*2.1. Study Area*

The samplings were carried out in three neighbouring Mediterranean brackish costal lakes located on the Tyrrhenian coast of central Italy (42◦2800" North–12◦5100" East): Lake Caprolace, Lake Fogliano and Lake Sabaudia (Figure 1). The three lakes respectively have a surface area of about 3 km2, 4 km<sup>2</sup> and 3.9 km2, and mean depths of 3 m, 2 m and 10 m. They are classified as non-tidal lagoons with a maximum tidal excursion of 0.21–0.23 m [44–46]. Salinity generally varies between 33.7 and 38.1 PSU in Caprolace, 29.9 and 39.2 PSU in Fogliano, and 28.8 and 33.7 PSU in Sabaudia. The annual average was 36.3 ± 0.8 PSU in Caprolace, 35.3 ± 0.8 PSU in Fogliano and 31.7 ± 0.9 PSU in Sabaudia in 2006–2010 [44]. Data are expressed as mean ± standard error.

**Figure 1.** Map of the sampling area. The map shows the costal lakes of Caprolace (LP), Fogliano (IP) and Sabaudia (HP) located on the Tyrrhenian coast of central Italy (42◦2800" North–12◦5100" East).

The lakes are a ffected by various forms of anthropogenic disturbance related to organic and inorganic nitrogen inputs from urban treated sewage, livestock farming and agricultural activities, which are widespread in the surrounding areas [2,3].

On average, the mean concentration of total nitrogen was 383.6 ± 23.21 μg/<sup>L</sup> in Caprolace, 662.6 ± 66.70 μg/<sup>L</sup> in Fogliano and 1006.1 ± 49.97 μg/<sup>L</sup> in Sabaudia in 2006–2010. Santoro et al. [2] found the same trend in nitrate concentrations, with 12.2 ± 2.9 μg/L, 42.4 ± 61.3 μg/<sup>L</sup> and 91.9 ± 70.24 μg/<sup>L</sup> in Caprolace, Fogliano and Sabaudia respectively in the same period.

Lake Caprolace and Lake Fogliano (hereafter respectively LP and IP), characterised respectively by low and intermediate levels of eutrophication [3,47], are Sites of Community Importance (SCIs) located within the Circeo National Park (Lazio).

Lake Caprolace does not receive water inputs from the hinterland, while Lake Fogliano is affected by nutrient inputs from both the River Rio Martino and the livestock breeding activities practised in the surrounding areas. The annual concentration of *Chlorophyll a* was generally lower in Caprolace (2.1 ± 0.4 μg/L) than Fogliano (5.8 ± 1.2 μg/L) in 2006–2010.

Lake Sabaudia, the southernmost lake (hereafter HP), is affected by the highest anthropogenic pressure [3], mainly due to runoff from both the city of Sabaudia and cultivated fields in the surrounding areas as well as fishing and mussel farming. In this lake, freshwater inputs are present throughout the year.

Annual algal biomass and *Chlorophyll a* concentrations in this lake vary from 10.2 to 40.9 μg/L, with an average recorded value in 2006-2010 of 24.2 ± 6.15 μg/L. Further details regarding the study area can be found in Santoro et al. [2] and Jona-Lasinio et al. [3].
