Nitrogen

Nitrogen Uptake

• (15N-ρNO3-) uptake New Production
• 15N-ρNO3/chl a (N assimilation rate)
• (15N-ρNH4+) uptake Regenerated Production
• (15N-ρurea) uptake Regenerated Production

Nitrogen Assimilation

• [[Eukaryotic Assimilatory nitrate reductase, NAD(P)H dependent, Nitrate -> Nitrite, Nitrate (NR)]]

Nitrification

• DIN inventory with inhibitors
• Inhibitors with 14 or 13CO2 uptake
• Nitrite oxidation (Nxr)
• amoA gene or transcript abundance
• Natural abundance of N and O isotopes in nitrate, nitrite and ammonium
• 15N tracers

Denitrification

• acetylene-block proxy for denitrifcation enzyme activity
• 15N tracer-based method
• N2:Ar ratio quantification
• Mass Balance
• Stoichiometric approach
• Natural Abundances of 15N and 18O

Dissimilatory Nitrate Reduction to Ammonium

• Isotopic measurements---15N-labeled ammonium (15NH4+) accumulation rate in 15NO3- added incubation

Anaerobic Ammonium Oxidation

• 15N tracers (15N labeled gases upon addition of 15NO3, 15NO2, or 15NH4)
• Functional gene quantification (hzs, hzo)
• FISH staining of anammox bacteria

Bacterial Assimilation & Remineralization

• 13C- and 15N-labeled algal exudates (isotope tracing & nanoSIMS)
• Degradation of dissolved organic nitrogen: Leucine-aminopeptidase activity
• Degradation of dissolved organic nitrogen: Endopeptidase activity