Hubbard Brook

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The Northern Hardwood Ecosystem at Hubbard
Brook in Relation to Other Forest Ecosystems in
the World
Hubbard Brook Experimental Forest
Forest and woodland 38 of continental area
11
92
46
34
11
50
68
71
79
100
100
100
100
100
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3,160 hectare reserve located in the White
Mountain National Forest
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Meteorologic input supplies 66 of the annual
sulfur uptake by green plant biomass.
Sulfur balance established by HB ecosystem model
and data gathered by small watershed technique
indicate that substantial amounts of dry
deposition are entering the ecosystem, even
though these watersheds are located more than
100km from major polluting industries or urban
areas.
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Meteorologic input supplies 26 of the annual
nitrogen uptake by green plant biomass.
Sulfur and nitrogen levels have been adjusted to
incorporate net gaseous input and dry deposition
of aerosols, as data has been obtained from an
analysis of the total ecosystem.
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Meteorologic input supplies 6 of the annual
magnesium uptake by green plant biomass.
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Meteorologic input supplies 5 of the annual
sodium uptake by green plant biomass.
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Meteorologic input supplies 4 of the annual
calcium uptake by green plant biomass.
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Meteorologic input supplies 1 of the annual
potassium uptake by green plant biomass.
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Most acidity in the rain and snow is traceable to
sulfur pollution, but during 1964-1974,
increases in the input of acid precipitation seem
to be primarily related to increases in
nitrate resulting from internal combustion
engines.
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Data in Table 24 encompass a wide range in
ecosystem analysis and sophistication. In some
cases these data represent averages of several
watersheds for several years. In others, data
are scanty and are derived from a poorly
defined hydrologic system. These data should be
treated with some caution.
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For some ions, nutrient budget parameters can be
established with only a few years of data (Ca,
Mg, Na), while for other ions (K, Cl, NO3), a
few years would give unreliable results, and
longer studies are necessary.
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Conclusions of Hubbard Brook Ecosystem study

• Chemicals in precipitation are significant
  additions to the nutrient budget.
• In general, there are net losses of calcium,
  magnesium, sodium, and potassium from forest
  ecosystems that must be made up by weathering.
• Geologic substrates play a major role in
  determining the amount and composition of
  chemicals lost in stream water.
• Forest ecosystems in coastal locations or
  otherwise dominated by maritime air masses have
  large inputs of sea salts in precipitation.
• A close correlation between the amount of
  precipitation and the loss of nutrients may apply
  to individual watersheds, but may not apply in
  forest ecosystems with different climates.
• Net loss or gain values for sulfur budgets are
  significantly affected by anthropogenic
  contributions to precipitation (e.g., Hubbard
  Brook)

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Conclusions continued...

• The ecosystem currently acts as a filter for
  atmospheric contaminants,a pollution buffer for
  society likely long-term ecosystem degradation
• Precipitation is first intercepted by forest
  canopy, leaves, and branches then herbaceous
  layer (living material) on the forest floor then
  dead litter, all before it reaches the mineral
  soil.
• Kinetic energy and chemical composition of the
  water may be appreciably altered. Erosion is
  minimized, nutrient flow regulated.
• Northern hardwood ecosystem is very resistant to
  particulate matter erosion. Particulate matter
  erosion is highly dependent on flow rate, as
  opposed to dissolved substance removal.
• Stream water samples obtained according to a
  standard time series may miscalculate the
  concentrations of particulate matter (Fe, P).
• DissolvedParticulate losses is a 51 ratio
• Total losses of dissolved and particulatePrecipit
  ation input is 1.51

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Conclusions concluded

• Three input-output patterns for small watersheds
  on a monthly basis
• Output always exceeds input Mg2, Ca2, Na,
  Al3
• Input always exceeds output NH4, H, PO43-
• Crossover pattern K, SO42-, Cl-, NO3-
• Calculations of weathering rates must include net
  losses of ions and net accumulation of biomass.
  Failure to include annual biomass accretion of
  nutrients results in a weathering estimate that
  it 50 too low.
• Aggrading ecosystems accumulate large amounts of
  nitrogen by microbial nitrogen fixation or other
  inputs of nitrogenous gases or aerosols. Field
  studies (acetylene reduction) indicate vigorous
  nitrogen fixation in dead wood.
• Relatively little is known about the
  transformations mediated by microorganisms.
  Aspects of nutrient cycling as they relate to
  nutrient flux must be more carefully evaluated in
  future studies.