Soil Temperature Damping Depth in Boreal Plain Forest Stands and Clear Cuts: Comparison of Measured Depths versus Predicted based upon SWAT Algorithms

Transcription

1 Soil Temperature Damping Depth in Boreal Plain Forest Stands and Clear Cuts: Comparison of Measured Depths versus Predicted based upon SWAT Algorithms G. Putz and B.M. Watson Civil & Geological Engineering, University of Saskatchewan Saskatoon, Saskatchewan, Canada J.A. Bélanger Faculty of Engineering, Lakehead University Thunder Bay, Ontario, Canada E.E. Prepas Faculty of Forestry & the Forest Environment Lakehead University, Thunder Bay

2 FORWARD Project: Boreal Plain Watersheds 14 long term forest watersheds 6 reference, 3 burned, 5 harvested 2 Large Scale (129 & 247 km 2 ) 12 Small Scale (2.6 to 15.6 km 2 ) 6 additional MPB watersheds Boreal Plain

3 Boreal Plain forest Upland dominated by lodgepole pine, trembling aspen, white spruce and balsam poplar Lowlands dominated by black spruce and tamarack 325 to 625 mm ppt annually 1/4 as snow, spring melt Sporadic storms May to Sept. Predominantly deep clay till soils (luvisols) Wetlands and organic soils in low areas (histosols)

4 Watershed Harvest Winter of 2003/2004

5 Soil Temperature and Water Content Monitoring 18 Automated Sites (2005/06) 3 Upland Harvest Sites 3 Upland Wildfire Sites 3 Upland Deciduous Sites 3 Upland Conifer Sites 3 Lowland Shallow Peat Sites 3 Lowland Deep Peat Site Continuous Monitoring +2000, 0, 100, 300, 500, 1000, 2000 & 3000 mm Water 100, 500 & 1000 mm

6 Soil Temperature versus Time and Depth 20 Harvested Site - H1 4 years post harvest 15 Soil Temperature ( o C ) mm 100 mm 300 mm 1000 mm 2000 mm 3000 mm mm labels indicate depth in soil profile Jan Feb Apr May Jul Sep Oct Dec-08 Date

7 Soil Water Content versus Time and Depth 60% Harvested Site - H1 4 years post harvest 50% Soil Water Content (%) 40% 30% 20% 1000 mm 500 mm 10% 100 mm labels indicate depth in soil profile 0% 01-Jan Feb Apr May Jul Sep Oct Dec-08 Date

8 Soil Temperature Equation in SWAT T soil z d T z, d df T T 1, n soil n 1 AAir ssurf T ssurf T soil (z, d n ) T soil (z, d n-1 ) λ df T AAir T ssurf soil temperature at a specific depth z (in mm) on the current day previous day s soil temperature lag coefficient depth factor average annual air temperature based on long-term data soil surface temperature on the current day All temperatures in o C

9 Damping Factor and Damping Depth Definition df df zd zd exp zd exp zd zd zd df zd z dd depth factor for a soil layer unitless depth ratio given by z/dd depth at the center of the soil layer damping depth Neitsch et al. (2005) define dd as the depth in the soil profile at which the soil temperature is within 5% of T AAir.

10 Damping Depth Equations dd max b 686exp SW dd dd b max b z expln tot 500 dd max b 1 1 dd max maximum damping depth. b bulk density of the soil in Mg/m 3 scaling factor based upon the water content of the soil SW/z tot water content in the soil profile in mm/mm SW water in the soil profile expressed as depth in mm depth of the soil profile in mm. z tot 2

11 Air and Soil Temperature Range H3, Harvested Site - H Air 2 metres -1.0 Depth (m) Minimums Averages Maximums Temperature ( o C )

12 Air and Soil Temperature Range C2-3.0 Conifer Site - C2-2.0 Air Temperature Range -1.0 Depth (m) Minimums Averages Maximums Min 2006Max 2006Avg 2006 Air 2007Min 2007Max 2007Avg 2007 Air Soil Temperature Range 2008Min 2008Max 2008Avg 2008 Air 2009Min 2009Max 2009Avg 2009 Air Temperature ( o C )

13 Revised Damping Depth Definition ground surface average temperature Avg. air temp. 20 o C Within 1 o C Depth minimum temperature maximum temperature Damping Depth Avg. air temp. 2 o C Within 0.1 o C Temperature within 5% of avg. air temperature Propose range of 2 o C to define the damping depth Nominally ±1 o C

14 Determination of Largest Damping Depth Harvested Site - H Depth, m m depth for 2 o C range in temperature y = e x R 2 = Temperature Range in Active Zone ( o C )

15 Largest Damping Depth and Average Soil Water Content Conifer Site - C2 Deciduous Site - D1 Deciduous Site - D3 avg. air temp. dd 1m avg. air temp. dd 1m avg. air temp. dd 1m Year o C m % o C m % o C m % % % % % % % % % % % % % avg % % % range % % %

16 Damping Depth vs. Soil Moisture Content Damping Depth (mm) Bulk Density = 1.45 Mg/m 3 Base Depth = 7000 mm Bulk Density = 1.45 Mg/m 3 Base Depth = 1000 mm Range in damping depth dd Range in damping depth max 2500b Base Depth 686exp SW dd dd max Range in soil moisture b b z tot 500 expln dd max b % 10% 20% 30% 40% 50% 60% SW/z tot (soil moisture content)

17 Comparison of Largest Damping Depths 6.0 (3.87 to 5.67 m) Range based upon modified Eq.5 with constant = 7000 mm Largest Annual Damping Depth (m) (1.85 to 2.35 m) Range based upon original Eq. 5 with constant = 1000 mm Conifer C2 Deciduous D1 Deciduous D3 Harvest H3 Harvest H Site Type

18 Predicted vs. Observed Soil Temp., 0.1 m, H Harvested Site - H3 0.1 m depth 15 Soil Temperature ( o C) Observed Observed Soil Temp Original dd SWAT Modified dd SWAT Original Modified /Aug/06 27/Nov/06 7/Mar/07 15/Jun/07 23/Sep/07 1/Jan/08 10/Apr/08 19/Jul/08 27/Oct/08 Date

19 Predicted vs. Observed Soil Temp., 1.0 m, H Harvested Site - H3 1.0 m depth Observed Soil Temp Original SWAT Modified SWAT Soil Temperature ( o C) Original Observed Modified /Aug/06 27/Nov/06 7/Mar/07 15/Jun/07 23/Sep/07 1/Jan/08 10/Apr/08 19/Jul/08 27/Oct/08 Date

20 Conclusions & Recommendations Damping depth calculation modifications are required for Boreal forest conditions increasing the base depth constant improves the damping depth representation a function to modify the base depth constant with latitude or annual average temperature is suggested The damping depth definition should be modified abandon the % of T AAir definition adopt an absolute definition (eg. 2 o C range in temp.) Improved damping depth representation provides significant effect upon soil temp. calc deep in soil profife little effect upon near surface temperatures

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22 Additional slides not used in presentation!

23 Toby & Pierre pre-harvest Photo credit: Tom Plouffe

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25 Watershed Harvest Winter of 2003/2004

26 Examples of vegetation 3 rd summer post harvest

27 Upper elevations 7 watersheds 198 sensors (702 tiny wires) = steady maintenance

28 Harvested, Conifer and Deciduous Sites Site ID Landcover Species Cover (approx %)* Canopy Cover (%) Elevation (m) H1 Harvested n/a H2 Harvested n/a H3 Harvested n/a C1 Conifer PL(90) AW(10) C2 Conifer PL(90) AW(10) C3 Conifer PL(90) AW(10) D1 Deciduous AW(70) SB(20) PL(10) D2 Deciduous AW(60) SB(20) PL(20) D3 Deciduous AW(90) PL(10) * PL: lodgepole pine, AW: trembling aspen, SB: black spruce.

29 Largest Damping Depth and Average Soil Water Content Harvest Site - H1 Harvest Site - H3 avg. air temp. dd 1m avg. air temp. dd 1m Year o C m % o C m % % % % % % avg % % range % %