Figure 4 . Map showing the distribution of different soil types on Kiawah Island ( USGS SSURGO )
Within maritime environments the primary source of freshwater recharge is in the form of rainfall . Rainfall events introduce freshwater in upland areas and percolate into the shallow subsurface groundwater aquifer ( Callahan et al ., 2012 ). This recharges the groundwater reserve and increases the elevation of the groundwater table . Another external source of freshwater includes irrigation which introduced up to 587 million gallons of water to Kiawah Island in 2017 .
The guiding principle of groundwater flow is related to differences in potential energy . Water flow results from a transfer from areas of high potential energy to areas of low potential energy . Measuring the potential energy of water is typically conducted by studying the elevation differences of open water areas and groundwater . In a natural freshwater aquifer system , freshwater has a higher potential energy and results in freshwater flowing into tidally influenced environments .
The freshwater within the subsurface aquifer on Kiawah Island is gradually reduced overtime via plant uptake , evaporation , discharge into ponds , and discharge into the tidal marsh . Groundwater discharge through the marsh platform in coastal environments typically occurs during low tide events . Similarly , the interconnected pond system on Kiawah Island also discharges excess water into nearby estuarine environments during a low tide events . Groundwater is also discharged into the pond system as levels recede . This produces a mechanism where freshwater is gradually introduced into the marsh and open water , flushing nutrients and salts within the soil and regulating groundwater levels to reach a stable equilibrium with adjacent tidal influences .
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