CV
Research Area
Research Description
Major Projects
Travel, work abroad

Balaton, cyanobacteria, light–temperature interaction, akinete, iron availability

Lake Balaton (Hungary) is the largest shallow lake in Central Europe (between the northern latitudes 46 62’ and 47 04’, and between the eastern longitudes 17 15’ and 18 10’) that has a large surface area (596 km² at mean level) and a mean depth is 3.25 m. The progressive eutrophication of the lake was perceived in the early seventies. In parallel with the accelerated eutrophication, the phytoplankton assemblage was observed to shift from eucaryotic algae (diatoms and dinoflagellates, especially Ceratium hirundinella) to a dominance of N₂-fixing cyanobacteria. The appearance of new N₂-fixing species was also observed. From 1975 to 1994 the development of summer blooms of N₂-fixing cyanobacteria became a regular phenomenon in the western part and sometimes in the eastern part of the lake. In the western part of the lake the maximum chlorophyll-a concentration generally exceeded 100 µg l^-1. During the latest bloom (1994) the whole water body of the lake was almost a pure culture of the cyanobacterium Cylindrospermopsis raciborskii (Woloszynska Seenayya et Subba Raju (95% of total phytoplankton biomass). Since 1995 the phytoplankton biomass, particularly N₂-fixing cyanobacteria, has decreased dramatically, i.e. the maximum chlorophyll-a concentration has not exceeded 70 µg l^-1. During this time the contribution of dinoflagellates to the phytoplankton biomass has increased again.

The N₂-fixing cyanobacteria in Lake Balaton generally form planktonic populations for only one-three months a year otherwise they exist as akinetes accumulating in the surface layer of the lake sediment. Earlier studies have used indirect counting methods (the number of germinated filaments in the germination experiment) for the determination of akinete abundance in the sediment.

The aim of my study was 

(i) to develop a direct counting method for determine the abundance of akinetes in sediment

(ii) to determine the akinete abundance of C. raciborskii and the total akinete abundance of N₂-fixing cyanobacteria in the sediment of Lake Balaton

(iii) to compare the data of available akinete abundance with the changes of the trophic state of Lake Balaton

(iv) to determine the interactive effects of temperature and light on growth, cell morphology, pigment composition, C:chlorophyll-a ratio, C:carotenoid ratio and C:N ratio composition of the most abundant cyanobacterum species (Cylindrospermopsis raciborskii, Aphanizomenon flos-aquae RALFS.) of Lake Balaton

(v) to determine the dynamics of different iron species (total iron, dissolved iron and biologically available iron [chelatable iron]) in Lake Balaton and in four inflows of the lake

(vi) to develop the easy molecular methods for proving of the iron limitation of the phytoplankton.

• 2002 Role of iron in algal development.
  (Principal investigator: Lajos Vörös)

• 2002 Phytoplankton and phytobenthos in Lake Balaton. 
  (Principal investigator: Lajos Vörös)

• 2001 Role of iron in algal development.
  (Principal investigator: Lajos Vörös)

• 2001 Phytoplanktpn and phytobenthos in Lake Balaton. 
  (Principal investigator: Lajos Vörös)

• 2000 Role of iron in algal development.
  (Principal investigator: Lajos Vörös)

• 2000 Phytoplanktpn and phytobenthos in Lake Balaton. 
  (Principal investigator: Lajos Vörös)

• 1999 Role of microbial communities in water quality formation of Lake Balaton. 
  (Principal investigator: Lajos Vörös)

• 1998 Role of microbial communities in water quality formation of Lake Balaton. 
  (Principal investigator: Lajos Vörös)

• 1997 Investigation of factors affecting growth and toxicity of blue-green algae. 
  (Principal investigator: Lajos Vörös)

• 1996 Investigation of factors affecting growth and toxicity of blue-green algae. 
  (Principal investigator: Lajos Vörös)

University of Leipzig, Leipzig, Germany November-December 2001