COMPOSITION OF LACUSTRINE SEDIMENTS IN AN AREA AFFECTED BY A HYDROCARBONS PRE-TREATMENT PLANT IN SOUTHERN ITALY (BASILICATA REGION)

Land degradation may be defined as the physical, chemical and biological decline in land quality by natural as much as anthropogenic processes (Zorn and Komac, 2016). The release and dispersion in the different environmental matrices of toxic chemicals and pollutants (usually for agricultural, industrial or urban purposes), is certainly one of the anthropic activities widespread and with a strong impact on the land quality. In southern Italy, the largest onshore hydrocarbon reservoir of the Europe is present, from which huge amounts of gases and crude oil have been extracted daily and pre-treated in the COVA (i.e., Centro Olio Val d’Agri) industrial plant for twenty years. The COVA, however, falls in an area of great regional and national interest being a portion of the natural Appennino Lucano-Val d’Agri-Lagonegrese National Park (Basilicata Region) with a strong naturalistic and touristic vocation also increased by the presence of the Pietra del Pertusillo Lake (PPL). This is the biggest manmade water dam of southern Italy that, since its commissioning in 1968, has represented the principal natural sink of waters, with their solid or dissolved components, deriving from the Agri River drainage basin. Here, we present the first results of a more comprehensive multidisciplinary study involving the PPL lacustrine sediments, aimed to understand if in the study area the land quality has declined over time and, possibly, what about the causes of this decline. To achieve these goals, the research was focussed mainly on the sedimentological, mineralogical and geochemical characterization of two sediment well cores, intercepting the whole sedimentary record of the lake. The cores were collected during an episodic low-stand of the water level (September 16th, 2019) at two strategic points of the reservoir: one (proximal core, S1) is at the Agri River entry point into the lake, where a negligible contribution of the COVA can be assumed; the other one (distal core, S2) is in a location mostly affected by the oil pre-treatment activity. During the sediment analyses, particular attention has been paid to stratigraphical levels showing a most abundant fine-grained (silty and clayey) sediment fraction, thanks to its great ability to interact (through ion exchange, sorption and/or adsorption processes) with the solutions and, therefore, with their inorganic and organic load. Although some differences in the grain-size distribution were recorded along both the cores, as expected, from a mineralogical and geochemical point of view, the PPL lacustrine sediments are characterized by a strong compositional homogeneity. Quartz, carbonates (calcite e/o dolomite), feldspars, mica, chlorite, rutile and clay minerals (I/S, kaolinite) are present in all samples. The abundances of major and trace elements normalized to the upper crust reference standards (PAAS, GLOSS) indicate the absence of elemental anomalies. As for the sediment organic component, in this study only the 16 polycyclic aromatic hydrocarbons (PAHs), listed as priority contaminants by the US Environmental Protection Agency, have been analysed. Their total concentrations in sediments are always very low (60.5 < 175.2 ppb in the proximal core; 45.7 < 175.5 ppb in the distal core) and indicate a relatively clean environment when compared to values reported by the literature for other similar sites worldwide. However, a slight increasing of the PAHs values, associated with the decreasing of LPAHs/HPAHs ratios, has been recorded upwards the sediment column, suggesting a higher supply of pyrogenic PAHs over time.