by Rebecca Herrera
Burgos et al. (2014) discuss seasonal variations of the greenhouse gases methane (CH4) and nitrous oxide (N2O) in the Guadalete River Estuary ending in the Cadiz Bay of southwestern Spain. They found that greenhouse gas concentrations were higher in the more inland parts of the estuary compared to the mouth of the river. Concentrations of methane and nitrous oxide varied depending largely upon the seasonal precipitation regime. It was also observed that the Guadalete Estuary acted as a source, rather than a sink, of greenhouse gases throughout the entire year, as observed by measuring the fluxes of CH4 and N2O from the Estuary.
Eight sampling sites were chosen along an eighteen kilometer stretch along the Guadalete River Estuary. The first was at the mouth of the River in a town of approximately 89,000 inhabitants, and the eighth was inland adjacent to a city of approximately 215,000 people. The majority of the land adjacent to the Guadalete River and Estuary is used for irrigated crops such as sugar beet, cotton, and wheat. Samples of surface water were taken seasonally over the year 2013.
Seasonal variations of seawater parameters including salinity, temperature, dissolved oxygen, chlorophyll, dissolved organic carbon, dissolved organic nitrogen, particulate organic carbon, and particulate organic nitrogen were found to be significant and all parameters except temperature were statistically different regarding the distance to the river mouth. Additionally, nutrient content increased from the mouth of the river towards the inner estuary in all seasons.
Dissolved greenhouse gas concentrations of methane and nitrous oxide increased from the mouth of the river inland toward the freshwater estuarine zone. This distribution can likely be attributed to organic matter inputs sourced from both the river itself as well as anthropogenic inputs like sewage and crop runoff. It is important to gain a thorough understanding of to what degree nutrient and gas exchange occurs in order to better target policies at reducing and eliminating sources of anthropogenic contributions to greenhouse gas inputs into estuarine ecosystems.
Burgos, M., Sierra, A., Ortega, T., Jorja, J.M. 2014. Anthropogenic effects on greenhouse gas (CH4 and N2O) emissions in the Guadalete River Estuary (SW Spain).. Science of the Total Environment, 503-504, 179-189.