Effects of aerobic respiration and nitrification on dissolved inorganic nitrogen and carbon dioxide in human-perturbed eastern Jiaozhou Bay, China

Aerobic respiration and nitrification are important processes for dissolved inorganic nitrogen (DIN) composition change and CO2 production in human-perturbed coastal waters. On-site incubations and field investigations were conducted in the eastern Jiaozhou Bay, a high-urbanization region, from May to August 2014. Results show that aerobic respiration rates reached 15.58 μmol O2 L− 1 d− 1, and NH4+ and NO2− oxidation rates were 0.53 and 0.13 μmol N L− 1 d− 1, respectively, in the human-perturbed northeastern area. The intense aerobic respiration there contributed to high-concentration NH4+, and meanwhile caused a pH decrease of 0.042 units and a pCO2 increase of 166 μatm per day. Moreover, the linear relationship between excess CO2 and apparent oxygen utilization suggested that the excess CO2 in the entire eastern Jiaozhou Bay was mainly from the aerobic respiration. This study may help us better understand the role of aerobic respiration in DIN composition and CO2 sink/source pattern in coastal waters.