Effect of settled diatom-aggregates on benthic nitrogen cycling

Area of Science:

• Marine ecology
• Biogeochemistry
• Microbial ecology

Background:

• Marine sediments contain diverse microhabitats.
• Phycodetrital aggregates alter local oxygen distribution and organic matter enrichment.
• These changes impact nutrient cycling, particularly nitrogen.

Purpose of the Study:

• To investigate how microscale oxygen shifts induced by diatom aggregates affect benthic nitrogen cycling.
• To quantify changes in nitrification, denitrification, and overall nitrogen transformations.

Main Methods:

• Sediment incubations with diatom aggregates.
• Oxygen microprofiling to assess micro-O2 distribution.
• 15N isotope enrichment experiments to quantify nitrogen fluxes.

Main Results:

• Diatom aggregates enhanced oxygen and nitrate consumption, stimulating nitrite and ammonium production.
• Anoxic niches formed within and under aggregates, increasing denitrification of overlying nitrate.
• Coupled nitrification-denitrification decreased, while nitrification at aggregate surfaces remained efficient.

Conclusions:

• Aggregate-induced oxygen microdistribution changes stimulate nitrate denitrification from overlying water.
• The coupling between benthic nitrification and denitrification is altered in time and space.
• This study enhances understanding of nitrogen cycling regulation in dynamic marine sediments.