AMMONIUM AND UREA CYCLING AND DEMAND IN THE NORTHERN GULF OF MEXICO MISSISSIPPI RIVER PLUME AND IN CYANOBACTERIA IMPACTED LAKES
Comparisons of nitrogen (N) dynamics in the northern Gulf of Mexico Mississippi River Plume (GOM-MRP) with those in tributary polluted bays of large lakes reveal interesting similarities. These similarities suggest that N transformations help explain the effects and fates of high nutrient inputs in both system types. Ammonium (NH4+) and urea recycling rates were measured in waters often experiencing cyanobacterial blooms. Community Biological Ammonium Demand (CBAD), defined as Potential NH4+ Uptake rate minus Actual NH4+ recycling rate (measured as NH4+ regeneration), constituted a large fraction of potential NH4+ uptake rates in natural light incubations, suggesting that NH4+ is a major factor controlling microbial growth and activity in these systems. Photic CBAD values, defined as the absolute difference between natural light and dark incubation CBAD results, were high in near-surface waters. In the GOM-MRP, NH4+ cycling rates decreased with depth, but increased in water immediately overlying sediments. In shallow bays of large lakes, the cycling rates decreased with distance from tributary nutrient inputs. In both systems, N cycling rate decreases can likely be attributed to removal of N by denitrification, which is driven by the formation and degradation of fresh labile organic matter resulting from high nutrient (especially N) inputs. We conclude that understanding internal N dynamics is crucial to developing accurate models to predict the effects of added nutrients to eutrophic ecosystems.
Gardner, W. S., The University of Texas, USA, firstname.lastname@example.org
McCarthy, M. J., Wright State University, USA, Mark
Newell, S. E., Wright State University, USA, 'Newell, Silvia Elena'
Hou, L., Eastern China Normal University, China, email@example.com
Dai, R., Fudan University, China,
Lu, K., The University of Texas, USA
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