Multivariate analysis of water quality parameters and phytoplankton composition in the southern of Caspian Sea

This study was conducted to analyze the water quality parameters and biological data of the southern Caspian Sea during two phases, Phase 1 (1996-97) and Phase 2 (2005). The invasion of the southern Caspian Sea by the alien species (Mnemiopsis leidyi) occurred between the two phases. This study highlights the advantage of multivariate statistical analyses to better understand a complex water system. On the basis of a canonical discriminant function analysis (CDFA) on water quality parameters and phytoplankton abundance at the euphotic layers, the southern Caspian Sea can be discriminated into four groups that are related to the four seasons of the year. The results also showed that the most significant variables that play the principal role in the classification comprises of temperature, salinity, DO, SD, and nutrient variables. A principle component analysis (PCA) indicated that the variables within each factor (PCs) could vary among seasons. An overall analysis showed that the first factor comprises nitrogen compounds, denoting the importance of nitrogen in this area during the phytoplankton proliferation (in spring and autumn). During Phase 1 and 2 of the study, canonical correspondence analysis (CCA) suggested that the most of the dominant phytoplankton taxon can substantially tolerate fluctuation in water quality variables.