Hidrológiai Közlöny 2002 (82. évfolyam)
XLIII. Hidrobiológus Napok: "Vizeink ökológiai állapota: természetvédelem, vízhasznosítás" Tihany, 2001. október 3-5.
102 HIDROLÓGIAI KÖZLÖNY 2002. 82. ÉVF. Présing M., Herodek S„ Preston T & Vörös L. (2000) Nitrogen uptake and the importance of internal nitrogen loading in Lake Balaton. Fresh-water Biol. 46, 125-139. Présing M„ Herodek S., Vörös L, Preston T. & Abrusán Gy. (1999) Nitrogen uptake by summer phytoplankton in Lake Balaton Arch. Hydrobiol 145, 93-1 10. Présing M. <4 Sprőber P. (2001 a) A fitoplankton nitrogénfelvételének jellemzése és a belső nitrogénterhelés vizsgálata. - In. Mahunka S. & Banczerowski J. (szerkj A Balaton kutatásának 2000 évi eredményei, MTA, Budapest, ISSN 1419-1075, 43-50. Présing M., Preston T„ Kovács A & Sprőber P. (2001 b) Internal and external nitrogen supply of phytoplankton in Lake Balaton (Hungary). - Biwako 2001, 9th Internat. Conference on the Conservation and Management of Lakes, Kyoto, Japan. Partnerships for Sustainable Life in Lake Environments, Conf. Proc. Session 5, 272-275. Slawyk G. & Raimbault P. (1995) Simple procedure for simultaneous recovery of dissolved inorganic and organic nitrogen in l sN-tracer experiments and improving the isotopic mass balance. - Mar. Ecol. Frog. Ser. 124, 289-299 Vollenweider R.A. (1969) A manual on methods for measuring primary production in aquatic environments - IBP Handbook 12, 123 pp. Blackwell Scientific Publications, Oxford. Vörös L. & V.-Balogh K. (1998) A Balaton Keszthelyi-medencéjének szénforgalma. - Hidrológiai Közlöny 78, 385-386. Vörös L„ V.-Balogh K & Herodek S. (1996) Microbial food web in a Urge shallow lake (Lake Balaton, Hungary). - Hydrobiologia 339, 57-65. Amonium regeneration in the water column and sediment of Lake Balaton 'iW. Présing, 2Tom Preston, *A. Kovács, 'P. Sprőber 'Balaton Limnological Research Institute of the Hungarian Academy of Sciences, H-8237. Tihany, 2Isotope Biochemistry Laboratory, Scottish Universities Research and Reactor Centre, Glasgow Abstract: Nitrogen uptake by phytoplankton and ammonium regeneration in the water column and sediment in Siófok and Keszthely basin of Lake Balaton were measured in May, June and August with l 5N tracer technique and isotope dilution, respectively. Two methods (microdiffusion and solid phase extraction) were developed to process ammonium from the water and make it measurable for isotope mass spectrometry. In Siófok basin the ammonium uptake velocity changed between 2-6 ng N/l/hour. Its regeneration rate varied from 1 to 10 ng N/l/hour being 50-90 % of the uptake velocities'. In Keszthely basin in June and at the beginning of the cyanobacterial bloom in August the uptake velocity of ammonium were 4.4 and 14 1 yg N/l/hour and the regeneration rate were 0.5 and 21.2 jig N/l/hour, respectively. The uptake velocities could be underestimated with 10-50 % in Siófok and 10-80 % in Keszthely basin by l sN tracer technique not taking into consideration the ammonium regeneration. The daily nitrogen and carbon uptake rates were close to the Redfield ratio (5.6) in both basins. By the experiments carried out in June and August, 1 cm 3 fresh sediment of the upper 5-cm layer can produce 1-3 .6 ug ammonium nitrogen daily, consequently from one square meter of the upper layer of sediment 50-180 mg ammonium could enter into the water column Depending of the depth of water these can provide 14-50 Hg/1 nitrogen concentrations. By our uptake and regeneration results there was no nitrogen limitation in the water at the time of experiments.
