US EPA

3306389 

Journal Article 

Ammonium-nitrogen: A key regulatory factor causing dominance of non-nitrogen-fixing cyanobacteria in aquatic systems 

Blomqvist, P; Pettersson, A; Hyenstrand, P 

1994 

Yes 

Archiv für Hydrobiologie
ISSN: 0003-9136 

132 

2 

141-164 

English 

WOS:A1994QA25900002 

Hypotheses concerning factors causing cyanobacterial dominance in freshwaters are reviewed against evidence from four different types of lakes. It is argued that either cyanobacteria should not be treated as a group or that more information is needed. It is suggested that the required piece of information is that non-nitrogen-fixing cyanobacteria have low competitiveness for nitrate nitrogen sources and high competitiveness for ammonium nitrogen sources. Supporting evidence from enclosure experiments with low-dose phosphate additions, and either ammonium- or nitrate-nitrogen in two lakes is presented. In both lakes, depletion of nitrate-nitrogen occurred before cyanobacteria started to develop. In the oligotrophic, low-alkaline, clearwater Lake Njupfatet, a non-nitrogen-fixing cyanobacterium, Merismopedia tenuissima usually dominates during late summer. Concurrent with Merismopedia's dominance, nitrate additions in one enclosure led to successively increased importance of dinoflagellates, whereas Merismopedia remained dominant in the enclosure to which ammonium was added. In a second experiment, performed in early summer, Merismopedia failed to become dominant after nitrate additions which led rather to complete dominance of dinoflagellates. Ammonium additions led to co-dominance by Merismopedia and a dinoflagellate. In mesotrophic, alkaline Lake Erken ammonium in combination with phosphate stimulated the growth of non-nitrogen-fixing cyanobacteria (Microcystis spp. and Synechococcus sp.), whereas nitrate additions produced no such outcome. Measurements of nitrate reductase activity in enclosure waters containing nitrate and phosphate indicated that eukaryotic nitrate reductase activity (NADH-NR) was induced more rapidly and to a greater extent than the prokaryotic (cyanobacterial) nitrate reductase activity (MV-NR). It is argued that dominance by cyanobacteria is attributable to the following factors: ability to minimize sedimentation and grazing losses in combination with i) the ability to fix molecular nitrogen (nitrogen-fixing species) in nitrogen deficient systems or ii) the ability to out-compete most other phytoplankton for ammonium-nitrogen (non-nitrogen-fixing species) in nitrate depleted systems.