Microbial activity at the sediment-water interface in halifax harbor, Canada

Area of Science:

• Marine Microbiology
• Environmental Science
• Biogeochemistry

Background:

• The sediment-water interface is a critical zone for microbial activity and nutrient cycling in aquatic ecosystems.
• Standard methods for assessing microbial heterotrophic activity may not accurately reflect in-situ conditions.
• Understanding microbial responses to nutrient availability is crucial for marine ecosystem health.

Purpose of the Study:

• To develop and validate an alternate technique for measuring heterotrophic activity at the sediment-water interface over extended periods.
• To compare microbial glutamic acid uptake using a standard method versus an undisturbed core method.
• To investigate the impact of substrate diffusion and water column microbial competition on interface microbial activity.

Main Methods:

• Enumeration of microbial populations in Halifax Harbor sediment-water interface.
• Measurement of glutamic acid uptake using a standard subsampling method in filtered seawater.
• Development and application of an undisturbed sediment core technique to assess microbial growth and substrate uptake over time.
• Autoradiography and direct counts to determine viable versus total microbial populations.

Main Results:

• Standard methods overestimated glutamic acid uptake by nearly an order of magnitude compared to undisturbed cores (113.5 ng/g/h vs. 12.7 ng/g/h).
• Microbial populations in undisturbed cores exhibited exponential growth (doubling times of 4.5 days for interface, 9.6 days for water column).
• Substrate diffusion and water column microbial competition significantly influence measured heterotrophic activity.
• Interface microbes demonstrated rapid and repeatable responses to nutrient additions, but autoradiography indicated a large portion of the viable population was unaffected by nutrient pulses.

Conclusions:

• Undisturbed sediment core techniques provide a more accurate assessment of sediment-water interface microbial heterotrophic activity.
• Substrate diffusion limitations and competition from planktonic microbes are critical factors influencing benthic microbial nutrient processing.
• While the active microbial community responds to nutrient inputs, a significant portion of the viable population may remain dormant or unaffected.