Size-fractionated (15N-ρNH4+) uptake Regenerated Production
| Ammonium uptake, size-fractionated |
|---|
| Approach: 15N tracer, size-fractionated filtration, EA-IRMS |
| Context: incubation, simulated in situ |
| Spatial scale: point sample |
| Temporal scale: 12–24 h |
| Units: µmol N L-1 d-1; µmol N m-2 d-1 (depth-integrated) |
| Community captured: 0.7 µm (GFF), 5 µm, and sometimes 20 µm size fractions |
| Co-measurements: background δ15N (PON), ambient [NH4+], temperature, PAR, Chl, initial blank |
Method Overview
The size-fractionated variant of the ammonium uptake method. After a 15NH4+ tracer incubation, samples are sequentially filtered through 0.7, 5, and sometimes 20 µm filters to partition ammonium uptake among plankton size classes. EA-IRMS measurement of 15N enrichment on each filter fraction yields size-class-specific regenerated production rates[1].
Scale of measurement
Point sample; 12–24 h incubation.
Data generated
Size-class-specific ammonium uptake rates (µmol N L-1 d-1). Reveals whether regenerated production is dominated by small (picoplankton) or large (microphytoplankton) cells.
Units & currency
Units are µmol N L-1 d-1 per size fraction. The currency is nitrogen.
Sample size
Typical samples are 0.5–2 L in volume.
Repositories & databases
Limitations
Same as the bulk ammonium uptake method. Additional limitation: isotope dilution from regeneration by heterotrophic bacteria in the sub-0.7 µm fraction can affect the 15N enrichment of the dissolved pool, potentially more severely in low-NH4+ samples.
Example Applications & Protocols
Classic examples
- Dugdale & Goering (1967) Uptake of new and regenerated forms of nitrogen in primary productivity [2]
- Dugdale & Wilkerson (1986) The use of 15N to measure nitrogen uptake in eutrophic oceans [1]
Recent applications
- Meyer et al. (2022) Phytoplankton size-class contributions to new and regenerated production during EXPORTS [3]
Common calculations/conversions
References
- ↑ 1.0 1.1 Dugdale, R. C., & Wilkerson, F. P. (1986). The use of 15N to measure nitrogen uptake in eutrophic oceans; experimental considerations. Limnology and Oceanography, 31(4), 673–689. https://doi.org/10.4319/lo.1986.31.4.0673
- ↑ Dugdale, R. C., & Goering, J. J. (1967). Uptake of new and regenerated forms of nitrogen in primary productivity. Limnology and Oceanography, 12(2), 196–206. https://doi.org/10.4319/lo.1967.12.2.0196
- ↑ Meyer, M. G., Davis, P. B., Vogt, M., & Tortell, P. D. (2022). Phytoplankton size-class contributions to new and regenerated production during the EXPORTS Northeast Pacific Ocean field deployment. Elementa: Science of the Anthropocene, 10(1). https://doi.org/10.1525/elementa.2021.00068