The ecohydrological challenge of woody-herbaceous transitions in the Chaco-Pampas plains
In sedimentary regions like the Chaco-Pampa plains, characterized by a very low regional topographic gradient (<0.1%), the networks of surface water and salt evacuation towards the ocean are poor and water excesses often translate into flooding and salt redistribution. Based on local and global experience we review the risks, challenges, and uncertainties opened by two vegetation transformations, dry forest replacement by agriculture and the conversion of grasslands to tree plantations, on the hydrological regulation and soil and water salinization of flat sedimentary landscapes. Evidence from dry forests, similar to those of the Espinal and Chaco, in Australia, Africa and North America suggests that their massive replacement by dryland crops causes water table level raises and salt transport towards the surface. These forests use precipitation inputs exhaustively, generating negligible deep drainage fluxes, being able to accumulate salts of atmospheric origin and those derived from rock weathering within their soils for millennia, and maintaining deep groundwater levels. The establishment of dryland agriculture generates strong deep drainage increases followed by gradual raises of groundwater level and the mobilization of salts that end affecting soil fertility at the regional scale after many decades, when water tables and the mobilized salts reach the surface. In the Espinal of Argentina we verified the negligible recharge typical of other dry forests and the storage of salts in the vadose zone (0.25 to 7 kg Cl- /m2 from 0 to 6 m of depth) and their leaching following agricultural use of these lands. This process may be related to the flooding and salinization phenomena observed in the Chaco and Espinal. In subhumid grasslands, like those in the Pampas, water table levels are naturally close to the surface and groundwater redistributes salts towards the lowest landscape positions. The localized water balance shifts, imposed by tree plantations established in these grasslands alter groundwater dynamics through its consumption generating an intense water and soil salinization process. This negative impact takes place under subhumid climates where tree plantations are able to switch the net water flux between ecosystems and groundwater, and under mid to coarse textured sediments, capable of maintaining a good supply of water towards the afforested stands. Salinization increases when the tolerance of tree species is higher. The regional topography of the Chaco-Pampa plains would lead towards a strong effect of land use changes on vertical and horizontal groundwater and intense salt transport in an intense and hard to anticipate way. This hydrological vulnerability requires a better understanding and management of the water and salt cycles from an ecohydrological perspective and possess the challenge of developing an “agronomy of water” capable to contribute to the regulation of water table levels through management of both natural and cultivated ecosystems.
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Asociación Argentina de Ecología
2008
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Jobbágy, Esteban G. Nosetto, Marcelo D. Santoni, Celina S. Baldi, Germán |
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Jobbágy, Esteban G. Nosetto, Marcelo D. Santoni, Celina S. Baldi, Germán The ecohydrological challenge of woody-herbaceous transitions in the Chaco-Pampas plains |
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Jobbágy, Esteban G. Nosetto, Marcelo D. Santoni, Celina S. Baldi, Germán |
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Jobbágy, Esteban G. |
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The ecohydrological challenge of woody-herbaceous transitions in the Chaco-Pampas plains |
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The ecohydrological challenge of woody-herbaceous transitions in the Chaco-Pampas plains |
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The ecohydrological challenge of woody-herbaceous transitions in the Chaco-Pampas plains |
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The ecohydrological challenge of woody-herbaceous transitions in the Chaco-Pampas plains |
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The ecohydrological challenge of woody-herbaceous transitions in the Chaco-Pampas plains |
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ecohydrological challenge of woody-herbaceous transitions in the chaco-pampas plains |
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In sedimentary regions like the Chaco-Pampa plains, characterized by a very low regional topographic gradient (<0.1%), the networks of surface water and salt evacuation towards the ocean are poor and water excesses often translate into flooding and salt redistribution. Based on local and global experience we review the risks, challenges, and uncertainties opened by two vegetation transformations, dry forest replacement by agriculture and the conversion of grasslands to tree plantations, on the hydrological regulation and soil and water salinization of flat sedimentary landscapes. Evidence from dry forests, similar to those of the Espinal and Chaco, in Australia, Africa and North America suggests that their massive replacement by dryland crops causes water table level raises and salt transport towards the surface. These forests use precipitation inputs exhaustively, generating negligible deep drainage fluxes, being able to accumulate salts of atmospheric origin and those derived from rock weathering within their soils for millennia, and maintaining deep groundwater levels. The establishment of dryland agriculture generates strong deep drainage increases followed by gradual raises of groundwater level and the mobilization of salts that end affecting soil fertility at the regional scale after many decades, when water tables and the mobilized salts reach the surface. In the Espinal of Argentina we verified the negligible recharge typical of other dry forests and the storage of salts in the vadose zone (0.25 to 7 kg Cl- /m2 from 0 to 6 m of depth) and their leaching following agricultural use of these lands. This process may be related to the flooding and salinization phenomena observed in the Chaco and Espinal. In subhumid grasslands, like those in the Pampas, water table levels are naturally close to the surface and groundwater redistributes salts towards the lowest landscape positions. The localized water balance shifts, imposed by tree plantations established in these grasslands alter groundwater dynamics through its consumption generating an intense water and soil salinization process. This negative impact takes place under subhumid climates where tree plantations are able to switch the net water flux between ecosystems and groundwater, and under mid to coarse textured sediments, capable of maintaining a good supply of water towards the afforested stands. Salinization increases when the tolerance of tree species is higher. The regional topography of the Chaco-Pampa plains would lead towards a strong effect of land use changes on vertical and horizontal groundwater and intense salt transport in an intense and hard to anticipate way. This hydrological vulnerability requires a better understanding and management of the water and salt cycles from an ecohydrological perspective and possess the challenge of developing an “agronomy of water” capable to contribute to the regulation of water table levels through management of both natural and cultivated ecosystems. |
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Asociación Argentina de Ecología |
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2008 |
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https://ojs.ecologiaaustral.com.ar/index.php/Ecologia_Austral/article/view/1377 |
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rev-ecoaus-article-13772020-11-04T19:43:55Z The ecohydrological challenge of woody-herbaceous transitions in the Chaco-Pampas plains El desafío ecohidrológico de las transiciones entre sistemas leñosos y herbáceos en la llanura Chaco-Pampeana Jobbágy, Esteban G. Nosetto, Marcelo D. Santoni, Celina S. Baldi, Germán Chaco forest agricultural expansion afforestation Pampa grassland hydrological regulation salinization land use bosque chaqueño expansión agrícola forestación pastizal pampeano regulación hidrológica salinización uso de la tierra In sedimentary regions like the Chaco-Pampa plains, characterized by a very low regional topographic gradient (<0.1%), the networks of surface water and salt evacuation towards the ocean are poor and water excesses often translate into flooding and salt redistribution. Based on local and global experience we review the risks, challenges, and uncertainties opened by two vegetation transformations, dry forest replacement by agriculture and the conversion of grasslands to tree plantations, on the hydrological regulation and soil and water salinization of flat sedimentary landscapes. Evidence from dry forests, similar to those of the Espinal and Chaco, in Australia, Africa and North America suggests that their massive replacement by dryland crops causes water table level raises and salt transport towards the surface. These forests use precipitation inputs exhaustively, generating negligible deep drainage fluxes, being able to accumulate salts of atmospheric origin and those derived from rock weathering within their soils for millennia, and maintaining deep groundwater levels. The establishment of dryland agriculture generates strong deep drainage increases followed by gradual raises of groundwater level and the mobilization of salts that end affecting soil fertility at the regional scale after many decades, when water tables and the mobilized salts reach the surface. In the Espinal of Argentina we verified the negligible recharge typical of other dry forests and the storage of salts in the vadose zone (0.25 to 7 kg Cl- /m2 from 0 to 6 m of depth) and their leaching following agricultural use of these lands. This process may be related to the flooding and salinization phenomena observed in the Chaco and Espinal. In subhumid grasslands, like those in the Pampas, water table levels are naturally close to the surface and groundwater redistributes salts towards the lowest landscape positions. The localized water balance shifts, imposed by tree plantations established in these grasslands alter groundwater dynamics through its consumption generating an intense water and soil salinization process. This negative impact takes place under subhumid climates where tree plantations are able to switch the net water flux between ecosystems and groundwater, and under mid to coarse textured sediments, capable of maintaining a good supply of water towards the afforested stands. Salinization increases when the tolerance of tree species is higher. The regional topography of the Chaco-Pampa plains would lead towards a strong effect of land use changes on vertical and horizontal groundwater and intense salt transport in an intense and hard to anticipate way. This hydrological vulnerability requires a better understanding and management of the water and salt cycles from an ecohydrological perspective and possess the challenge of developing an “agronomy of water” capable to contribute to the regulation of water table levels through management of both natural and cultivated ecosystems. En regiones sedimentarias como la llanura Chaco-Pampeana, caracterizadas por una muy escasa pendiente regional (<0.1%), las redes de evacuación de agua superficial y sales hacia el océano son pobres y los excesos hídricos se traducen, con frecuencia, en inundaciones y redistribución local de sales. Sobre la base de la experiencia local y global revisamos los riesgos, desafíos e incertidumbres que plantean dos transformaciones de la vegetación, el reemplazo de bosques secos por agricultura y la conversión de pastizales a plantaciones forestales, sobre la regulación hidrológica y la salinización de aguas y suelos de llanuras. La evidencia de bosques secos de Australia, África y Norteamérica, similares a los del Espinal y Chaco de Argentina, sugiere que su reemplazo masivo por cultivos de secano causa ascensos de napas y transporte de sales a la superficie. Estos bosques utilizan exhaustivamente la precipitación, reducen de forma drástica la recarga de la napa, son capaces de acumular, a lo largo de milenios, sales de origen atmosférico y derivadas de la meteorización en los suelos, y mantienen niveles freáticos profundos. El ingreso de la agricultura aumenta el drenaje profundo, seguido por ascensos graduales en el nivel freático y una fuerte movilización de sales disueltas, lo que afecta la fertilidad de los suelos cuando los niveles freáticos y las sales movilizadas alcanzan la superficie. En el Espinal argentino verificamos bajo bosques secos la nula recarga y el almacenamiento de sales en la zona no saturada de los suelos (0.25 a 7 kg Cl- /m2 de 0 a 6 m de profundidad), y el lavado de esas sales luego del uso agrícola. Este proceso podría explicar la inundación y salinización observadas en el Chaco y el Espinal. A diferencia de los ambientes de bosques secos, los niveles freáticos en los pastizales subhúmedos suelen estar cerca de la superficie, y las napas redistribuyen las sales hacia las zonas topográficamente bajas del paisaje. En estos pastizales, los cambios en el balance hídrico que acompañan al establecimiento de plantaciones forestales alteran la dinámica de las napas freáticas, debido al mayor consumo de estas plantaciones. Esto genera un intenso proceso de salinización de aguas y suelos. Este impacto negativo ocurre en climas subhúmedos, donde las forestaciones pueden revertir el flujo neto hacia las napas, en sedimentos de texturas medias a gruesas (capaces de mantener un buen abastecimiento de agua) hacia las masas forestales, y donde las especies forestales toleran en particular la salinización. En un relieve extremadamente plano como el de la llanura Chaco-Pampeana, los cambios en el uso de la tierra afectarían en forma intensa y difícil de anticipar el transporte vertical y horizontal de agua subterránea y sales. Esta vulnerabilidad hidrológica exige comprender y manejar los ciclos del agua y las sales desde una perspectiva eco- hidrológica y plantea el desafío de desarrollar una “agronomía del agua” capaz de contribuir a la regulación de los niveles freáticos a través del manejo de los ecosistemas naturales y cultivados. Asociación Argentina de Ecología 2008-12-01 info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion application/pdf https://ojs.ecologiaaustral.com.ar/index.php/Ecologia_Austral/article/view/1377 Ecología Austral; Vol. 18 No. 3 (2008); 305-322 Ecología Austral; Vol. 18 Núm. 3 (2008); 305-322 0327-5477 1667-7838 spa https://ojs.ecologiaaustral.com.ar/index.php/Ecologia_Austral/article/view/1377/743 Derechos de autor 2020 Ecología Austral |