Abstract

MUJICA, Claudio R; MILIONE, Germán M; BEA, Sergio A  and  JOBBAGY, Esteban G. Modeling soil chemical changes induced by afforestation of natural grasslands in large plain ecosystems. Ecol. austral [online]. 2019, vol.29, n.3, pp.433-445. ISSN 1667-782X.

The replacement of grasslands by forests is one of the most extreme changes in land use due to its impact on soil and vegetation functioning. On large plain ecosystems, this shift causes, in many cases, soil chemical changes such as salinization, sodification and alkalization/acidification. Although the hydrological, chemical and biological processes involved have been extensively characterized, due to their coupling and non-linearity, their quantification is a hard task, and until the present day, they were not addressed by any research work. The present work intends to capture though reactive transport modeling, the physical-chemical processes that take place in an afforested grassland with Eucalyptus camaldulensis located on the Flooding Pampas (Castelli, province of Buenos Aires), using hydrological and chemical information (water, soil and plants). The numerical model simulates the water flows and chemical reactions in the context of reproduce 1) the hydrological changes induced by forest, and 2) the intrusion of deep saline water, 3) the absorption and exudation of nutrients by the roots, and 4) the respiration and solutes recycling. Modeling results suggest that factors such as the water table chemical composition, the cation exchange processes with the soil solution, the mineral precipitation/dissolution, and the interaction of the solution with the rhizosphere (solutes uptake/ exclusion/exudation), are the dominant mechanisms that control the direction of chemical change in the soil. This change shows marked contrasts in the short distance (250 m) from grassland passes through the outer belt and reaches the core of the afforested plot. Finally, the change intensity and direction, and transformation of soil will depend both on the new ecosystem that humans impose and on the chemical and hydrological nature of the site.

Keywords : Land use change; Salinization; Sodification; Acidification; Alkalization; Reactive transport model.

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