Distribution of Nutrients and Chlorophyll-a in coastal waters and mesotidal estuary of Ilaje, Ondo state, South Western, Nigeria [post]

Opeyemi Otolorin Oyatola, Olubunmi Ayoola Nubi, Samuel Olatunde Popoola, Falilu Olaiwola Adekunbi, John Paul Unyimadu
2021 unpublished
The nutrients (nitrate, nitrite, phosphate and silicate) of thirty-two stations in Ilaje, coastal waters and estuaries of Ondo state, Nigeria were studied in the month of August (during the wet season). The stations consist of two estuaries; Awoye (A1-A6), Abereke (AB1-AB7), anthropogenic impacted stations (I1-I12) and control stations (C1-C7). The aim of this study is to evaluate the eutrophication status of Ilaje coastal waters and estuaries in response to the stress caused by anthropogenic
more » ... by anthropogenic inputs from land use changes, agriculture, and industrial effluents. Our study reveal highest nitrate (3.20-6.98 mg/l) and phosphate (11.59-17.48mg/L) concentrations at the Abereke Estuaries. The significant correlation of nitrate with chlorophyll-a (p<0.01, r= +0.886) and the low N/P (<0.25) ratio suggest that nitrate is the primary limiting nutrient for phytoplankton production, and accounted for the high chlorophyll-a concentrations in the study area. The strong correlation of nitrite and silicate from the statistical bi-plots at the impacted stations, and the accompanied lowest dissolved oxygen (<5 mg/L) and acidic pH (<6) values suggest nitrite and silicate are sourced from anthropogenic effluents. The mean nitrite concentrations of 0.13mg/L at the impacted stations above the maximum permissible limit of nitrite (0.06 mg/L) for Tilapia production suggest an unfavorable environment for the Tilapia growth at the impacted stations. The chlorophyll-a concentrations scale further showed that the study area is characterized as bad eutrophication status (> 2.21 µg/L) an indication of the presence of heterogeneous phytoplankton community during the wet season. The study highlights the use of nutrients and chlorophyll-a scaling to determine the eutrophication status of coastal area.
doi:10.21203/rs.3.rs-255613/v1 fatcat:3lehnywjyjb7rkrx2rww56cpeu