traits. Hyperspatial sensing techniques are suitable for detecting chlorophyll dynamics, but NIR information and related vegetation indices may mask the detection of periods of saline stress in citrus orchards. Water Environ. Res., 86, 2242Res., 86, (2014.