estimating c ritical acid loads across the lower 48 us: opportunities and challenges
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Estimating c ritical acid loads across the lower 48 US: Opportunities and challenges. Steven McNulty USDA Forest Service Southern Research Station Raleigh, NC [email protected]. 3. Discuss why historic definitions of a “healthy” forest may need to change. . - PowerPoint PPT PresentationTRANSCRIPT
Estimating critical acid loads across the lower 48 US: Opportunities and challenges
Steven McNultyUSDA Forest Service
Southern Research Station Raleigh, NC
Three Parts to the Presentation
1.Development of a simple mass balance equation of critical acid loading and exceedances to forest soils across the conterminous US at a 1 km2 resolution
3. Discuss why historic definitions of a “healthy” forest may need to change
2. Assess how a changing climate could impact forest soil critical acid loads
Part 1. Development of a simple mass balance equation of critical acid loading and exceedances to
forest soils across the conterminous US
When pollutant loads exceed the critical load it is considered that there is risk of harmful effects. The excess over the critical load has been termed the exceedance. A larger exceedence is often considered to pose a greater risk of damage.
UK Centre for Ecology and Hydrology
Standard definition of a critical load
A critical load can be defined as a quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge.
Simple Mass Balance Equationfor Forest Soils
CL(S+N) =
BCdep – Cldep + BCw – BCu + Ni +Nu +Nde – ANCle(crit)
BCdep = Base Cation DepositionCldep = Chloride DepositionBCw = Base Cation WeatheringBCu = Base Cation Uptake
Ni = Nitrogen ImmobilizationNu = Nitrogen UptakeNde = Nitrogen DenitrificationANCe(crit) = Acid Neutralizing Capacity
Simple Mass Balance Equationfor Forest Soils
CL(S+N) =
BCdep – Cldep + BCw – BCu + Ni +Nu +Nde – ANCle(crit)
BCdep = Base Cation DepositionCldep = Chloride DepositionBCw = Base Cation WeatheringBCu = Base Cation Uptake
Ni = Nitrogen ImmobilizationNu = Nitrogen UptakeNde = Nitrogen DenitrificationANCe(crit) = Acid Neutralizing Capacity
Data Wet Deposition Ca, Mg, K, Na, Cl, N, SO4,NH4,NO3
– Eastern US Grimms and Lynch, 2003 Incorporates elevation into calculation ~300 m2 resolution
– Western US USGS NADP/NTN 6.25 km2 resolution
Climate– Spatial Climate Analysis Service Prism– Temperature, Precipitation– 4 km2 and 16 km2 resolution
Data
National Forest Cover Dataset– USGS/USFS – 25 tree classes– 1 km2 resolution
Soil– Miller and White, 1998– Soil fraction, depth to bedrock, soil unit– 1 km2 resolution
Data
Resolution– 1 km2 across all forested soils
Temporal Extent– Average 1994 - 2000
Spatial Extent– Conterminous United States
• BC = Ca + K + Mg + Na
eq/ha600 - 728
400 - 600
200 - 400
100 - 200
50 - 100
< 50
Base Cation Wet DepositionAverage: 1994 - 2000
Data Source:USGS NADP/NTNGrimms and Lynch, 2003
eq/ha400 - 555
200 - 400
100 - 200
50 - 100
< 50
Chloride Wet DepositionAverage: 1994 - 2000
Data Source:USGS NADP/NTNGrimms and Lynch, 2003
Mean Depth to Bedrock
meter0 - 0.34
0.35 - 0.7
0.71 - 1.03
1.04 - 1.34
1.35 - 1.52
No Bedrock Detected
Caution:"Many STATSGO component table entries for depth to bedrock used 60 inches (1.52 m) to indicate that bedrock was not encountered within this distance of the surface. As a result, the mean depth to bedrock values in this dataset should be used primarily to identify mapunits in which bedrock may be enountered at depths shallower than 1.52 m" (Miller and White, 1998)
BC = Ca + K + Mg + Na
eq/ha/yr3,000 - 3,739
2,000 - 3,000
1,000 - 2,000
27 - 1,000
Base Cation WeatheringSoil Type Texture Method
Data Source:SASC ClimateSoil Data, Miller and White, 1998
BC = Ca + K + Mg
eq/ha/yr252
613
Base Cation Uptake
Data Source:Hall et al., 1998
eq/ha/yr 278
279
Nitrogen Uptake
Data Source:Hall et al., 1998
eq/ha/yr-250 - 0
-500 - -250
-1000 - -500
-2000 - -1,000
-3,664 - -2,000
Acid Neutralizing Compacity
Data Source:USGS NADPGimms and Lynch, 1998USGS/USFS Forest Type
Acid Neutralizing Capacity
eq/ha600 - 1,388
400 - 600
200 - 400
100 - 200
50 - 100
< 50
Sulfur + Nitrogen Wet DepositionAverage: 1994 - 2000
Data Source:USGS NADPGimms and Lynch, 1998
Estimated Forest Soil Critical Acid Load
Estimated Areas of Forest Soil in Exceedence of the Critical Acid Load
McNulty, Steven G.; Cohen, Erika C.; Moore Myers, Jennifer A.; Sullivan, Timothy J.; and Li, Harbin. 2007. Estimates of critical acid loads and exceedences for forest soils across the conterminous United States. Environmental Pollution 149: 281-292
For more details on this study see
Define environmental conditions impacting forest soil critical acid loads that will likely change with climate
Assess the directions an magnitude of change
Recalculate critical acid loads based on updatedparameters
Part 2. Climate change Impacts on forest soil critical acid loads
Simple Mass Balance Equationfor Forest Soils
CL(S+N) =
BCdep – Cldep + BCw – BCu + Ni +Nu +Nde – ANCle(crit)
BCdep = Base Cation DepositionCldep = Chloride DepositionBCw = Base Cation WeatheringBCu = Base Cation Uptake
Ni = Nitrogen ImmobilizationNu = Nitrogen UptakeNde = Nitrogen DenitrificationANCe(crit) = Acid Neutralizing Capacity
Climate change factors
Base cation weathering - as air temperature increases, BCW will increase(increasing the CAL)
Nitrogen uptake – as air temperature increases, productivity increases and nitrogen uptake will increase (increasing the CAL)
Acid Neutralizing capacity (2 components)- as air temperature increases, productivity increases and base cationuptake increases (reducing ANC the CAL)
- as air temperature increases, forest evaportanspiration increases and runoff decreases (reducing ANC and reducing CAL)
Gross ecosystem productivity change
ImplicationsChanging climate could signficantly impact the amount of forest soilIn exceedance of the critical acid load
- total forest area in exceedance could decrease by 6%
However, most of the exceedance occurs in New England whereThe impacts of climate change will be felt the most.
- Therefore, the amount of area in the highest catogory of Exceedance (i.e. 750 eq/ha/yr) could decrease by over 20%
HOWEVER!Before we all go rushing out turn up our thermastats and purchaseCadillacs to do our part to contribute to global warming, we should listen to the last part of the talk....
Part 3. Beyond altering the forest soil critical acid loading on a forest, can climate change
Impact how healthy forests respond to stress?
A Case Study entitled
“The Rise of the Mediocre Forest”
Picea rubens (red spruce) mortality near Asheville, NC
The loss of the red spruce in the southern Appalachian Mountains
Western NC experienced a moderate three year droughtfrom 1999-2002. In 2001, red spruce (Picea rubens) treesbegan to die in large numbers in and around Mt. MitchellNC, USA. The initial evidence suggested that the affectedtrees were killed by the southern pine beetle (SPB). This insect species is not normally successful at colonizing these tree species. Subsequent investigations revealed an interesting pattern where trees died or survived theSPB attack.
Background
12.0
12.5
13.0
13.5
14.0
14.5
1996-2000
1991-1995
1986-1990
1981-1985
1976-1980
1971-1975
1966-1970
1961-1965
1956-1960
1951-1955
Periods
Mea
n A
ir Te
mpe
ratu
re
o C
200
300
400
500
600
700
800
Mea
n P
reci
pita
tion
(mm
)
Mean Air TemperaturePrecipitation
Five Year Averaged Climate (1951 – 2001), Mt. Mitchell, NC, USA
Sampling damaged Southern Appalachian red spruce stand
0
4
8
12
16
20
1996-2000
1991-1995
1986-1990
1981-1985
1976-1980
1971-1975
1966-1970
1961-1965
1956-1960
1951-1955
Years
Bas
al A
rea
Gro
wth
(c
m2/
5 ye
ar a
vera
ge)Dead
Live
Drought Stress
Drought, Temperature, Insect, & N deposition
Stresses
1.0
1.1
1.2
1.3
1.4
Folia
r N C
once
ntra
tion
(%)
Dead Plots
Live Plots
0.04
0.06
0.08
0.1
0.12
Folia
r Mg:
N R
atio
Foliar N Foliar Mg:N
Residual Tree Foliar Chemistry
y = 1.67x - 23.0R2 = 0.84
y = 3.70x - 48.9R2 = 0.75
0
4
8
12
16
20
15.5 16 16.5 17 17.5 18 18.5 19Wood tissue Δ C12/13(‰)
Bas
al A
rea
Tree
Gro
wth
(c
m2 / 5
year
ave
rage
)
Dead
Live
Basal Area Growth as a Tree Water Stress
Questions
What conditions allowed the red spruce to be colonized?
Why did only the larger, more vigorous trees on some plots die?
• The ratio between above ground growth (i.e., stem wood, branches and foliage) and below ground growth (i.e. coarse and fine roots) increased
Hypothesis for mortality
• The area in and around Asheville received elevated
nitrogen deposition, but these levels are below that considered critical acid load
• The increased level of nitrogen inputs likely had a
fertilization impact
The lack of oleoresin (especially in large trees) allowed for the colonization of and large scale forest mortality witnessed during that time.
Hypothesis for mortality (cont.)
• The drought conditions reduced available water, carbohydrate reserves for the production of secondary carbon compounds such as oleoresin.
• The larger more vigorously growing trees had a higher AG/BG ratio than the small trees
Stress interactions
Forest Mortality
Elevated nitrogen depositionCausing altered tree
physiology
Climate ChangeReducing carbohydrate
reserves
InsectsCausing tree mortality through
colonization and tree girdling by larval feeding
ConclusionsAs the climate warmers, insects become more active
(no big surprise)
As the climate warms, trees use more water and the potential for soil drying and tree desiccation increases
Interactions between air pollutants and climate change can exacerbate the insect stress by altering the tree physiology and morphology
Insect damage is likely to occur in new ways and more frequently in the future
If any one of the three environmental stresses were removed, the mortality
would not likely have occurred
How a different critical nitrogen load could be determined within the same ecosystem
N dep = 10 kg/ha/yr
N leaching = 0Mortality = 0%
Critical N > 10 kgLoad
N dep = 10 kg/ha/yr
N leaching = 1Mortality = 5%
Critical = 10 kgLoad
+ 3 yr Drought Stress
N dep = 10 kg/ha/yr
N leaching = 10Mortality = 10%
Critical = 8 kgLoad
+ 3 yr Drought Stress+ insects
N dep = 10 kg/ha/yr
N leaching = 25Mortality = 100%
Critical < 5 kgLoad
+ 3 yr Drought Stress+ insects+ temperature
McNulty, Steven G., and Johnny Boggs. 2009. A Conceptual Framework for Redefining Forest Soil Critical Acid Loads under a Changing Climate. Environmental Pollution (In Press).
For more details on this study see
SolutionsCoarse scale application of simple mass balance equation predictions of forest soil critical acid loading can provide some guidance on potential areas of forest acid load exceedence, continue to use them
Climate change will likely reduce the red spruce growth and acid uptake. Account for these reduction by reducing the ecosystems critical acid load level.