**1. Introduction**

Trace metals enter coastal lagoons through several pathways, such as atmospheric depositions [1], industrial and urban discharges [2,3], agricultural run-o ff [4,5], riverine inputs [6], groundwater discharges [7], as well as benthic fluxes [8,9]. Upon reaching the lagoons, trace metals, under variable physicochemical gradients, participate in a series of complex physical, geochemical, and biological processes that greatly a ffect the distribution of trace metals over the particulate and dissolved phases, as well as the composition of the deposited sediment, and eventually, the fluxes of metals that reach the adjacent sea. These critical biogeochemical processes include complexation reactions of trace metals with dissolved organic and inorganic ligands, adsorption/desorption reactions onto inorganic and organic suspended particles, flocculation and coagulation of colloidal and particulate species, and remobilization from sediments. All these processes vary with pH, ionic strength, the amount and the composition of suspended particles, as well as with redox conditions [10,11].

The limited water exchange with the open sea and the dominant low energy regime from tides, waves and currents, favors the long residence time of water and suspended particulate matter at the fresh – saline water interface, which in turn, kinetically enables the chemical reactions between the dissolved and particulate phase to take place [12]. Furthermore, the prevailing low energy hydrological regime, favors the accumulation of major and trace elements in sediments [2,13] as well as the accumulation of high amounts of organic matter of autochthonous and allochthonous origin [14,15]. Oxidation of organic matter directly influences the redox potential of the sediment pore water [15]. Once oxygen is consumed, the oxidation of organic matter proceeds via other oxidants following the theoretical sequence: O2 > NO3/MnO2 > Fe(OH)3 > SO42- [16,17]. Diagenetic processes may have a profound, direct or indirect, e ffect on the mobility, thus the bioavailability of trace elements [1,18,19]. The remobilization of trace metals occurs principally when Fe and Mn oxyhydroxides are reduced, but such remobilization can be partially or totally prevented in the presence of sulfide, which reacts to form metal sulfide complexes whose solubility controls the fraction of metals dissolved in solution [17,20]. Furthermore, a number of other natural or anthropogenic disturbances, such as re-suspension of sediments due to storms and waves, eutrophication events, and dredging of sediments, could turn sediments from sinks to a long-term source of contaminants to the water column [4,11], particularly when occurring in shallow settings [21] with potentially hazardous e ffects for the biota.

The Antinioti Lagoon is a rather remote, non-industrialized, moderately urbanized, shallow coastal system located at the northern part of Corfu (Kerkyra) Island in northwestern Greece. The site is of grea<sup>t</sup> ecological significance, and as such, is included in the Natura 2000 network as special area of conservation for Europe and is declared as a Site of Community Importance and Special Protection Area [22]. It is also important for fisheries supplying the local market. Despite its importance, previous studies on the area are rare.

The site is also of scientific interest from the geochemical perspective. In a previous publication it was shown that post-depositional formation of iron sulfide minerals, predominantly pyrite, and incorporation of trace elements into the pyrite phase takes place extensively in deposited sediments, limiting the mobility, and thus the bioavailability of trace metals [23]. In the present study, the distribution of trace metals in three phases, the dissolved, suspended particulate matter, and deposited sediments is examined. The interactions of trace metals between the three phases are investigated in relation to the physicochemical and geochemical parameters. Core sediments are used to estimate the local background levels and reveal temporal trends of accumulation of trace metals due to natural and anthropogenic sources. The main purpose of this study is to identify the critical processes that define trace metals' mobility and fate within the transitional fresh-saline water interface and beyond. In a broader context, the results of the study may contribute to the understanding of the overall behavior of trace metals in similar coastal lagoonal systems, which represent a typical set of transitional ecosystems in the Mediterranean Sea.
