STUDY OF THE PHYTOPLANKTON POPULATION IN THE MBOI KA'E STREAM, ENCARNACIÓN, PARAGUAY.

Albrecht M 1 and Rodríguez E 2 . 1. Doctorado en Gestión Ambiental. Escuela de Pos Grado Universidad Nacional de Itapúa. Encarnación, Paraguay. 2. Universidad Nacional de Itapúa, Facultad de Ciencias y TecnologíaEncarnación, Paraguay. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

The study was conducted during the four seasons of 2015 in the water basin of the Mboi Ka'e stream in the city of Encarnación. The objective of the research was to evaluate the phytoplankton population in the Mboi Ka'e watershed in the four seasons of the year. The samples were collected in six different points included within the study area, in each of the seasons of the year by means of the water filtration method through an aperture mesh network of 25 μm were fixed with 5% formaldehyde. The analyzes were carried out in the laboratory of the Faculty of Science and Technology of the State University of Itapúa with 10x, 40x, 100x optical microscope. For these, Sedwick-Rafter camera was used by random fields or bands. In the study, three classes of phytoplankton Cyanophyta, Chlorophyta and Bacillariophyta were identified. An analysis of variance (ANOVA) was performed for each class identified in the four seasons of the year. The ANOVA presented a significant difference for the Cyanophyta class in relation to the seasons, the Chlorophyta class showed no significant difference for the seasons as for the number of individuals (cells, colonies or filaments) while the Bacillariophyta class presented a difference not significant for the seasons of the year while the difference was highly significant for the number of cells. Results yielded that in the watershed of the Mboi Ka'e stream, the phytoplankton population is dominated by three main classes, Cyanophyta, Chlorophyta and Bacillariophyta.

Introduction:-
The district of Encarnación is characterized by having different water basins consisting of streams and rivers, the modifications of the ecosystems can be influenced by the physical-chemical and biological characteristics, thus registering alterations in the water quality of the basins.
The term phytoplankton comes from the Greek φιτον (phytonplant) and πλαγκτος (planktos -wandering). It includes organisms that form microscopic photosynthetic communities that live suspended in the photic zone of the water column (Reynolds, 1984).

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During the initial stage of the process of production of organic matter in water systems (oceans and rivers) phytoplankton is formed and occupies the base of the traditional trophic chain, it comprises the largest portion of primary producing organisms of the ocean and is the basic food for consumers (Platt et al., 1992) The phytoplankton sampling was performed by filtering 50 liters of water through an aperture mesh network of 25 μm were fixed with 5% formaldehyde. They were carried out in the four seasons of the year (spring, summer, autumn and winter). The results were expressed in number of individuals (cells, colonies or filaments) per milliliter per identified classes.
The quantitative analysis was carried out by means of a 10x, 40x, 100x optical microscope. Sedwick-Rafter chamber was used for random fields or bands. For the specific systematic determination of each group, different bibliographies were consulted (Huber-Testalozzi 1955, Bourelly, 1970, 1972, 1981, Prescott, 1982, Komarek & Fott, 1983, Conforti & Tell, 1986, Kramer & Lange-Bertalot, 1986, 1991, Anagnostidis & Komarek, 1989, Bicudo & Menezes, 2006, Dos Santos, 2016. The obtained data were subjected to analysis of variance, the means that presented significant difference were compared by the Duncan test 0.05%.  The analysis of variance presented significant statistical difference for the class Cyanophyta for the seasons and the species within the class, on the other hand, the class Chlorophyta presented statistical difference not significant for the two effects, the class Bacillariophyta presented non-significant difference for the effect of the seasons, the difference was highly significant for the different species within the class. The Cyanophyta type showed a variation in the number of individuals according to the different seasons of the year. It is observed that the largest amount was presented in the summer being statistically similar to the amount found in the fall, understanding that population decreases as seasons changes, which could be associated to the variations that occur between the seasons of the year in the studied environment. It could be inferred that this decrease is due to the variation of environmental factors such as the decrease in photoperiod and temperature. The results obtained in this study coincide in part with that expressed by Meichtry de Zaburlín et al. (2013) who expressed the presence of dominant populations of phytoplankton corresponding to Cryptophyceae and Bacillariophyceae, likewise the above mentioned authors found that the Cyanophyceae vary in quantity according to the changes of the different seasons of the year in the Paraná river where the Mboi Kaé stream ends.

Conclusion:-
In this study it was shown that the phytoplankton population in the Mboi Ka'e stream basin is dominated by three main species: Cyanophyta, Chlorophyta and Bacillariophyta. Determining a variation in the population density in the taxon Cyanophyta in the summer and autumn in relation to the other taxa, from which it is understood that the increase in the population of the aforementioned phytoplankton class increased in the warmer months.
Thanks to the Consejo Nacional de Ciencias y Tecnologías (CONACYT) for the scholarship for the doctorate.