PICOPHYTOPLANKTON BLOOMS IN TRANSYLVANIAN HYPERSALINE LAKE

Zsolt Gyula Keresztes, Babes-Bolyai University, Cluj-Napoca, Romania
Boglárka Somogyi, Balaton Limnological Institute, Centre for Ecological Research of the HAS, Hungary
Tamás Felföldi, Eötvös Loránd University, Budapest, Hungary
Erika Nagy, Csaba Bartha, Nicolae Dragos, Gyöngyi Székely, Lajos Vörös, Babes-Bolyai University, Cluj-Napoca, Romania

Abstract

The saline lakes of the Carpathian Basin were emerged in the last century from the flooding of abandoned salt mines. The concentration of salt in these relatively young, deep lakes is extremely high, nearly saturated. During last decades these lakes underwent high human modifications and became popular spas. The bath season starts in May and lasts until September. The shore of most lakes is a built up area, the inflow water is mainly rain water. Water samples were collected from nine saline lakes situated near Cluj-Napoca, in July 2010, in February and July 2011. Summer samples were taken from the lake surface, while winter samples were collected from different depths. The major physicochemical characteristics of the water such as temperature, conductivity, pH, dissolved oxygen concentration, Secchi-disk transparency, and ice-thickness were determined in the field. The chlorophyll a concentration, the abundance and the biomass of the phytoplankton were determined in laboratory. The abundance and composition of picophytoplankton was determined with epifluorescence microscopy, in the case of nanoplankton the composition and abundance were determined with inverted (plankton) microscope. Molecular biology techniques (DGGE, cloning, sequencing) were applied for the identification of phytoplankton taxa. Based on our results, most of the lakes were hypertrophic, meromictic and highly stratified. During winter, in most cases we observed a deep (approximately 4 m) chlorophyll maximum. The stratification observed in winter disappeared in summer due to the bathing. In these lakes the phytoplankton at least in one occasion was dominated by picocyanobacteria and/or picoeukaryotes. Diatoms (e.g. Cymbella sp., Amphora sp.), common halophytic species (Dunaliella salina (Dunal) Teodoresco), and marine phytoplankton taxa (Picochlorum, Nannochloris, Synechococcus marine clade VIII. and Isochrysis species) were identified. The presence of marine phytoplankton species and the dominance of picophytoplankton make these continental salt lakes very particular environment. The study was sponsored by the Hungarian Research Fund (OTKA K 73369), Human Resources Development, Contract POSDRU 88/1.5/S/60185, POSDRU/107/1.5/S/76841 – Doctoral studies: through science towards society, CNCSIS PN II. Grant nr: TE 306/70, Collegium Talentum.