Phytoplankton variability with relationships to environmental factors in a temporary salt lake

To establish a relationship between environmental variables and phytoplankton dynamics, physicochemical characteristics and phytoplankton sampling were performed in Sabkhet El Adhibet (Southeastern Tunisia) monthly from November 2005 to April 2006 and from November 2006 to April 2007 (the site dries annually between May and late October). All measured water quality variables showed considerable seasonal variation, and quantitative and qualitative differences in phytoplankton communities were recorded. The maximum phytoplankton density was recorded in January 2006, whereas lowest values occurred in November 2006. Sixteen species belonging to 6 orders were recorded, among which diatoms (52.1 %) and chlorophytes (39.8 %) were the most abundant. The correlation analysis between phytoplankton (density and composition) and abiotic variables revealed that orthophosphate is the major factor affecting the phytoplankton dynamics, and there were no correlation between phytoplankton and all the other environmental parameters. The PCA analysis of the phytoplankton composition and density revealed two main PCA axis explaining 82.99 % of the variance. The first axis was associated with diatoms, cryptophytes, euglenophytes, dinophytes and total phytoplankton, with a contribution of 21.8, 21.6, 21.3, 17.4 and 17.4 %, respectively. The second axis was correlated with chlorophytes (55.3 %) and cyanobacterias (26.3 %).