Nitrate uptake rates in freshwater plankton: the effect of food web structure

• Published in: Marine and Freshwater Research
• Main Authors: Rojo, Carmen, Rodrigo, María A., Salazar, Guillem, Álvarez Cobelas, Miguel
• Format: Article in Journal/Newspaper
• Language: English
• Published: Commonwealth Scientific and Industrial Research Organization (Australia) 2008
• Subjects: Cell size; Cladocerans; Copepods; Freshwater plankton; 15N; Nitrogen isotopes; Rotifers; Ruidera Lakes National Park; ren
• Online Access: http://hdl.handle.net/10261/17604; https://doi.org/10.1071/MF08023

9 pages, 3 figure, 1 table Nitrate incorporation rates by primary producers and the transfer of nitrogen to upper planktonic food web levels in different seasons (spring and summer of different years) were studied using a microcosm experimental approach. The study communitieswere natural plankton communities from Colgada Lake (central Spain),which is heavily polluted by nitrate. Natural δ15N in phytoplankton and zooplankton was measured and experiments were performed on the 15N supply. Naturally derived δ15N varied from 7.4 to 8.6‰ and from 10.0 to 16.8‰ in phytoplankton and zooplankton respectively. Nitrogen incorporation rates ranged from 0.006 to 0.036μMh−1 and from 0.0004 to 0.0014μMh−1 in phytoplankton and zooplankton respectively. The differences in natural δ15N levels and nitrogen incorporation rates between plankton fractions from seasonally different communities reported in the present study suggested that the nitrogen uptake by planktonic communities in Colgada Lake depend on different combinations of dominant zooplankters and phytoplankton size structure. A higher level of nitrogen uptake by phytoplankton occurred when small algae were dominant without competitors (larger algae) or main predators (herbivorous zooplankters). This was because copepods, with the lowest zooplankton nitrogen uptake, were dominant. Phytoplankton nitrogen uptake was lower when big algae were dominant The authors wish to thank the Spanish Ministry of Education and Science for the funding of the research projects REN-2002-558 and CGL2006-2346.We also acknowledge American Journal Experts for English language correction Peer reviewed