Soil denitrification P.M. Murphy, M. Castonguay, Jae Ogilvie, P. Arp, Faculty of Forestry & Environmental Management

Jag Bhatti, Canadian Forest Service, Edmonton, Alberta

Atmospheric deposition

NH4, NO3, H, S, Ca, Mg, K

N, S, Ca, Mg, K

Uplands: nitrification (hardwoods) Lowlands: denitrification

DON, DOC, S, Ca, Mg, K DON, DOC, S, Ca, Mg, K

N2ON2O

DTW

North American Forest Soil Conference, Blacksburg, Virginia, 20-22 June 2008

Soil denitrification: forest ecosysytem context

Soil leaching: SO42-, NO3

-, Ca 2+ , Mg 2+, K+, Al3+, Na+, Cl-, + , N + -

Atmospheric input for wet and dry deposition: H+, NH4

+, NO3-, SO4

2-, Ca2+ , Mg2+, K+, Na+, Cl-

Exports:

Soil weatheringCa, Mg, K, P

& acid buffering

Denitrificationincreases with

increasing soil wetness

Litter fall (S, N, Ca, Mg, K)

+ -

Forest Harvesting / Fires

Soil weatheringCa, Mg, K, P

& acid buffering Uptake (NH4+, NO3

-, Ca2+ , Mg2+, K+) Uptake (NH4+, NO3

-, Ca2+ , Mg2+, K+)

Litter fall (S, N, Ca, Mg, K)

, DOC, DON

NO3-

N application / denitrification rates (g / ha day): note relationship between de-nitrification and with soil wetness

Denitrification rates (g / ha day)

Modeling soil moisture (pore space fraction) and denitrification (kg / ha day)

2006 Heinen, pH); T, S, loads, (N f )yr ha (eqation Denitrific -1-1

AET) ty,permeabili soil y, topographather,f(daily we fraction) space pore (S,index Moisture Soil

Atmospheric deposition

NH4, NO3, H, S, Ca, Mg, K

N, S, Ca, Mg, K

Uplands: nitrification (hardwoods) Lowlands: denitrification

DON, DOC, S, Ca, Mg, K DON, DOC, S, Ca, Mg, K

N2ON2O

DTW

Depth to water, DTW0(cartographic index)

DEM surface

Mapped Streams

N2ON2O

N2O

p

ridge

weatherridge

])DTWexp(-k -1

DTW)exp(-k -1)[S-(1-1 fraction) space pore ( moisture Soil

0 20 40 60 80 1000

50

100

Depth to water table (cm)

Soil moisture (% pore space)

2

ridge

weatherridge

])DTW exp(-1.77-1

DTW) exp(-1.77-1)[S-(1-1 fraction) space pore ( moisture Soil

Grasslandsandy loamDobbie & Smith

Field Capacity

0 20 40 60 80 100-1

1

3

5

Soil moisture (S, % pore space)

log10denitrification (g-N ha-1 day-1 )

Meadow: y = 4.32 + 5.33 (1- S/100)

Field: y = 4.32 + 7.47(1- S/100)

Dobbie and Smith (2006)

Slope decreases with earlier onset of anaerobic condition, or with increasing biological oxygen demand within the soil.

Measurement variations and associated uncertainties are high: about one order of magnitude.

Dpot

log10(N2O flux, g ha-1 day-1)

0 20 40 60 80 100-1

0

1

2

3

4

Depth to water table (cm)

S)-(1 w- Dp )]yr ha (eq [Dlog -1-1a10

Grasslandsandy loamDobbie & Smith

Denitrification decreases rapidly with increasing depth to water , and decreasing soil moisture content

equation Arrhenius )]; 2881-

T1(

REa[- exp f

2006 Smith, and Dobbie from derived S)];-exp[-w(1 f

ExpertN ;NNNN290014

NNNNf

discharge stream

)DD -NNN(N]N-[NO3

f f f point stream above areawet

point stream above areacatchment )D -NNNN ,min(D

D

f f f )NNNN ,min(D D

T

S

immuptakefixdep

immuptakefixdepN

channels flow and areas wet a,uplandsa,immuptakefixdepstream

TSNuplandsa,immuptakefixdeppot

channels flow and areas wet a,

TSNimmuptakefixdeppotuplands a,

Soil denitrification (g/ha day): generalized model

0

10000

20000

30000

40000

0 10000 20000 30000 40000

Dpot (g NO2-N / ha day), from Heinen, 2006

Best-fitted Dpot (g NO2-N / ha day)

0.94r (%),OM 825(%)Sand 100.9D 2wwpot

Peat

Sand

LoamClay loam

Denitrification potential increases with increasing soil permeability

DEM

DEM + hydrographic

features

“Burn” hydrographic features into DEM

Reintroduce hydrographic features

Determine flow directions and accumulations

Determine depth-to-water next to all open water features

Wet-areas mapping, at 10 m

resolution:

80-90% field

conformance

Blue:

flow channels,previouslymapped

Grey to green:

water 0 to 1 mbelow

soil surface

…And Using it for Wet-Areas Coastal Mapping…Mapping extent of costal wetland features – Point Comeau, NB

…wet areas mapping for enhanced visualization …

0

5

10

15

20

25

30

35

40

45

50

RF RM RC UF UM UCSite Category

Den

itrifi

catio

n ra

te (k

g N

/ ha/

yr)

Potential denitrification rates in wet areas (RF, RM, RC)and even on fine-textured uplands (RF, RM, RC)

far exceed usual atmospheric N deposition rates (<1 to 8 kg N / ha year) for North America

Texture classes

F – fineM – mediumC - coarse

Nmax NADP

Depth to water (m)

Estimated denitrification rate (kg N ha / year)

for the same area, based on depth- to-water and corresponding literature-derived model

High- resolution mapping of flow channels (blue)

Same area, with depth-to-water overlay

-High-(blue

-

Modeling potential denitrification rates, at high (10 m) resolution

Upland soil acidification exceedances, eq / ha year related to BEC classes

Upland and wetland soil acidification exceedances, eq / ha year accounting for denitrification in wet areas

Upland and wetland soil acidification exceedances, eq / ha year accounting for denitrifcation in wet areas

…considering the replenishment of cumulative nutrient depletions and deficits through fertilization and/or liming…

Economic Implications for Nova Scotia

Product Application TransportationCa 125 45 45

Mg 175 45 45K 455 45 45N 639 45 45

Fertilization costs ($/ton)

Critical soil acidification load model (steady state):

net acid in = net acid out,

calculable from known S, N, Ca, Mg, and K inputs and exports

Upland areas are more sensitive to soil acidification then wet areas

Exceedance (in equivalents / ha year) =S+N deposition – base cation input – N uptake and return

Base cation depletion = loss of exchangeable bases, from rooting zone

Nutrient deficits =

Exchangeable bases

Time

Depletion>0

Deficit / rotation > 0

nutrient export – site-level inputs (atm. + soil)

Deficit / rotation = 0

CLsoil acidification = BCdep + BCweathering− BCuptake

+ Nuptake + Nimmobilization + Ndenitrification − ANCleach(crit)

Exceedancesoil acidification = Ndep + Sdep – CLsoil acidification

Nimmobilization = 0

Ndenitrification = f (Ndep, texture, drainage, topography, weather)

CL acidification calculations

Atmospheric deposition H+, NH4

+, NO3-, SO4

2-, Ca2+ , Mg2+, K+, Na+, Cl-

Ecological Land Classification (DNR)

Dominant Species: optimal MAI (tons / ha year)wood density (ton of biomass /m3 of wood) nutrient concentrations (N, Ca, Mg, K, P)in: foliage, branches, stem wood, bark

Soil type (CANSIS)texture, organic matter, coarse fragments, soil depth, ratio of exchangeable bases

Bedrock type 4 weathering classes: low, intermediate, high, calcareous

Data Layers needed

$0

$1,000,000

$2,000,000

$3,000,000

$4,000,000

NS Depletion Costs (harvest + acid leach)

NS Nutrient Deficit Costs (harvest only)

Decreased atm. deposition

Develop economic implications of N, S, Ca, Mg, K deposition and depletion, in the context of local nutrient supply-demand contexts

Develop model useful for assessing nutrient sustainabilities: uplands, wetlands

Develop model assessing atmospheric deposition and upland-wetland nutrient uptake, exports and losses in relation to water quality issues

Outlook

Above calculations and maps are approximatebased on available and fairly generalized information

For operational use in forestry, need to focus on stand-level MAI expectations

Need to conduct more analyses: wood, bark, branches, foliagewood density, biomass fractions, nutrient concentrations

Develop operational performance tests

Notes

Acknowledgements

Environment Canada, Acid Rain Program (T. Clair, Y. Bourassa)

NEG-ECPENFOR (CFS)

ARNEWS (CFS)Nexfor-Bowater Forest Watershed Centre (UNB)

BowaterFraser Papers Inc.

John-Paul Arp (MCSc)Vincent Balland (MScF)

NEG-ECP Acid Rain Mapping GroupEsp. Rock Ouimet, Eric Miller