The use of ammonia-elphidium (A-E) index in Jakarta Bay and Semarang coastal waters, Indonesia

Abstract

The Ammonia-Elphidium index (AE index) was used to interpret the ecological conditions of coastal waters especially on hypoxic conditions in coastal waters. The purpose of this study was to identify ecological changes in Indonesian coastal waters by using the AE index. The research was conducted in two locations, Jakarta Bay and Semarang coastal waters at 2016; there are two core sampling sites at each location. Sediment samples were taken using a simple core made of two inches diameter of PVC pipe, and divided for grain size analysis, foraminiferal analysis and absolute chronological age detection. The grain size analysis was carried out using the granulometry method, the absolute chronological age and sedimentation rate were measured through Pb210 isotope detection at National Nuclear Energy Agency of Indonesia (BATAN), Yogyakarta. Based on the analysis of the AE index and chronological age, intermediate level of hypoxia has occurred in the coast of Tangerang since more than 100 years ago. The initial symptoms of hypoxia in the coast of Cilincing occurred at 1940s in a lower level than Tangerang waters. In the East Canal Flood (ECF) of Semarang coastal waters, hypoxia was indicated higher than Tangerang since the end of 1940s through recent years. Ammonia was found at all sampling sites, but Elphidium was hardly found in West Canal Flood (WCF) therefore the AE index cannot be calculated. Sediments fraction of WCF was dominated by fine. The A-E index not solely depends on the presence of Ammonia and Elphidium, but also the physio-chemical conditions of the waters and sediment grain size. Fine sediment in WCF Semarang revealed as the limiting factors in using the index in such coastal waters.