Changes in hydrology and salinity accompanying a century of agricultural conversion in Argentina

Abstract

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 of Land Use Change on Soil Carbon Storage and Water Consumption in an Oasis-Desert Ecotone

“…The increased water consumption resulting from irrigation will potentially limit the water supply to other sectors as well as the amount of available water for downstream areas. Such changes in water resource allocation will have significant impacts on the long-term sustainability of the socio-ecological systems in the middle and lower reaches of the Heihe River, as water-related environmental degradation problems have been observed in this region (Qi and Luo 2007), including natural vegetation dieback of up to 80 % and surface runoff decreases of up to approximately 30 % ), groundwater depletion (Wei et al 2007), desertification, secondary salinization incurred by over-irrigation (Ma et al 2013), and agricultural non-point source water pollution (Nan et al 2010), which were also widely observed in other dryland areas such as those existing in Australia and Argentina (Beverly et al 2011;Jayawickreme et al 2011;Kienzler et al 2012).…”

Assessing the impacts of land cover change on climate in non-Amazonian South America

“…Likewise, hydraulic redistribution by deep-rooted plants maintain soil moisture in dry seasons and prevent water table rises and subsequent soil salinization (Jayawickreme et al, 2011).…”

Evaluating plant community response to sea level rise and anthropogenic drying: Can life stage and competitive ability be used as indicators in guiding conservation actions?

“…Recent, studies assessed the ability of halophytes and other plant types to desalinize soil via phytoremediation (Qadir et al, 2003(Qadir et al, , 2007Van Oosten and Maggio, 2015). Conversely, other studies have shown that conversion of land into different habitat types can lead to higher, more saline water tables and saltier soils than what was there prior to land conversion (Nosetto et al, 2007;Jayawickreme et al, 2011). As SLR impacts coastal communities salinizing the groundwater and soil, it becomes important to understand how halophytes affect soil salinity under saline groundwater conditions (Van Oosten and Maggio, 2015).…”

“…In 1980, ENP biologists initiated a monitoring project to study the effects of SLR on ENP coastal plant communities 22 . As part of that project, they created a map from 1978 aerial photos of the coastal communities stretching across the Flamingo portion of ENP and sampled vegetation on a 700m transect along an elevational gradient ranging from less than 0.5m to 1.5m above mean sea level 23 .…”

“…Increases in groundwater salinity and inundation periods and depth drive shifts in plant community composition (4,9); however, organisms themselves can act as ecosystem engineers, modifying habitats to increase their survival (16). The effect of salt on plants, communities, and plant competition is well established (17)(18)(19)(20), but there are conflicting results on whether and how plants influence soil salinity (21)(22)(23)(24)(25). As SLR salinizes coastal groundwater and soil, it becomes important to understand how halophytes (salt-tolerant plants) invading glycophytic (non-salt-tolerant) communities affect soil salinity (24), to determine whether a biological component should be added to the causes of community change predicted with SLR.…”