Climate and Tidal Changes
Concerns arise when the potential energy of tidal influences rises beyond the height of the water table . In this instance , the flow direction changes , allowing saline water to intrude upon the existing freshwater aquifer and result in saltwater intrusion . This has become a salient topic in the coastal community due to changes in tidal forces and the gradually increasing threat of sea level rise .
The primary source of saltwater intrusion that typically impacts subsurface aquifers in coastal environments is the result of tidal forces . King Tides , in particular , cause a seasonal variation in the seawater which can increase the salinity content within a shallow aquifer . Saltwater intrusion during these events is especially prevalent in areas adjacent to land inundated with tidal seawater . When inundation occurs over land during extreme high tide and severe weather events , saltwater is introduced to upland soils and percolates the subsurface aquifer . These effects are compounded with wind , drought , and sea level rise . This form of saltwater intrusion can be intensified by storm surges and degrades the aquifer over time as the salts need to be purged from the system after each event . Furthermore , intense tropical storms produce storm surges and heavy rainfall which exacerbate tidal flooding conditions .
Climatic change also poses a long-term threat to freshwater resources on Kiawah Island . As sea levels continue to rise , available freshwater in coastal areas is threatened by the change in the energy gradient between groundwater and tidally influenced seawater . With the continued rise in sea level , the energy gradient between tidal forces and groundwater will shift upwards in elevation . Also , as a result of climate change , droughts have become more common while rainfall events have become less frequent but more intense . These conditions altogether will gradually cause the subsurface freshwater aquifer to rise and become more saline .
The combination of press and pulse events continually introducing seawater significantly impacts groundwater resources on coastal barrier islands . Over time , the freshwater lens on barrier islands will become shallower and more saline . This change in groundwater will affect the native upland vegetation and facilitate changes to coastal habitats . Offsetting some of these negative effects are the use of landscape irrigation adjusted based on the prevalence of rainfall events . Irrigation in this fashion artificially introduces freshwater into the local hydrological system during times of low rainfall and mitigates the negative impacts of climate change and sea-level rise to a minor extent .
Hydrology and Plant Communities
The primary concern of changes to groundwater resources is the change in coastal ecosystems as a result of impacts to plant communities . Vegetation in the upland regions of barrier islands supports a wide range of resident and migratory wildlife species , as well as provides a significant portion of ecosystem services to humans . Appropriately sized buffer zones , canopy trees , dense understory , and proper salinity levels all play equally important roles in the health of the maritime forest system . Understory growth is an especially important factor in maintaining groundwater resources , because it retains soil moisture by slowing direct evaporation of freshwater from the ground . The understory coverage helps to retain moisture during saltwater inundation by slowing the rate of evaporation that leaves behind accumulated salts in the soil .
Though maritime forests continue to thrive , there is an ever-present possibility that the environment will become too saline and the area may convert into ghost forests over time ( Kirwan and Gedan , 2019 ). At the core of this conversion is the increased salinity levels in groundwater and topsoil . Although vegetation in coastal environments have adapted to tolerate saline conditions , landward migration of saltwater intensifies saline conditions within
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NATURE-BASED SOLUTIONS MANUAL FOR KIAWAH ISLAND