@inproceedings{RueckerKnieNixdorfetal.2015, author = {R{\"u}cker, Jacqueline and Knie, Matthias and Nixdorf, Brigitte and Kolzau, Sebastian and Voss, Maren and Wiedner, Claudia}, title = {Nitrogen fixation in two polymictic lakes}, series = {Aquatic Sciences Meeting of the Association for the Sciences of Limnology and Oceanography (ASLO) held in Granada, Spain, 22-27 February 2015}, booktitle = {Aquatic Sciences Meeting of the Association for the Sciences of Limnology and Oceanography (ASLO) held in Granada, Spain, 22-27 February 2015}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-37082}, year = {2015}, abstract = {The ability to fix molecular nitrogen is considered to be a competitive advantage of Nostocales to overcome periods of nitrogen shortage but it is unclear to what extend these cyanobacteria import nitrogen into freshwaters and if they are able to compensate the efforts of reducing anthropogenic nitrogen input. We studied nitrogen fixation, cyanobacterial biovolume and species composition and abiotic parameters in two polymictic lakes (Germany) over three years. Although Nostocales were present from April to November N2-fixation was found only from June/July to September. In the summer months, it amounted up to 40 mgN m-²d-¹ or up to 500 mgN m-²d-¹ resulting in rather low annual N-inputs between 0.1 and 8 gN m-²a-¹. We found a high variation in N2-fixation rates between the two lakes and the years, which could neither be explained by total Nostocales biovolume nor heterocyte numbers. N2-fixation rates measured in the field will be analyzed on Nostocales species level, be compared to those of laboratory cultures and be discussed in the context of possible phosphorus or light limitation of Nostocales.}, subject = {Nostocales; Nitrogen fixation; Cyanobacteria; Light; Nitrogen input in lakes; Cyanobakterien; Nostocales; Stickstofffixierung; Lichtabsorption}, language = {en} }