Abstract
This chapter aimed to investigate the record of climatic and environmental change in the sedimentary filling of sebkha Mhabeul and their effect on hydric and eolian erosion within the wetland and its watershed. Along a 37 cm core, the sedimentary, geochemical, and geophysical signals at the Holocene-Anthropocene transition were followed. Sampling was carried out each 1 cm to obtain 37 samples. All studied parameters and clustering techniques indicate that the first 7 cm represent the Anthropocene strata. According to the age model, this upper part of the core records the last 300 yrs. The sedimentary record of the Anthropocene is marked by an increasing rate of sedimentation, grain size fining, heavy metals (Pb, Cu, Ni, Mn, and Fe) enrichment, which is related to increased erosion. Other intrinsic parameters such as CE, pH, Na, K, and CaCO3 enhance sediment erodibility. The measurement of the magnetic susceptibility along a 37 cm core collected from the sebkha Mhabeul shows an obvious upward increase related to a high content of heavy metals for the first 7 cm.
TopIntroduction
The sedimentary record of salt lakes has been used as a proxy to monitor eolian and hydric erosions either from their surfaces (Liu et al., 2011; Han et al., 2014; Young & Evans, 1986; Yang et al., 2021) or from their catchments (Coronato & Del Valle, 1993; Essefi, 2021).
The Anthropocene is a geologic epoch related to the setting of noticeable human direct and indirect impacts on terrestrial environments and subsequent geochemical, geophysical and sedimentological repercussions (e.g., Essefi, 2020; Gharsalli et al., 2020). In spite of the controversy on the Anthropocene starting date and its stratigraphic status, some common geochemical, sedimentary and mineralogical signals, including a variation in the rate of erosion (Bernier et al., 2021) were recorded in inland saline systems related to a polluted environment and changing climate. To set a new chronostratigraphic subdivision at the beginning of the Anthropocene, the signal should be persistent, sharp, global, and synchronous to indicate the required Global Stratotype Section and Point (GSSP). This GSSP would deal on the worldwide signal of erosion as an indicator of the starting date of this epoch since the Anthropocene is marked by an increasing erosion (Marx et al., 2014; Owens, 2020), leading to a noticeable research gap concerning the issue of land erosion (Poesen, 2018)
Actually, it is the first notice in the history of the geological sciences to include the human scale within the geological scale. As a new emerging epoch, the Anthropocene scaled on a few hundreds of years would be integrated on the geological scale extending millions of years. In doing so, even the most efficient traditional dating techniques (e.g., radiocarbon dating) letting errors ranging on hundreds of years are good for nothing to file a case for the setting of the Holocene-Anthropocene transition. In this vein, tephrochronology having a good accuracy seems promising to solve the issue (Wagreich and Draganits, 2017).
Anthropocene geochemical signal includes enrichment with heavy metals, organic pollutants and the modification of other geochemical parameters, including Ce and pH. This enrichment may be related to their amounts increase in the lithosphere, biosphere, hydrosphere and atmosphere as it may be related to their easy dissolution into the eroded materials. Several proxies and methods were developed to evaluate the scale of anthropogenic effect, including the computation of some geochemical parameters such as enrichment and contamination factors, geo-accumulation index and pollution load index (Essefi, 2020). The sedimentation during the Anthropocene is modified in two ways. (1) The geochemical modification of the elemental composition of sediments with industrial and agricultural pollutants due to direct human activities. (2) Modification of sedimentary flux related to eolian activity and/or erosion of the outcropping sediments (Foucher et al., 2021).
In this chapter, the aim was to infer the record of environmental and climatic changes during the Anthropocene strata within the sedimentary filling of sebkha Mhabeul based on the multi-proxies study. These changes would have an effect on eolian and hydric erosion and deposition within this wetland and its hydrological catchment. To make it, a dated core from the sebkha of Mhabeul underwent sedimentary, geochemical, and geophysical analyses to determine the Holocene-Anthropocene transition.
Key Terms in this Chapter
Endorheic System: An endorheic basin, also called an internal drainage system, is a drainage basin, or watershed, that does not flow to one of the Earth's major oceans.
Clustering Techniques: Clustering is a Machine Learning technique that involves the grouping of data points.
Erodibility: Soil erodibility reflects the inherent susceptibility of soils to erosion processes and depends therefore on various soil properties. Sedimentary flux: Also known as the deposition rate (DR) is the vertical flux of sediment to the depositional surface. It a good proxy to monitor the increasing erosion.
Magnetic Susceptibility: It is the degree to which a material can be magnetized in an external magnetic field. Magnetic susceptibility of soil is a fast, cheap, and non-destructive technique that could be used to quantify soil erosion or soil redistribution on a long-term scale.
Anthropocene: The Anthropocene Epoch is an unofficial unit of geologic time, used to describe the most recent period in Earth's history when human activity started to have a significant impact on the planet's climate and ecosystems.
Heavy Metals: They are generally defined as metals with relatively high densities, atomic weights, or atomic numbers.