Impacts on Agriculture
Subsidence and uplift are permanent. Land lost to the sea (Class D of the FAO Damage Classification) cannot be reclaimed. The immediate impact of subsidence is thus that farmers have to be relocated if they lost their lands, and also in these areas that are now very close to sea and will have continuing problems with lateral seawater intrusion.
There are other less visible slow-onset problems that can be expected, however:
1) Because of the subsidence the drainage system has changed. Field and channel drainage can be submerged, because of higher water level in estuaries and river mouths due to the influence of the higher sea water table. Submersion reduces the drainage capacity and may cause problems of water logging and salinisation.
2) The relative rise of the sea level will cause a change in water balance between the fresh water layer and the saline water layer. Generally, saline water will push the fresh water lense further to the inland. This can affect a strip of several hundreds of meters. Especially in areas where groundwater is pumped for irrigation this effect has to be carefully monitored to prevent saline water intrusion and degradation of water quality.
Other problems related to lateral and vertical movement of the islands are slow changes in island morphology that may occur over time through processes of scouring and sedimentation. This could have various effects on agricultural land. All these processes are slow and will not be easily determined. Assuming that in-depth research is not possible everywhere it is best to monitor regularly and investigate in detail when problems become apparent.