Spatiotemporal patterns of water quality, nutrient dynamics and chlorophyll a concentrations in Five Cowries Creek from 2022 to 2024

The Five Cowries Creek (FCC), a crucial estuarine ecosystem in Southwest Nigeria, was investigated to assess the spatiotemporal distribution of nutrients and chlorophyll-a from 2022 to 2024. Water samples were collected for two months interval from 20 stations across three zones; zone A (western part of FCC), zone B (Central part of FCC, and zone C (eastern part of FCC). The physicochemical parameters were analyzed in-situ using a Hanna HI-9828 probe, while the nutrients (ammonia, nitrites, nitrates, phosphates) and chlorophyll-a were analyzed using a colorimetry and a UV/Visible-1700 Pharma double-beam spectrophotometer. The creek exhibited temporal and spatial variations in physicochemical characteristics, which were influenced by temperature fluctuations, salinity gradients, and freshwater input. Nutrient concentrations were higher during the wet season, with the highest values recorded in Zone B and Zone C, attributed to residential effluents, and marine debris. Highest turbidity values of 71.80 Nephelometric units (NTU) was recorded in Zone A, in 2023 during the wet season, which exceeded the permissible limit of 10 NTU by the World Health Organization and the Federal Ministry of Environment for discharge of wastewater. The high values suggest the influence of run-off of wastewater discharge into the study area. The calculated Weighted Arithmetic Water Quality Index (WAWQI) falls within the fair to poor water quality status (76 ≤ WAWQI ≤ 100) in Zone B, and Zone C, with a value of 91.48 and 82.74, respectively during the wet season of 2022. The poor WAWQI values were influenced by high concentrations of ammonia, nitrate, and nitrite levels within the two zones. The rainfall patterns significantly influenced the nutrient loads and chlorophyll-a distribution, with peak rainfall corresponding to the highest turbidity, lowest water temperature, and lowest salinity. Principal Component Analysis revealed that salinity, electrical conductivity, and pH are the main factors influencing the variability of water quality across the three zones. Comparing results from this study with those from earlier studies in other regions indicates that obtained values of parameters are strongly influenced by geographical, climate, and anthropogenic influences. This study contributes to the broader understanding of how estuarine ecosystems respond to seasonal and human-induced changes.