The seasonal heavy metal signature and variations in the microbial mat (petola) of the Sečovlje Salina (northern Adriatic)
2015
Glavaš, Neli | Šmuc, Nastja Rogan | Dolenec, Matej | Kovač, Nives
PURPOSE: The Sečovlje Salina is a part of Sečovlje Salina Nature Park situated in south-western Slovenia (northern Adriatic). The key element of the centuries-old Slovenian tradition of salt production is the “petola”, i.e. the few-millimetre-thick microbial mat which covers the bottom of the crystallizing salt basins. Petola cultivation proceeds over the whole year, with seasonal variations of petola composition/characteristics. The purpose of this study was to investigate seasonal petola composition variability including heavy metals content. MATERIALS AND METHODS: Petola samples from 2010 (rainy salt production season) and from 2009 (favourable weather conditions) were analyzed for pH, major elements and heavy metals (X-ray fluorescence method) and mineral composition (X-ray powder diffraction). The total organic carbon (TOC) and total nitrogen (TN) content of the petola were determined using a CHNS elemental analyzer. Seasonal variations in temperature, salinity and pH value of the brine were also determined. RESULTS AND DISCUSSION: Quartz, halite, calcite, gypsum, aragonite and clay constitute the major fraction of the petola, while the organic matter content was low. The main mineral composition was associated with the base sediment while gypsum, aragonite and halite formed during crystallization processes. The increase of salinity and the decrease of organic matter were reflected in the elemental composition with highest (Ca, Cl, Mg, S) and lowest (Si, Al, Fe, K) summer concentrations. Similarly, a decrease in heavy metal concentrations (As, Cu, Cr, Mn, Ni, Pb, Zn) was also determined and was related to the lower organic matter and pH values present during this period. CONCLUSIONS: Basic sediment composition, the brine salinity gradient, salt production processes, redox conditions and the content of organic matter contribute to seasonal variability of petola composition. These factors favourably affect the petola characteristics that allow manual (seasonal) gathering and contribute to the quality of natural salt from the Sečovlje Salina.
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