TY - CONF A1 - Rücker, Jacqueline A1 - Knie, Matthias A1 - Nixdorf, Brigitte A1 - Kolzau, Sebastian A1 - Voss, Maren A1 - Wiedner, Claudia T1 - Nitrogen fixation in two polymictic lakes T2 - Aquatic Sciences Meeting of the Association for the Sciences of Limnology and Oceanography (ASLO) held in Granada, Spain, 22-27 February 2015 N2 - 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. KW - Nostocales KW - Nitrogen fixation KW - Cyanobacteria KW - Light KW - Nitrogen input in lakes KW - Cyanobakterien KW - Nostocales KW - Stickstofffixierung KW - Lichtabsorption Y1 - 2016 UR - https://opus4.kobv.de/opus4-btu/frontdoor/index/index/docId/3708 UR - https://nbn-resolving.org/urn:nbn:de:kobv:co1-opus4-37082 ER -