Topic 5 Biogeochemical Cycling and Water Quality

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Topic 5 Biogeochemical Cycling and Water Quality

• Overview
• Geochemical Nutrient Cycling
• Biological Nutrient Cycling
• Major Biogeochemical Cycles
• Forest Management, Biogeochemistry, and Water
  Quality

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Reading so far

• Valett et al 2002
• Binkley et al 1999
• Lowrance et al 1997
• Wigington et al 2005
• Willard et al 2005
• Grace 2005

Appalachian Hardwoods
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I. Overview

• Ebermayer 1876 Bavarian Forests
• Litterfall and nutrient return
• Understanding ecosystem function depends on
  understanding flow of elements
• Water as bloodstream of ecosystem

N
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• Two major components of biogeochemical cycles
• External geochemical cycles
• Import/export of nutrients across
  ecosystem/catchment boundaries
• Internal biological cycles
• Exchange of nutrients within plant-soil system

Abundant Downed Wood
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II. Geochemical Cycling

• Inputs
• Atmospheric (wet, dry)
• NO, N2O to NO3 via lightning
• Air pollution (NO, NO2, N2O) 5-30 kgha-1yr-1
• Biological N fixation
• Nonsymbiotic
• Symbiotic
• Weathering of parent rock (P cations)
• lossweathering - (atm input accum in veg/soil)
• Fertilizer
• Can accelerate cycling

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Nutrient Inputs
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Nutrient Outputs

• Leaching and surface runoff
• Dissolved, colloidal, suspended
• Harvesting
• 5-10 kg/ha/yr N, Ca, K equiv. loss (taken at
  once)
• 1 kg/ha/yr P, Mg equiv. loss
• Soil disturbance accelerates decomposition
• Potential leaching/runoff loss
• Immobilization via microbes, clay
• Importance of tree uptake

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Nutrient Mobility in Soil

• Mobile
• NO3-, S, Na, Cl, B
• Immobile
• K, Ca, Mg, NH4
• Very Immobile
• P, Mo, Mn, Fe, Cu, Zn

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• Volatile Losses
• N loss
• Ammonia volatilization at high pH
• buthigh pH increases N mineralization
• Denitrification
• Fire (20-80 kg/ha prescribed burn)

Greater losses with wildfires
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Nutrient Balance

• Lossesweathering inputs
• Nutrient pools increase as succession progresses
  (ecosystem develops)
• Nutrient pools equilibrate with maturing
  ecosystem
• Nutrient pools altered by harvesting, fire,
  fertilization-creates potential for imbalance

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III. Biological Nutrient Cycling

• Nutrient transfer forest floor, plant, animal
  communities
• Nutrient transfer within tree

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Nutrient Uptake

• Most nutrients returned to forest floor annually
  or translocated within tree
• Relatively small amount retained each year in
  biomass accretion
• Factors
• Soil type
• Stage of stand development
• Earlyincreasing uptake
• Canopy closureconstant uptake

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Nutrient Retention

• Net Annual Nutrient Retention
• Total Annual Uptake-Total Annual Returned to Soil
  (dead roots, litterfall, leaching)

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Nutrient Retention

• Increases with increasing biomass
• Successional process
• Initial nutrient transfer from mineral soil
• Early growthretention in foliage
• Increasing retention in increasing biomass
• Late growthretention in wood
• Increasing retention in dead organic matter

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Nutrient Retention

• Management factors
• Species selection
• Loblolly-peak foliage retentionage 15
• Doug-fir-peak foliage retentionage 70-80
• Fertilization
• Density management/thinning

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Nutrient Returns

• Most of uptake becomes litterfall, canopy wash
  (throughfallstemflow)
• Larger litter returnshorter residence time in
  forest floor (higher decomp, k)
• Accumulation of nutrients in forest floor with
  stand age

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Internal Transfers

• Seasonal variation of nutrient composition of
  plant parts
• Translocation from senescent to active portions
  of tree
• Nutrient budgetsdiagnostic of ecosystem status

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Internal Transfers-Mobility in Plant

• Mobile
• N, P, K, Na, Mg, Cl, (S)
• Immobile
• Fe, Mn, Zn, Cu, Mo
• Very Immobile
• Ca, B

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IV. Major Biogeochemical Cycles

• Carbon
• Nitrogen
• Phosphorus
• Potassium, Calcium, Magnesium

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Carbon
Fixation via photosynthesis
Atm POOL
Biomass POOL
Respiration
Respiration
Decomposition
Soil POOL
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Carbon turnover (decomp)

• C turnover 2-100 yrs
• Exponential decay
• C chemistry (quality)
• 50,000 kg C5,000 kg N (CN 101)
• k.01 50 kg N released/yr
• k.02 100 kg N released/yr

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Carbon leaching
CO2 dissolves in H2O CO2 H2O -gt H2CO3
Carbonic Acid H2CO3 dissociates H2CO3 -gt
HCO3- H
replaces leached cations soil weathering lowers
pH
bicarbonate
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Foresters and Carbon

• Manipulate C cycle for tree growth
• Accumulate C in wood and fiber pools
• Uptake of C via photosynthesis responsive to
  nutrient water additions
• Each N atom in foliage can yield 50-100 C atoms
  fixed by photosynthesis/yr
• 500-1000 kg H2O to fix 1 kg C

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Nitrogen
Fixation
Volatilization
Uptake
Denitrification
Leaching
Min/Immob
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Nitrogen

• Most often limiting nutrient
• Symbiotic N fixation plant provides energy via
  carbos. N2 reduced to NH3 (proteins)
• N2 8H 8e- -gt 2NH3 H2
• NH3 organic acids -gt amino acids-gtproteins

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N Mineralization/Immobilization
organic N
inorganic N
Mineralization
Nitrosomonas
Nitrobacter

• R-NH2 lt-gt R-OH NH4 lt-gt NO2- 4H lt-gt NO3-

/- 2H2O
/- O2
/- ½ O2
Immobilization
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Denitrification (NO3 reduction)
-2O
-2O
-O
-O
2NO3- -gt 2NO2- -gt 2NO -gt N2O -gt N2
nitrate
nitrite
nitric oxide
nitrous oxide
dinitrogen gas

• Conditions
• NO3
• Anaerobic
• Carbon source
• Warm

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Phosphorus
Uptake
Mycorrhizae
Dissolution
Dissolution
Fixation
Organic POOL
Soluble POOL
Mineralization
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Forms of phosphate

• PO43-
• HPO42-
• H2PO4- (most common)
• Depends on soil pH

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P form depends on pH
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More on P

• P losses minimal
• P inputs minimal (.1-.5 kg P/ha/yr)
• No gaseous or leaching losses
• Loss associated w erosion

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K, Ca, Mg

• Atm weathering inputs
• 1-30 kg/ha/yr
• Transformation
• Mineral weathering litter decomp release K
  Ca2 Mg2
• Loss via leaching

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V. Forest Mgt, Biogeochemistry, Water Quality

• Binkley Brown 1993 gt40 studies
• PO4 few problems (fire)
• NO3-N 70 studies lt.5 mg/L
• 45 mg NO3/L 10 mg NO3-N/L

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Forest Harvesting vs NO3-N
Hubbard Brook
Coweeta
Binkley Brown 1993
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Forest fertilization vs peak NO3-N
Binkley Brown 1993
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Fertilizer vs. Stream NO3-N
Binkley et al. 1999
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Fertilizer vs. soil solution NO3-N
Binkley et al. 1999
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Shepard (1994)

• 9 wetland studies
• Harvesting, site prep, bedding, planting,
  drainage, fertilization
• Drainage SC hdwd increased NO3
• Drainage no effect UP MI
• NC bedding, fert, drainage, thinning fert
  increased N P

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Weekly solute in drainage6-yr-old loblolly
fertilized
Shepard 1994
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Streamwater quality following harvesting, site
prep, reforestation w slash pine in FL.
Shepard 1994
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Context for effect?
Disturbance
Improved
Unchanged
Soil or Water Quality Indicator
Recovered
Degraded
Time