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Universidade de Coimbra (2014)

Prediction of salinisation effects on soil ecosystems due to climate changes

Pereira, Carla Sofia

Titre : Prediction of salinisation effects on soil ecosystems due to climate changes

Auteur : Pereira, Carla Sofia

Université de soutenance : Universidade de Coimbra

Grade : Mestrado em Ecologia 2014

Résumé
The increase of global mean temperature is a rising problem due to its potential negative effects such as melting of glaciers and ice caps and sea level rise. Soil salinisation problems are increasing with the rising of the sea level and intrusion of seawater. Impacts of exposure to seawater (mainly constituted by sodium chloride - NaCl) on the soil compartment are still unknown. The present study aimed at (1) evaluating the effects of salinisation on soil invertebrates, (2) assessing the possibility of using NaCl as a surrogate of seawater effects on soil fauna, (3) evaluating the ability of two standard soil invertebrates to acclimate to low concentrations of NaCl, and the resistance of acclimated organisms exposed to a range of concentrations of the same salt, (4) evaluating the effects of salinisation on a soil natural community due to intrusion and irrigation with saltwater. To fulfill aims (1) and (2), standard ecotoxicological reproduction tests were performed using standard artificial OECD soil spiked with serial dilutions of seawater or a gradient of sodium chloride concentrations. The reproduction and mortality of three standard soil invertebrates (the springtail Folsomia candida, the enchytraeid Enchytraeus crypticus and the predatory mite Hypoaspis aculeifer) were evaluated. Results showed no effects of seawater and sodium chloride addition in adult mortality. However, for reproduction, an increased sensitivity was observed in the following order : H. aculeifer << E. crypticus ≈ F. candida. These results are consistent with the different ways of exposure : springtails and enchytraeids are exposed by ingestion and contact while mites are only exposed by ingestion due to a continuous and thick exoskeleton. Although the small differences observed in the calculated EC’s values, seawater and NaCl had the same overall effects. To assess the acclimation ability of two standard soil invertebrates (the springtail Folsomia candida and the enchytraeid Enchytraeus crypticus ; aim (3)), the organisms were exposed to artificial OECD soil spiked with the equivalent EC20 concentration previously derived for NaCl exposure, during 26 weeks (acclimation). After that period, acclimated organisms were extracted and exposed to a gradient of NaCl concentrations already tested with unacclimated organisms. In a long-term exposure of springtails to NaCl, a drastic effect on survival and reproduction of the population, more than theoretically expected (20%), was observed.

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