Nutrient Dynamics in a Tropical Lagoon: Seasonal Patterns of Nitrogen and Phosphorus in Fresco Lagoon, Côte d’Ivoire

Some nutrients from anthropogenic discharges contribute to the pollution of aquatic ecosystems due to the mineralization of the organic matter contained therein. The mineralization of organic matter influenced by the physicochemical factors of open waters often leads to the phenomenon of eutrophication due to the enrichment of waters in nitrogen and phosphorus in particular. Eutrophication is a serious environmental problem. The main objective of this study is to monitor the seasonal dynamics of nitrogen and phosphorus nutrients in the open waters of two locations in the Fresco lagoon, designated zone I and zone II. To do this, the physicochemical parameters of the open waters were determined using a multiparameter and the ammonium (NH4+), nitrite (NO2-), nitrate (NO3-) and phosphate (PO43-) contents of the waters by spectrophotometric dosage. The results reveal acidic waters in the main rainy season (pH = 6.25 ± 0.08 in zone I and pH = 6.31 ± 0.53 in zone II), high temperatures in the main dry season (32.04 ± 0.52°C in zone I and 30.59 ± 0.90°C in zone II) and low dissolved oxygen contents in the short rainy season (1.40 ± 0.43 mg/L in zone I and 1.78 ± 0.06 mg/L in zone II). The waters show high levels, respectively in zone I in the short rainy season for NO3- (15.46 ± 9.03 mg/L) and in the short dry season for PO43- (0.84 ± 0.18 mg/L) and in zone II, in the short rainy season for NO3- (16.77 ± 9.82 mg/L) and in the long dry season for PO43- (3.28 ± 3.20 mg/L). These high contents characterize a eutrophic environment due to the large quantity of nitrate and phosphate from coastal rivers. Wastewater treatment techniques before their discharge into nature and raising awareness among populations on environmental preservation could be considered.