## 5 Discussion
The surface water salinity increased from west to east, and the groundwater salinity decreased from west to east. In another study conducted by [41], in the Seven Palm system in July 2015, the surface water salinity ranged from 25 PSU in the northern tip of Seven Palm and gradually increased to 45 PSU in Monroe Lake. These hyper-salinity conditions are associated with drought and produced seagrass die-off [8; 41]. In July 2019, the surface water salinity ranged from 5 PSU in the northern tip of Seven Palm and gradually increased to 49 PSU in Monroe Lake. Generally, in the West Lake system, the surface water salinity is lower than the groundwater salinity, but in the Seven Palm system, the surface water salinity is higher than the groundwater salinity (Figure 12A). In addition, in both lakes, the salinity of the surface water and groundwater increased from north to south. This result suggests a freshening of the groundwater and may reflect the effects of increased flow due to restoration efforts. In the Mangrove Lakes of ENP, surface water salinity is driven by seasonally variable winds and evaporation, whereas groundwater salinity is less temporally variable and reflects regional groundwater flow. In the EM data, the apparent conductivity change of the surface water is significant compared to the groundwater (Figure 7). In the VES data, viewed in a west to east profile, less saline surface water in West Lake overlies more saline groundwater (Figure 11). In contrast, in Seven Palm Lake, the vertical salinity profile is inverted with denser, more saline surface water overlying less dense, fresher groundwater. This inverted salinity profile is gravitationally unstable and likely has a profound effect on recharge and discharge mechanisms to and from the aquifer. These results suggest the floating electrical resistivity array can map the resistivity of the subsurface formation effectively. Some limitations of the estimated formation factor and EM measurements include the following. In the Mangrove Lakes of ENP, the shallow wells only extended to the base of the peat layer and did not penetrate the underlying limestone. This method assumes that the groundwater sampled from the wells is derived from the underlying limestone. Furthermore, repeated measurements would be useful to determine the accuracy of the estimated formation factor value with minimum standard deviation. In the EM data, the apparent conductivities at certain locations where the EM survey line crosses have different measurements. This difference could be due to instrument drift, the operator changing position during the survey which affects the position of the coils, and calibration problems after Bluetooth connection failure which causes a new calibration in different environmental settings. Furthermore, the EM result is not inverted as the inverted model is not consistently reliable. As a result, the EM data are presented in apparent conductivity. The authors of [42] suggested that discrepancies in inversion for soils having a high surface electrical conductivity relative to deeper depths using EM 38 can be compensated through the vertical or horizontal coil configuration response curve. The EM method provides a faster alternative to DC soundings [16], but it is sensitive to electromagnetic noise produced by metals, pipelines, etc. An integrated approach of electrical resistivity and EM methods can produce the best result [43]. In a saline environment, once areas of high salinity are delineated, alternative methods of salinity measurement can be utilized to provide a detailed description of the study area [42]. Therefore, an integrated approach of using EM, resistivity, and other geological information is necessary to characterize the subsurface formation accurately.