Mangrove Functions as a Prevention of Seawater Intrusion
According to (Costall et al., 2018) Seawater intrusion is seepage or the entry of seawater into groundwater aquifers because groundwater pressure is less than seawater pressure. Under normal conditions, although the density of salt water is slightly higher than the density of fresh water, and will push fresh water upstream, groundwater has a higher piezometric pressure than sea level, so that pressure can be neutralized and no intrusion occurs. sea water.
Seawater intrusion occurs when the balance is disturbed. One of the activities that cause seawater intrusion is excessive groundwater extraction. If the intrusion has entered the well, the well will become salty and can no longer be used for daily needs.
Various steps were taken to reduce the impact of groundwater subsidence and seawater intrusion, such as by constructing several dikes to prevent seawater from entering the ground, changing pumping patterns, Extraction Barriers, Injection Barriers and so on.
However, this is an engineering technology that can break down with time and age. Therefore we need a natural and sustainable effort that can reduce the impact of sea water intrusion. Several previous studies have shown that one of the functions of the mangrove ecosystem is to withstand seawater intrusion.
Based on research from the Indonesian Institute of Sciences (LIPI), that in addition to the characteristics of the substrate or rock in an area, seawater intrusion is also influenced by the density or thickness of mangrove vegetation and the size of mangrove trees. This is evidenced by research on sea water intrusion in the Wayheru area, Ambon. Based on the resistivity value of the substrate or rock in the area, seawater intrusion should occur at a depth of 10 meters, but seawater intrusion only occurs at a depth of 12 meters. This is presumably due to the involvement of 100 m thick mangroves in the area.
According to research (Hilmi et al., 2017) the foremost mangrove species such as Avicennia marina, Avicennia alba, Rhizophora styllosa, Sonneratia alba and Sonneratia caseolaris are mangrove species that have the best ability to reduce seawater intrusion. This is also relevant because this type of mangrove is a salt-secretor mangrove. This type of mangrove has salt glands on its leaves that allow it to secrete Na+ and Cl- fluids.
