Problems Related to Coastal Lowland Development in the Tropics

Abstract

Coastal swamp areas are the object of reclamation for agricultural and aquacultural development in southeast Asia. First, reasons for an extraordinarily wide distribution of mangroves and swamp forests in insular southeast Asia were considered in terms of climate, vegetation, geology, geomorphology and geo-history. Then the problems expected to arise from reclamation of these swamp lands were considered. The pres-ent and past mangrove swamps, the latter being broad depressions engulfed in a delta proper due to rapid sedimentation along the delta front, are often associated with pyritic sediments which, upon drainage and reclamation, rapidly develop into acid sulfate soils. The difficulty of their amelioration was discussed. Swamp forests in the tropics are developed on woody peats that are sometimes more than 10m thick and extremely oligotrophic. Reclamation of swamp forest lands inevitably accompanies drainage, which in turn leads to land subsidence due to dewatering and compaction, and eventually to decomposition of peat itself. Results of a recent study concerning the changes brought about by peat land reclamation were presented concerning oligotrophy, peat decomposition and land subsidence. Sterility of rice on peat was also dealt with based on experimental results.