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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.