Spatial Distribution of Diatoms and Nutrients in a Mangrove Swamp of Eastern Obolo, Niger Delta

Abstract

The spatial distribution of diatoms and nutrients concentration in a mangrove swamp of Eastern Obolo was investigated during dry and wet seasons. This research was to establish the distribution pattern of diatom at ten stations with nutrients level, salinity, TDS (Total Suspended Solid), conductivity, pH across the coastal water, and to evaluate centric/pennate diatom’s ratio in the system. It was observed that during dry period, the salinity, conductivity, TDS and pH level increased progressively toward the Atlantic Ocean. The species taxa encountered at respective station could be affected by TDS, conductivity and salinity level as it correlated significantly with these variables, TDS (r = .929**), conductivity (r = .889**) and salinity (r = .760**). The species diversity during dry season correlates significantly with TDS (r = .700**), conductivity (r = .658*) and salinity (r = 0.545). Reactive phosphate peaked 0.038 mg/L at S9 during wet season and dropped to 0.002 mg/L at S2 during dry season, whereas reactive nitrate recorded a higher value of 1.10 mg/L at S5 during dry season and lower value of 0.018 mg/L at S4 & S6 during wet season. During wet season, salinity level affects diatom density positively as it responded significantly (r = .795**). TDS showed a strong significant correlation with reactive nitrate (r = .810**), reactive phosphate (r = .728*) and with SDI (r= 0.265) during wet period. The ratio of centric to pennate diatom recorded a lower value of 0.41 and 0.37 at S1 & S2 during wet season, and 0.47 and 0.47 at S1& S2 during dry season. The following species of diatoms showed a wider range of distribution during wet and dry period; Coscinodiscus centralis Ehrenberg, Ditylum brightwelli (T. West) Grunow, Biddulphia mobiliensis (J.W. Bailey) Grunow, Thalassiothrix frauenfeldii (Grunow) Grunow and Asterionella japonica Cleve. The centric to pennate diatom ratio could be used to quantify the degree of disturbance of benthic environment. The distribution and composition of the diatom species in the coastal water was affected by salinity level, conductivity, pH and TSD for the seasons majorly, and least by the nutrient level.