Drivers of the Ceratium hirundinella and Microcystis aeruginosa coexistence in a drinking water reservoir

EnglishThe spatial and temporal patterns of phytoplankton in relation to physical and chemical properties were studied in a drinking water reservoir - the Lazberc Reservoir - located in north-east Hungary. The main objectives were to determine the role of the hydrologic regime in structuring algal growth and the effects of physical and chemical variables on the coexistence of a dominant species: cyanobacteria, Microcystis aeruginosa (Kutzing) Kutzing and an eukaryotic dinoflagellates, Ceratium hirundinella (O.F. Muller) Dujardin. The results suggest that nutrients (TP, NH4–N and NO3–N), turbidity, and the hydrologic regime play an important role in regulating the occurrence of investigated species. The rainy summer period resulting in a mixing of the water column, and the low level of nitrogen coupled with the internal release of phosphorus from the lake sediment under brief periods of anoxia promote cyanobacterial bloom. During this period, the water column was characterised by high turbidity, which created favourable conditions for developing a huge C. hirundinella biomass and the simultaneous occurrence of M. aeruginosa. This study also demonstrated - that contrary to what was previously known, deep standing waters in the temperate zone are not only dimictic (mixing twice a year during the spring and the fall), but they can also be mixed during the summer period due to continued rainfall, which equalizes the temperature in the whole water column. This can promote the occurrence of cyanobacterial and eukaryote planktonic organisms portuguesOs padroes espaciais e temporais do fitoplâncton e sua correlacao com as especificidades variaveis fisicas e quimicas, foram examinados no nordeste da Hungria, localizados em um reservatorio tipico de agua potavel no reservatorio de Lazberc. Nosso principal objetivo foi para esclarecer o papel da hidrologia, e os diferentes especificidades fisicas e quimicas na coexistencia de especies dominantes: cianobacteria, Microcystis aeruginosa (Kutzing) Kutzing e Dinoflagellata eucariotica, Ceratium hirudinella (OF Muller) Dujardin. De acordo com os resultados, os nutrientes (TP, NH4-N, NO3-N), turbidez e os condicoes hidrologicas desempenham um papel importante na regulacao da ocorrencia das especies examinadas. O periodo de verao chuvoso que resulta um equilibrio do nivel da agua, o baixo nivel de nitrogenio, juntamente com a liberacao interna de fosforo do sedimento, durante um curto periodo anoxico promove a floracao de cianobacterias. Durante este periodo, a coluna de agua foi caracterizada por alta turbidez, criando condicoes favoraveis para o surgimento de uma enorme expansao da biomassa C. hirundinella e a aparicao simultânea de M. aeruginosa. Este estudo mostrou tambem que as aguas profundas nas areas da zona moderada, nao tem apenas dimictic especialidade (misturando duas vezes por ano, na primavera e no outono), mas tambem durante a estacao do verao pode ser misturada por chuvas continuas que compensam a temperatura em toda a coluna da agua. Isso ajuda a presenca de cianobacterias e organismos eucariotas planctonicos