Microscale distribution of nitrification activity in sediment determined with a shielded microsensor for nitrate

Area of Science:

• Environmental Science
• Microbiology
• Geochemistry

Background:

• Understanding nutrient cycling in aquatic ecosystems is crucial.
• Nitrification and denitrification are key processes in nitrogen cycling.
• Sediment microbial communities play a vital role in these processes.

Purpose of the Study:

• To investigate oxygen and nitrate microprofiles in freshwater sediment.
• To determine nitrification and denitrification depth profiles using computer simulation.
• To understand the response of nitrifying bacteria to environmental changes.

Main Methods:

• Simultaneous measurement of oxygen (O(2)) and nitrate (NO(3)) microprofiles using coaxial microsensors.
• Computer simulation to determine nitrification and denitrification rates from microprofile data.
• Perturbation experiments involving oxygen and acetylene (C(2)H(2)) addition.

Main Results:

• Nitrifying bacteria responded rapidly to environmental changes, reaching steady-state microprofiles within hours.
• Nitrification initiated quickly upon oxygen introduction in anoxic layers, suggesting survival during anaerobiosis.
• Coupled nitrification-denitrification occurred at the oxic-anoxic interface.
• Acetylene addition eliminated nitrate peaks, confirming autotrophic nitrification as the primary nitrate source.

Conclusions:

• Nitrifying bacteria in freshwater sediments are highly adaptable to environmental shifts.
• Sediment microbial communities can sustain nitrification even after prolonged anaerobic periods.
• The oxic-anoxic interface is a critical zone for coupled nitrogen cycling processes.
• Autotrophic nitrification is the dominant pathway for nitrate production in these sediments.