Nitrogen dynamics and microbial food web structure during a summer cyanobacterial bloom in a subtropical,shallow, well-mixed,eutrophic lake (Lake Taihu,China) |
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Authors: | Mark J McCarthy Peter J Lavrentyev Longyuan Yang Lu Zhang Yuwei Chen Boqiang Qin Wayne S Gardner |
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Institution: | (1) Marine Science Institute, The University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX 78373, USA;(2) Department of Biology, The University of Akron, Akron, OH 44325, USA;(3) Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing, Jiangsu, 210008, P.R. China |
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Abstract: | Nitrogen dynamics and microbial food web structure were characterized in subtropical, eutrophic, large (2,338 km2), shallow (1.9 m mean depth), and polymictic Lake Taihu (China) in Sept–Oct 2002 during a cyanobacterial bloom. Population
growth and industrialization are factors in trophic status deterioration in Lake Taihu. Sites for investigation were selected
along a transect from the Liangxihe River discharge into Meiliang Bay to the main lake. Water column nitrogen and microbial
food web measurements were combined with sediment–water interface incubations to characterize and identify important processes
related to system nitrogen dynamics. Results indicate a gradient from strong phosphorus limitation at the river discharge
to nitrogen limitation or co-limitation in the main lake. Denitrification in Meiliang Bay may drive main lake nitrogen limitation
by removing excess nitrogen before physical transport to the main lake. Five times higher nutrient mineralization rates in
the water column versus sediments indicate that sediment nutrient transformations were not as important as water column processes
for fueling primary production. However, sediments provide a site for denitrification, which, along with nitrogen fixation
and other processes, can determine available nutrient ratios. Dissimilatory nitrate reduction to ammonium (DNRA) was important,
relative to denitrification, only at the river discharge site, and nitrogen fixation was observed only in the main lake. Reflecting
nitrogen cycling patterns, microbial food web structure shifted from autotrophic (phytoplankton dominated) at the river discharge
to heterotrophic (bacteria dominated) in and near the main lake. |
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Keywords: | Lake Taihu Eutrophication Nitrogen Cyanobacterial blooms Denitrification |
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