The nutrient load introduced into flooded rice fields is one of the main factors that impact this type of ecosystem, contributing to the development of blooms of pigmented euglenoids. This study was carried out to investigate the behavior of red euglenas, a group of pigmented euglenoids, forming blooms in this type of environment. Sedimented spores in the soil after water drainage, as well as water samples from vegetative cells in living blooms were collected. The collected material was

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... ed into a culturing medium for microalgae and incubated for three weeks. The cultures grown in nutrient medium were used for morphometric analysis to identify the species. In order to characterize the water environment, chemical and physical parameters were also monitored "in situ". The results indicated Euglena sanguinea Ehr. as the bloom-forming species and nitrogen as a key element in the behavior of this species in this type of ecosystem. It was suggested, however, that more studies are needed to indicate the use of red euglenas as biomarkers of nitrogen overload in flooded rice fields.