Nitrogen Impacts on Carbon Storage and Fluxes in Wetlands
Anthropogenic Nitrogen Enrichment in Coastal Ecosystems N load (kg N ha -1 4000 3000 2000 1000 0 y -1 ) Lawns & Turf Chesapeake Connecticut R. 2 Capitalizing on Coastal Blue Carbon Conference | May 12-13, 2015
Groundwater-borne Nitrogen Yields from Coastal Watersheds Sewered 3
Isotopic evidence for anthropogenic N in estuarine food webs Cole et al. 2004 NLM: Land Use Based Model Supported by Groundwater 4 N Isotopic Data
“Moderate” loads with major effects in estuaries 5
IMPACT OF NITROGEN Capitalizing on Coastal Blue Carbon Conference | May 12-13, 2015 6
Surprising shift: N 2 O sink to source in response to a nitrogen pulse Plots received single pulses of nitrate (0.5L of 300 m M) = Nitrate added = Control 4 mol N 2 O m -2 h -1 3 2 1 0 0 m -1 July ‘09 April ‘10 June ‘10 -2 Moseman-Valtierra et al. 2011. Atmospheric Environment
The “Grand Experiment” N gradient in Narragansett Bay RI High N loading Passeonkquis: *2418 kg N ha -1 y -1 Fox Hill: *10 kg N ha -1 y -1 Low N loading *=Wigand et al. 2004
Narragansett Bay marshes = high N load (Pass.) = low N load (Fox) 80 0.4 mol CH 4 m -2 h -1 0.35 60 mol N 2 O m -2 h -1 0.3 40 0.25 20 0.2 0 0.15 0.1 -20 m 0.05 -40 0 m -0.05 -0.1 200 M) 5 ammonium ( m mol CO 2 m -2 s -1 4 Porewater 150 3 100 2 1 50 m 0 0 -1
N 2 O emissions vs marsh nitrogen load Narragansett Bay, RI Passeonkquis Cove 300 Average Fall 2012 N 2 O emissions nmol N 2 O m -2 h - 250 200 150 1 100 Waquoit Bay, MA 50 0 0 50 100 150 200 250 N load (g N m -2 y -1 )
Nitrogen loads in our experiments Narragansett Bay, RI Winyah Wigand (EPA) Passeonkquis Cove Bay mesocosms 300 Plum Island (NC) TIDES Jamaica 250 nmol N 2 O m -2 h -1 Bay, NY Phragmites 200 experiments (Mozdzer) 150 100 50 0 365 0 50 100 150 200 250 N load (g N m -2 y -1 ) Waquoit Bay, MA
IMPACT OF NITROGEN Capitalizing on Coastal Blue Carbon Conference | May 12-13, 2015 12
Quantify carbon credit: Net Ecosystem Carbon Balance (NECB = dC/dt) CH 4 CH 4 R R F(L) F(L) N GPP GPP C stocks C stocks NECB = dC/dt = GPP – R – F(CH 4 ) – F(L) NEP
CO 2 fluxes across N gradient Hamblin Pond Low N 10 10 NEP GPP 5 5 R Flux ( mol m-2s-1) Flux ( mol m-2s-1) 0 0 -5 -5 NEP GPP -10 R -10 -15 -15 -20 0 50 100 150 200 250 300 350 400 -20 0 50 100 150 200 250 300 350 400 DOY Great Pond Eel Pond High N 10 NEP 10 GPP R 5 NEP 5 GPP Flux ( mol m-2s-1) R Flux ( mol m-2s-1) 0 0 -5 -5 -10 -10 -15 -15 -20 -20 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 DOY DOY
CH 4 fluxes across N gradient Low N 3.0 8 2.5 Sage Lot Hambin CH4 CH4 Flux (nmol m-2s-1) Flux (nmol m-2s-1) 6 2.0 1.5 4 1.0 2 0.5 0.0 0 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 DOY DOY High N 3.0 3.0 Great Pond Eel Pond CH4 2.5 2.5 CH4 Flux (nmol m-2s-1) Flux (nmol m-2s-1) 2.0 2.0 1.5 1.5 1.0 1.0 0.5 0.5 0.0 0.0 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 DOY DOY
Short-term N addition experiment: N 2 O fluxes responding to 1.4 gN/m 2 Adding time ： 11:50-11:55 am High tide started Marsh platform was flooded
Aboveground biomass gC ≈ g biomass/2
Root and Rhizome biomass 5.00 5.00 Roots Roots Eel Pond Hamblin Pond (N = 4) (N = 4) Rhizomes Rhizomes 4.00 4.00 Average Dry Weight (g) Average Dry Weight (g) 3.00 3.00 2.00 2.00 1.00 1.00 0.00 0.00 0-10 10-20 20-30 30-40 40-50 0-10 10-20 20-30 30-40 40-50 5.00 5.00 Roots Sage Lot Pond Roots Great Pond (N = 9) (N=3) Rhizomes 4.00 4.00 Rhizomes Average Dry Weight (g) Average Dry Weight (g) 3.00 3.00 2.00 2.00 1.00 1.00 0.00 0.00 0-10 10-20 20-30 30-40 40-50 0-10 10-20 20-30 30-40 40-50 Soil Depth (cm) Soil Depth (cm)
Above- and belowground biomass High N High N Low N Low N
Preliminary conclusions • Small amounts of N loading (1-10 gN m -2 y -1 ) did not change the carbon fluxes, likely because N loaded via groundwater was primarily used by microbes and phytoplankton. Salt marsh and GHG emissions may be significantly changed when N loading increased to a threshold level. • N 2 O fluxes are not significant in these salt marshes, but adding N may result in high N 2 O fluxes. • Higher belowground biomass were found in relatively high N loading marshes, but not seen for aboveground biomass.
IMPACT OF NITROGEN LOADING ON CARBON BURIAL Capitalizing on Coastal Blue Carbon Conference | May 12-13, 2015 21
There is a moderate nitrogen loading gradient Core locations to Waquoit Bay marshes. 0.5 N Loading g/m 2 /year 2.9 0.5 12.6 Hamblin Sage Lot Great Pond Pond Pond 6.3 Eel Pond Capitalizing on Coastal Blue Carbon Conference | May 12-13, 2015 22
Nitrogen isotopes indicate anthropogenic additions are increasing across the salt marshes. 5 d 15N organic matter 1950-present 4 R² = 0.66 3 2 1 0 0 5 10 15 Nitrogen load (g m -2 y -1 ) Capitalizing on Coastal Blue Carbon Conference | May 12-13, 2015 23
There is no difference in carbon burial across the nitrogen gradient within Waquoit Bay. 250 Carbon burial 1950-present (g m -2 y -1 ) 200 150 100 50 High Marsh 0 0 2 4 6 8 10 12 14 Nitrogen load (g m -2 y -1 ) Capitalizing on Coastal Blue Carbon Conference | May 12-13, 2015 24
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