Improving statistical distinctness in assessing trophic levels: the development of simulated normal distributions.

The statistical distinctness in assessing differences of the trophic status between sampling sites was investigated in the present study. Nutrient (phosphate, nitrate, nitrite, ammonia) and phytoplankton (chlorophyll, cell number) variables from nine sampling stations were used for the validation of the statistical procedures. Raw data, transformed data, and simulated data derived on normalized nutrient-phytoplankton frequency distribution were tested. The Kruskal-Wallis (KW) nonparametric statistical procedure was also applied on the raw data as well as the analysis of variance on transformed and simulated data. In all cases, pairwise comparisons for each parameter between stations were performed. The results showed that maximum distinctness between sampling sites for all the six variables was attained using the simulated data. The KW method showed the poorest discrimination between stations. The methodology of producing and using simulated data is described step by step, and the advantages in cases of unequal sampling design or small sample size are discussed.