Dissolved oxygen saturation controls PAH biodegradation in freshwater estuary sediments

Area of Science:

• Environmental Science
• Environmental Chemistry
• Microbiology

Background:

• Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants found in aquatic environments.
• PAHs contribute significantly to the carbon pool in coastal sediments.
• Understanding PAH biodegradation is crucial for assessing environmental contamination and remediation strategies.

Purpose of the Study:

• To investigate the seasonal dynamics of PAH biodegradation and heterotrophic bacterial production in a freshwater estuary.
• To identify the key biogeochemical factors controlling PAH degradation.
• To compare PAH biodegradation responses to temperature and dissolved oxygen levels with previous studies.

Main Methods:

• An 18-month seasonal study was conducted in a tidally influenced freshwater estuary.
• 186 sediment samples were collected from approximately 250 km(2).
• Measurements included PAH biodegradation, heterotrophic bacterial production, temperature, and dissolved oxygen (DO).

Main Results:

• Bacterial production correlated with ambient temperature, but not with DO or PAH concentrations.
• PAH biodegradation showed no significant effect of temperature on naphthalene, phenanthrene, or fluoranthene.
• PAH mineralization strongly correlated with bottom water DO saturation above 70%.

Conclusions:

• Dissolved oxygen, particularly levels above 70% saturation, is a critical factor controlling PAH biodegradation in this estuary.
• PAH utilization by bacteria is significantly higher during cooler months when DO levels are elevated.
• Seasonal influxes of cooler, oxygenated water may preferentially stimulate PAH metabolism over other organic matter.