engleski

Atmospheric Deposition of Biologically Relevant Trace Metals in an Oligotrophic Adriatic Sea Area

Atmospheric deposition (AD) is considered to be an important source of nutrients and pollutants to the sea, and is expected to increase in the future scenarios of a warmer atmosphere with increased atmospheric particulate matter (PM) emissions and deposition rates. This is especially important in oligotrophic marine areas during summer stratification which prevents the input of nutrients from the deeper layers to the sea surface, making the aquatic systems dependent on the nutrient supply from the external, atmospheric sources. While the majority of the data related to the AD impacts generated so far in the Mediterranean have been conducted on its western and eastern regions, the effects of the AD inputs to oligotrophic surface waters of the Adriatic Sea sub-basin are mostly unknown. A field campaign was conducted from February to July 2019 at the Central Adriatic coastal site (approx. 43°43'25"N, 15°50'16"E) to assess the impact of AD of biologically relevant trace metals (Zn, Cu, Co, Ni, Cd and Pb) on the complex biochemical responses of Adriatic oligotrophic systems, considering the sea surface microlayer (SML ; up to 1000 m tick sea surface layer) at the air-water interface. A comprehensive data set, comprising TM concentrations of aerosol PM10, bulk atmospheric deposition, rain water, as well as of the SML and the underlying water (ULW ; 0.5 m depth) was determined simultaneously, providing valuable information of the TM deposition processes at the air-sea interface as well as on their role in the linkage between the sea and the atmosphere. The first comprehensive insight into concentration levels of TM in atmospheric samples, their transport history, and deposition fluxes to the oligotrophic Central Adriatic area will be presented. The temporal dynamics of the TM within the sea surface layers as well as atmospheric samples enabled the assessment of their potential sources and the nature of the enrichments taking place within the SML. Seasonal variations in TM concentrations of the PM10 as well as deposition samples were significantly affected by local emission sources (residential biomass burning and traffic), meteorological conditions as well as by long-range transport of air masses from contrasting marine and continental sectors. The estimated ratios of the TM atmospheric deposition and riverine inputs to the Central Adriatic area were orders of magnitude higher than those estimated for the North Adriatic, pointing to the particular importance of the external TM atmospheric deposition inputs to the oligotrophic Central Adriatic Sea. Moreover, we observed that particular events such as intensive open-fire emissions characteristic for the area as well as occasional Saharan dust inputs in the spring strongly impacted the concentrations and distribution of TM in environmental compartments studied, especially the sea surface microlayer. We will show that intensive open-fire events as well as Saharan dust inputs observed during the campaign accounted for a significant amount of total atmospheric deposition flux in comparison to the non-event data. Once deposited to the sea surface, TM partitioning between the particulate and dissolved fraction as well as distribution between the SML and ULW layers is highly dependent on physico-chemical parameters as well as the biological reactivity of the sea surface layers. This work highlights the need to further explore the links between the atmosphere and the sea surface in order to expand the knowledge of the TM cycling through different atmospheric/sea water compartments as well as to reconsider their impacts on the biological community in oligotrophic marine environments.

trace metals ; aeroso ; bulk deposition ; coastal environment ; biomass burning

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