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Historical Roots of Forest Hydrology and Biogeochemistry
Kevin McGuire and Gene E. Likens 2011
Provides an historical context on how the science of forest hydrology and biogeochemistry (or
hydrochemistry) developed!
Late 1800s and early 1900s – interest was primarily focused on how forest removal
affects floods and erosion; considerable uncertainty about the role of forests in water
management
The importance of forests for flood control and water storage was accepted by foresters
but not by engineers
Initial watershed study sites were established to resolve this controversy – first
experimental station at Wagon Wheel Gap in CO in the early 1900s
Wagon Wheel Gap Station
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http://www.foresthistory.org/education/curriculum/Activity/activ11/essay.htm
A tramway carried employees and visitors to the remote Fremont Experimental Station!
http://www.fs.fed.us/outernet/rm/main/history/rmrs_a_look_back.pdf
1909 – establishment of first paired watershed study site at Wagon Wheel Gap to study the
effects of forest removal on runoff yields
Forest removal did increase runoff yield (decreased evapotranspiration)
As a result of the 1936 Omnibus Flood Control Act, USDA Forest Service created more
experimental stations across the country which included – Coweeta Hydrologic Laboratory,
Hubbard Brook, HJ Andrews, etc.
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Coweeta Hydrologic Laboratory http://coweeta.uga.edu/
Located in the Blue Ridge Physiographic province of North Carolina
2185 hectares
Streamflow monitoring in 1934
Stream chemistry monitoring – 1968
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Hubbard Brook Ecosystem Forest (HBEF) http://www.hubbardbrook.org/
Established in 1955 in the White Mountains of New Hampshire
3307 ha watershed
Stream chemistry monitoring started in 1963
First watershed where budgets for element cycling were developed
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Initial studies were focused on – impact of forest and silvicultural management practices
on streamflow and sediment yield
Later on – a wider set of questions were addressed – such as changes in forest type,
vegetation types, density of forests, et. on water storage and evapotranspiration.
These study locations were also very beneficial and instrumental in stimulating new
paradigms and concepts in forest hydrology --like the Variable Source Area (VSA)
concept
Coweeta hydrologic laboratory – Hewlett’s and Hibbert’s observations and results
Infiltration was seldom limiting in forest landscapes.
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Forest Management to Ecosystem Science Then came the Ecosystem Concept in Ecology – pioneered by Eugene Odum – in the late 1950s.
Eugene Odum
E. P. Odum’s (1953) definition of the ecosystem as a ‘‘. . . natural unit that includes living and
nonliving parts interacting to produce a stable system in which the exchange of materials
between the living and nonliving parts follows circular paths . . . .’’
Led to the characterization of ecosystems has having specific and well defined compartments
with fluxes of energy and nutrients among the compartments.
Figure 1.2
Really helped the development of ecosystem models and quantification of the fluxes.
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The Small Watershed Approach
Defining boundaries and compartments in forest stands was always a problem
Bormann and Likens at Hubbard Brook thought that the watershed could serve as a
nicely contained unit – with topographical and physiological boundaries of ecosystems -
to apply the ecosystem concept!
Thus, started the use of the small watershed approach to study watershed biogeochemistry!
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http://www.hubbardbrook.org/overview/HBEF_establishment.htm
Hydrologically gauged watersheds at HBEF allowed for study of inputs and outputs of water as
well as nutrients and the role of atmospheric, biotic, geologic and hydrologic components in the
fluxes and budgets of nutrients.
Hubbard Brook Ecosystem Study began in June 1963 when Likens and Bormann received a NSF
grant to study the “Hydrologic-mineral interaction in a small watershed”
Observations and results from HBES paved the way for important scientific discoveries on how
ecosystems and watershed function and also helped address some key environmental
challenges!
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Watershed-ecosystem nutrient budgets –
First site to develop watershed scale ecosystem budgets for nutrients – Ca, Mg, Na,
K…etc.
Helped understand the role of mineral weathering and biogeochemical reactions in the
transport and retention of these solutes
Lot of the details in book by Gene Likens – Biogeochemistry of a Forested Ecosystem (now 3rd
edition in 2013) –
http://www.springer.com/life+sciences/ecology/book/978-1-4614-7809-6
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Role of Vegetation and its growth status in nutrient cycling
Conducted a number of maniputation experiments – where forest vegetation was
removed and the impacts on water and nutrient losses from watershed was studied
Forest removal lead to – increase in streamflow runoff, and greater exports of NO3 and
other associated nutrients such as Ca, Mg, Na, and K from the watersheds
NO3 was lost because of loss of nutrient uptake by vegetation
Results showed that in absence of vegetation, watershed ecosystems had limited
capacity to retain nutrients!
Had important implications for forest management practices such as – clear-cutting!
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Acid Rain and insights from HBEF
The detailed monitoring of water chemistry sampling, development of watershed
budgets, and computations of nutrient fluxes at HBEF also allowed it to address one of
the greatest challenges of the 60s and 70s – Acid rain and its impacts on watershed
ecosystems
The long term water and chemical records being collected at HBEF were especially
valuable in deciphering trends from Acid Rain
First published account about the effects of Acid Rain in North America came from
HBEF!
Losses and depletion of cations from the watersheds as a result of acid inputs!
The long dataset also revealed the decrease in the loss of cations in the 90s when
controls on sulfate emissions were implemented by the industry
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Development of watershed nutrient models and their use as predictive
tools
The large collection of data, synthesis of this information into budgets and fluxes, and
the use of the ecosystem concept - all facilitated the development of models
Models were used to test hypotheses and understand watershed functions
Models have also been used as a predictive tool – future long-term changes in
ecosystem processes
Examples of some models –
BROOK
JABOWA
PnET
PnET-BGC
These models have led to the development of many other ecosystem and catchment models of
hydrology and biogeochemistry.