Seasonal pH and carbondioxide level as indicator of vulnerability of fresh and marine aquatic systems to climate change in Nigeria

Abstract

Rising atmospheric carbon dioxide (CO₂) concentrations over the past two centuries have led to greater CO₂ uptake by the oceans; raising concern over the current and future effects it may have on world climates. Certain changes are already evident but the impact of these changes on marine and coastal living resources is only poorly understood at this stage, particularly in sub-Saharan Africa. This study assessed seasonal dissolved carbon dioxide and pH of fresh and marine aquatic systems in Nigeria. Dissolved CO₂ was non-significantly (p=0.07) higher in freshwater during the wet season (20±7ppm) compared to dry season (15 ± 1ppm), while in the marine system, dissolved CO₂ level was significantly (p=0.02) higher (42±6ppm) during the dry season compared to the rainy season (31±5ppm). Mean pH values was significantly higher (p=0.003 and 0.05) in freshwater (6.8±0.8 and 6.9±0.2ppm) relative to marine (6.2±0.2 and 6.5±0.3ppm) during wet and dry seasons, respectively. The pH values were generally at the borderline of the acidic limit of the recommended pH values for aquaculture (6.5-9) during the two seasons. Rising atmospheric carbon dioxide (CO₂) concentrations over the past two centuries have led to a greater CO₂ uptake by the oceans, acidification and consequently, saturation, thereby affecting the ocean’s continued ability to store CO₂. This study therefore provides preliminary information on seasonal changes in CO₂ and pH of fresh and marine systems in Nigeria; and their potential impacts on global climate and aquatic ecosystems.

Keywords: Acidification, Aquatic system, Carbon dioxide, Climate change, Fresh water, Marine water