Title: Hubbard Brook
1The 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
23,160 hectare reserve located in the White
Mountain National Forest
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4Meteorologic 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.
5Meteorologic 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.
6Meteorologic input supplies 6 of the annual
magnesium uptake by green plant biomass.
7Meteorologic input supplies 5 of the annual
sodium uptake by green plant biomass.
8Meteorologic input supplies 4 of the annual
calcium uptake by green plant biomass.
9Meteorologic input supplies 1 of the annual
potassium uptake by green plant biomass.
10Most 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.
11Data 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.
12For 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.
13Conclusions 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)
14Conclusions 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
15Conclusions 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.