**2. The Study Area**

Antinioti Lagoon (39◦ 49' N, 19◦ 52' E) is part of the homonymous wetland consisting of the lagoon itself (40 ha), and marshes and wet meadows (60 ha) that extend to the southeastern part of the lagoon. The lagoon is shallow with depths ranging from 20 cm to 150 cm and communicates with the Ionian Sea through two channels, separated by the Agia Aikaterini Islet (Figure 1).

Besides surface runo ff and precipitation, the freshwater inputs included a series of groundwater springs seeping at the bottom of the lake (close to sites A3, A5, A8; Figure 1) with various yields; another spring flows as a surface stream (site A13) discharging at the southeastern part of the lake (hereafter "stream"). These springs are related to the karstified carbonate formations outcropping in the study area [24]. Two major karstic formations are developed: the upper unit of medium permeability represented by Upper Jurassic – Upper Cretaceous Vigla limestones and the underlying highly permeable Jurassic limestones and dolomites of Pantokrator. An impermeable sequence of Jurassic Posidonia schist interposes between the carbonate rocks and influences the penetration of water from the upper carbonate strata to the lower one, as well as the surface water and groundwater flow paths [24,25]. The main solid phase characterization of sediments by powder XRD [23] revealed

the abundance of quartz followed by calcite, the presence of common phyllosilicates (clays and micas), traces of dolomite, as well as significant amounts of pyrite. This is in accordance with the previous study by Tserolas et al. [26], describing the geology of the wider area.

The wetland sustains a variety of habitats (marshes and water fringed vegetation) and is important for several species of flora, fauna, in particular avifauna, some of which are endangered. Antinioti Lagoon supports also the local economy, as it is exploited for semi-natural extensive fish farming of mullets, seabreams, and eels. Its catchment area is partly agricultural (mainly olive trees) and partly touristic, with intense seasonality in the tourism flow. The greatest threats to the site and its conservation derive from lack of effective management, combined with: (a) the unauthorized disposal of solid wastes and occasionally of domestic wastewater; (b) the excessive use of fertilizers and pesticides in adjacent cultivated areas (e.g., olive groves); (c) the increase of dwellings and tourist infrastructures; and (d) the lack of awareness of the local community about the importance of the wetland [22].

**Figure 1.** Location of the study area and sampling stations. Rectangles mark groundwater discharges.
