Taxonomical and ecological characteristics of the desmids placoderms in reservoir: analyzing the spatial and temporal distribution/Características taxonômicas e ecológicas de desmidias placodermes em reservatório: analisando a distribuição espacial e temporal

This study aimed to evaluate the influence of river-dam axis and abiotic factors on the composition of Closteriaceae, Gonatozygaceae, Mesotaeniaceae and Peniaceae in a tropical reservoir. Water samples for physical, chemical and periphyton analysis were collected in April and August 2002 in different regions along the axis of the river-dam of Rosana Reservoir, River Basin Paranapanema. To examine the relationship of abiotic variables with reservoir zones and between the floristic composition of desmids, the authors used principal component analysis (PCA) and canonical correspondence analysis (CCA). The results of the PCA explained 81.3% of the total variability in the first two axes. In the first axis, the variables of conductivity, water temperature and the pH were related to the sampling regions of April with higher values, while for the month of August, nitrate, total phosphorus and dissolved oxygen showed higher values. They identified 20 taxa, distributed in the genera Closterium (14), Gonatozygon (4), Netrium (1) and Penium (1).