Soil denitrification

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1 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 Uplands: nitrification (hardwoods) Lowlands: denitrification N 2 O DTW N 2 O N, S, Ca, Mg, K DON, DOC, S, Ca, Mg, K DON, DOC, S, Ca, Mg, K North American Forest Soil Conference, Blacksburg, Virginia, June 2008

Soil denitrification: forest ecosysytem context Atmospheric input for wet and dry deposition: H +, NH 4+, NO 3-, SO 2-4, Ca 2+, Mg 2+, K +, Na +, Cl - Exports: Forest Harvesting / Fires

2 Soil denitrification: forest ecosysytem context Atmospheric input for wet and dry deposition: H +, NH 4+, NO 3-, SO 2-4, Ca 2+, Mg 2+, K +, Na +, Cl - Exports: Forest Harvesting / Fires Denitrification increases with increasing soil wetness Litter fall (S, N, Ca, Mg, K) Soil weathering Ca, Mg, K, P & acid buffering NO 3 - Uptake (NH 4+, NO 3-, Ca 2+, Mg 2+, K + ) Soil leaching: SO 2-4, NO 3-, Ca 2+, Mg 2+, K +, Al 3+, Na +, Cl -, DOC, DON

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

4 Modeling soil moisture (pore space fraction) and denitrification (kg / ha day) Atmospheric deposition NH4, NO3, H, S, Ca, Mg, K Uplands: nitrification (hardwoods) Lowlands: denitrification N 2 O DTW N 2 O N, S, Ca, Mg, K DON, DOC, S, Ca, Mg, K DON, DOC, S, Ca, Mg, K Soil Moisture index (S, pore space fraction) f(daily weather, topography, soil permeability, AET) Denitrification (eq ha -1 yr -1 ) f (N loads,s, T, ph); Heinen, 2006

5 N 2 O DEM surface N 2 O Depth to water, DTW 0 (cartographic index) N 2 O Mapped Streams Soil moisture ( pore space fraction) 1- (1- S weather ridge 1- exp(-k DTW) )[ 1- exp(-k DTW ridge ] ) p

6 Soil moisture (% pore space) 100 Grassland sandy loam Dobbie & Smith 50 Field Capacity Depth to water table (cm) Soil moisture ( pore space fraction) 1- (1- S weather ridge )[ 1- exp(-1.77 DTW) 1- exp(-1.77 DTW ridge ] ) 2

7 log 10 denitrification (g-n ha -1 day-1 ) Dobbie and Smith (2006) 5 D pot Meadow: y = (1- S/100) Field: y = (1- S/100) Soil moisture (S, % pore space) 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.

8 4 log 10 (N 2 O flux, g ha -1 day-1) Grassland sandy loam Dobbie & Smith 3 2 log 10 [D a (eq ha -1 yr -1 )] Dp - w (1- S) Depth to water table (cm) Denitrification decreases rapidly with increasing depth to water, and decreasing soil moisture content

9 Soil denitrification (g/ha day): generalized model D a, uplands min(d pot, N dep N fix N uptake N imm ) f N f S f T D [NO3 - N f a, wet areas and flow channels N min(d stream ] pot (N N N dep N, N dep dep fix dep N N N N fix fix fix uptake N N N N uptake uptake uptake imm N N N - D - D stream discharge imm imm imm a,uplands ; ExpertN a,uplands ) D catchment area above stream point wet area above stream point a, wet areas and flow channels ) f N f S f T f S exp[-w(1- S)]; derived from Dobbie and Smith, 2006 f T Ea exp[- R 1 ( T 1 - )]; Arrhenius equation 288

10 D pot (g NO2-N / ha day), from Heinen, D pot Sand w (%) 825 OM w (%), r Peat Sand Loam Clay loam Best-fitted D pot (g NO2-N / ha day) Denitrification potential increases with increasing soil permeability

11 DEM

12 DEM + hydrographic features

13 Burn hydrographic features into DEM

14 Reintroduce hydrographic features

15 Determine flow directions and accumulations

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

17 Wet-areas mapping, at 10 m resolution: 80-90% field conformance Blue: flow channels, previously mapped Grey to green: water 0 to 1 m below soil surface

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

19 wet areas mapping for enhanced visualization

20 50 Denitrification rate (kg 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 RF RM RC UF UM UC Site Category Texture classes F fine M medium C - coarse N max NADP

21 Modeling potential denitrification rates, at high (10 m) resolution High - resolution mapping of flow channels (blue) Same area, with depthto-water overlay 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

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

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

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

26 Economic Implications for Nova Scotia considering the replenishment of cumulative nutrient depletions and deficits through fertilization and/or liming Fertilization costs ($/ton) Product Application Transportation Ca Mg K N

27 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

28 Base cation depletion = loss of exchangeable bases, from rooting zone Nutrient deficits = nutrient export site-level inputs (atm. + soil) Deficit / rotation = 0 Exchangeable bases Deficit / rotation > 0 Depletion >0 Time

29 CL acidification calculations CL soil acidification = BC dep + BC weathering BC uptake + N uptake + N immobilization + N denitrification ANC leach (crit) Exceedance soil acidification = N dep + S dep CL soil acidification N immobilization = 0 N denitrification = f (N dep, texture, drainage, topography, weather)

30 Data Layers needed Atmospheric deposition H +, NH 4+, NO 3-, SO 4 2-, Ca 2+, Mg 2+, K +, Na +, Cl - Ecological Land Classification (DNR) Dominant Species: optimal MAI (tons / ha year) wood density (ton of biomass /m 3 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

31 NS Nutrient Deficit Costs (harvest only) NS Depletion Costs (harvest + acid leach) $4,000,000 Decreased atm. deposition $3,000,000 $2,000,000 $1,000,000 $0

32 Outlook 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

33 Notes Above calculations and maps are approximate based 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, foliage wood density, biomass fractions, nutrient concentrations Develop operational performance tests

34 Acknowledgements Environment Canada, Acid Rain Program (T. Clair, Y. Bourassa) NEG-ECP ENFOR (CFS) ARNEWS (CFS) Nexfor-Bowater Forest Watershed Centre (UNB) Bowater Fraser Papers Inc. John-Paul Arp (MCSc) Vincent Balland (MScF) NEG-ECP Acid Rain Mapping Group Esp. Rock Ouimet, Eric Miller

Soil Chemistry. Key Terms.

Soil Chemistry. Key Terms. Soil Chemistry Key Terms Key Terms in Soil Chemistry Buffering capacity - this is the soil's ability to resist changes in soil ph. Soils with a high buffering capacity require a great deal of amendment