research article: evaluation of biodiversity of phytoplankton and determination of biological health quality of arvand river (south west of iran) using trophic diatom index (tdi)

Phytoplankton is considered the primary producer of any ecosystem and is sensitive to environmental changes. therefore, phytoplankton is a suitable indicator for evaluating river water quality. change of the environment leads to changes in abundance, diversity, and dominance of phytoplankton communities. six stations were selected from beginning of arvand river (the point of tributary from karun river, station 1) to the sea estuary (in arvand kenar, station )2015-2016). phytoplankton sampling was conducted using a plankton net with 30-μm mesh size, with three replications in each station. meanwhile, temperature, salinity, ph, dissolved oxygen (in field operations), nitrate and phosphate were measured in the laboratory with three replications. the results showed that 43 phytoplankton species were present in the sampling area. ochrophyta division was most abundant with 32 species, followed by four divisions chlorophyta (5 species), cyanobacteria (3 species), myzozoa (2 species), and charophyta (1 species). the most dominant species in different seasons were coscinodiscus marginatus from bacillariophyceae, followed by oscillatoria sp. from cyanophyceae and ulothrix aequalis from chlorophyta. mean total value of diatom trophic index was calculated to be 62.31+3.09 during the study period, indicating poor quality of the ecosystem and eutrophic condition. according to the results of correlation analysis (pca), phosphate content was one of the most important factors affecting abundance and diversity of phytoplankton.