RESUMO
Episodes of drought that Morocco experienced in the years 1984-1986, 1993-1995, and 1997-2000 had repercussions that were felt many years later and continue to pose serious problems for environmentalists, as some of the affected lands have become practically deserted. These problems acted on the socio-economic conditions and created severe constraints for the development of the country. This work was conducted to study and identify changes that occurred in vegetation cover in the Oued Lahdar watershed (Rif, Morocco) between 1984 and 2017 using Land Surface Temperature (LST), Normalized Difference Vegetation Index (NDVI), Landsat TM 5, and Landsat OLI 8. The LST had significantly increased overall from 1984 to 2017, where it moved from a mean value of 29.4 °C in 1984 to 40.4 °C in 2007 and then reduced slightly to 37.9 °C in 2017. The vegetation cover index for the study area indicates that in 1984, fully vegetated areas represented 94.3% before deteriorating to 35.4% in 2007 and recovering in 2017 to 54.3%. While bare soil, which previously constituted 5.7%, reached a very high value of 64.6% in 2007 and then decreased to 47.7%. This study contributes towards society as it provides interesting data about the consequences of climate change in the area studied as well as potential protective strategies to protect vegetation cover.
RESUMO
The purpose of this study is to understand and quantify the relationships between current 137Cs inventories and the soil properties and the physiographic characteristics. A total of 36 cores were taken in seven transects with different slopes, lithology and land use. The analysis focused on the 137Cs mass activity as well as inventories and its relationship with soil properties as grain size and organic matter. The mass activity of 137Cs and the inventories varied between 3.6 and 63.7 Bq kg-1 and between 521.7 and 3304.4 Bq m-2, respectively. At uncultivated soils, high concentrations of 137Cs are located in the top 10 cm and decreased exponentially in depth. Cultivated soils record disturbed and heterogeneous 137Cs profiles with values of mass activity and inventories up to 38.7 Bq kg-1 and 2510.8 Bq m-2, respectively. The 137Cs inventories were significantly higher in uncultivated soils (mean: 2086.9 Bq m-2) compared to cultivated soils (mean: 1397.1 Bq m-2). The 137Cs mass activity showed a significant positive correlation with organic matter, silt and clay, but it was negatively correlated with sand and pH respectively. High levels of 137Cs were found at altitudes between 500 m and 640 m a.s.l, and at slopes from 8° to 11°, as well as in dense scrub land and Fersialitic soils. A principal component analysis showed that more than 86.7% of the variance in 137Cs mass activity was explained by the organic matter content and the land use. The results of this study provide insights into the effects of soil properties and physiographic factors on the behaviour of 137Cs in soils of Mediterranean environments of North Africa and strengthen the reliability of this radioisotope as an erosion tracer.
