Arid groundwater dependent ecosystem response to salinization processes in a coastal aquifer: deriving vegetation indicators of the aquifer condition

摘要

To maintain the groundwater quality represents a critical concern because of the increasinglevels of groundwater contamination globally. This goal is particularly important in aridzones, where due to the scarce rainfall the groundwater is a significant source of freshwatersupply to society and ecosystems. Here we follow an ecohydrological approach to deriveeffortless indicators of the aquifers condition, based on the monitoring of phreatohyticvegetation, a particular case of Groundwater Dependent Ecosystems (GDEs). This is thecase of Z.lotus a deciduous arid shrub from North of Africa and Southeast Spain. This studyaims to relate the biological condition of Z. lotus with the groundwater condition to explorethe feasibility for using vegetation indicators to inform about the salinization levels ofgroundwater in coastal aquifers. With this goal we: 1) evaluate the salinization levels of anaquifer from the Cabo de Gata-Níjar Natural Park, by wells sampling; 2) determine thebrackish water distance gradient based on the use of Vertical Electrical Sounding (VES),thephysiological condition of Z. lotus through leaf chemical analysis and spectral vegetationindices (NDVI and NDWI) along a salinity gradient. The results showed that the phreaticlevel, distance from the sea and therefore the salinity and freshwater available to GDE, arereflected in the leaf chemical composition of Z. lotus. However, salinity levels did notreflected clearly in vegetation greenness (NDVI) and vegetation water content (NDWI),probably because of Z. lotus showed salt tolerance within the range of salinity found in theaquifer. As a conclusion, we propose leaf ion concentration as a good indicator ofgroundwater salinization, while the spectral indices are good indicators of vegetation healthbut not for the groundwater salinization. Z.lotus is probably the only terrestrial GDE in thearid zones of Europe and its study is essential for the management and conservation of thisecosystem.