Distribution of Foraminiferal Assemblages in Contemporary Bottom Sediments of Qua-Iboe River Estuary, Southeast Nigeria

Abstract

Abstract Qua-Iboe River estuary, Southeast Nigeria, was studied to determine the relationship between foraminiferal distribution and bottom water physicochemical parameters including salinity, temperature, depth, dissolved oxygen, pH, tidal energy, and sediment. Fifty-five bottom sediment samples from geo-referenced stations were collected at water depths of 0–10 m across the channel. Ten species of foraminifera were identified in the estuary. Q-mode cluster analysis resulted in two biotopes (1 and 2), each representing distinct sub-environments. Biotope 1 included two sub-groups namely, 1a and 1b. Biotope 1a represents the upper estuary environment and is distinguished by the non-recovery of foraminifera. It has a maximum water depth of 8.3 m and occurs in freshwater conditions (0 ppt) with slightly acidic to neutral pH and fine- to medium-grained sands. Biotope 1b is found in the mid-estuarine environment and has a maximum water depth of 4 m. It is distinguished by an abundance of Arenoparrella mexicana. Biotope 2 occurs within the subtidal lower estuarine environment with a maximum water depth of 4 m. It is characterized by slightly acidic to slightly alkaline (pH = 6–8), brackish to marine waters, with fine to very fine-grained sands. Foraminiferal species commonly found in this biotope include Ammonia beccarii, Pseudononion japonicum, and Cribroelphidium excavatum. As salinity increased seawards, agglutinated taxa were gradually replaced by calcareous species. Foraminiferal assemblages in bottom sediments are strongly influenced by salinity.