Denitrification in Marine
Sediments: An Unknown
Environmental Feedback
Owen L. Coyle
September 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
N2
The N Cycle
Internal Cycling
atmosphere
N fixation
Phytoplankton
(marine food web)
N2
NO3
overlying
water
In & Out
transport,
mixing
Organic N
sinking, mixing
sediments
N2
denitrification
Organic N
NO3
mineralization
Sedimentary
Processes
courtesy Bess Ward
N-Transformation in
Sediment
N2
Complicate
d
nitrite oxidation
NO3-
denitrification
dnrn
NO2-
anammox
ammonium
oxidation
ammonification
NH4+
dnra
Organic N
new biomass
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!
clean glassware
safely use hazardous chemicals
Results-Low OM
Key Points:
•NH4+ ∼ constant, then falls rapidly
•NO2- peak < NO3- peak
•Sequential: NH4+ → NO2- → NO3-
Practically Identical
Results-High OM
Key Points:
•NH4+ initial rise
•NO2- peak > NO3- peak
•Sequential: NH4+→NO2-→NO3-
Practically Identical
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