Quantitative and Qualitative Assessment of Groundwater from Semi-Arid Zones in the Context of Climate Change, Example of Essaouira Region, Morocco

This study aims to assess the effect of climate change on water resources in semi-arid environments, taking the Essaouira region as an example. Analysis of climate data shows a downward trend in precipitation of 12 to 16% and an increase in air temperature of 2.3 °C over the past three decades. The piezometric study shows a continuous drop in the piezometric level which exceeds 12 m for the Cenomanian-Turonian aquifer, 17 m for the Plio-Quaternary aquifer, around 8 m for the Barremian-Aptian aquifer and 5 m for the Hauterivian. Hydrogeochemical analysis shows that (i) the groundwater mineralization is controlled by the dissolution of evaporitic and carbonates minerals, by the reverse ions exchange phenomenon, and by the marine intrusion, especially at Plio-Quaternary aquifer; (ii) the groundwater quality in the study area deteriorates gradually over time and space. The isotopic technique shows that (i) the groundwater recharge in the study area is ensured by precipitation of oceanic origin without significant evaporation and that (ii) climate change has no remarkable effect on the isotopic content of the groundwater of the study area. However, the results of this article reflect that the Essaouira basin is very vulnerable to climate change.

Multiple Methods to Partition Evapotranspiration in a Maize Field

Partitioning evapotranspiration (ET) into soil evaporation E and plant transpiration T is important, but it is still a theoretical and technical challenge. The isotopic technique is considered to be an effective method, but it is difficult to quantify the isotopic composition of transpiration δT and evaporation δE directly and continuously; few previous studies determined δT successfully under a non-steady state (NSS). Here, multiple methods were used to partition ET in a maize field and a new flow-through chamber system was refined to provide direct and continuous measurement of δT and δE. An eddy covariance and lysimeter (EC-L)-based method and two isotope-based methods [isotope combined with the Craig–Gordon model (Iso-CG) and isotope using chamber measurement (Iso-M)] were applied to partition ET. Results showed the transpiration fraction FT in Iso-CG was consistent with EC-L at both diurnal and growing season time scales, but FT calculated by Iso-M was less than Iso-CG and EC-L. The chamber system method presented here to determine δT under NSS and isotope steady state (ISS) was robust, but there could be some deviation in measuring δE. The FT varied from 52% to 91%, with a mean of 78% during the entire growing season, and it was well described by a function of LAI, with a nonlinear relationship of FT = 0.71LAI0.14. The results demonstrated the feasibility of the isotope-based chamber system to partition ET. This technique and its further development may enable field ET partitioning accurately and continuously and improve understanding of water cycling through the soil–plant–atmosphere continuum.