Abstract
Water is a scarce resource in the Mediterranean region where adverse climatic conditions promoting water shortages tend to increase with climate change. Under water scarcity conditions and high atmosphere evaporative demand, the risks of decreased water quality, and land salinization are major threats to the sustainability of irrigated agriculture in this region. The assessment of the quality of irrigation water is increasingly important to ensure the maintenance of long-term salt balance at a crop, farm, and regional scale. This study is focused on the spatial and temporal variability of water quality for irrigation in the Alqueva reservoir (Southern Portugal). The assessment was performed every 2 months during a distinctive drought year (2017) and included inorganic ions (Na+, Ca2+, Mg2+, K+, NH4+, Cl-, F-, SO42-, NO3-, and NO2-), pH, and electric conductivity (ECW) of water. Sodium adsorption ratio (SAR) was calculated, and potential soil permeability problems were estimated. The assessment showed significantly higher values of the physicochemical parameters in the most upstream sites, located near tributaries inflows, and an upward trend in ion concentrations throughout the year, with significantly higher concentrations of Na+, Mg2+, Cl-, and SO42, registered through May to November, reflecting the severe drought felt in the summer, autumn, and winter. The evaluation of water quality for irrigation indicated a slight to moderate risk of reduced infiltration rates, which should be considered whenever sprinkler irrigation is used, mainly in fine-textured soils, which are prevalent in the irrigated area. The multivariate statistical approach, using principal component analysis and factor analysis, identified two principal components related to salinity and nutrient concentrations. The cluster analysis revealed three groups of similarity between samples pointing to a more time- than space-controlled pattern. Overall, the temporal dynamics of the water physicochemical parameters could indicate that an abnormal annual distribution of precipitation and temperature may distort seasonal differences. To prevent water and soil degradation, a more frequent assessment of the water quality should be considered, allowing for the selection of appropriate soil and water management measures in irrigated areas.
Highlights
Pronounced seasonal and interannual variability in the distribution of precipitation is a trait of the Mediterranean climate
The main water chemistry of the reservoir may reflect the geology of the area, and its weathering dynamics, as reported by Etteieb et al (2017) that, in a study for the assessment of the suitability of surface water for irrigation in Northern Tunisia, found the main chemistry of the river system controlled by the dissolution of gypsum and halite
In accordance with Morais et al (2007) and Palma et al (2010, 2014a), ion concentrations were higher in Lf, followed by Mr, the most upstream sites, both located near tributary inflows, near the border, and more permeable to the influence of the input flux from Spain
Summary
Pronounced seasonal and interannual variability in the distribution of precipitation is a trait of the Mediterranean climate. This variability can lead to long drought periods whose severity has increased in the past decades because of greater atmospheric evaporative demand resulting from temperature rise caused by climate change (EEA 2012; IPCC 2014; Vicente-Serrano et al 2014). Several recent studies focusing on the evaluation of drought impacts on the degradation of water quality in rivers, lakes, and reservoirs (e.g., Mosley et al 2012; Mosley 2015; van Vliet and Zwolsman, 2008), or on water and soil salinity (e.g., Etteieb et al 2017; Gkiougkis et al 2015; Hu et al 2019; Jones and van Vliet 2018; Merchán et al 2013), have exposed a global growing trend in regions with water limitations and under climatic uncertainty conditions
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