Ecological status assessment of Litani river, Lebanon using Chlorophyll a

Eutrophication of Litani River, the most important water resource in Lebanon, has become a pressing national concern. In spite of the intensive efforts on studying the physiochemical properties of its water, not enough attention has so far been given to the biological quality elements and trophic status of the river. Considered as the most sensitive indicator for nutrient enrichment and algal biomass, seasonal levels of sestonic chlorophyll-a (Chl-a) were determined in this study at five stations of Litani River during 2013 and 2014 and the relationship with transparency (Secchi disk), nutrients and mineralization levels was tested. Findings revealed statistically significant spatial variations in chlorophyll-a between the stations under study with Upper Litani River forming a homogenous subset characterized by hypereutrophic levels (54.54±38.61 µg/L in Rayak; 57.39±42.67 µg/L in El Marj and 67.21±60.94 µg/L in Jib Janine), while oligotrophic levels were observed at the Lower Litani River (2.60±2.82 µg/L in Dellafi and 3.14±1.49 µg/L Khardali). Correlation coefficients between chlorophyll-a and levels of phosphates, nitrites and ammonia were significantly positive. Negative correlation was revealed with Secchi disk readings and nitrate levels, yet no statistical significance was reached with nitrates. It is concluded that phosphates and both nitrites and ammonia have positive influences on algal proliferation and eutrophication of Upper Litani River. However, the negative correlation with nitrates suggests that Chl-a did not relate to nitrates and it may be a poor criterion for assessing the ecological status and nutrient-related problems of the river possibly due to the complex nitrogen cycle dynamics of the river. Thus, it is of importance to explore total nitrogen and total phosphate and their relationship with chlorophyll-a as potentially a more reliable tool.