Structural map of Sicily with location of the studied areas; the dark grey polygons represent volcanic areas. 

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... Earth surface is covered by the hydrosphere for about 2/3, distributed between oceans and marine waters, representing 98% of the total water; the remaining 2% is arranged in continental ice, snow, lakes, rivers and ground waters. Only 0.4% of the total continental waters are stored in lakes, of which 80% is accumulated in the 40 largest lakes of the Earth (Encyclopaedia Britannica on line). Although small endhoreic (topographically closed) lakes represent a minor proportion of total continental waters, they constitute noteworthy appealing geoniches of great scientific and environmental interest. Most of little endhoreic lakes originated through processes which are very fast on a geological time scale, like meteoric impacts, volcanic phenomena, landslides, sink-holes or biotic activities such as plant accumulations and/or animal fabrics; due to their fast genesis these lakes often suffer metastable hydrological and morphological equilibria, easily altered by climatic and environmental changes. Differently with respect to lakes resulting from the "normal" hydro-geologic evolution of the landscape, they are abruptly inserted into independently- evolving catchment basins and their surface and underground drainage systems are not able to supply the amount of water needed to compensate the evaporation losses from the lake surfaces, eventually causing a complete desiccation during pro- longed drought periods. In arid or sub-arid regions endhoreic lakes allow the development of special ecosystems inserted in a dry landscape, characterized by a fragile hydrologic re- silience, seriously affected by climatic changes and anthropic activity [Nicholson 1998, Coe and Foley 2001, Jones et al. 2001, Roshier et al. 2001, Shi et al. 2002, Demlie et al. 2007]. The study of the hydro-morphological evolution of endhoreic lakes may give interesting insights in the preser- vation of geo-biodiversity and, more in general, of the natural landscape. A critical issue can arise while studying small lacustrine features (i.e. with areal extensions even minor than 1,000 m 2 ): the obligation of using light field techniques. This topic be- comes particularly relevant in the study of small lakes protected as nature reserves, where the very restrictive rules, often imposed by the local legislation for the protection of these environments, normally permit only field activities based on non-invasive techniques, like basic echo-sounder (fish-finders) and GPS mounted on small non-motorized vessels and/or underwater visual/photographic surveys carried out without any breathing apparatus. Lake Specchio di Venere and Lake Sfondato, both nature reserves located in South Italy, represent two paradigmatic ex- amples of small endhoreic lakes quickly formed and inserted in highly significant natural contexts, potentially prone to ecological involutions driven by environmental changes. Lake Specchio di Venere is a volcanic lake located on Pantelleria Island (Sicily Channel, Mediterranean Sea), Lake Sfondato a sink-hole lake formed at the beginning of 20 th century in Central Sicily [Madonia et al. 2006, and references therein]. Our work describes the morphological and bathymetric characteristics of the two lakes inferred from field analy- ses based on low environmental impact techniques, with a special attention to the influence of the survey methodolo- gies on the interpretative results. Bathymetric surveys and direct measurements of changes in lake surface elevations have been applied, in the Lake Sfondato case, to check the reliability of different hydrological balance hypotheses and to evaluate the role potentially played by environmental and climatic changes on the chances of survival of this lacustrine ecosystem. Sicily is located in the Central Mediterranean, along the main Eurasia-Nubia convergent plate boundary [Dewey et al. 1989, Serpelloni et al. 2007, Catalano et al. 2009], where three main elements mark both the collisional complex of Sicily and its offshore continuation (Figure 1): (i) the Hyblean Foreland outcropping in southeastern Sicily; (ii) the Caltanissetta Basin, a dynamic foredeep basin from the Late Miocene to the Quaternary; (iii) a complex chain, thrust towards the east and southeast, consisting of the Calabrian Arc and the Maghrebian thrust belt [Vallone et al. 2008 and references therein]. A powerful evaporitic succession, the Ges- soso-Solfifera Formation was deposited in the Caltanissetta Basin during the Messinian (Upper Miocene) salinity crisis in the Mediterranean Sea; from bottom to top, it consists of bedded diatomites (Tripoli Formation), limestones (some- times evaporitic), gypsum deposits interbedded with clay levels and Na-K salts [Mezzadri 1989]. Lake Specchio di Venere is located on Pantelleria Island (South Mediterranean Sea; Figure 2a), a Pleistocene strato- volcano whose subaerial portion is mainly composed of ex- plosive volcanic products ranging from trachytes to peralkaline rhyolites [Civetta et al. 1984]. Each major erup- tion results in the formation of calderas, the most recent ones are the "La Vecchia" and the "Monastero" calderas (known as "Cinque Denti"), whose formation is dated at 45- 50 ky [Rotolo et al. 2007, and references therein], in which Lake Specchio di Venere is located. The lake water is hyper- alkaline (pH ca. 9), showing a chloride-alkaline composition, with the dominance of Na and Cl ions typical of most thermal waters of Pantelleria, primarily determined by the mixing of marine, hydrothermal and meteoric waters [Parello et al. 2000]. This particular environment allows the growth of unusual mixed siliceous and carbonate microbialites, recently described by Cangemi et al. [2010]. Lake Sfondato (Figure 2b), located close to the city of Caltanissetta (Sicily, Italy), is a sink-hole lake formed at the beginning of 20 th century [Madonia et al. 2006, and references therein], in gypsum terrains pertaining to the Gessoso- Solfifera evaporitic formation. Its genesis was due to the dissolution of a salt diapir in the underground and the sub- sequent collapse of the overlying terrains. Topographic data were derived from the Sections no. 626910 (Lake Specchio di Venere) and 630040 (Lake Sfondato) of the Sicilian regional technical cartography (Car- tografia Tecnica Regionale, C.T.R.) at a scale of 1:10,000, and converted from the original Gauss-Boaga system to UTM WGS84 format. To compare hand-drafted bathymetric maps based on non−GPS surveys reported in the scientific litera- ture with more recent products derived from gridding and contouring software the former, available as image raster files, were transformed into geo-TIFF using the roto-trans- lational geo-referencing algorithm implemented in Quantum GIS software (release 1.0.2). Metric coordinates (UTM WGS84) for each of the depth measurement points recorded in the maps were read on the geo-TIFF, associating each point with the corresponding depth value. The obtained cartesian coordinate triplets (Easting, Northing, Depth) were elaborated with a kriging algorithm using Golden Software Surfer (release 8). A total of 6 differential GPS surveys ( 2 at Lake Specchio di Venere and 4 at Lake Sfondato) were carried out between October 2006 and May 2009 (Table 1), using a pair of Thales Magellan single frequency GPS units; the position data acquired were post-processed using Thales Mo- bile Mapper software. Depths were measured with a Garmin echosounder coupled to the antenna of the GPS rover re- ceiver rigidly mounted on a kayak (Figure 3). Errors were <0.5 m for position, 10 cm for depths in the range 0−10 m and 1 m for the depths >10 m. Depth measurements were randomly performed to avoid the generation of pseudo-ba- thymetric features due to alignments. During the May 2009 field campaign a video-photographic, free-diving survey of Lake Specchio di Venere bottom was performed using a wa- terproof digital camera. Lake level excursions were measured at Lake Sfondato using a fixed control point made of an iron nail plunged into outcropping bedrocks over the lake surface; meteorological data for hydrological calculations were taken from the database of the Agro-Meteorological Informative Service of the Regional Sicilian Government (SIAS) and were collected in the nearest available station (Caltanissetta). Prior to the advent of GPS techniques two bathymetric surveys were carried out at Lake Specchio di Venere. Both focused on the recognition of the general morphology of the lake floor for volcanological researches [Bocchi et al. 1988, Aiuppa et al. 2007]. Positioning of the measurement points were obtained using topographic instruments and a metric rope strung between the opposite shores of the lake. In recent years two more GPS−based surveys (in 2007 and 2009), gave new insights into lake bottom morphology, changing the focus from a volcanological to a sedimentary point of view. The latter was an extension of the 2007 survey, aimed to detail the southern shallow sector of the lake ...