Cartography and Diachronic Study of the Naama sabkha (Southwestern Algeria) Remotely Sensed Vegetation Index and Soil Properties

Abstract

The present study focuses on the past (1985) and current (2018) status of the Naama's Sabkha, particularly its salinity, vegetation, and water status. The acquired results will be useful for the preservation of Sabkha biodiversity. The representative sampling allowed us to make 136 soil samples over two depths: topsoil (0-4 cm) and down soil (4-30 cm) layers. The salinity analyses revealed that the maximum values are 115.3 g/l at 4 cm and 80.3 g/l at 30 cm depths. Regarding the soil conductivity, the highest values recorded at 4 cm and 30 cm are 198.4 mS.cm^-1 and 141.89 mS.cm^-1, respectively. At the same time, the results highlight that the Sabkha soil is weakly alkaline with strongly alkaline. The diachronic study based on the NDVI analysis of the Landsat_5, Landsat_8, and Sentinel_2 satellite imagery showed the installation of varied vegetation during 33 years. The outcomes of the statistical analysis of NDVI₁₉₈₅ and NDVI₂₀₁₈ (p<0.01, R²=0.77) show a significant development of vegetation. The use of NDWI for the period (1985 to 2018) highlights the importance of the water deficit in the region (p<0.01, R²=0.72). The results of the imagery geostatistical treatments reveal the changes which have occurred in particular the increase in the area of Sabkha, which was 431ha in 1985 to 514 ha in 2018. This is an increase of 83 ha for 33 years (2.5 ha per year). In other words, there was an evolution of 19.25% compared to the area in 1985.