Nitrogen deposition acidifying potential

Nitrogen is the most commonly limiting nutrient in North American forest ecosystems (20, 21). The form of N used by terrestrial ecosystems strongly affects the acidifying potential of N deposition (Figure 1). Ammonium uptake is an acidifying process (i.e., uptake of NH4+ releases 1 mole of H per mole of N assimilated). 

The procedure involves adding APDC to a final concentration of 25 pmoVL, and a pH buffer (pH values between 7 and 8.5) to a final concentration of 0.01 mol/L, to seawater in the voltammetric cell. If the seawater had been acidified then its pH should be adjusted to a more neutral pH using ammonia prior to the reagent addition. Oxygen is removed by 7 min purging with water saturated nitrogen. A deposition potential of -1.3 V is used for a period of 3 min, followed by a 10 s equilibration time the scan is initiated from -0.8 V and stopped at -1.3 V. The reaction is electrochemically reversible which means that a wave modulation can be used like the differential-pulse (10 Hz) or the square-wave (50 Hz or faster) modulation. 

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