Impact of geology and climate change on wetlands: Case of Lake Aguelmam Azegza (Middle Atlas, Morocco)

The AguelmamAzegza lake is located in the Middle Atlas mountain range, this region consists of carbonate rocks of Lias. It is the best-watered and richest region in Morocco in terms of wetlands, especially natural lakes, rivers and fresh springs. The lake’s water supply is ensured by the inflows of water in the form of underwater sources fed by precipitation (rain and snow) following tectonics and the genesis of karstic formations by the dissolution of carbonate rocks. The declining trend in lake levels in recent years results from the decrease in precipitation which decreases during these years.


Introduction
The AguelmamAzegza lake is a natural lake located 30 km east of the town of Khénifra in the heart of the Middle Atlas (Ajdir Causse) at an altitude of 1546m. It belongs to the structural domain of the Middle Atlas Causse, a karstic domain affected by tectonics, formed by carbonate rocks (limestone and dolomites) of the Lias which lies on soft red clay rocks and altered basalts of the Triassic (Lepoutre and Martin, 1967). The Middle Atlas, to which the AguelmamAzegza lake belongs, constitutes a favourable environment for the genesis of karstic formations following the dissolution of the carbonate rocks that form the major part of the Middle Atlas landscape. This dissolution is due to the intense fracturing that the mountain range has undergone the humid climate, the low temperatures and the accumulation of snow during the winter (Martin, 1981). This karstification allows, on the one hand, the penetration and storage of a very high proportion of meteoric water by infiltration (Bentayeb and Leclerc, 1977), and on the other hand, the filling of the groundwater network. The specific objectives assigned to this work consist in the synthesis of geological and hydrological data from different sources of punctual observations, analyses and spatialized information in the years 2012/13/15/16/17/18/19/2020 to note the effect of the dissolution of the carbonate geological formations and of the climatic changes on the water levels of lake AguelmamAzegza. Lake Azegza is one of the lakes of tectono-karstic origin (Hinaje and Ait Brahim, 2002). The Ajdir causse, of which the lake is a part, is located between the Aghbal and Srou limestone plateaus and constitutes the western part of the Bekrit syncline. In the western part of the Bekrit syncline, the structuring has generated submeridian faults and folds.

Tectonics
The AguelmamAzegza lake is fed through the anomalous contact between the crushed and faulted limestone formations that lead the water to the lake (Fig. 3).

Karstification
The karstification consists of the dissolution of rocks following an intense fracturing affecting the carbonate formations near the lake. These formations feed the lake by precipitation (snow and rain) (Fig.4). In addition to the caves located to the north-east of the lake, such as Ifri Waman, the IfriWadou mountain on the eastern shore of the lake contains several caves, the largest of which is IfriWadou, named after the mountain. The latter has been studied by a team of Spanish speleologist (Subies and Benedito, 1993) (Fig.5).

Sedimentation of the lake
The study of sedimentation at AguelmamAzegza shows that the rate of accumulation is around 4 to 5 mm/year. The sediments present a granoclassification where the distribution is decreasing from the edges towards the centre of the lake. At the edges, the proximity of the inflow and the strong hydrodynamic energy allow the deposition of coarser materials of millimetre size by excess load. These coarse particles are favoured by the inflow from the gullies, especially the one situated to the SE of the lake (Fig. 6). The winds also exert a significant erosive action on the banks. Towards the centre of the lake, the decrease in hydrodynamic energy favours fine micrometric sedimentation.  3 Climatic conditions

Precipitations
The annual rainfall measured at AguelmamAzegza over the period 2000 to 2019 has recorded fluctuations that are particularly significant. This annual rainfall was very high in 2009-10 (844mm -680mm) and after a decrease in rainfall from 2011 onwards becomes lower in 2019-20 (13mm), these results are strongly correlated with those obtained from the study of lake level variation and therefore explain the trend of decreasing lake level in recent years (Fig.7).

Temperatures
The temperature of the lake waters shows strong variations during the year, with a maximum value of 24.8°C recorded during the month of July, and a minimum value of 7.8°C recorded during the month of January, i.e. a difference of 12.64°C. Indeed, lake waters are strongly dependent on external climatic conditions (Adallal et al., 2014). Underground water inputs (~12°C), which are in the form of sub-aquatic springs feeding the lake, also contribute to the decrease in lake water temperatures (Gayral and Panouse, 1954). The average temperature values of the AguelmamAzegza station for the period 2000 to 2019 show that January is the coldest month (5°C), while July and August are the warmest (25°C) (Fig. 9). The average temperature is 13.48°C, with annual average values between 12.46°C and 14.25°C.

The temporal evolution of the lake edge
The understanding of the recent, past and future fluctuations of the AguelmamAzegza lake level, requires a good knowledge of the physiographic parameters of the lake (height h, surface S and volume V), in order to describe the relationship between the changes of the lake volume and the inflow and outflow of the interconnected lake basin which will be defined as the AguelmamAzegza lake system in an accurate way. These parameters can be determined directly by placing oneself in the site, which requires adequate equipment and instruments, or by using the geographic information system (GIS). The latter alternative will be adopted in this study to achieve our objective. In this context, data from different sources of point observations and spatial information were collected and synthesised in order to clarify the water balance of the lake in a sensitive context of environmental changes. In order to record the effect of climate changes on the water level of the lake, weproceeded to plot the lake's edges in two ways. The two ways adopted here are based on satellite images corresponding to the last years (from 2012 to 2020). The first one allows delimiting the lake borders using ArcGIS software, while the second one allows having them directly on Google Earth Pro. According to the results, there is generally a narrowing of these curves representing the level of the lake as a function of time (Fig. 10), which reflects a decrease in the volume of water during these years. In contrast, the expansion of the curve corresponding to the year 2016 implies an increase in water volume during that year. These results are in good agreement with those found using the second method (Fig. 11). This trend of decreasing lake level has been demonstrated previously by Flower and Foster (1992) in earlier studies and that moreover the lake has varied in depth by 8m during the 20th century. Using data on the level of Lake AguelmamAzegza obtained from previous works (Gayral and Panouse, 1954;Flower and Foster, 1992; aerial photos from the mapping service, Rabat, 1964Rabat, , 1973 and data acquired in the framework of this study, we were able to establish a chronicle of past lake levels based on satellite images and recent photographs(Tab.