Supervisors info:
Καραβόλτσος Σωτήριος, Επίκουρος Καθηγητής, Τμήμα Χημείας, ΕΚΠΑ (Επιβλέπων)
Μπακέας Ευάγγελος, Καθηγητής, Τμήμα Χημείας, ΕΚΠΑ,
Εμμανουήλ Δασενάκης, Ομότιμος Καθηγητής, Τμήμα Χημείας, ΕΚΠΑ
Summary:
Surface Microlayer (SML) is the interface between hydrosphere and atmosphere, constituting a water limit of 1-1000 μm. Its position makes it a special and variable system, which differs from the underlying water column in terms of its both abiotic and biotic content. The main species occuring in SML belong to the group of neuston and phytoplankton. SML comprises a mixture of anthropogenic and biogenic chemical compounds, characterized by high hydrophobicity. Proteins, lipids, carbohydrates, pollutants (polycyclic aromatic hydrocarbons (PAHs), transparent extrapolymeric particles (TEPs) etc.) compose a reduced surface tension system.
Phenomena such as forest fires, intensified due to climate change and continuous alterations of anthropogenic land uses, may be responsible for the disturbance of such equilibriums in aquatic systems, such as a lake system. Ash inflows into the water column of a lake system cause short or long-term changes in physicochemical parameters (increase of pH, decrease of dissolved oxygen etc.) and water quality (increase in nutrient salts, minerals, concentrations of PAHs etc.), which directly affect the life cycle of aquatic organisms.
The aim of this thesis is the better understanding of an understudied system, the SML of a lake and the effects of ash on the water column. For the accomplishment of this purpose the targets of the study include the investigation of several parameters in natural samples and the simultaneous elaboration of a series of batch experiments simulating the effect of ash on the water column following ash production at two temperatures (350 and 550 οC) and presence in lake water for 4, 24 and 72 hours, respectively.
The results showed enrichment of the surface microfilm relative to the underlying water column in metals such as Al (EF=3.5), Mn (EF=2.9), Cd (EF=2.0), and Cu (EF=1.9). In general, in most metals the enrichment is higher during summer, with the exception of nickel. Metal concentrations are relatively low compared to those of similar works in lakes around the world. Regarding the complexing capacity of copper ions, a different tendency was recorded between the two layers, with the surface microlayer favoring the presence of labile forms of copper (4.9-22.2 nM) and the subsurface layer containing complexed forms of the metal. Copper ion complexing capacity ranged from 19 to 98 nM. The analysis of PAHs showed the prevalence of low molecular weight compounds (3-4 aromatic rings), with phenanthrene predominating both in the particulate and soluble phases of the samples. The mean value of total PAH concentration in the soluble phase was 6.6 ng/L and in the particulate one 48.7 ng/L. Both in the second and the third station, SML enrichment relative to the surface layer was observed, for particulate and soluble carbon, with enrichment factor values above 1,5 units.
Regarding eluates with ash produced at 350 οC an increase in concentrations of Na, Mg, K, Cr and Rb was observed, whereas a decrease in the metals Ca, Mn, Fe, Zn, Ni, As and Sr. Copper is mainly found in labile forms. In the corresponding eluates with ash produced at 550 οC, a significant increase in concentrations of Mn, As and Co was recorded. The increase in concentrations is due to ash solubilization, while the decrease is attributed to the phenomena of metals adsorption from water to ash. Copper is found mainly in complexed forms. Regarding PAH concentrations, those with lower molecular weights dominate, especially phenanthrene, while increasing temperature favors the detection of compounds of higher molecular weight (5-6 rings). Total PAH concentrations were equal to 65.1 ng/L for ash eluates at 350 °C and 195.3 ng/L for those with ash produced at 550 °C. The persistence of ash leads to increases in alkalinity and conductivity in both series of eluates, while pH increases are recorded in the ash eluates at 550 oC.
Keywords:
surface micro layer, forest fires, ash, metals, complexing capacity of copper ions, polycyclic aromatic hydrocarbons
