Water and isotope balances of Aguelmam Azigza lake (Middle Atlas, Morocco)
Bilans hydrique et hydro-isotopique du lac Aguelmam Azigza (Moyen Atlas, Maroc)
Résumé
Stable isotopes of water (18O, 2H) and their associated isotope fractionation during water-cycle phase changes produce a natural labelling of the water cycle and can be efficiently use to study hydrological and climatic processes at the local, regional and global scales. Moreover, understanding the seasonal and inter-annualstable isotope behaviour in a lake system is a key for interpretingthe 18O data obtained from inorganic fractions of lake sediments in order to reconstruct past changes in local hydro-climatology. The natural mountain lake system, Aguelmam Azigza (32°58’N, 5°26’W, 1470 m asl), is located in the karstic Tabular Middle Atlas (Morocco), one of the most humid regions of Morocco, which can be seen as the “water tower” of the country. The regional climate receives alternative influences of Mediterranean, Atlantic and Saharan air masses. A lake monitoring has been implemented since October 2012 with a monthly water sampling (precipitation, lake, well and springs) for water isotope measurements,in order to characterize seasonal variations of its water and isotope balance. Precipitation amounts at Azigza lake are very variable and high (1421 mm recorded between Oct. 2012 and Oct. 2013 for ex.). The lake waters isotopic composition plot along an evaporation line, and show a clear seasonality mainly linked to evaporation/rainfall, while groundwaters plot above the GMWL and close to regional rainfall composition suggesting a rapid transfer in the fractured karstic system. A first estimate of the lake water balance using Craig-Gordon equations shows that less than 20% of the water of the lake is lost by evaporation, and that the lake a very sensitiveto climatic parameters.