Nitrogen uptake and the importance of internal nitrogen loading in Lake Balaton

• Published in: Freshwater biology Vol. 46; no. 1; pp. 125 - 139
• Main Authors: PRESING, Matyas, HERODEK, Sandor, PRESTON, T. O. M, VÖRÖS, Lajos
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Science 2001; Wiley Subscription Services, Inc
• Subjects: Algae; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; Hungary; Synecology; Hungary; Europe; Hungary, Balaton L; Ammonium; Plant community; Environmental factor; Trophic status; Nitrates; Biomass; Spatial variation; Uptake; Freshwater environment; Urea; Nitrogen cycle; Seasonal variation; Nitrogen fixation; Lakes; Phytoplankton; Remineralization
• ISSN: 0046-5070; 1365-2427
• DOI: 10.1046/j.1365-2427.2001.00622.x

The large shallow Lake Balaton, Hungary, became eutrophic in the 1970s because of increased nutrient loads. Eutrophication control measures have since reduced phosphorus loads and algal biomass in the lake has decreased, but a dominance of cyanobacteria in summer phytoplankton is a concern. The study investigated the importance of various nitrogen sources to phytoplankton in the lake's mesotrophic eastern and eutrophic western basins at different seasons. Ammonium, urea, and nitrate contributed 11 80%, 17 73%, and 1 15%, respectively, of the phytoplankton's daily N supply. N sub(2) fixation provided 5 30% of the daily N supply in the eutrophic basin, but was negligible in the mesotrophic basin. Annual riverine inputs supplied only 10% of the N assimilated by phytoplankton. The main process supplying N to phytoplankton in summer is very fast recycling of ammonium and urea in the water column.