The ria coasts of the Yellow Sea, western Korean peninsula, have served as important areas for agricultural development, mainly due to their extensive shallow estuaries. Many sea-dikes have been constructed for agricultural reclamation projects since the 10th century. To date, the aggregate length of sea-dikes from 1,944 estuaries totals 1,214 kilometers, including the world’s longest sea-dike of Saemangeum. As a result, around 135,100 hectares of agricultural land has been created. Although sea-dikes contribute to economic benefits, there are concerns that the construction of large-scale sea-dikes is altering the dynamics of some species communities in these wetlands. In fact, it has been clearly identified that the distribution of halophytes along the coasts has gradually changed after the construction. In the present study, therefore, the underlying processes that drive these changes are described in terms of two major factors of community dynamics: interspecies competition and seed recruitment. These factors are examined by comparing the dominant species’ ecological niches in the community and their seed dispersal routes with germination condition. These niches are being restricted by the changing environment driven mainly by the construction. In addition, abiotic factors in wetlands, such as water salinity, are periodically measured and mapped by GIS software.
Results/Conclusions
Most crucial factor is that sea-dikes prevent periodic inflows of seawater into the coastal wetlands. Salinity gradually drops as inflow of salt water from the ocean is blocked, while freshwater from inland rivers accumulates behind the sea-dikes. Additionally, the load of sediments and nutrients carried by rivers continues to benefit populations which have high efficiency in resource exploitation. This leads to conversion of salty habitats of halophytes’, where direct competition with nonhalophytic plants is avoided, to habitats in which other species are able to invade and compete strongly. As a result, the populations of Limonium tetragonum or Suaeda maritima, halophytes that previously dominated coastal wetlands despite their narrow ecological niches (Standard Deviation of EC 0.129ds/m, organic-matter 0.102mg/kg), are now decreasing, whereas those of Phragmites communis are rapidly expanding, outcompeting others by having a broader ecological niche (SD EC 0.419ds/m, organic-matter 0.148mg/kg). Considering the fact that halophyte seed dispersal, which largely depends on tidal currents, is being blocked by sea-dikes, and the germination competition is decreasing with the decrease in soil salinity, seed recruitment of halophytes has decreased. Shortly, sea-dike construction lowers environmental barriers, opens halophyte habitats to other competing nonhalophytes, and reduces their recovery by blocking seed dispersal and establishment.