## 2 Materials and Methods  
### Subsection  
The temporary ponds investigated were located within the coastal area of Latium (central Italy). Surveys were carried out no more than 1 km away from the shore along a 360 km shoreline, for a total surface of about 360 km\({}^{2}\) (Figure 1). The mean distance of the ponds from the shore was 550 m.  
Before starting field surveys, a preliminary observation was conducted using Google Earth satellite imagery (Google Earth Pro software, version 7.3) to detect both permanent and temporary coastal water bodies. To understand their actual temporariness, surface size changes over time were observed by using the Historical Imagery routine. However, this approach is not free of uncertainties and biases, as not all historical images allow such an analysis because of different sensors' spatial resolution and cloud coverage.  
After the preparatory virtual checking, field inspections of the study area were carried out to assess the effective temporary nature of the selected water bodies. Two sessions of 14-day inspections were performed on the entire coastal region in early spring 2017 and late summer 2017. Spring inspections were essential to verify the actual presence and spatial arrangement of water bodies in order to assess their accessibility (given that many temporary wetlands were located within private and/or agricultural areas with limited or forbidden access). The second session was carried out to ensure that all ponds identified during the first session went dry during the summer, confirming the temporariness of the water bodies, whose coordinates were subsequently recorded using a GPS device.  
A subset of temporary ponds (Figure 1) was selected over the entire Latium coast to be monitored monthly from January to December 2018 to study their hydroperiod and surface area. To this end, the Parrot Bebop 2 unmanned aerial vehicle (UAV) was used to take aerial images during each monitoring session. The UAV flight settings for the surveys  
Figure 1: Permanent (light blue squares) and temporary (green and red circles) coastal wetlands within the study area. The 21 selected and monitored Mediterranean temporary ponds are indicated with red circles and divided into five groups according to proximity amongst pools and land use context: A, pastures; B, agricultural with grasses; C, reserves; D, urban; E, mixed agricultural and pastures.  
included altitudes ranging from 70 to 145 m above ground, with a 90\({}^{\circ}\) camera angle with respect to the pond centre.  
During each monitoring session, pH, water and air temperature (Tw and Tatum, respectively), electric conductivity (EC), and dissolved oxygen (O\({}_{2}\), in mg/L and %) were measured using a Hach HQ40d Portable multi-parameter probe (as required by the Habitat Directive guidelines). Furthermore, water samples were collected at each sampling site for spectrophotometric analysis of nitrate (NO\({}_{3}\)\({}^{-}\)) and phosphates (PO\({}_{4}\)\({}^{3-}\)).  
Data on temperature and precipitation in proximity to the surveyed coastal wetlands were obtained from six coastal meteorological (thermo-pluviometric) stations (Figure 1).  
An ordination through principal component analysis (PCA) was performed by using all the physico-chemical descriptors to observe eventual differences in water quality amongst the investigated temporary ponds.  
Furthermore, temperature and precipitation data from the closest stations were downloaded to assess the relationship between the thermo-pluviometric diagrams and pond size variation.