Estimation of Rivers and Coastal Carbon Fluxes in the Lebanese Waters

Abstract

Rivers and coastal waters transport carbon from continents to deep oceanic systems and act as important links in the carbon cycle. To the best of our knowledge, no studies have quantified the riverine and coastal carbon fluxes in the Lebanese waters, and hence this study aims to assess for the first time the carbon inputs in three major Lebanese rivers: Nahr Ibrahim, Nahr Damour and Nahr el Litani; and the coastal waters affected by their discharges. A monthly and seasonal sampling of key bio-physico-chemical parameters was conducted for Temperature, Salinity, pH, Dissolved Oxygen, Nitrates, Phosphates, Total Alkalinity (AT) and Dissolved inorganic Carbon (DIC), and subsequently the partial pressure of CO2 (pCO2) was derived according to the DOE handbook. The results show a clear seasonal variation of the physical parameters. The Alkalinity yield increased in all monitoring stations mostly in the river areas ranging from 0.24 to 1.8 mmol/L. DIC contribution to alkalinity is significant in rivers with relatively low alkalinity concentrations, and the DIC had a general opposite trend compared to AT; ranging from 57 and 39 mmol/L respectively. When computing the pCO2, the results show that the a range from 817 to 3283 µatm, higher than the atmospheric CO2 concentration showing that the studied rivers acted as a source for atmospheric CO2. This study can be considered as benchmark to understand the mechanisms of riverine-coastal ecosystem change and help the Lebanese community manage their coastal resources.