The effect of physicochemical parameters, diversity and abundance of phytoplankton on the different sites was determined using multivariate analysis (Principal component Analyses, PCA), to rank the many factors under investigation based on their magnitude o interactions.
The density of the most abundant species (cells/l) was calculated from the formula :
Density= Xn/M^x44μl
Where: Xn = number of individuals in species X; M = number of drops observed under the microscope. A drop of sample taken up by the micropipette = 44μl (Moser et al., 2004).
Trophic class of the different paddy field sites were calculated using Stockner (1972). This was calculated using the Eugelnophycean index (Bellinger and Siegee, 2010).
The Species Richness Index (d) according to Margalef (1958) was used to evaluate the community structure. The following equation was applied and results were recorded to two decimal places:
D=(S-1)/log_θN
Where : D = Species richness index; S = number of species in a population; N = Total number of individuals in S species.