Ammonium uptake and regeneration rates in a coastal upwelling regime

Authors

Mary-Lynn Dickson, University of Rhode Island
Patricia A. Wheeler

Document Type

Article

Date of Original Version

1995

Department

Oceanography

Abstract

Ammonium uptake and regeneration rates were measured in time course experiments with ¹⁵N as a tracer. Both ammonium uptake and regeneration rates measured over 12 to 18 h remained essentially constant. However, as the length of the incubations increased the amount of usable data decreased dramatically due to substrate depletion and recycling of ¹⁵N. Mass balance calculations indicated that 22 to 51% of the ammonium removed from the dissolved pool was not recovered in the particulate fraction. This appeared to be a more serious problem at 0 and 8 m (47%) than at 25 m (22%). As a result, ammonium uptake rates were probably underestimated. At 0, 12, and 20 m uptake rates either balanced or exceeded regeneration rates, while at 8 and 25 m net regeneration occurred. The fastest rates were measured during upwelling-induced phytoplankton blooms, intermediate rates characterized post-bloom conditions and the lowest rates coincided with an active upwelling event. Ammonium uptake rates were highest during the upwelling season (11 to 17 mmol N m^-2 d^-1) and lowest during the non-upwelling season (3 mmol N m^-2 d^-1), whereas regeneration rates did not differ significantly between seasons (11 to 20 mmol N m^-2 d^-1).

Citation/Publisher Attribution

Dickson, M-L, & Wheeler, P. A. (1995). Ammonium uptake and regeneration rates in a coastal upwelling regime. Marine Ecology Progress Series, 121, 239-248. doi: 10.3354/meps121239

Available at: http://dx.doi.org/10.3354/meps121239