Denitrification in Marine Sediments: An Unknown Environmental Feedback

Owen L. CoyleSeptember 24, 2010

Overfertilizing with Nitrogen

• 1 of Gus Speth’s 8 Global Environmental Problems

• Known Consequences

•Algae Blooms

•Eutrophication

• Unknown Consequences

•Effects on N-Cycle

Duce et al. 2008

The N Cycle

N2

N2

Phytoplankton(marine food web)

Organic N

sinking, mixing

Organic NNO3N2

NO3

atmosphere

overlyingwater

sediments

transport,mixing

denitrification mineralization

N fixation

courtesy Bess Ward

Internal Cycling

In & Out

Sedimentary Processes

N-Transformation in Sediment

Organic N

NH4+

NO2-

NO3-

N2

ammonification

ammoniumoxidation

nitrite oxidation

denitrification anammox

dnrn

dnra

new biomass

Complicated

Project Outline

•Question

- Does supply of organic matter affect N cycling in marine sediments?

• Experimental Setup

- simulate environment with 4 mesocosms

- add NH4+ and NO3

- (i.e. fertilizer) to all mesocosms

- add little OM to 2 tanks (A & C) and lots to 2 tanks (B & D)

- daily measurements of DIN (NH4+, NO2

-, and NO3-)

Mesocosms filled with Chesapeake Bay sediment and water

Skills Needed•Sample Mesocosms w/o

contamination

- acid-wash containers

- prepare samples for long term storage at -40℃

•Measure DIN species

- prepare standards and reagents

- analyze using a spectrophotometer

•Lab Protocol

- keep thorough notes!keep thorough notes!

- clean glassware

- safely use hazardous chemicals

Key Points:•NH4

+ ∼ constant, then falls rapidly•NO2

- peak < NO3- peak

•Sequential: NH4+ → NO2

- → NO3

-

Practically Identical

Results-Low OM

Results-High OM

Practically Identical

Key Points:•NH4

+ initial rise•NO2

- peak > NO3- peak

•Sequential: NH4+→NO2

-→NO3-

Summary

•Observed N cycling was different in high and low treatments

•Data will be used to model sedimentary N processes

•I would like to revisit this topic in my JP

Thank You To:

• Andrew Babbin

• Bess Ward

• Sarah, Jenna, Johanna, and all of the office mates and lab mates who made me feel at home