1. Denitrification in Delaware Bay Tidal Marshes and Creeks
February 2011
Mike Owens, Jeffrey Cornwell
Chesapeake Biogeochemical Associates
& UMCES Horn Point Laboratory
Delaware Estuary Science and Environmental Summit

2. Sediment Fluxes
July 19, 2007: Cores collected for subtidal fluxes at 4 stations (triplicate cores)
July 23, 2007, April 27, 2008: Cores collected for marsh fluxes (2 marsh cores, 1 creek core). Standard fluxes carried out both time, plus two levels of NO3- addition in 2007
We utilized our “standard” core incubation procedures and measured fluxes of ammonium, nitrate, di-nitrogen, oxygen and soluble reactive phosphorus.

3. Study Goals
Measure net nutrient fluxes at the sediment-water interface of Murderkill River, creek and marsh environments
Utilize N2:Ar approach to measure denitrification to examine denitrification in high and low nitrate seasons
Compare denitrification rate estimates to other nitrogen sinks (i.e. burial) and to estimates of N input

5. Wetland Plant Community
Atmospheric DIN
Wetland Plant Community
DIN + PN
Surface Water
Nitrogen
N2-N
Point/Non-Point
N Inputs 3 2
DIN
DIN 4
Wetland Soil
DIN + PN 1
Measured Parameters
NOx flux into soil
NH4+ efflux from soil
Soil denitrification
Nitrogen burial
Groundwater DIN
Exchange 5
“Permanent”
Burial

6. Putting Microbes to Work
Denitrification requires 1) reducing conditions (no oxygen) and 2) a source of nitrate (NO3-)
In many environments, nitrate come from the oxidation of ammonium (nitrification)
This process represents a bona fide loss of nitrogen; burial, incorporation into fish and washout at the bay mouth are the other major sinks for nitrogen

8. Marshes

11. Nitrate Addition Experiment July 2007

13. Conclusions
Marsh nitrogen burial and denitrification rates are similar. Both could account for an important portion of watershed N inputs.
Denitrification is similar in early spring to summer rates, despite different nitrate sources (summer nitrification, spring water column nitrate)