Seasonal Changes of N-Alkanes in Water and Suspended Particulate Matter from Cross River Estuary, South-east Nigeria

Abstract

Several studies worldwide have attributed the seasonal variation in aromatic compound levels to changes in riverine discharges and rainfall, yet similar correspondence with n-alkanes distributions is scarcely undertaken. Assessment of the behavior of n-alkanes in water and suspended particulate matter from Cross River estuary, South-South Nigeria, with depth in reaction to anthropogenic pressure/hydrological cycles and their source contributions were carried out by gas chromatography–flame ionization detector. Higher mean levels of n-alkanes in water and suspended particulate matter were recorded in the wet season than in the dry season, linked to the effects of higher wet precipitation and surface run-off as well as proximity to point sources where anthropogenic activities were at the peak of the rainy season. Evaluation of diagnostic indices values such as long-chain hydrocarbon/short-chain hydrocarbon, terrestrial aquatic ratio, carbon preference index, carbon maximum, proxy aquatic ratio, n-alkanes/C₁₆ and unresolved complex mixture as well as multi-variate statistics [eg. Multiple linear regression and principal component analysis] revealed that vascular plant/wood combustion predominated with moderate-to-minor contributions from macrophytes, degraded oil, petrochemicals and algae/photosynthetic bacteria. Changes in hydrological parameters, including suspended sediment concentration, temperature, salinity, and anthropogenic pressure, influenced n-alkanes distribution in the estuary.