New data on the periodic evolution of a Holocene lagoon ecosystem: The case of Khnifiss lagoon, southwest Morocco

Abstract

The Khnifiss lagoon, the only lagoon within Morocco's Saharan bioclimatic zone, is an exceptional environment rich in biodiversity. The study assesses the spatiotemporal evolution of Khnifiss using an innovative multidisciplinary approach, combining geospatial and sedimentological studies confronted with climate-eustatic data. The Normalized Difference Water Index (NDWI) revealed that the water extent of the main channel experienced its greatest contraction in 1994. The inlet on the right bank migrated west-southwest, with the entrance widening from 762 m in 1986 to 1331 m in 1994, then to 1891 m in 2002 and further to 1942 m in 2014. However, by 2024, it had contracted to 1747 m. The total emerged surfaces varied from 855,347.477 m² in 1986 to 1,392,621.931 m² in 1994. The rates of change in the emerged surfaces showed positive trends during 1986–1994 (62.814 %) and 2002–2014 (5.211 %), but negative trends during 1994–2002 (−28.917 %) and 2014–2024 (−15.203 %). These changes are controlled by the interaction of multiple climato-eustatic factors. The granulometric analysis of the core deposits (C21, C22) revealed fine sediments, well to very well sorted, suggesting excellent sorting and a dynamic combining marine and aeolian processes. The carbonate content of the cores (C21, C22) shows relatively high levels of biodetritic origin. The comparison of the sedimentological characteristics of the lagoonal cores with those of the dunes shows a high degree of similarity, confirming a predominantly aeolian origin of the lagoonal sediments, likely resulting from a significant advance of the dunes, highlighting the need for a sustainable and effective protection strategy.