Temperature Decouples Ammonium and Nitrite Oxidation in Coastal Waters

Area of Science:

• Environmental microbiology
• Oceanography
• Biogeochemical cycles

Background:

• Nitrification, a key process in the nitrogen cycle, involves two steps: ammonia-oxidation and nitrite-oxidation.
• These steps are typically coupled, preventing nitrite accumulation in most coastal environments.
• However, elevated nitrite levels have been observed in estuarine waters, prompting investigation into their causes.

Purpose of the Study:

• To investigate the causes of nitrite accumulation in aerobic coastal waters.
• To determine the role of temperature versus hypoxia in uncoupling nitrification steps.
• To assess the potential ecosystem impacts of increased nitrite accumulation.

Main Methods:

• Field data analysis from 270 stations across 29 estuaries and lagoons.
• Laboratory experiments simulating temperature shifts on natural nitrifying microbial communities.
• Comparison of temperature effects with hypoxia as a potential uncoupling factor.

Main Results:

• Nitrite accumulation in coastal waters is primarily driven by water temperature, not hypoxia.
• Ammonia- and nitrite-oxidation become uncoupled within a specific temperature range (20–30 °C).
• Field data confirmed a correlation between water temperature and transient nitrite accumulation.

Conclusions:

• Increased summer temperatures in coastal waters can decouple nitrification, leading to nitrite accumulation.
• Warming oceans and climate variability may increase the frequency of these events.
• Potential consequences include N2O production, nitrite toxicity, and altered phytoplankton communities.