engleski

Distribution of trace metals in the Arno River and its estuary

The objectives of this work were to examine the distribution of TM along the Arno river, to evaluate the influence of its major tributaries (Canale della Chiana, Sieve, Bisenzio, Ombrone and Era), to identify the main sources and finally, to assess the behavior of TM in estuarine salinity gradient. During the field campaign organized in September 2015, water samples were taken either by hand grab sampling (in river ; 18 sites) or by using Van-Dorn type horizontal water sampler (in estuary ; surface and bottom layers ; 10+6 sites). Samples were immediately on-site filtered using syringe filters (0.22 µm) and afterwards acidified to pH<2 and UV digested. Hydrolab DS5 multiprobe was used for in-situ profiling of salinity, temperature, pH, dissolved oxygen. Analyses of TM were performed either by HR ICPMS or by stripping voltammetry. For most of the metals very low concentrations were measured in samples collected at the first site (12 km from the spring), before any evident anthropogenic inputs, representing the location comparable to other clean freshwater systems. A generally increasing trend of TM concentrations along the entire freshwater part was registered for most of the examined TM. TM showed a highly variable concentration among the examined tributaries. After merging with the Canale della Chiana, Bisenzio and Ombrone Rivers an obvious increase of TM concentrations was observed in the Arno River. The particular characteristic of the examined 12 km long estuarine segment was a strong salinity stratification. In the surface layer, seawater- conservative metals (Cs, Li, Mo, Rb, U, Sr) showed a clear linear increase inconcentration as a function of salinity . TM followed a near- conservative behavior (Cr, Co, Ni, Pb, Sb) or were under the influence of anthropogenic or natural process (As, Cd, Cu, Fe, Mn, Zn), as exemplified by dissolved Cu, for which an additional input from antifouling paints of the numerous boats was evidenced. Out of the plume, the concentrations of metals reached the range characteristic for clean costal Mediterranean Sea. In the bottom seawater layer, a strong hypoxia was registered in the upper estuary region. In combination with the progressive accumulation and partial TM scavenging, either increase (Co, Cr, Fe, Mn, Ni, Sb) or removal (Cd, Cu, Pb, U, V) of TM was observed in the upstream direction of seawater flow.

Trace elements ; Estuaries ; Mediterranean Sea

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