The effect of the land use on phytoplankton assemblages of a Cerrado stream (Brazil) Os efeitos do uso do solo sobre as assembleias fitoplanct nicas de um riacho de Cerrado (Brasil)

AIM: Our aim was to investigate whether land use from the adjacent terrestrial environment influences phytoplankton assemblage structure (composition, richness, diversity, and abundance) and biomass (chlorophyll-a) in a Cerrado stream during different periods of the year. METHOD: The fieldwork was carried out at each 3 months during two years. RESULTS: The physical and chemical variables that better indicated differences in water condition were conductivity, dissolved oxygen, and transparency. There was also a noticeable increase in the concentration of nitrogen, phosphorus, and suspended matter in the water during summer due to the direct effects of rainfall. The phytoplankton assemblages were composed by 64 species. Cryptophyceae was the most abundant group, followed by Bacillariophyceae. For both years, richness and diversity were higher during spring and autumn, while phytoplankton abundance and chlorophyll-a concentration were greater during autumn and summer. The cluster and the canonic correspondence analyses evidenced that seasonality and land use are important factors in structuring phytoplankton communities along the year. Alterations in phytoplankton assemblages registered herein were probably a consequence of variations on intensity and frequency of water mixing, along with the input of nutrients from the adjacent terrestrial system. CONCLUSION: Overall phytoplankton assemblage structure showed to be highly influenced by land use, corroborating our initial hypothesis. OBJETIVO: Nosso objetivo foi investigar se o uso do solo do ambiente terrestre adjacente influencia a estrutura das assembleias fitoplanct nicas (composi o, riqueza, diversidade e abundancia) e biomassa (clorofila-a) em um riacho de Cerrado durante diferentes períodos do ano. MéTODOS: Os trabalhos de campo foram realizados trimestralmente durante dois anos. RESULTADOS: As variáveis físico-químicas que melhor indicaram as diferen as nas condi es da água foram condutividade, oxigênio dissolvido e transparência. Também houve um notável aumento na concentra o de nitrogênio, fósforo e material em suspens o na água durante o ver o devido aos efeitos da pluviosidade. As assembleias fitoplanct nicas foram compostas por 64 espécies. Cryptophyceae foi o grupo mais abundante, seguido por Bacillariophyceae. Para ambos os anos, a riqueza e a diversidade foram maiores durante a primavera e no outono, enquanto que a abundancia do fitoplancton e a concentra o de clorofila-a foram mais elevados durante o outono e ver o. A análise de agrupamento e a analise de correspondência can nica mostra