Suivi de l’étendue d’eau du site Ramsar de la zone humide des Marais de la Macta-Est (wilaya de Mostaganem)

Abstract

The Macta marshes Ramsar site (study area), located in north-west Algeria in latitude (35°41'N) and longitude (0°10'W), remains one of the most interesting areas to study. The site is considered to be a wetland of international importance, and was included in the Ramsar Convention in 2001. It occupies a strategic position in the country. It covers an area of 45,000 ha. The methodological approach used is based on the application of investigative tools (GIS and remote sensing). Using ArcGis 10.8 software, we applied georeferencing methods to cartographic documents (general maps, soils, geology and vegetation), processing of 21 Sentinel-2 images (classification + calculation of spectral indices) and one (01) radar image (Shuttle Radar Topography Mission (SRTM)) of 30 m resolution, Bing Microsoft and Google Earth images. In the field, we used a Garmin GPS to locate the samples and validate the remote sensing results. Using GIS and remote sensing methods, we were able to produce a series of digital topographic and thematic maps for the study area that are accurate, up-to-date and valid to the extent of 96% of ground reality. Analysis of the maps shows that the study area lies on a flat topography and covers five (5) land-use areas (artificial, agricultural, forest, wetland and aquatic). Wetlands cover 919 ha, or 25% of the total surface area. Monitoring of the hydrological cycle shows that the extent of water observed in the field between 13/03/2023 and 30/08/2023 (6 months) has undergone a regression in flood levels and surfaces. The area of open water fell from 181 ha on 13/03/2023 to 71 ha on 30/08/2023, corresponding to a loss of 110 ha in 6 months, or around 18.5 ha/month. This shows that the surface area and duration of flooding have been reduced as a result of climate change and anthropogenic pressure.