Hydrological controls on salinity exposure and the effects on plants in lowland polders

The Dutch lowlands may be subject to salinization, through saline upward seepage and increased salt concentrations in the surface water, which may affect agriculture and nature areas with floating fens. A simple approach was proposed to estimate root zone salinization in areas with fresh water lenses that float on upward seeping saline groundwater, based on analytical solutions and approximations, which could be used for prioritization. The hydrology of floating fens was investigated and important processes and parameters were identified, which could be used to estimate root zone exposure to salinity. The flow processes are mostly controlled by the root mat geometry, which determines which part of the root mat floats within the surface water. A greenhouse experiment showed that salinity may affect the growth of some plant species from floating fens, which implies that salinization may affect species composition in these nature areas.